# A new ignition circuit



## jgedde

EDIT:  This circuit has been revised and improved.  See post #11.

For my Farm Boy build, I wanted to wind my own ignition coil and build my own ignition circuit.

I searched around for suitable circuits, but found virtually all unacceptable.  They usually had one or more of the following faults:

1) Excessive power consumption.
2) Just plain poor design.
3) Would overheat the driver transistor and/or the coil if the engine was not running with the crank in a position where the ignition was triggered.
4) Consumed power to keep the coil turned off.

So, as an Electronics Engineer by trade, I designed my own.  I haven't yet built this, but I have run a PSPICE simulation and it works.

My design goals were:
1) No heatsink required for the driver transistor to keep the unit small.
2) Very low current draw with the motor not running and when the coil is off.
3) A timing indicator (LED).
4) Robust design.
5) Turn off coil current if the engine is stopped with the hall effect sensor triggered.
6) Prevention of internal arcing in the coil if no spark plug is connected.
7) Usable with breaker points instead of Hall effect sensors.
8) 4.5 to 14V operation.  Nominal is 6V (4 AA cells)
9) Very small.

Q1 is a 400V Darlington power transistor with internal flyback diode.  It serves as the coil driver.  

D1 and D2 have a few functions.  The obvious one is to clamp the voltage across the transistor to less than 400V.  The second function, believe it or not, is preventing the coil output voltage from getting too high (how high it will get is dependant on your coil) if the spark plug is disconnected.  Allowing the coil voltage to get too high can damage the itsy bitsy coils we use.  Being connected between the collector and base rather than collector to ground protects the transistor's collector to base junction as well.  If the two zener diodes conduct, it will actually turn on the transistor by feedback enough to keep voltages within limits.

Q2 is a small Darlington used to provide enough base current to Q1.

D3 is the timing indicator.  JP1 is a jumper that can be removed to save power if the LED isn't being used.

R3, R4, D4, and R2 are the input circuit.  The coil charges when the Hall sensor output goes low (or breaker points close).  The coil fires when the sensor output goes high (or the points open).  C2 prevents the coil from being turned on too long.  It'll turn the coil off after about 0.3 seconds if the hall is stuck low (or shorted to ground), or the points don't open.  This keeps Q1, the coil, and batteries from being killed.

Again, I haven't built the circuit yet.  I just ordered the parts  from Digikey.  I'll follow up with more info when it's wrung out.

IN the meantime, I hereby solicit comments from the gang...

John


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## dalem9

Well John it is wonderful for you to share this with us . Just goes to show were their a will their is a way . Dale


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## Niceonetidy

John,

Thanks for sharing, I'm very interested in this and look forward to seeing the results.

Kind regards,

Colin


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## canadianhorsepower

Nice circuit but R1 at 470 the led wont work are barely at 6 volts
would a 1k trim pot be better it would cover all the voltage your mentionning
4.5 to 14v


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## cheepo45

Thanks for your efforts. I will be following this closely, as I am building a 1/4 scale Gade motor and I would like to find an ignition that fits in the battery box. Let us know what kind of coil you will be using.
         cheepo45


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## Walsheng

I will be following as well.  I have a Little Brother casting kit for one of my next projects.

John


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## 123RWO

I think you need to get rid of the flyback diode.  If you don't it seems to me that it will clamp the coil primary pulse preventing any seconday output.    I suggest this transistor instead:
http://www.irf.com/product-info/datasheets/data/irgb14c40lpbf.pdf  Digikey carries them.

RWO


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## jgedde

RWO said:


> I think you need to get rid of the flyback diode.  If you don't it seems to me that it will clamp the coil primary pulse preventing any seconday output.    I suggest this transistor instead:
> http://www.irf.com/product-info/datasheets/data/irgb14c40lpbf.pdf  Digikey carries them.
> 
> RWO


 

The primary pulse is positive, so the diode won't conduct.  The flyback diode is built into the part.  If the diode were in parallel with the coil however, you'd be right.

I like your choice of the output transistor.  I discovered those IGBTs designed for logic level ignition coil drive after I posted the circuit.  I've started designing a new and better circuit that uses an IGBT from Fairchild.

An IGBT has some notable advantages over a Darlington (a Darlington cannot saturate.  But this is a good thing in some cases - no issues with recovery time in trying to turn it off)
1) An IGBT can saturate yielding lower collector to emitter voltages.
2) MUCH less base current is required - hence it'll use less battery power.

Thanks,
John


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## jgedde

canadianhorsepower said:


> Nice circuit but R1 at 470 the led wont work are barely at 6 volts
> would a 1k trim pot be better it would cover all the voltage your mentionning
> 4.5 to 14v


 
The LED I chose will give me about 5 mA at the low limit of 4.5 volts.  It'll be lit, albeit nowhere near as bright.  That's another reason I chose a green LED.  The human eye, especially mine (being red colorblind) is much more sensitive to green.  I chose power consumption over brightness.

At the high limit of 14V, the LED would be overdriven.  I honestly put no thought into the LED when I considered the circuit at 14V.

My new circuit will have a choice of LED drop resistors for the voltage for which the circuit will be used.  I designed it for use (in my case) of 4.5 to 6V - what I'd get from 4 standard alkaline AA cells.

John


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## CallMeAL

This looks very interesting for an IC engine I hope to build soon.  I wish I understood electronic schematics better and knew how to build a circuit!

I'll follow this and see if I can figure it out!

Al


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## jgedde

OK.  Here is a version I'm happy with.  It uses an IGBT instead of a Darlington output transistor.  This reduces power consumption of the driver circuit, reduces part count, and gives about 20-30% more coil voltage at 6V.

I'm relatively sure the hand drawn schematic with the Darlington will work if you want to try it.  However, I no longer have plans to build that one.  I will be building this one instead.

I've also addressed the LED resistor issue.

Operation of the circuit is more or less the same on the input side.  As far as the output part, Q1 is the coil driver (an IGBT), Q2 drives the IGBT gate.  Q3 is used to quickly turn off Q1 which is what is needed for a good hot spark.  I could have eliminated a transistor by driving the gate of the IGBT to ground when it needed to be turned off.  But, this would have consumed power just to keep the coil off...

If anyone is curious, I used Altium for the CAD schematic.  Also attached is a PDF version which is easier to read.

John

[Edit: 4/1/13 The circuit has been built and tested.  See final version in post #47.  J. Gedde]


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## canadianhorsepower

Curious to know what kind of coil your planning to use at 6 volts

do you use PCB artist for your PCB board?

cheers


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## jgedde

For PCB layout and schematic CAD I use Altium Designer.  I have a license for it through my job.  

I don't plan on making a PCB, although if I see any interest, I may lay one out and put together a kit for sale.  

My version will just be put together on a small solder type protoboard. The coil and driver circuit will live inside a small model buzzcoil box on the engine (although it isn't a buzzbox).  See the picture...

The CAD model for the engine was done using Alibre.

For the coil, I plan on making my own.  The book on model ignition coils by Bob Shores gives lots of info on how to do it.  We have coil winders and laminations at work.  

To test the circuit I have a small 6V coil from J.E. Howell.

John


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## Maxine

Thanks for posting that schematic.


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## stevehuckss396

Will the circuit fire a coil with a primary resistance of 0.8 ohms


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## Lakc

stevehuckss396 said:


> Will the circuit fire a coil with a primary resistance of 0.8 ohms


I am not so sure it can. Resistance is only one measure of a coil. In your case, what is probably different then a standard coil is its reluctance, "L" measured in henries.


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## jgedde

stevehuckss396 said:


> Will the circuit fire a coil with a primary resistance of 0.8 ohms


 
Yes and no.  The 0.8 ohms isn't necessarily a problem, but the inductance of the coil is _really_ what matters.  Do you have any further info on your coil?

If we consider the coil as a plain inductor (there's a bit more to consider): The inductance divided by the resistance represents a time constant.  After 5 time constants, the current through the coil will be set by the resistance.  

The idea is that your dwell angle only turns on the coil for 4 or 5 time constants after which it will obtain no more energy and just heat up.  Of course this doesn't happen in practice since spark timing is an issue and the time the coil be be on will be reduced at higher RPMs since dwell angle is fixed.

All that said, this circuit can and will drive automotive ignition coils.  Inn fact, the output transistor was designed for just that.

I've done a PSPICE simulation using a MSD HEI coil with a primary resistance of 0.7 ohms and a primary inductance of 8 mH.  It does work, but the transistor would need a heatsink.  This was without using a ballast resistor.

For what it's worth, my coil has a primary resistance of 1.05 ohms and a primary inductance of 4.4mH.

John


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## dsage

jgedde said:


> OK.  Q3 is used to quickly turn off Q1 which is what is needed for a good hot spark.  I could have eliminated a transistor by driving the gate of the IGBT to ground when it needed to be turned off.  But, this would have consumed power just to keep the coil off...
> 
> John



John:

Yes your circuit looks remarkably like mine. Great minds thing alike I guess.

I had mentioned in my original post:

http://www.homemodelenginemachinist.com/f26/ignition-circuit-help-19673/index2.html

 that I was lazy and used the symbol for a regular transistor just to make the circuit more familiar looking.
 Something else you might not have noticed about my circuit (and now yours too since you quoted the same IGBT) is that I'm using the "L" variant of the IGBT with has a Logic input (can't speak for the alternate part number you spec'd). 
 You can drive this transistor directly from a microprocessor or other logic level device. I have used this driver end after a simple 555 timer oscillator to create a BUZZ COIL like output. You set the 555 for a frequency around about the equivalent of 1000 rpm and the hall sensor or whatever enables/disables the 555 to produce a burst of sparks instead of just one. Works really well. My friend also uses the same IGBT driven by a PIC micro on his EEVIC engines.
http://www.evicengines.com/

A couple of comments on your variation on the circuit. I haven't checked them..

Is there enough leakage from the base of the IGBT to actually make Q3 work? Q3 would need some voltage on it's emitter and enough current to bias Q3 off. I guess you could tell by measuring the voltage emitter to collector on Q3 when sitting idle or with a scope. It should be pretty low (like 0.2v) if Q3 is turned on.

You have different resistor values around the coupling capacitor I and and I haven't checked but, is the coupling capacitor value high enough to pass REALLY slow rpm's as you get when cranking the engine. If not you will only get a very short dwell time passing through it. I selected mine to pass everything up to several tenths of a second ( I've forgotten exact figures). Basically anything BUT a continuous input. It's just there for safety.
I had to use a scope to see that the capacitor was NOT charging up enough to have the circuit time out for very low RPM's

The last point is that like any darlington bipolar transistor the IGBT has a Collector Emitter voltage of around 2volts when ON. If you're going to run it on 6v your coil would need to be rated for 3 or 4 volts or so, else it will be starving a bit. (6bat - 2Vce = 4) Having said that, there is usually enough output from most coils for a model plug regardless of what voltage you have.
You only need about 2Kv on a small plug under compression.

Good work.

Sage


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## jgedde

dsage said:


> John:
> 
> Yes your circuit looks remarkably like mine. Great minds thing alike I guess.
> 
> I had mentioned in my original post:
> 
> http://www.homemodelenginemachinist.com/f26/ignition-circuit-help-19673/index2.html
> 
> that I was lazy and used the symbol for a regular transistor just to make the circuit more familiar looking.
> Something else you might not have noticed about my circuit (and now yours too since you quoted the same IGBT) is that I'm using the "L" variant of the IGBT with has a Logic input. You can drive this transistor directly from a microprocessor or other logic level device. I have used this driver end after a simple 555 timer oscillator to create a BUZZ COIL like output. You set the 555 for a frequency around about the equivalent of 1000 rpm and the hall sensor or whatever enables/disables the 555 to produce a burst of sparks instead of just one. Works really well. My friend also uses the same IGBT driven by a PIC micro on his EEVIC engines.
> http://www.evicengines.com/
> 
> A couple of comments on your variation on the circuit. I haven't checked them..
> 
> Is there enough leakage from the base of the IGBT to actually make Q3 work? Q3 would need some voltage on it's emitter and enough current to bias Q3 off. I guess you could tell by measuring the voltage emitter to collector on Q3 when sitting idle or with a scope. It should be pretty low (like 0.2v) if Q3 is turned on.
> 
> You have different resistor values around the coupling capacitor I and and I haven't checked but, is the coupling capacitor value high enough to pass REALLY slow rpm's as you get when cranking the engine. If not you will only get a very short dwell time passing through it. I selected mine to pass everything up to several tenths of a second ( I've forgotten exact figures). Basically anything BUT a continuous input. It's just there for safety.
> I had to use a scope to see that the capacitor was NOT charging up enough to have the circuit time out for very low RPM's
> 
> The last point is that like any darlington bipolar transistor the IGBT has a Collector Emitter voltage of around 2volts when ON. If you're going to run it on 6v your coil would need to be rated for 3 or 4 volts or so, else it will be starving a bit. (6bat - 2Vce = 4) Having said that, there is usually enough output from most coils for a model plug regardless of what voltage you have.
> You only need about 2Kv on a small plug under compression.
> 
> Good work.
> 
> Sage


 
Thanks Sage,

Yes, I have checked the values in the input circuit.  They'll give up to about 350mS of on time.

Both the Fairchild and the IR IGBTs have very good Vce(sat) figures, even at 4.5V of drive.  Much less than 2V or so like a Darlington...  The datasheets show about 1.4 to 1.6V being the max value, with more like 1.2V-1.3 being typical at max coil current.  Of course, the coil doesn't draw this current as it charges as the inductance limits the current.  That said, during charge-up, Vce is very low...   Maybe about 0.2 to 0.3 volts - it's hard to tell from the graphs in the datasheets.  Of course, if Vce rises as the coil charges, the coil wil lose some energy.  

0.2-0.3V is way better than a Darlington, simply because a Darlington cannot saturate while an IGBT can.  I'd have considered using a MOSFET with a low Rds on, but then I'd have to somehow get 8-12V of gate drive and add the clamp zeners back in.  Also, a low Rds on, high voltage MOSFET has a _huge_ amount of gate charge which will cause issues in getting the device to turn on or off fast.  There are ways around all of these issues that I employ at work (I design motor controllers for space vehicles), but they add unwanted complexity and would be hard to make work at low RPMs (bootstrapping a switched capacitor circuit).

In any case, my current coil design gives about 12kV at 4V. I'm using ultra high mu, high saturation, laminations so I get a high energy product.  The usual trick of tearing apart a power transformer is not what I'm doing... 

As far as Q3 is concerned, an IGBT has a comparably large amount of gate charge (17nC for the Fairchild, 27nC for the IR) which has to be dumped in order to get it to turn off fast.  That's where the current for Q3 comes from.  When Q3 turns on, it dumps the gate down to about 400mV.  This is because Q3 doesn't saturate.  The internal resistor in the IGBT from gate to emitter pulls it down the rest of the way.

There is a vintage appnote from TI that I believe details the turn off circuit I'm using.  If you Google MOSFET gate drive, you'll find it. 

I think I might play around with a 555 timer to generate multiple sparks at some point.  But, wouldn't multiple sparks wear out the spark plug faster?  Certainly it will use more battery power.  If the first spark effectively ignites the mixture, then all is well.  My CR is only about 4.5:1 so I don't think I'll have too much trouble unless my carburetion is really bad.

Thanks,
John


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## jgedde

dsage said:


> John:
> 
> My friend also uses the same IGBT driven by a PIC micro on his EEVIC engines.
> http://www.evicengines.com/
> 
> Sage


 
Wow!  Those EEVIC engines are amazing!  Electronically controlled and actuated valves, are in my opinion, the Holy Grail of engine design.

I wasn't aware that anyone had really pulled it off at high RPMs...

I dream about a small block Chevy with electrically controlled valves!  Turn a knob for a mean choppy idle!     Seriously though, in these days of high fuel prices and environmental concerns, that technology would be the cat's meow in a motor vehicle...

John


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## Walsheng

I will be following as soon as you guys start speaking English again!

John


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## 123RWO

What is the function of C1?   Speaking of multi-spark pulsers, this link has some info: http://www.sci-experiments.com/HighVoltagePulser/

RWO


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## jgedde

RWO said:


> What is the function of C1?   Speaking of multi-spark pulsers, this link has some info: http://www.sci-experiments.com/HighVoltagePulser/
> 
> RWO


 
Don't get me started on that one!     It's a myth that the condensor across the points does nothing more than protect the points from arcing.  

It does do that with points, but it also beefs up the spark by creating a resonant circuit with the coil.  The same thing holds true when using a transistor as a switch. 

You will get a spark without a condensor (or C1), but for all intents and purposes, the coil's output voltage duration will be shortened.  This is of course a practical explanation - keeping it in English!

John


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## dsage

Yeah. For sure you're going to waste a lot of battery power at low RPM's but once the engine moves up toward the RPM near to the repitition rate of the 555  it starts trimming back sparks until you have only one just like without it. It takes a bit of balancing point dwell and timing components to get it where you want.
 The selling point for commercial multi-spark ignitions is easier starting and better low end torque. The claims come from when a performance engine is running slow the mixture is usually crap because the cam timing is tuned for high RPM's. So theoretically one spark might not take. So the answer is - hit it a few times to be sure. Model engines usually have poor carburetors so everything helps.
A small 4Ah or 7Ah battery will last quite a while running a small hit-miss engine. I'd say long enough to cover a weekend show either way.

It's also cool to say you have a multi-spark ignition. 

I'm sure someone will chime in that a 555 is old school but they run on a wide range of voltage and don't change timing vs voltage so you could run the same circuit from say 5v to 25v and still be fine. You could use a processor and have no discrete components but then you'd have to have a regulator and the ability to program a processor etc. etc...

I have a small circuit board layout in Eagle for the whole thing.

It's all trade offs.



Sage


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## canadianhorsepower

jgedde said:


> Don't get me started on that one!  It's a myth that the condensor across the points does nothing more than protect the points from arcing.
> 
> It does do that with points, but it also beefs up the spark by creating a resonant circuit with the coil. The same thing holds true when using a transistor as a switch.
> 
> You will get a spark without a condensor (or C1), but for all intents and purposes, the coil's output voltage duration will be shortened. This is of course a practical explanation - keeping it in English!
> 
> John


 
I'm happy to see that I'm not the only one that knew this.
one recent post create a storm when I mention that:fan:


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## dsage

Boy this is a busy place. A whole slew of replies popped in while I was editing my response - which is Waaay back there now.

Yes the EEVIC engine that Dave Bowes designed is exceptional. I'm not sure if you get to the shows but he brings it to Cabin Fever and NAMES. Only NAMES this year since they changed the Cabin Fever date. He is in the the same club as me.
tsme.ca
Unfortunately the technology does not scale up so well for a lot of reasons which he could explain to you. Lots of companies have tried.

We digress.

Sage


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## dsage

John:

Do you have a quick calculation for a proper capacitor value?

Sage


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## jgedde

dsage said:


> John:
> 
> Do you have a quick calculation for a proper capacitor value?
> 
> Sage


 
Alas, no.  Certainly it'll depend on the the inductance of the coil, turn ratio, etc.  But beyond that, I tend to think it'll depend also on the dynamics of the spark gap, engine requirements, etc...

I think the good news is that it isn't all that critical.

John


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## 123RWO

Re: C1.  I have heard the resonant tank circuit theory for a long time, but the transistor ignition circuits I have seen in the literature and including the couple I have designed and built didn't use the parallel cap.  I never had a problem with low output even at 6000 RPM ( 4 cylinder).   How about running a test for spark peak voltage and duration with and without the cap when you get your new system going?   That should put the question to bed one way or another.   

RWO


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## jgedde

It's no theory, it's basic AC electronics.   http://www.allaboutcircuits.com/vol_2/chpt_6/3.html 

If you look at elelctronic ignition circuits for cars, you'll see them there too.  There are many examples, some good, some bad to be found by Googling "Electronic Ignition Circuits".

Again, you will get a spark without the cap and your engine will likely run fine.  

John


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## tornitore45

The circuit is clever and will work for sure. Clamping is a good feature 180Vzener x 100 ratio will clamp at around 18kV secondary, plenty for a spark but not enough to fry the transistor or the coil is the gap is too high.
Basically you AC coupled the drive contact/hall sensor the ON state can only be temporary.

I had the same concer about a straight Kettering (inductive) system and opted for a Capacitive discharge.  We like to run our model engine as slow as possible to show all the moving parts.  At LOW RPM the coil is practically on all the time at highest current.  The energy to charge the cap is fixed, no matter how low the RPM, even not running the cap get charged once and the current goes low after that.

I bought a CDI kit mostly to get the impregnated HV coil. The circuit works but is pretty cludgy design. I plan to redesign the boosting charge pump and utilize the coil which is really small.


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## jgedde

Thanks for the good words.  The clamping in the circuit of post #11 is built into the IGBT and happens at 370-430V.  You'd think because of the 100:1 turns ratio, the clamping would occur at 40kV, but because of the parasitic capacitance and core losses in the coil, the output voltage is lower.

What CDI kit did you use? 

John


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## jgedde

dsage said:


> John:
> 
> Do you have a quick calculation for a proper capacitor value?
> 
> Sage


 
I've done some more research and experimentation on this subject. As it turns out the cap in parallel with the switching element (transistor or breaker points)does matter. In fact, in my test setup, I get no spark with no cap (using breaker points). .01 uF gives me a small (but likely usable spark), .1uF gives me a robust spark. I couldn't resist the potential for damaging the coil, but .1 uF could give me sparks 1/4" long with a 6V supply. Beyond .1 uF I didn't see further improvement. And, at higher values of capacitance, the output voltage was sufficiently lowered to prevent the spark from occurring at all!

Bear in mind that this is but one case: using a only one coil and breaker points. 

Without the cap present, the oscillation frequency on my coil was 1.67 MHz! Certainly much too high to couple well to the secondary with an iron core and not enough time to ionize the spark gap. .1 uF lowered the frequency to 38 kHz.

That said, it turns out there is much more to designing with an ignition coil than I expected. I needed to add intrawinding capacitance and leakage inductance to my PSPICE model to get it to reflect reality. The leakage inductance made the biggest effect.

So, as far as a capacitor value, I haven't yet come up with a reasonable equation to cover most possible cases.

John


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## varonicaleon

It's very informative for me thanks for share.


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## jgedde

varonicaleon said:


> It's very informative for me thanks for share.


 

Thanks.  I've been trying to beg or borrow a high voltage scope probe to make life easier during experimentation so I can use a regular oscilloscope.  

I have an old CRT type ignition analyzer, but it's big, bulky and has no waveform storage capability so documentation would be nearly impossible.

John


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## Lakc

jgedde said:


> Thanks.  I've been trying to beg or borrow a high voltage scope probe to make life easier during experimentation so I can use a regular oscilloscope.
> 
> I have an old CRT type ignition analyzer, but it's big, bulky and has no waveform storage capability so documentation would be nearly impossible.
> 
> John



That kind of specialized equipment wont likely be easy to come by. I just inductively couple into the primary for the most part. Couple turns of wire wrapped around the primary lead. Will work the same for the secondary once I get that far.
I can only dream of a scope with storage capability I have an old HP scope with a finicky trigger circuit.


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## 123RWO

Well, John, let's think about your assertion.  Let's look at cars per your suggestion.  How about GM cars?  The GM HEI ignition is certainly well known and many millions were made over many years.  As to performance, the late versions were good to 8000 RPM on a V8.    Did it use a C1?   No.  Of course, the HEI is now obsolete as the car makers have all gone to coil-on- plug or coil-near-plug.  Some of the systems put the transistor switch inside the individual coil can.  Do the coils have a parallel cap?  None that I have seen.   My old 86 Nissan put the transistor switch on the coil's mounting bracket.  There was no C1.

RWO


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## jgedde

RWO said:


> Well, John, let's think about your assertion. Let's look at cars per your suggestion. How about GM cars? The GM HEI ignition is certainly well known and many millions were made over many years. As to performance, the late versions were good to 8000 RPM on a V8. Did it use a C1? No. Of course, the HEI is now obsolete as the car makers have all gone to coil-on- plug or coil-near-plug. Some of the systems put the transistor switch inside the individual coil can. Do the coils have a parallel cap? None that I have seen. My old 86 Nissan put the transistor switch on the coil's mounting bracket. There was no C1.
> 
> RWO


 
RWO,

I'm not so sure yet that we can or cannot draw an analogy to a full size car coil wiuth huge inductances as compared to the small 6 or 12V coils used in model engines. The fact remains that without a cap across the breaker points in _my_ test setup, I get no spark.

I've been struggling to get a PSPICE model of my ignition coil that reflects reality. :wall:As of this morning I am much closer with the help of a fellow EE. A phenomenon known as leakage inductance dramatically changes the behavior of the coil vs an ideal model. Also, interwinding capacitance has an effect. 

We have been successful in measuring these parameters with my 6V coil. ;D

I have a GM HEI coil from my Camaro (Optispark not distrubutor cap HEI). At some point I'll characterize that as well and can make a model of that. Maybe that will tell why the cap is not used.

There seems to be a lot of conflicting information about whether a cap is or isn't needed and I'm honestly questioning under what circumstances it's needed. 

I'll agree HEI doesn't use a cap. On the other hand, my little coil won't sparkat all without a cap. I need to reconcile this for my sake as well as the gang here at HMEM. It would be great to come up with some rules of thumb as to allow guys to make a working ignition system on the first try.  Do you know if anyone has ever drawn a schematic of what's inside there?  I remember having one apart like 20 years ago and there was a hybrid circuit inside.

In any case, the good news is that I got my parts for the ignition circuit shown in post #11 and I'll be building it up over the weekend.

John


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## dsage

John:

A small point but back in post #33 you should edit to correct your statement that the capacitor goes across the COIL (I think that was a typo). As you know the cap goes across the POINTS (and you've said that all along previously) The cap across the points makes the cap and coil a series resonant circuit of L1(coil) and C1(cap) when the points open (or the transistor turns off). From other posts I think that's what you meant to write. Certainly a cap ACROSS the coil would suppress any oscillations not enhance them.

It would be good to clarify this for those reading in the future looking for information.

As Lakc has pointed out a scope connection to the primary side is just as effective at looking at the secondary directly due to the transformer effect.     In fact I believe your big ignition system analyzer connects to the primary side. As I remember them you could see all 8 cylinders at once as the same coil supplied sparks to all 8 in turn.
 I always wish I had one of those. I once saw plans to convert a TV set to an ignition analyzer.

Sage


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## 123RWO

Here is the GM HEI circuit or at least one that will work with the original coil and reluctor: http://www.jaycar.com.au/images_uploaded/MC3334R0.PDF
Note the 350V Zener clamp used with nonselected MJ10012 and the wide voltage range.


RWO


----------



## jgedde

dsage said:


> John:
> 
> A small point but back in post #33 you should edit to correct your statement that the capacitor goes across the COIL (I think that was a typo). As you know the cap goes across the POINTS (and you've said that all along previously) The cap across the points makes the cap and coil a series resonant circuit of L1(coil) and C1(cap) when the points open (or the transistor turns off). From other posts I think that's what you meant to write. Certainly a cap ACROSS the coil would suppress any oscillations not enhance them.
> 
> It would be good to clarify this for those reading in the future looking for information.
> 
> As Lakc has pointed out a scope connection to the primary side is just as effective at looking at the secondary directly due to the transformer effect. In fact I believe your big ignition system analyzer connects to the primary side. As I remember them you could see all 8 cylinders at once as the same coil supplied sparks to all 8 in turn.
> I always wish I had one of those. I once saw plans to convert a TV set to an ignition analyzer.
> 
> Sage


 
Sage,

Thanks for pointing that out.  I went back and fixed it.

As far as the ignition scope is concerned, I got mine from a coworker for $50 which is what he paid for it at a flea market.  It's still in its original box (including the corrugatred overbox) and is in perfect condition.  We all get lucky sometimes, right?  I've used it a few times, but not for several years.

John


----------



## dsage

RWO:

I forgot about that chip. I might have one of those chips in my ancient stock from "back in the day". Nice chip but I think they are obsolete. No matches on a search at Digikey anyway. Something like that for a hall sensor input would make things really simple. To do it any justice you'd need a trigger device with a differential output like the reluctor it's designed for though. Nice that it automatically controls dwell as well. 

Sage


----------



## mayhugh1

Hi,
        I might be able to shed some light on why a capacitor is needed for a mechanical points (Kettering) ignition system but not for a transistorized (non-CDI) ignition. When the mechanical points open in order to interrupt the current flow to the ignition coil and generate the flyback pulse, they are not ideal and do not switch instantaneously from zero ohms to infinity. They spend a small amount of time during their initial opening (as the spring pressure holding them closed starts to release) in the range of a few ohms to several ohms on their way to being an open circuit. While the points are in this low (but not zero) resistance area, the coil current continues to flow; and the IR drop across the points starts to disssipate the energy that was intended to generate the flyback voltage and produce the nice big fat spark at the plug. A lot of heat is generated across the points while this is happening and a 'plasma' which is conductive is generated and allows the current to continue flowing for a time even after the points have mechanically separated. This dissipation drains off the flyback energy and eventually burns up the points, and is the source of the visible arcing you would see if the distributor was transparent. If you put a capacitor across the points this capacitor will keep the voltage across the points at zero during the initial opening time of the points and even extend the current flow to the coil for a little while longer. The capacitor one would put here is for all practical purposes ideal and it does not dissipate any significant portion of the flyback energy. As the current continues to flow through this capacitor its voltage starts to rise after the points actually separate. If the capacitor is large enough there will be little or no arcing at the points to kill the flyback voltage or the points themselves. In fact it turns out that the current charging the cap is the same current charging the coil and the voltages across each of them are almost 180 deg out of phase; and so the energy oscillates between them for a short period of time extending the effective width of the flyback pulse. If you get to look at the flyback pulse with a scope you will see the remnants of the damped sinusoid on the back edge of the waveform after the plug fires and the bulk of the flyback energy is dissipated where it is wanted - across the plug gap. In a transistorized ignition (Kettering system with the points replaced by a solid state switch) the switch in this case is nearly ideal. It switches very quickly to interrupt the coil current and you can get an even higher flyback pulse without a lot of dissipation during the switching time. Of course the transistor, coil, and wiring all have stray capacitances and these and the non-zero switching time of the limit the flyback voltage to something other than infinite spikes. But none of these components are dissipative as are the mechanical points and so a big capacitor is not required.
I think your project goal of coming up with a universal bullet-proof ignition for model engines is a great idea. But, I'd like to offer one suggestion. The coil is an integral part of the design. I think the problem many of us have with model IC ignitions is that we mix and match ignition circuits with various coils and we get mixed results. There doesn't seem to be consistent source for universal model engine coils. And the primary resistance, inductance, and saturation characteristics usually aren't even spec'd when we do find one. (Most of us wouldn't know what to do with them if we did have them.) And they are very expensive. Ignition coils are difficult to reliably and consistently make because of the many turns of fine gage wire needed for the secondary and the vacuum potting that must be properly done so the cumulative effects of corona don't shorten their lives. The design parameters of the coil are intimately connected with the design of the engine. It would seem like designing an ignition circuit around a commonly available COP would be just the ticket for having an ignition that would be cheap, reliable, readily available, and be to a reasonable scale mode for model engine building. - Terry


----------



## 123RWO

The MC3334 chip is $2.67 from http://www.aliexpress.com/wholesale/wholesale-motorola-mc3334.html

RWO


----------



## jgedde

mayhugh1 said:


> Hi,
> I might be able to shed some light on why a capacitor is needed for a mechanical points (Kettering) ignition system but not for a transistorized (non-CDI) ignition. When the mechanical points open in order to interrupt the current flow to the ignition coil and generate the flyback pulse, they are not ideal and do not switch instantaneously from zero ohms to infinity. They spend a small amount of time during their initial opening (as the spring pressure holding them closed starts to release) in the range of a few ohms to several ohms on their way to being an open circuit. While the points are in this low (but not zero) resistance area, the coil current continues to flow; and the IR drop across the points starts to disssipate the energy that was intended to generate the flyback voltage and produce the nice big fat spark at the plug. A lot of heat is generated across the points while this is happening and a 'plasma' which is conductive is generated and allows the current to continue flowing for a time even after the points have mechanically separated. This dissipation drains off the flyback energy and eventually burns up the points, and is the source of the visible arcing you would see if the distributor was transparent. If you put a capacitor across the points this capacitor will keep the voltage across the points at zero during the initial opening time of the points and even extend the current flow to the coil for a little while longer. The capacitor one would put here is for all practical purposes ideal and it does not dissipate any significant portion of the flyback energy. As the current continues to flow through this capacitor its voltage starts to rise after the points actually separate. If the capacitor is large enough there will be little or no arcing at the points to kill the flyback voltage or the points themselves. In fact it turns out that the current charging the cap is the same current charging the coil and the voltages across each of them are almost 180 deg out of phase; and so the energy oscillates between them for a short period of time extending the effective width of the flyback pulse. If you get to look at the flyback pulse with a scope you will see the remnants of the damped sinusoid on the back edge of the waveform after the plug fires and the bulk of the flyback energy is dissipated where it is wanted - across the plug gap. In a transistorized ignition (Kettering system with the points replaced by a solid state switch) the switch in this case is nearly ideal. It switches very quickly to interrupt the coil current and you can get an even higher flyback pulse without a lot of dissipation during the switching time. Of course the transistor, coil, and wiring all have stray capacitances and these and the non-zero switching time of the limit the flyback voltage to something other than infinite spikes. But none of these components are dissipative as are the mechanical points and so a big capacitor is not required.
> I think your project goal of coming up with a universal bullet-proof ignition for model engines is a great idea. But, I'd like to offer one suggestion. The coil is an integral part of the design. I think the problem many of us have with model IC ignitions is that we mix and match ignition circuits with various coils and we get mixed results. There doesn't seem to be consistent source for universal model engine coils. And the primary resistance, inductance, and saturation characteristics usually aren't even spec'd when we do find one. (Most of us wouldn't know what to do with them if we did have them.) And they are very expensive. Ignition coils are difficult to reliably and consistently make because of the many turns of fine gage wire needed for the secondary and the vacuum potting that must be properly done so the cumulative effects of corona don't shorten their lives. The design parameters of the coil are intimately connected with the design of the engine. It would seem like designing an ignition circuit around a commonly available COP would be just the ticket for having an ignition that would be cheap, reliable, readily available, and be to a reasonable scale mode for model engine building. - Terry


 
Terry, I think you've done a terrific job of describing the situation and hit the nail on the head to be sure.  That said, I think the dream of a more or less universal ignition coil circuit is nonetheless attainable.  However, the coil characteristics and the engine dynamics are indeed unavoidable gotchas.  

From what I'm finding both experimentally and in practice, the coil's _leakage inductance_ is all important in predicting what a particular coil will do. http://en.wikipedia.org/wiki/Leakage_inductance

All that said, I am in hopes that a common circuit with some "cut and try", with regard to only the capacitor across the points (or the output transistor), may be necessary to achieve an optimum solution with a given coil and a given engine.

All in all, if the circuit can successfully drive any coil with only a capacitor experiment necessary to match the circuit with the coil, this leaves only the coil matching to the engine and the power source up to the builder.

I think what you were describing in practical, non-technical terms was the characteristic of an arc called negative resistance.  http://en.wikipedia.org/wiki/Negative_resistance
Even after 25 years as an electronics engineer, the concept is non-intuitive for me, especially when it rears its head...

Cheers!
John


----------



## jgedde

RWO said:


> The MC3334 chip is $2.67 from http://www.aliexpress.com/wholesale/wholesale-motorola-mc3334.html
> 
> RWO


 
RWO,  I been meaning to experiment with that part just for the fun of it.  I wasn't aware that was the basis for the GM HEI circuit.  I wonder, though, how applicable the reluctor input is to us?  On the other hand, the input circuit would be easily adapted to a hall sensor, at least from what the datasheet shows.

The only gotcha would be the fact that a reluctor's output voltage drops to zero inately when it stops turning where the hall sensor and magnet could be positioned in such a way as to cause the coil to be "stuck on."

That's not a good thing for both the coil, the output transistor, and the batteries.  That's where dsage's as well as my circuit have an advantage - maybe...  It looks like the IC chip has some sort of dwell time enforcement circuit in it that may come to our aid.  I honestly haven't really dug to deep into it to say whether it fits the bill. 

I can't help but wonder, though, whether a hybrid of the jgedde/dsage input circuit with the chip yield a [email protected]#$ solution.

John


----------



## jgedde

The circuit is built and working.    

I needed to increase the value of the AC coupling capacitor to make it easier to test.  I am getting a strong spark with no cap across the transistor.  This lends a lot of creedence to Mayhugh's explanation since my coil with breaker points gave no spark without a cap.

Here is the final version...  (see below)

Quiescent current draw (except for hall sensors) was 0.2 microamps when the coil is on.  So, you could say I was successful in meeting my goal of low power consumption in standby mode.  If it weren't for the hall sensors, I could even get away without a power switch!

Now the ugly...  My engine has two Allegro A1102 sensors.  One is used as the spark timing and another is used to inhibit the spark when the governor engages the exhaust pushrod.  The current draw from both of those is almost 10 mA!

So now I need to ask the question: what good is a circuit that takes virtually no power when I have Halls that need to be powered and take vastly more supply current? 

OK, it's elegant, and seems to be bulletproof, but simplicity is often better.

If you want to build it and use it, it's a working circuit.  That said, it has little advantage over Dsage's circuit except for exceptionally low power consumption and a lot more circuit protections.  His will undoubtedly work better from low voltage supplies (say 6V) due to no diode drop driving the IGBT.

Here's a link to Dsage's circuit:

http://www.homemodelenginemachinist.com/f26/ignition-circuit-help-19673/index2.html#post210702

John 







View attachment Ignition Coil Driver.pdf


----------



## jixxerbill

Great work John. many thanks to you and Sage both.. Now whats the chances you could show me how to make a small coil ? lol... Something that could be put into a small base under an engine ? I know im a bum.. You work hard and finish a great looking project and all I want is more lololol.... Reminds me of ancient proverb ..Doing something good around here is like wetting your pants while wearing dark colored slacks!! You get a warm feeling all over but nobody notices..lol...Bill


----------



## jgedde

jixxerbill said:


> Great work John. many thanks to you and Sage both.. Now whats the chances you could show me how to make a small coil ? lol... Something that could be put into a small base under an engine ? I know im a bum.. You work hard and finish a great looking project and all I want is more lololol.... Reminds me of ancient proverb ..Doing something good around here is like wetting your pants while wearing dark colored slacks!! You get a warm feeling all over but nobody notices..lol...Bill


 
No worries Bill!  I love that ancient proverb.  I will remember that one!

The book "Ignition Coils and Magnetos in Miniature" by the late Bob Shores is a good source of info.  The book is still available from Mrs. Shores at a very reasonable price.  

http://www.bobshores.com/home.html
Scroll down to the bottom. 

I haven't yet wound my own, but plan to.  When I do, I'll photo-document the process.  I got my circuit up and running with a small (1" dia, 1.25" long) 6V coil from J.E. Howell (available from his son Allen's website).  

I also tried it with an MSD automotive coil:  http://www.msdignition.com/product.aspx?id=5073&terms=8231  That one was just scary!

John


----------



## dsage

jixxerbill:

Have look for Bob Shores book on coils and magnetos. All the info you need to make a coil of your own is in there. I made a couple from his book but it's almost not worth the effort. Winding 10,000+ turns of #44 wire is a really difficult. Then there is the wax potting and vacuum source required.
There is a way to use the magneto coil from an old lawnmower. Apparently they work ok and are pretty small. There is a bit hack sawing and soldering required. I read an article on it but didn't save it so I haven't tried one. Maybe someone can enlighten both of us on their use. I'll try that next time I need a coil.

BTW you don't need extremely high voltage. An old school car coil can produce at least 25Kv if not a lot more. You'll probably only need about 3-4K - probably less for a model sized spark plug. In fact having 25kv is just asking for trouble and should be avoided. (Hence the problems you've already experienced).

Sage


----------



## dsage

John:

I guess we must have been typing at the same time but you won.  - and as usual great minds think alike. Our recommendations are the same. 

Re: your circuit. I wouldn't have thought the hall sensors would consume so much power just sitting there, but a quick look at the spec sheet confirms your observations. Surprising.

I guess it's a challenge to try to reduce power consumption but lets face it, your control circuit would run for at least 350 hours on a 7ah battery. I think it's about as good as it going to get.

BTW for those of you out there looking for a circuit to build, I would stick with building John's circuit over mine. Given that there is little control over the installation of the circuit in a users engine (proper grounding procedures, lead length etc.) the additional protection items in John's circuit will add a measure of reliability.

Sage


----------



## dsage

John:

One more small thing. The suggested values for LED resistors a IMHO are too low.
For 6v your 270 ohm resistor would set about 15ma for the LED. Very roughly (6-2)/270 = 15ma.

I have found that if you purchase the newer "High Bright" red LEDS with the clear 3mm package they CAN be blindingly bright at as low as 0.5ma - 1ma.
Sorry I don't have a part number but if you go on Digikey and look at the highest milli-candle (mcd) leds you can find in a 3mm package they work well.
Typically they are at least 2000mcd some are even higher. Check that their brightness ratings are at the same test current. They try to cheat a bit in the specs.
Red because they are the most efficient and 3mm because the die is smaller (less power) and the lens has a tighter pattern ( appears brighter).
 If you use one of those you could probably get away with about 4k resistor for the 6v operation. (subject to the led chosen).

Sage


----------



## jgedde

Thanks for the advice.  I reduced the values of the current limiting resistors to account for the additional drop introduced by the 100 ohm series resistor on the output of the hall.  It's only there to avoid "spiking" the hall if there is a breakdown somewhere else in the circuit.

So, the 270 ohm is really 370 ohms, the 910 ohms is really 1.01k.

The LED has a Vf of about 2.1V (green) so this gives about 10 mA in the LED.  If you like a red LED instead, the resistor values should be larger.

All that said, you're spot on regarding the new LEDs and the user could likely use much larger resistors if he/she didn't buy their LEDs from Radio Shack.

Being colorblind to red, I usually shy away from red LEDs since what looks bright to others isn't to me.  Many years ago I was dating an X-ray tech.  She took me into the developing room because I was interested in the process.  She could see fine and was showing me how it works.  I couldn't see a damn thing.  At first I thought she was pulling a joke on me!  As far as I could tell it was pitch black, but I was making funny faces at her and she knew exactly what I was doing!

John


----------



## jgedde

dsage said:


> John:
> 
> I guess we must have been typing at the same time but you won.  - and as usual great minds think alike. Our recommendations are the same.
> 
> Re: your circuit. I wouldn't have thought the hall sensors would consume so much power just sitting there, but a quick look at the spec sheet confirms your observations. Surprising.
> 
> I guess it's a challenge to try to reduce power consumption but lets face it, your control circuit would run for at least 350 hours on a 7ah battery. I think it's about as good as it going to get.
> 
> BTW for those of you out there looking for a circuit to build, I would stick with building John's circuit over mine. Given that there is little control over the installation of the circuit in a users engine (proper grounding procedures, lead length etc.) the additional protection items in John's circuit will add a measure of reliability.
> 
> Sage


 
How about a hybrid taking the best of both designs?  In other words, add my protections to your circuit and call it a day.  OK, so my circuit takes much less power.  Does that even matter if we have to supply juice to the halls?  

In addition, I have a diode drop in the gate drive to the IGBT - you don't.  That means you'll have a somewhat beefier spark at low supply voltages 

I'm running my circuit and coil right now from 4 AA cells.  It works fine, but what happens as the batteries start to drop out? I'll need all the gate drive I can get.  

I was considering a bulk storage cap to help lower the supply impedance, but a rough computation showed something like 47000 uF to be necessary to keep the voltage within 1V through a coil charge and spark cycle.  That bloody cap is as big as my coil!

I am feeling funny about having my circuit recommended when I'll likely use a variation of your circuit in my engine!  

Cheers,
John


----------



## dsage

10-4 on the 100 ohms you added. I forgot about that being in the LED circuit as well.

Re: the combined circuit:
Well, the way I look at it, they are variations of each other. I'm happy to recommend yours considering all the benefits you've added. There is a lot of merit in the additional protection seeing as you/we have little control over how people wire it up.  Messy or long wiring, improper grounding etc.  is going to be a big factor in how well it works or even if it will self destruct. The extra protection is good. Let the masses choose.

 I'm not so interested in saving power. But it never hurts. I have a whole stack of NiMH and Lithiium Ion batteries from old cell phones and a lot of gel cells as well. Both my Atkinson engine and the Sage/Howell V8 have flat cell phone batteries at 1600mah hidden underneath. The Ford engine uses a 4Ah gell cell.
I could probably do better with some of the newer 2500mah+ Lion or NiMh AA batteries out there today. I assume that's what you are using.
I use what I've got around free.

BTW I assume you know about Super caps at a few farads. But they have really low voltage ratings.


http://davesage.ca

PS> I notice the spam generator has turned my word "cellphones" above into a link for cell phones.
Not my doing.

Sage


----------



## metalmad

Hi Guys
I hate replying to posts like this as I simply don't know anything about it, but this time I have a question!
Can a Hall effect circuit be made at home in the shed that has automatic timing advance?
Based on RPM for example??
Even I might be tempted with something like that:hDe:
Pete


----------



## Lakc

metalmad said:


> Hi Guys
> I hate replying to posts like this as I simply don't know anything about it, but this time I have a question!
> Can a Hall effect circuit be made at home in the shed that has automatic timing advance?
> Based on RPM for example??
> Even I might be tempted with something like that:hDe:
> Pete


Patience young padwan. ;D
There are several designs out there already. Most appear to be CDI type with a microcontroller running the show. Eventually, I will have a design good enough to release here.
As several recent other threads have pointed out, its really impossible to have the "perfect" ignition circuit where the coil is not specified, its electrical characteristics are too important. Not to discount the work done here and elsewhere, this is a very fine circuit and should serve people well, but to design a modern bulletproof ignition _system_, you need the whole ball of wax in front of you. I applaud the work of John and Sage, both here and elsewhere, and hope to be able to make my own contribution sometime in the future.


----------



## dsage

Lakc:

Yes and we are patiently waiting for that CDI unit. I'd like to build one. 

But holy smoke - what a can of worms to release that to the masses - unless you plan on selling pre-programmed PIC's and boards. 

I have a nice circuit built but I'm not happy with the size and don't know enough about winding transformers to reduce it down. It's way overpowered for a model so it's on the shelf for now.

Sage


----------



## tornitore45

Late response, I have been offline for a while.
The CDI kit I mention was purchased at www.cncengines.com [email protected] 
I have not utilized yet since the engine is not finished, but tested with a primary load rougly equivalent to the primary L+R, and got some waveform.
The design and modeling of a miniature ignition is quite a challenge, there are several parameters hard to define:
Behavior of the coil with a high turn ratio and high insulation lead to high leakage and the high frequency of a CDI oscillation give core losses hard to predict. Coil + Leads Capacitance is an integral part of the circuit and the circuit has two distinct modes of operations: initial rise to spark is "open circuit" (not really open since is loaded by the sec capacitance) after spark is practically a shorted load oscillating between leakage inductanca and capacitance.


----------



## jgedde

In case any of you don't know...  Dave Sage and I are collaborating on a ignition circuit combining the best of his design and mine...

Here's where we're at...  We have almost completed the documentation (schematics, wiring diagrams, etc).  In addition, I've prototyped the improved circuit (two transistor version).  

Here's a sneak preview: a video of it firing a full size spark plug...  The coil is from J.E. Howell.  Power is 6V from 4 AA alkaline cells.

[ame="http://www.youtube.com/watch?v=b8vc_2LUddE"]http://www.youtube.com/watch?v=b8vc_2LUddE[/ame]

John


----------



## Mosey

Absolutelywonderful! Thanks.
Mosey


----------



## steam58

Looking good would like to build here.
Thanks
Jay


----------



## jgedde

OK.  Here is the final circuit.  I've tested the heck out of this one, including driving full size coils, simulating the input from high RPMs, low RPMs, multicylinder ignitions, etc.

Higher resolution PDF versions of the schematics below are attached...

John 

View attachment Sheet1.pdf


View attachment Sheet2.pdf


----------



## vridhisharma

Great Sharing I really want to know about this.


----------



## canadianhorsepower

Thanks guys great circuit, had some spare time yesterday
and all parts in stock and put it together. works great.
I think with a little bit of tweeking with a double side PCB
it will be the size of a quarterThm:


----------



## gbritnell

Thanks guys for all the time and effort put into this ignition. I'm sure there will be many building it, including myself. I have one question. I have tried to find the terminal strips that you show in the video. I have a DigiKey catalog and for the life of me I can't find something like you show. Any info would certainly be appreciated.
gbritnell


----------



## canadianhorsepower

gbritnell said:


> Thanks guys for all the time and effort put into this ignition. I'm sure there will be many building it, including myself. I have one question. I have tried to find the terminal strips that you show in the video. I have a DigiKey catalog and for the life of me I can't find something like you show. Any info would certainly be appreciated.
> gbritnell


 
here George

http://www.digikey.com/product-sear...d/1442751?k=PCB 5mm terminal block side entry


----------



## jgedde

gbritnell said:


> Thanks guys for all the time and effort put into this ignition. I'm sure there will be many building it, including myself. I have one question. I have tried to find the terminal strips that you show in the video. I have a DigiKey catalog and for the life of me I can't find something like you show. Any info would certainly be appreciated.
> gbritnell


 

George,  It was one of these that I used...  

http://www.digikey.com/scripts/dkse...tm=0&fid=0&quantity=0&PV1075=9&PV89=1&stock=1

John


----------



## jgedde

canadianhorsepower said:


> Thanks guys great circuit, had some spare time yesterday
> and all parts in stock and put it together. works great.
> I think with a little bit of tweeking with a double side PCB
> it will be the size of a quarterThm:


 
Thanks Luc,

I think the size of a quarter is very achieveable.  My prototype is roughly 1 x 1".  If we we to use SMT components (don't be afraid guys - no smaller than 0805 sizes), we could get it even smaller!

John


----------



## canadianhorsepower

jgedde said:


> Thanks Luc,
> 
> I think the size of a quarter is very achieveable.  My prototype is roughly 1 x 1".  If we we to use SMT components (don't be afraid guys - no smaller than 0805 sizes), we could get it even smaller!
> 
> John


 
Hey John your sugesting a heat sink for high RPM you think
that SMT would handle it?:fan:

i didnt understand 0805 sizes


----------



## jgedde

canadianhorsepower said:


> Hey John your sugesting a heat sink for high RPM you think
> that SMT would handle it?:fan:
> 
> i didnt understand 0805 sizes


 
The SMT version of the IGBT has a theta jc (thermal resistance from junction to case) similar to the TO-220, so assuming you built a thermal path into the board (or a heatsink plane), it would be fine.  

I ran the circuit using an input of 533 Hz (an 8 cylinder engine at 8000 RPM with a dwell angle of about 15-20 deg ), and the transistor ran rather warm with no heatsink. You could likely get away with no heatsink, but in any case only a small heatsink would be needed)

The coil was also very warm showing that a ballast resistor would beneficial in this case!  

At 5 Hz (a hit and miss engine at 600 RPM, Q1 and the coil are ice cold)

That said, I'd still use the TO-220 on an SMT board mounted vertically.  That would allow the board to be smaller (the SMT version has to lay flat).

As far as 0805 is concerned, that may not be familiar outside the US.  I'm presuming you use metric sizes in Canada.  In that case, using the metric designation, they're known as 2012 resistors.  I usually use the Panasonic ERJ-6ENF series of resistors...

The four digits are a size code.  0805 is 0.08" long by 0.05" wide.  That's about the smallest resistor that can be hand soldered.  A 1206 (.120" long by .060") wide is easier and probably gives the best balance of ease of assembly and size.  

I have soldered 0402 and 0603 resistors by hand, but I needed a microscope.  Now they even have 0201 and 0202 resistors.  Those are so small that even a small breeze (like your breath) sends them off the bench into neverland. 

John


----------



## gbritnell

Hi John,
I'm going through the Digikey catalog to assemble a parts list but not being totally electronic savvy I and I'm sure others could use a little more help. Case in point, I looked up the Diode 1N4148 and got 4 pages of product. Q1, Q2, D1 and D2 aren't a problem but could you be a little more specific for the caps and resistors, type, voltage, wattage etc.  In you last post you mentioned size of the resistors. I'm not trying to miniaturize this unit to fit into the size of my distributor so using components that are fairly easy to handle would be ok.  
Thanks again,
gbritnell


----------



## jgedde

Give me an hour or so, I'll post a BOM with links to the parts.

John


----------



## jgedde

See attached: The Bill of materials...

Cheers!
John 

View attachment BOM.pdf


----------



## gbritnell

John,
Thanks ever so much. I certainly didn't want to be a pest about it but you fellows are the experts on this stuff and while I enjoyed reading all the posts on this subject sometimes I had no idea of what you were talking about. 
gbritnell


----------



## jgedde

gbritnell said:


> John,
> Thanks ever so much. I certainly didn't want to be a pest about it but you fellows are the experts on this stuff and while I enjoyed reading all the posts on this subject sometimes I had no idea of what you were talking about.
> gbritnell


 

No problem.  It was my pleasure.

Maybe one day you'll share how you do radii and features in three axes with a manual mill!  Or how you get rid of tooling marks so effectively.    J/K!

John


----------



## canadianhorsepower

gbritnell said:


> John,
> Thanks ever so much. I certainly didn't want to be a pest about it but you fellows are the experts on this stuff and while I enjoyed reading all the posts on this subject sometimes I had no idea of what you were talking about.
> gbritnell


 

gbritnell, I was looking at the BOM and just
 to make sure trhat all angle are covered
c1&c3  could be mark 104 instead of the .1 micro
c2 could be marl 105 instead of 1 micro


----------



## jgedde

canadianhorsepower said:


> gbritnell, I was looking at the BOM and just
> to make sure trhat all angle are covered
> c1&c3  could be mark 104 instead of the .1 micro
> c2 could be marl 105 instead of 1 micro


 
Luc is right.  To be clear, he's talking about the code marked on the side of capacitors.  

The first two digits are the first two numbers in the capacitance value in picofarads, the last number is the number of zeros to append.  So 105 is 10,00000 = 1,000,000 pF = 1 uF.   121 would be 120 pF and so on.  The caps in the ignition circuit will be 104 or 105.

John


----------



## jgedde

I was thinking, if I did a PCB layout and I had enough interest, I could have good quality boards made (FR4, double sided, with silkscreen, and plated through holes). 

I'm not looking to make any money on this, but I'd need enough takers to cover the tooling costs at the PCB house (figure about $500-600).  It could be made cheaper eliminating the silkscreen, but that's a big aid in assembly and test.

John


----------



## ChrisLister

Hi,

If you look around you can find PCB-manufacterers who are much cheaper.

I make my prototype PCB's in china (more than 6 layers) or in Belgium/Holland and I never pay for tooling cast. A 2 layer eurocard PCB with soldermask and silkscreen will cast about 120euro or 150 dollar just for one piece.

I will look up the addresses and post them here this weekend if needed

Greetings,

Chris


----------



## Johnvankoeveringe

Hi John 
I watched your video and was able to capture the big spark in a still pic.
I'm in the process off putting it together today .
Thanks again for all the help and sharing.
John VK.


----------



## jgedde

Hi John VK,

Can you post that picture?  How did you make out with your circuit build?  

Cheers!
John


----------



## Johnvankoeveringe

Hy guys.
I've never posted anything yet as I'm pretty new to this stuff.
Here are the frames I was able to capture off John's video.
The pic's are no hell but they do show a very good spark.
I've asembled the circuit but hv'nt tested it yet.
I had a little trouble finding out the output pins of the alegro HED but found the data sheet for the device today
will test run tomorrow.
JohnVK


----------



## mayhugh1

Hi,
      I was just wondering if anyone had yet actually used this in a working model and is so what your experiences/results were?

Terry


----------



## choefer

Have any of you thought of adding a charging system so that you could run without batteries?


----------



## dsage

mayhugh1 said:


> Hi,
> I was just wondering if anyone had yet actually used this in a working model and is so what your experiences/results were?
> 
> Terry




Hi Terry:

The circuit works well. John and I worked together on this design. It's essentially a little more elegant and durable version of what I've been using for quite some time with good success. As with any ignition it comes down to the coil you have to throw at it. But it should be able to drive anything including a full sized car coil. (with a ballast resistor). See the connection diagrams posted a ways back.




Dave Sage


----------



## dsage

choefer said:


> Have any of you thought of adding a charging system so that you could run without batteries?



Choefer:

Without a battery - How would you start it in the first place?
I can imagine one could easily create a generator to charge the battery if that's what you mean.

Sage


----------



## stevehuckss396

dsage said:


> Choefer:
> 
> Without a battery - How would you start it in the first place?
> Sage




Battery drill!  

What did I win?


----------



## canadianhorsepower

dsage said:


> Choefer:
> 
> Without a battery - How would you start it in the first place?
> I can imagine one could easily create a generator to charge the battery if that's what you mean.
> 
> Sage


 
If your drill spin it fast enough your charging system
(small dc motor) should give you enough voltage power 
to ignite the circuit, but will you have enough current
to get your coil to work:hDe:


----------



## phrodo

Just FYI for those of you looking for a cheap place in the US or Canada for PCB's. I've been using Alberta Printed Circuits (www.apcircuits.com) for years. Usually a few days normal delivery for boards and cheap, cheap, cheap. I paid $50 for 4 pcs of a small, double sided (1x2") board with plated through holes, solder mask and silkscreen.


----------



## choefer

dsage said:


> Choefer:
> 
> Without a battery - How would you start it in the first place?
> I can imagine one could easily create a generator to charge the battery if that's what you mean.
> 
> Sage



I have several normal small engines that run and start without batteries. though i am new to the 'model' engine universe i am not new to small engines. some machines that have engines that run in this manner are: weedeaters, generators, push-mowers, snow-blowers, rototillers, small outboard boat engines, etc. while many of these are run with magnetos, some run with small generators. one example of which is a 1970s Mercury outboard engine with thunderbolt ignition. similar to a magneto, it uses small stator coils and magnets under the flywheel to create a voltage, but with the generator the voltages are lower (200-300V) and that power is then fed to the main ignition coil and control circuit. in fact it is kinda cool how they work. Often there are more than one type of stator coils that function at different rpms, allowing the spark to be strong no matter. i just thought it would be a fairly simple step to take the battery out of the loop so that you no longer have to worry so much about current draw or going to a show without good batteries. 

Casey


----------



## ozzie46

I have some questions about the grounds for this board. I'm sorry but I can't read electrical schematics.

 I do know what the ground symbol is though.

  1. Where does the ground go for at line E3 that runs off C3.
  2   "          "      "     "         "    "   "  "   E5. I'm assuming this is batt neg post.
  3   "          "      "     "         "    "    " "   E7.
  4   "          "      "     "         "    "    " "   E8 off of D3.
  5  And finally where does the ground go at E4 off of Q1 where it says "see note 5"


   I'm sorry if this seems obvious to most people but I'm not learned in electronics. My son can read the plan and build the board but he doesn't know ignition systems so he doesn't know where they go either.

  Thanks 

Ron


----------



## canadianhorsepower

pretty hard to answer if their is no diagram


----------



## ozzie46

The diagram is at post # 63 of this thread. Sorry I should have included that.

 Ron


----------



## canadianhorsepower

1. Where does the ground go for at line E3 that runs off C3.

*E3 and E1 are tide together they are live +*

  2   "          "      "     "         "    "   "  "   E5. I'm assuming this is batt neg post. 

*yes that batt ground* 


  3   "          "      "     "         "    "    " "   E7. *connect with any other ground* 

  4   "          "      "     "         "    "    " "   E8 off of D3.

*E8 is the input signal from your hall sensor*

  5  And finally where does the ground go at E4 off of Q1 where it says "see note 5"

*all ground can be attached to the battery but note 5 says to connect both emitter together (the pin with an arrow on your diagram)*

hope it help


----------



## ozzie46

Thanks Luc, I'm still a little confused though.

 On lineE3 there is a component C3 that shows a ground, are you saying it can be tied to the ground at E5?

  At line E8 there is a component D3 that has a ground, where does it go? 

 Also B3 goes to batt., but which ground goes to the engine? and does one get screwed to the distributor?

  Thanks for your help on this.

Ron


----------



## canadianhorsepower

On lineE3 there is a component C3 that shows a ground, are you saying it can be tied to the ground at E5?

*Yes the ground of C3 can bi tied to E5
*
  At line E8 there is a component D3 that has a ground, where does it go? 

 Also B3 goes to batt., but which ground goes to the engine? and does one get screwed to the distributor?

*their is only one ground, it's common practice to draw a circuit like this*
*to only show wires that are important*

*all ground MUST be tied together on the engine, battery and distributor*


----------



## ozzie46

Thanks Luc. I think I'm getting it. 

 Ron


----------



## canadianhorsepower

it should look like this when finish
curious what are you planning to use this on


----------



## ozzie46

Thanks Luc. Now that makes it much more understandable for me.

Thanks for being so patient with me and making it clear.

  Ron


----------



## jgedde

canadianhorsepower said:


> it should look like this when finish
> curious what are you planning to use this on


 

Thanks Luc!  That's exactly what I had in mind.  

Also, thanks for making that sketch.  I haven't had a lot of free time to work on my engines and post on forums, so you saved me a bunch of time by taking care of this.

Cheers!
John


----------



## jgedde

ozzie46 said:


> I have some questions about the grounds for this board. I'm sorry but I can't read electrical schematics.
> 
> I do know what the ground symbol is though.
> 
> 1. Where does the ground go for at line E3 that runs off C3.
> 2   "          "      "     "         "    "   "  "   E5. I'm assuming this is batt neg post.
> 3   "          "      "     "         "    "    " "   E7.
> 4   "          "      "     "         "    "    " "   E8 off of D3.
> 5  And finally where does the ground go at E4 off of Q1 where it says "see note 5"
> 
> 
> I'm sorry if this seems obvious to most people but I'm not learned in electronics. My son can read the plan and build the board but he doesn't know ignition systems so he doesn't know where they go either.
> 
> Thanks
> 
> Ron


 
Ron,  the second drawing in post 63 shows how the circuit gets wired externally.  The yellow box is the circuit board and everything outside of the box is either on or near your engine.

The power switch is basically akin to an ignition switch.

I suggest that the circuit be built first with terminal strips or equivalent for each of the E designators.  Now, you can follow the second diagram to wire it all up.

Best of luck to you!
John


----------



## ozzie46

Thanks John.  That helps too.

 Luc I 'm using it on a "Mastiff" 4 cyl 4 stroke enine that was in Model Engineer back in 1973.

  I just finished the plugs and took them to friend that has a buzz coil and checked them out. All 4 spark where they should , not where they shouldn't. ;D;D

    Here's a link.

http://www.modelenginemaker.com/index.php/topic,1932.0.html

  Ron


----------



## ozzie46

ozzie46 said:


> Thanks John.  That helps too.
> 
> Luc I 'm using it on a "Mastiff" 4 cyl 4 stroke enine that was in Model Engineer back in 1973.
> 
> I just finished the plugs and took them to friend that has a buzz coil and checked them out. All 4 spark where they should , not where they shouldn't. ;D;D
> 
> Here's a link.
> 
> http://www.modelenginemaker.com/index.php/topic,1932.0.html
> 
> Ron









Here is the picture of the motor cycle coil. Orange with white stripe is positive. The side posts of the cylinder is ground. The white wire is unknown ( any idea please let me know). Please advise on how to connect this coil to the sage/circuit we have been chatting about.


----------



## canadianhorsepower

> Here is the picture of the motor cycle coil. Orange with white stripe is positive. The side posts of the cylinder is ground. The white wire is unknown ( any idea please let me know). Please advise on how to connect this coil to the sage/circuit we have been chatting about.


 

BEFORE YOU BLOW ANYTHING UP

*put POSITIVE wire from battery to your ORANGE wire *
*this is the same positive of your circuit*

*put a ground wire from your battery to your side post *

*NOW USE ANOTHER WIRE FROM GROUND AND FLASH IT" SMALL TOUTCH" WITH THE WHITE ONE, IT SHOULD CREATE A SPARK.*

*from the HT wire to ground*




*if you don't see any, ask your wife to hold the coil in her hand and do the same thing*




*You might not see a spark, but you will feel the slap in your face if there is oneRof}*Rof}Rof}


----------



## canadianhorsepower

it should look like this when it's done


----------



## ozzie46

Luc,

 All these connections I'm talking about now are on the board only.

 I have E1, E2and E3 all connected together as Positive (+). Tha'ts what it appears to be in the digram. It has E1,E2 and E3 all as (+) E1 says vcoil. What is "vcoil" There is a dotted line connecting E1 and E3 so I'm guessing that means to connect them together by a jumper. Then E2 says coil (+) so I'm guessing that means to connect it to E1and E3. Is this correct?

E4 is connected to the emiter side of Q2 only.


  All grounds are connected and come out at E5. Is this right?

  I keep looking at the video John posted on youtube and it looks like he has a wire from either E2 or E3 connected to the metal casing of the spark plug but that is where the negative (-) or E5 should go right? That would be engine ground.

 Sorry to be such a dunce about this. :wall::wall::wall:

 Ron


----------



## canadianhorsepower

Luc,

 All these connections I'm talking about now are on the board only.

 I have E1, E2and E3 all connected together as Positive (+). Tha'ts what it appears to be in the digram. It has E1,E2 and E3 all as (+) E1 says vcoil. What is "vcoil" 

*v coil is what supply voltage to the Positive side of your coil,*
*you are using single voltage so E1,2,3 are tied together*

There is a dotted line connecting E1 and E3 so I'm guessing that means to connect them together by a jumper. 

*yes tied them together*




Then E2 says coil (+) so I'm guessing that means to connect it to E1and E3. Is this correct?


*yes tied them together*

E4 is connected to the emiter side of Q2 only.

*yes right again*


  All grounds are connected and come out at E5. Is this right?

*yes again*

  I keep looking at the video John posted on youtube and it looks like he has a wire from either E2 or E3 connected to the metal casing of the spark plug but that is where the negative (-) or E5 should go right? That would be engine ground.

don't bother about that video, follow the diagram I posted yesterday
and you will be fine
IF YOU DON'T HAVE ANY SPARKS .............................
YOUR LEAD SHOULD BE FLASHING. AT LEAST

 Sorry to be such a dunce about this. :wall::wall::wall:


----------



## ozzie46

Thanks Luc, will give it a try today. after I fix a few more mistakes on the circuit.
  Will let you know the results.
  Ron


----------



## ozzie46

OK here's what I have;

E1 to orange on coil
E2 to Orange on coil
E3 to Batt (+)
E4 to white on coil
E5 to Batt (-) and grounded to coil mounting screws
Plug grounded to coil mounting screws
Hall sensor in E6,7and 8

Nothing happens when I try magnet.

Using test lite this happens
test lite to R3= plug sparks 
test lite to R6 = plug sparks
test lite to R5 = LED lites
test lite to D3 = plug sparks
test lite on E8 side of C2 = LED lites

test lite to other resistors shows nothing.
Any ideas?

 Ron


----------



## canadianhorsepower

your all sensor is in backward
or burned
or your magnet is backward
you need south pole to energise

now E6 = positive
       E7 = ground
       E8 = signal in


----------



## ozzie46

I thought I had it in right. I'll double check.

  I'm using 2 different magnets that oppose each other for testing.

 Ron


----------



## ozzie46

Looked up sensor data sheet found correct polarity, changed out sensor for new one, still won't work.  :wall::wall::wall:

  Ron


----------



## ozzie46

Remembered that on magnets opposites attract so I flipped one magnet, still no luck.

 Ron


----------



## canadianhorsepower

Try one magnet at a time
Check polarity of wire at all sensor


----------



## ozzie46

Progress!!!
 I got the LED to lite but still no spark. 

 Son had put two 100K resistors where there were supposed to be 100 ohm resistors plus he had put Q1 in wrong. Changed it out and put a new one in.

 So since Led flashes do you think the problem is in coil and plug wiring. I know plugs are good. A friend checked them out on his buzz coil and they all sparked.

 Ron


----------



## ozzie46

I did that coil check test from post # 105 and I get a very very weak spark from plug wire ( high tension) to ground. you can't hardly even see it. The white wire flashes pretty good.

  Maybe problem is coil now?

Ron


----------



## stevehuckss396

Some coils are made to work with CDI ignitions and magnitos and require a higher voltage to the primary side of the coil. Try a standard coil for a early 70's chevy or something like that.


----------



## ozzie46

Thanks Steve I'm trying to come up with one. This coil is out of a 70s or something motorcycle. Maybe a Suzuki.


----------



## canadianhorsepower

stevehuckss396 said:


> Some coils are made to work with CDI ignitions and magnitos and require a higher voltage to the primary side of the coil. Try a standard coil for a early 70's chevy or something like that.


 

Thanks Steve  I totally forgot your coil can come from anything that has 
a points and condenser or it wont work
substitute your coil with a test light again


----------



## ozzie46

ok ,
E1 not hooked up
E2to test lite probe
E3 to Batt +
E4 to test lite ground
E5 to Batt -

LED flashes, Test lite does not lite
Tried it with E1 and E2 tied together at test probe, same results.

 Ron


----------



## canadianhorsepower

ozzie46 said:


> ok ,
> E1 not hooked up
> E2to test lite probe
> E3 to Batt +
> E4 to test lite ground
> E5 to Batt -
> 
> LED flashes, Test lite does not lite
> Tried it with E1 and E2 tied together at test probe, same results.
> 
> Ron


Ron I cant help you if you try different stuff that I'm telling you to do
please be with me

E1 E2 E3 TIED TOGETHER POSITIVE BATTERY


E5 E7 D3 EMITER OF Q2 AND Q1  ARROW TIED TO GROUND


NOW PUT A BULB ACROOS E2 AND E4 DO NOT REMOVE IT

NOW USE A LED AND CHECK PULSE  BETWWEN R6 AND Q2 
IF IT FLASH YOUR OK
IF NOT YOUR HALL IS NOT WORKING

IF A PULSE CHECK BETWEEN R4 AND PIN 1 OF Q1 
AND NO FLASHS OF THE BULB BETWEEN E2 AND E4 
Q1 IS BADLY WIRED OR FRIED

NOW USE A LED WITH PROPER RESISTANCE TO VOLTAGE USE

IF YOU FOLLOW THESE STEPS IT WILL WORK


----------



## ozzie46

Luc, I thought I was doing it right.

You understand that the LED on the board flashes by me waving the south pole of a magnet at the hall sensor right?  

 I will do all these test tomorrow. I have been at this thing since 4 am this morning and need a break. You probably do as well. I know it's frustrating trying to help over the web.and I do really appreciate all the help you've given me. 


E5 E7 D3 EMITER OF Q2 AND Q1  ARROW TIED TO GROUND.         These are all tied to ground


NOW PUT A BULB ACROOS E2 AND E4 DO NOT REMOVE IT.        This is what I did with my test lite.



NOW USE A LED AND CHECK PULSE  BETWWEN R6 AND Q2 
IF IT FLASH YOUR OK
IF NOT YOUR HALL IS NOT WORKING

IF A PULSE CHECK BETWEEN R4 AND PIN 1 OF Q1 
AND NO FLASHS OF THE BULB BETWEEN E2 AND E4 
Q1 IS BADLY WIRED OR FRIED

NOW USE A LED WITH PROPER RESISTANCE TO VOLTAGE USE     

    Will do these tomorrow.

  Thanks you very much Luc. If nothing else I have learned a lot about tracking circuits and reading data sheets.


  Ron


----------



## ozzie46

Took one last look for the night and it looks like my son put a 100k 1/2 watt resistor in at R3 instead of a 100K 1/4 watt. 

 Could this be the problem?
 Will change it out for the 100K 1/4 watt one in the morning as its not what the schematic calls for.

 Ron


----------



## canadianhorsepower

That resistor 1/2 watt to 1/4 watt is not your problem
keep posting
cheers

Luc


----------



## ozzie46

Luc,  It occurred to me that what I call a test light ( coming from a automotive background) and what you call a test light ( coming from a electrical engineering background) might be two different things.

 This is what I have as a test light.   I also have a cheap multimeter I got from harbor freight but am not sure how to use it.
That's all I have as test equipment.

http://www.autozone.com/autozone/ac...it-tester/_/N-2714?itemIdentifier=186543_0_0_


NOW USE A LED AND CHECK PULSE  BETWWEN R6 AND Q2 

What kind of LED and how do you do this?

IF IT FLASH YOUR OK
IF NOT YOUR HALL IS NOT WORKING

IF A PULSE CHECK BETWEEN R4 AND PIN 1 OF Q1 
AND NO FLASHS OF THE BULB BETWEEN E2 AND E4 
Q1 IS BADLY WIRED OR FRIED

NOW USE A LED WITH PROPER RESISTANCE TO VOLTAGE USE
IF YOU FOLLOW THESE STEPS IT WILL WORK


What is proper resistance?


 Sorry about all the questions but I know nothing about this stuff. I'm a complete baby lost in the woods.

Ron


----------



## canadianhorsepower

that test light is fine
now proper resistance would be different depending your voltage supply
in this case it should be the same that what your using with your LED now
(R1)

because a LED is a polarize component it will only work in one direction
so for not mixing things up later in testing

plug you test on your battery source and when it will turn on mark the leads
accordingly... the positive with a + and negative with a-

the test after this will be very important that you notice what the polarity is
 and go one step at a time and give me the answer to my question
cheers


----------



## ozzie46

OK Luc, this may take a while.

 Ron


----------



## ozzie46

Which pin on Q2 do I use for check between R6 and Q2?

Ron


----------



## ozzie46

Put leads of LED on batt posts and it flashed on, went out and won't come on anymore. I guess it burned it out.

 Ron


----------



## canadianhorsepower

ozzie46 said:


> Put leads of LED on batt posts and it flashed on, went out and won't come on anymore. I guess it burned it out.
> 
> Ron


 
if you didn't have a resistor attaché to it
it's like a match .. it works only ounce


----------



## canadianhorsepower

ozzie46 said:


> Which pin on Q2 do I use for check between R6 and Q2?
> 
> Ron


 between positive and center pin 

this is why you need an LED
to do the test


----------



## canadianhorsepower

these might help you


----------



## ozzie46

Thanks Luc, I have those. That's how I found out son had put Q1 in wrong. You mentioned which pin on Q1 but didn't say which pin on Q2. 
I don't have another LED at the moment plus I just got my laptop back from repair shop. I will be working on it to get set back up as I lost all my programs and files.  So I will be taking a break from this for a bit.

 Ron


----------



## canadianhorsepower

OK  on Q2 it would be gate instead of Base
both Q work the same  its only the power that's different
all this circuit is really is a relay between your signal and your coil
If you want you can do some testing with a test light but something has to be between  E2 and E4 
what voltage source are you using

and the signal at B and G is positive you can check that with a millimetre also


----------



## ozzie46

12 volt car batt.

 ron


----------



## canadianhorsepower

ozzie46 said:


> 12 volt car batt.
> 
> ron


 
then you'll need a 3.9k resistor it should be the same one you use in your circuit

when do you want to check this in PM if we do this one shot it should not be more than 4 test 0r 15 min


----------



## ozzie46

Sorry wife commandeered me for house cleaning. Relatives coming Friday.

  Maybe we can try tomorrow evening.

  Also I don't have any more 3.9k 1/4 watt resistors. Local radio shack has 3.3k 1/4 watt or 4.7k  1/4 wat tbut no 3.9k 1/4 watt. 
 They do have 3.9k 1/2 watt resistors if they will work. If it has to be 3.9k 1/4 watt, I will have to order it and that will take at least a week. Probably cost .50 cents and cost $8.00 Shipping.:wall:


 Edited to put in wattage of resistors.
  Ron


----------



## canadianhorsepower

ozzie46 said:


> Maybe we can try tomorrow evening.
> 
> Also I don't have any more 3.9k resistors. Local radio shack has 3.3k or 4.7k but no 3.9k. .:wall:
> 
> Ron


 
3.3 or 4.7 will work grab any of them it would be good if you have an extra diode 1n400?? or a 1n4148

where are you but tomorrow at 6PM should be good for me


----------



## ozzie46

I'm in Pueblo Colorado. Mountain time zone I believe you are in Central Time Zone and that  would put you 1 hr ahead of me. Your 6 pm would be my 5 pm.
 I have two 1N4003 diodes and one  NTE 116 diode.  Also three Q1s and  two Q2s. Also Have spare capacitors on hand. The only thing I don't have I guess is the LEDs and radio shack doesn't have them.

Ron


----------



## canadianhorsepower

ozzie46 said:


> I'm in Pueblo Colorado. Mountain time zone I believe you are in Central Time Zone and that  would put you 1 hr ahead of me. Your 6 pm would be my 5 pm.
> I have two 1N4003 diodes and one  NTE 116 diode.  Also three Q1s and  two Q2s. Also Have spare capacitors on hand. The only thing I don't have I guess is the LEDs and radio shack doesn't have them.
> 
> Ron


 
That's fine by me is tomorrow 7 your time good, if so get that resistor
 a few strip wires and it should work tomorrow

cheers
Luc


----------



## ozzie46

UHH   Luc if it's 6 pm your time it will be 5 pm my time ok?
Ron


----------



## canadianhorsepower

ozzie46 said:


> UHH   Luc if it's 6 pm your time it will be 5 pm my time ok?
> Ron


 

yes so  7pm your time will be 6pm my time


----------



## jgedde

Hey guys, I feel like a heel right now... It has come to my attention that there is an error in sheet 2 of the schematics. The ignition module's external wiring is not correct because the E numbers on the circuit block are in error. Looks as if my design tool assigned numbers the way it wanted and not the way I did...  To be clear, the error is only on sheet 2.  The circuit diagram on sheet 1 is correct.

It was my intent to have a one to one match between the E point location on the sheet 1 schematic and the E location on the block in sheet 2.

Even worse, I haven't been following this thread closely enough to support those who have been having problems.

I've attached revised diagrams. Hopefully an admin can go back and edit the post with the schematics to point to this post.

I am hoping that any miswiring that happened as a result of the problem didn't break any components and cost money for those who decided to give it a try.

Special thanks to Dsage and CanadianHorsepower for their work!

John 

View attachment Sheet1.pdf


View attachment Sheet2.pdf


----------



## jgedde

One more thing about the circuit...  Remember that it's designed to prevent the coil overheating or the battery going dead if the engine is stopped with the hall sensor positioned in front of the magnet?

I've heard that guys are having trouble testing the circuit and this feature is to blame.  While it's on an engine, and the magnet passes by hall sensor quickly, it's not an issue.

OK, so here's what happens.  If you put the magnet right in front of the hall sensor during testing, you'll get a weak spark.  This is because the circuit times out thinking the engine is stopped.  What happens is the IGBT is turned off slowly and a weak spark is produced.

I will say this...  My circuit build up fires a full sized lawnmower plug with a 0.045" gap using the J.E. Howell coil.  But, the hall needs to be triggered in a similar fashion to what it sees on a real engine.

To test it, I need to pass a magnet rapidly across the front of the sensor.  I've been using a magnet on the end of a small, but somewhat long screwdriver.  The magnet is waved past the hall sensor quickly.

Doing this, I get a very strong spark.  In fact, I've been zapped a bunch of times by this, and it feels stronger than off a lawnmower engine!  Ouch!  Is it a GM HEI type zap?  No, but those of you who've been caught off guard by an HEI will never forget it!

Luc built the circuit also.  He says he puts a fixtured magnet in his drill press and the circuit fires just fine.

So, what to do during testing....  You can either speed up the magnet speed past the hall sensor or temporarily put a short across C2.  If C2 remains shorted, the circuit will work fine, but the protection against coil overheating and battery drain will be lost. 

I've also found that the coil's polarity makes a big difference.  If you still get a weak spark, try swapping the + and - leads to your coil.

John

John


----------



## fourstroke

I have been following this thread with interest as I hope to use this system on my hired hand engine, you can see the progress in the "engines from castings" section
However I am having some difficulty obtaining the Q1 and Q2 components here in the UK. I also dont know what kind of hall sensor I need
Can anybody help me with the part number of a hall sensor and perhaps alternative part numbers for Q1&2
Regards
Dougie


----------



## canadianhorsepower

ok here we are even here in Canada some of these parts number are 
not "on the shelf " thing
2n4124 can be replace with 2n3904 

as for the 2 others this what the specs are "close enough"

if you go to a GOOD reseller finding a match should be a breeze
good luck

http://pdf1.alldatasheet.com/datasheet-pdf/view/183702/IRF/IRGB14C40LPBF.html

as for the hall sensor, pick a number that will suit your project application
and respect polarity and you'll get a spark:fan:


----------



## fourstroke

Thanks Luc
I dont know anything about hall sensors, when I search I get lots of things that are industrial size
Do the come in different voltages, configurations etc
Thanks Again
Dougie


----------



## jgedde

I've tried several different Hall sensors with this circuit and all worked reasonably well. The clear winner for performance and reliability is the OH090U from Optek. Those things are absolutely bullet proof.

Not being one to follow my own advice, I was grounding my engine with just a alligator clip. Of course, the alligator clip popped off and the spark discharged through the hall sensors I had on there (A1302). They didn't make it....

I replaced them with the OH090U's and the engine ran better and the spark was stronger. Then, the clip came off again. I could actually hear and see a small spark jumping between the engine block and the hall sensor ground lead! After I reconnected the ground, both halls still worked fine! Amazingly robust units.

The OH090S is a no-frills hall sensor with a open-collector output. There is no "chopper stabilization" or other stuff we don't really need. Just a hall element, an amplifier and a comparator.

Here's where I got mine: http://www.digikey.com/product-detail/en/OH090U/365-1001-ND/374779  They are slighly larger than from Honeywell or Allegro.  I was able to sand the sides of the OH090U to be the same width as the A1302...  I don't recommend this - just saying what I did...

Cheers!
John


----------



## jgedde

canadianhorsepower said:


> ok here we are even here in Canada some of these parts number are
> not "on the shelf " thing
> 2n4124 can be replace with 2n3904
> 
> as for the 2 others this what the specs are "close enough"
> 
> if you go to a GOOD reseller finding a match should be a breeze
> good luck
> 
> http://pdf1.alldatasheet.com/datasheet-pdf/view/183702/IRF/IRGB14C40LPBF.html
> 
> as for the hall sensor, pick a number that will suit your project application
> and respect polarity and you'll get a spark:fan:


 
Be careful specifying the 2N3904 as a replacement for the 2N4124...  

It'll likely work, but the circuit wasn't designed for that unit.  The 2N4124 has much higher DC current gain (Hfe or Beta) than the 2N3904, especially operating at a switch.  When a transistor is operated as a switch (i.e. in either saturation or cutoff), the DC current gain is dramatically reduced.  You often have to dig in the datasheet for this information.

In any event, replacing it with the 3904 will cause more base current to be drawn from the input circuit and will change the duration of the "timeout" feature.

In fact when I was designing the circuit, I originally had the 2N3904 or 2N2222A in mind since they are so easy to get.  But, to ensure things would work for others the way they did in my prototype, I rejected those.  The DC current gain was marginal - right on the edge of being OK.

Just keep in mind that I designed the circuit around the 2N4124's characteristics.  This holds true for the other parts as well.  Switching to other parts is done at risk of things not working as expected.  It's hard for others to support problems if things are changed that have no verification history.

All that said, many of the parts are not Radio Shack items.  But, all are available from Digikey or Digikey Canada (digikey.ca).  Apart from the transistors, the LED specified is also crucial.  They do more than just light up as a timing indicator...  They are also part of the timing.

To all, build the circuit using the parts list and schematics from Dave Sage and I and you'll run less risk of things not working.  

This isn't meant as a dig at Luc.  Sometimes my writing style can be abrasive without intending it...  Luc has done excellent work supporting this circuit, especially since I haven't kept up with this thread as well as I should have.

John


----------



## jgedde

UK source for 2N4124

http://www.digikey.co.uk/product-se...ducts/transistors-bjt-single/1376376?k=2n4124

John


----------



## fourstroke

Thank you for the part number of the hall sensor and for the links
Unfortunately digikey and mouser who advertise as UK based ship all products from the US
This means shipping four times the cost of components and VAT to pay when its delivered
I have managed to find all the correct parts in the UK other than the hall sensor but I will keep trying
Thanks for the help
Dougie


----------



## canadianhorsepower

> Be careful specifying the 2N3904 as a replacement for the 2N4124...


 
I've got 5 circuits running with 3904 
and no problem yet:hDe:


----------



## fourstroke

Success
I managed to source all the parts I needed here in the UK
I did a bit of soldering today and after one or two rewiring of mistakes I got a big fat spark from a full size plug
I tested the setup with a magnet in a battery drill running at 1700 rpm and no problems
It looks like this setup will be perfect for my model hired hand engine
Thanks to all who took the time to reply to my questions
Regards
Dougie


----------



## fourstroke

One question about the circuit
The plug fires when the led comes on, is this correct?
Thanks
Dougie


----------



## canadianhorsepower

yes , this led serve as a test circuitThm:Thm:


----------



## jgedde

fourstroke said:


> One question about the circuit
> The plug fires when the led comes on, is this correct?
> Thanks
> Dougie


 
Yes - sort of.  When you set your timing, bear in mind that the plug fires when the light just turns off.

John


----------



## fourstroke

Thats what I thought but my circuit fires when the light comes on
If I move the magnet towards the hall sensor the led comes on and the plug fires, the led stays on till I move the magnet away but the plug dosnt fire when it turns off
Dougie


----------



## jgedde

fourstroke said:


> Thats what I thought but my circuit fires when the light comes on
> If I move the magnet towards the hall sensor the led comes on and the plug fires, the led stays on till I move the magnet away but the plug dosnt fire when it turns off
> Dougie


 
The circuit has protection against coil overheating or battery drain if the engine is stopped with the hall sensor triggering the coil. After a very short delay - likely imperceptible - the circuit will "lock-out" and fire the plug. It will seem as if the spark occurred when the magnet is applied but it's really happening a short time after. When this happens, the circuit has already discharged the coil and no spark will result when the magnet is removed.

In other words, the circuit fires the plug whenever the first of two conditions occur:
1) Hall sensor is removed from the magnet.
2) A fixed delay time of approximately 20 milliseconds.

When the engine is actually running, the trigger magnet will pass by hall sensor fast enough such that the lock-out circuit will not activate (condition 1 is satisified). In this case the plug will fire just as the light goes off. So, the transition from light-on to light-off is the reference point from which ignition timing should be set.

I ended up changing the 1 uF capacitor in my circuit to 6.8 uF. This increased the lock-out inhibit time and makes the delay much more obvious along with when the plug will fire under normal conditions. 6.8 uF is a standard value but is less common. That said, a 4.7 uF capacitor would be a reasonable choice as well and much easier to get. Most 4.7uF caps you can readily get will be polarized. IN this circuit, the (-) pin goes to the hall sensor input side.

Cheers!
John


----------



## ozzie46

Finally got my engine to run for a little bit. ( N0 fault of the circuit. Had other issues.)


Battery wire came loose as I was trying to start the engine.


 Now when I turn on the switch the LED is on constantly but dim when I turn the engine over the LED flashes brighter but plugs don't fire. 

  What do you think is the problem? Do you think I could have fried the Hall sensor or what?

   Help!!


 Ron


----------



## jgedde

ozzie46 said:


> Finally got my engine to run for a little bit. ( N0 fault of the circuit. Had other issues.)
> 
> 
> Battery wire came loose as I was trying to start the engine.
> 
> 
> Now when I turn on the switch the LED is on constantly but dim when I turn the engine over the LED flashes brighter but plugs don't fire.
> 
> What do you think is the problem? Do you think I could have fried the Hall sensor or what?
> 
> Help!!
> 
> 
> Ron


 
Ron,

Classic fried hall sensor...

John


----------



## ozzie46

Thanks John, but you know what? I went out today and switched it on and tried it and it works!! :wall::wall:  It fires the plugs just fine.:shrug::shrug: I have extra sensors if I need them though.

  Ron


----------



## jgedde

ozzie46 said:


> Thanks John, but you know what? I went out today and switched it on and tried it and it works!! :wall::wall: It fires the plugs just fine.:shrug::shrug: I have extra sensors if I need them though.
> 
> Ron


 
Hi Ron,

The output transistor in the hall sensor is partially destroyed (on the internal silicon die, it's made up of several small transistors in parallel - I have a microscope picture somewhere we took during a failure analysis of hall sensors at work after the hall sensor was "de-lidded"). In any case, the output transistor(s) is leaking current and that's what's keeping the light on dimly. You'll likely get a stronger spark if you replace it.

I had exactly the same problem_ multiple times_ because of poor grounding (my own fault) with exactly the same symptom (light on dimly, then full brightness when the hall triggers)

I've since switched to the Optek OH090U. Those things are nearly indestructible! I've literally had sparks jumping from the ground lead on the hall sensor to the engine frame after a loss of ground and they survived!

To all... Keep your grounds secure, fool-proof, and with a short run to the battery (-) terminal and you'll keep risk of sensor damage to a minimum... When the plug fires, the energy transferred from the spark electrode to the engine "ground" has to go somewhere. If it can't return through a good ground to the (-) on the battery, it'll arc to the hall sensor if it can and return through the hall sensor wiring. That is not a good thing...

Or use the OH090U and ground your engine through 3 feet of wire with an alligator clip to a tiny screw like I was doing!  LOL.

John


----------



## ozzie46

Thanks John. Will change out sensor today.

  Ron


----------



## ozzie46

Some one had asked a while back if there were any engines running on this circuit, well here is one. My very first IC engine , a flat 4 cyl boxer 4 stroke. A Mastiff by designed L.C. Mason in England back in the 70s.






   Made out of bar stock, no castings.


  Ron


----------



## canadianhorsepower

thanks for sharing 
but please post this in finish project also
and some pictures

Thm:Thm:


----------



## ozzie46

I posted in finished projects too.

 Thanks  Luc

  Ron


----------



## jgedde

ozzie46 said:


> I posted in finished projects too.
> 
> Thanks Luc
> 
> Ron


 
She's a beauty Ron! 

John


----------



## jgedde

I've already posted this to this photos and videos section, but here it is again since it's running using this circuit.

[ame]http://www.youtube.com/watch?v=DoI33CuWYsU[/ame]

John


----------



## ozzie46

That's super John. I Have plans for a Webster and a  Kersel and will have to give them a shot some day.

  Thanks for the comments.

 Ron


----------



## jgedde

I just got a PM from another member about problems he was having.  The A1121 hall sensor is problematic for him too as it was for me.  They can be damaged by high voltage VERY easily.  

The OH090U fixes the problem.  They are very robust...

The big problem with the OH090U is availability outside the US.  The fellow that needs them is in Scotland.

Any advice from other members on the other side of the pond?

Thanks!
John


----------



## fourstroke

Hi John
Thanks for the reply to my message and the advice about the sensors
I have finally gotten some OH090U sensors sent from the US and straight away my problems with fried components went away
Now I just need to work on getting the fuel setup correct and getting the engine to run for more than a minute or two
The ignition circuit is perfect, thanks for posting it
Regards
Dougie


----------



## dsage

I'd just like to add that if your fried Hall sensor was because of something silly that you did, like having a wire fall off or something, that's one thing.
  But if you were/are regularly blowing sensors then it's probably due to poor wiring practices. That problem should be eliminated first.
  It's not usually a good thing to insert bigger and stronger parts to overcome a fundamental wiring problem. That issue will eventually come back to haunt you.

 The circuit should work properly with almost any Hall sensor if your wiring follows good practices.

 i.e. keep all wires as short as possible, one common ground point etc. etc. You've heard it all before.


 Sage


----------



## Stefan-K

Hello Guys
I´m new here in this forum and i was reading this Thread with much interest. Today i received my IGBT order and breadboarded the circuit. I saw that some folks here in Europe have trouble finding some parts. I didn´t have the 2N4124 Transistor here, so i used an easy to obtain  BC 547 as a substitute. It works just fine. Same with the Hall sensor. I`ve been using the unipolar "H 501" Hallswitch sensor for a long time on different ignition systems with success. So do i here. You can buy the sensor at Conrad Electronics or even on ebay (might be easier for some people). I will attach the datasheet. At the moment i am designing a small circuit board with solderpads for the power, the coil and the sensor lines. I don´t use the terminal blocks cause they sometimes give you a bad connection. And i don´t want to fry my sensor.....
If anyone is interested i can post the board here or send it via PM. Thanks to all here for the information specially to jgedde and dsage for sharing this excellent circuit and givin`so much help.

Stefan 

View attachment Datenblatt Unipolarer Hallschalter H 501.pdf


----------



## jgedde

Latest schematics and bill of materials.  Here's the latest info.  Nothing new here, but you'd have to go back through 18 pages of threads to find all these.

John 

View attachment BOM.pdf


View attachment Sheet1.pdf


View attachment Sheet2.pdf


----------



## dsage

Hi Guys:

Just one last minor note. I did some testing of the circuit at the extreme ends of operating conditions. I found that if you are running the circuit on four dry cells (6v or a bit less) and you are waving the magnet in front of the hall sensor, sometimes the LED lights but you get no spark. It  was pretty intermittent and may be fine depending on your coil. It worked fine at engine running speeds.
  In any case I found that changing R6 from 39k down to 22k made the spark more reliable waving the magnet (i.e. very low rpms like cranking speeds). If you have issues like this change R6 to 22k.

Thanks

Sage


----------



## larz001

i realize this is an old thread but would anyone here have built a couple extra ignition circuits that they would be interested in selling, I am not good with schematics and soldering


----------



## willray

Performing a bit of thread necromancy here, and moving a previously point-to-point conversation out here, in case it benefits someone else who scratches their head about this:

I'm interested in using this design to make the ignitions on ancient chunks of farm machinery that we use mostly for show purposes, more reliable. I don't want to significantly alter the engines, so using the points in place, rather than cobbling in a hall sensor and magnet carrier seems like a reasonable approach.

I'm wondering however, whether the dwell time at cranking speed with points, runs afoul of the "You're boring, I'm going to sleep" timeout you've built into the circuit. Not relishing the thought of what some of my battery-ignition, but hand-crank started engines would do, if the timeout effectively looks like super-advanced timing, at cranking speed!




jgedde said:


> If you were to use points to drive the circuit, it will be necessary to remove the condenser at the very least.
> 
> You raise a valid point about the dwell time triggering the timeout during low engine speeds and cranking. But, required dwell time is required dwell time and that's completely independent of whether a hall sensor or contact points are used.
> 
> Basically what I'm saying is that if you were to replace the points with a cobbled magnet and a Hall sensor, you'd have to consider the time the Hall sensor is triggered and make it match the behavior of the points. That said, it's much easier just to retain the points. As an aside they'd likely last much longer in this application since they'd be carrying no current and never arcing. However, I believe they'd need to be cleaned more often since a small amount of arcing tends to keep the contacts clean.
> 
> Worse comes to worst, you could always use a larger value capacitor in the circuit if timeout is occurring, but I tend to think you won't have a problem with just driving the circuit as-is with points.



I actually hadn't thought about that at all, and now that you've made me think about it, I'm wondering why this circuit works with the hall effect sensors at all...

I had previously (erroneously) assumed that with the hall sensor, the design de-energized the coil when the hall sensor stopped sinking current (the transition from sensing the magnet, to not sensing the magnet), and energized the coil again immediately afterward.  Obviously this can't be the case, partly because that would imply that the coil was running with almost a full 360deg dwell, which seems unlikely to be healthy, and also because Jgedde has repeatedly mentioned the safety timeout for the system stopping with the hall sensor over the magnet, but nothing about needing to worry about stopping with the sensor away from the magnet.

Just to be sure that I was right about having been wrong, I hooked it up to my 'scope and yup, the coil output is de-energized until the hall sensor sees the magnet. It then comes up, and remains up for the shorter of either approximately 20ms, or when the magnet leaves, then it drops again until the next time it sees the magnet.

So now I understand how the circuit works, but I don't understand _why_ it works.  With the hall sensor, the dwell duration is only the period between when the hall sensor sees the magnet, and when the magnet leaves its sensing radius.

At any kind of realistic engine speed, for anywhere that I can think of that's easy to place magnets (i.e., flywheel, crank) that time gets down into the sub-millisecond range pretty quickly. With wild gesticulation instead of actual number-crunching, at 60RPM, 1 degree of revolution is about 3ms.  It's been a long time since I worried about performance engines, but dim memory says that's just barely enough to build field in a coil on a particularly cheerful and optimistic day.

Assuming people are shooting for running speeds in the high hundreds to low-couple-thousand RPM, does this mean that you're finding some way to coat 50 or so degrees of some spinning component with magnets, to develop sufficient hall sensor on-time?   Or is there some other magic at work here?


----------



## Lakc

Why it works is a cute trick of physics. The sudden inrush of current to a coil builds the magnetic field, the current required to hold this magnetic field is much smaller. The rate of collapse, and strength of, that magnetic field across the secondary winding of the coil determine the effective energy transfer. 
Old ignition systems used resistance wire or a ballast resistor to avoid full current across the primary winding, this kept the coil from overheating at low rpm but limited performance at higher rpm. 
So, dwell was always a balancing act anyway. At low rpm, you will almost always have enough current to get the job done. Those electrons are pretty quick.


----------



## dsage

Willray:

You didn't specify how many cylinders your "old time" engines have but I'll assume single cylinder engines.
 It was also tough to weed out your exact question from your post.
But I think what you're wondering is if the default 20ms time out of the ignition circuit will play havoc with a very slow turning (single cylinder) engine such that the spark would occur too quickly because of circuit time-out rather than the points actually opening.
 The 20ms time-out may be too short for a SINGLE CYLINDER engine at hand cranking speeds making the spark occur sooner than expected. And, like you said, appear to act like a "super advance" at low rpm's. 
 The 20ms can be increased by increasing the value of C2. It wouldn't matter if C2 were increased in value to provide something as crazy as one second of time-out. It's just there as a safety circuit to protect the coil.
BUT
 Personally I would leave the 20ms time-out as it is. The engine will soon start and be up to a reasonable running speed and a bit of extra advance while cranking should pose no problem.
Don't forget you should adjust the timing of the engine with a timing light and the timing marks of the  engine. 

Sage


----------



## jgedde

willray said:


> Performing a bit of thread necromancy here, and moving a previously point-to-point conversation out here, in case it benefits someone else who scratches their head about this:
> 
> I'm interested in using this design to make the ignitions on ancient chunks of farm machinery that we use mostly for show purposes, more reliable. I don't want to significantly alter the engines, so using the points in place, rather than cobbling in a hall sensor and magnet carrier seems like a reasonable approach.
> 
> I'm wondering however, whether the dwell time at cranking speed with points, runs afoul of the "You're boring, I'm going to sleep" timeout you've built into the circuit. Not relishing the thought of what some of my battery-ignition, but hand-crank started engines would do, if the timeout effectively looks like super-advanced timing, at cranking speed!
> 
> 
> 
> 
> I actually hadn't thought about that at all, and now that you've made me think about it, I'm wondering why this circuit works with the hall effect sensors at all...
> 
> I had previously (erroneously) assumed that with the hall sensor, the design de-energized the coil when the hall sensor stopped sinking current (the transition from sensing the magnet, to not sensing the magnet), and energized the coil again immediately afterward. Obviously this can't be the case, partly because that would imply that the coil was running with almost a full 360deg dwell, which seems unlikely to be healthy, and also because Jgedde has repeatedly mentioned the safety timeout for the system stopping with the hall sensor over the magnet, but nothing about needing to worry about stopping with the sensor away from the magnet.
> 
> Just to be sure that I was right about having been wrong, I hooked it up to my 'scope and yup, the coil output is de-energized until the hall sensor sees the magnet. It then comes up, and remains up for the shorter of either approximately 20ms, or when the magnet leaves, then it drops again until the next time it sees the magnet.
> 
> So now I understand how the circuit works, but I don't understand _why_ it works. With the hall sensor, the dwell duration is only the period between when the hall sensor sees the magnet, and when the magnet leaves its sensing radius.
> 
> At any kind of realistic engine speed, for anywhere that I can think of that's easy to place magnets (i.e., flywheel, crank) that time gets down into the sub-millisecond range pretty quickly. With wild gesticulation instead of actual number-crunching, at 60RPM, 1 degree of revolution is about 3ms. It's been a long time since I worried about performance engines, but dim memory says that's just barely enough to build field in a coil on a particularly cheerful and optimistic day.
> 
> Assuming people are shooting for running speeds in the high hundreds to low-couple-thousand RPM, does this mean that you're finding some way to coat 50 or so degrees of some spinning component with magnets, to develop sufficient hall sensor on-time? Or is there some other magic at work here?


 
The trick is the magnet has to be wide enough to give the desired dwell time...  On model engines, this isn't much of an issue since the size ratio between the magnet and whatever is driving it is likely to be large.  On a full size engine, you need a scaled up magnet or just use the existing points to drive the circuit...

John


----------



## Cogsy

dsage said:


> a bit of extra advance while cranking should pose no problem.


 
No experience myself, but my dad has told me stories of guys forgetting to retard the ignition on hand cranked engines before trying to start them, getting a kick-back and breaking their arm.

The odd kick-back I've gotten from kick starting badly timed motorbikes makes me believe it too.


----------



## ShopShoe

I've also heard the same thing about Model T Fords. The doctors were calling it "Ford Fracture."

--ShopShoe


----------



## willray

Cogsy said:


> No experience myself, but my dad has told me stories of guys forgetting to retard the ignition on hand cranked engines before trying to start them, getting a kick-back and breaking their arm.
> 
> The odd kick-back I've gotten from kick starting badly timed motorbikes makes me believe it too.



Exactly.  On full-scale hand-cranked engines, you absolutely, only, pull the crank handle around the bottom of the rotation towards you, and you do it with your hand outside the crank handle, palm facing in, thumb beside palm (not wrapped around handle).  This at least maximizes the chance that a kick-back will just jerk the crank out of your hand, rather than ripping your thumb off, or breaking your elbow.

On a typical hand-cranked engine, cranking speed might be in the range of 60 to 120 RPM.    With a "use the points" solution (what I'm planning on doing), and assuming 30-40deg of points dwell, (unless my math is off) you're looking at 50-100ms of points "on time" at cranking speeds.

Assuming the points open somewhere TDC and say 20deg after TDC, that means the points close between 10 and 40deg bTDC, and with dwell duration and 20ms default timeout, the ignition will fire based on when the points close, rather than when they open.  That firing time will be somewhere between 30ms before TDC, to just after TDC.  This adds up to a highly probable big "ouch".

This potential problem for full-scale engine ignitions, should be easy enough to eliminate by the simple "use a larger capacitor at C2" trick.  Something that moved the timeout up to say 250ms would probably be safe in almost any situation.  I wanted to bring this part of the discussion out here, just in case it might save someone else's knuckles on a real engine with points.


----------



## willray

jgedde said:


> The trick is the magnet has to be wide enough to give the desired dwell time...  On model engines, this isn't much of an issue since the size ratio between the magnet and whatever is driving it is likely to be large.  On a full size engine, you need a scaled up magnet or just use the existing points to drive the circuit...
> 
> John



Ah - thanks.  I had considered the possibility that everyone was working on engines with, i.e., small-diameter crankshafts, and therefore even small rare-earth magnets subtended an adequate angle to create enough on-time at the hall sensor.

Not being sure, I thought this might be a valuable discussion to have out here, since the interaction between diameter of the magnet-mount and RPM didn't appear to have been discussed for the hall-sensor version, and this it could explain some variability in performance of the ignition in some people's hands.

Dsage's observation of occasional non-sparking situations /could/ lay at the feet of this.  Consider, it's not difficult to get your hand moving at well over 2 meters per second (most of us can probably do 10-20M/s relatively easily).  If the magnetic field density is adequate to trigger the hall sensor within a radius of 1cm, then even at a relatively lazy 2M/s of "hand waving magnet", your effective dwell is only 10ms.   That's traditionally considered enough to build field and get a decent spark, but go twice that fast, and you'll be in questionable territory.

No clue whether that's /actually/ what's been observed, but, I figure I'm not a clever enough bear to be the first who has pondered most of these things, but I do seem to be one of the few who is sufficiently unashamed of his ignorance to ask questions when his puzzler is puzzed.

Will


----------



## willray

Lakc said:


> Why it works is a cute trick of physics. The sudden inrush of current to a coil builds the magnetic field, the current required to hold this magnetic field is much smaller. The rate of collapse, and strength of, that magnetic field across the secondary winding of the coil determine the effective energy transfer.
> Old ignition systems used resistance wire or a ballast resistor to avoid full current across the primary winding, this kept the coil from overheating at low rpm but limited performance at higher rpm.
> So, dwell was always a balancing act anyway. At low rpm, you will almost always have enough current to get the job done. Those electrons are pretty quick.



Umm, not to be contrary, but the physics magic is slightly backwards of that...  The current builds in the coil and reaches its maximum once the field saturates.  Back-EMF is produced by the changing field while the field is building, and this limits the in-rush current.  The ballast resistor is there to cap the current through the coil, once the field is saturated and the back-EMF has reduced to zero.

Depending on who you ask, a typical automotive coil takes on the order of 5ms to reach saturation, maximum current, and therefore maximum stored energy.  If the hall sensor in this ignition "sees the magnet" for less time than that, then the spark energy will be affected.

Ideally Dsage and Jgedde could design a circuit that could provide power to the coil uniformly 10ms or so before the magnet _leaves_ the hall sensor, but this would require them to either design a psychic circuit that knows that the hall sensor will open in 10ms, even though the hall sensor (at higher RPMs) hasn't closed yet, or, (as far as my circuit design skills allow) would require including a microprocessor to predict when the sensor will next see the magnet based on the last revolution.

Neither of those seem particularly likely, or appealing solutions, so it looks like you're left tuning this circuit both with respect to the rotational position of the hall sensor for timing, and with respect to the radial position of the sensor towards or away from the rotating magnet, and the size of the magnet, for dwell.

The next option would be to switch to a rotating optical slit-disk and optical sensor for the timing detector.  Dwell could easily be set in that system by controlling the (arc angle subtended) length of the slits.


----------



## Blogwitch

Hall sensors, magnets and model engines brings back memories when I was building them.

No one yet has mentioned the diameter of the rotating part that the magnet is embedded in.

If say you embedded it (them) in the outer rim of say a 3" flywheel, then you would require about 3 x 3mm magnets side by side in a line around the rim to give you enough dwell angle for the hall sensor to be turned on and so to charge up the coil. The reason for this is that the outer surface speed is much faster than the surface speed of say the hub even though they are rotating at the same revs.
I used to mount an ali disc on the end of the camshaft (for single cylinder 4 stroke engines) of around 5/8" to 3/4" diameter with the 3mm (1/8") magnet embedded in the outer rim. This worked perfectly for engines up to around 5,000 rpm. Never made any that ran faster, but I would suggest going down 1/8" or even 1/4" on diameter of the ali disc if the engine runs any faster, this will give a longer dwell angle.

As usual I have an old picture of one I did showing the disc with a hall sensor epoxied into a holder so that it could be advanced and retarded.
Please excuse the condition of the engine, it has had a good dose of running in with WD40 added to the fuel.








John


----------



## willray

dsage said:


> Willray:
> 
> You didn't specify how many cylinders your "old time" engines have but I'll assume single cylinder engines.
> It was also tough to weed out your exact question from your post.
> But I think what you're wondering is if the default 20ms time out of the ignition circuit will play havoc with a very slow turning (single cylinder) engine such that the spark would occur too quickly because of circuit time-out rather than the points actually opening.
> The 20ms time-out may be too short for a SINGLE CYLINDER engine at hand cranking speeds making the spark occur sooner than expected. And, like you said, appear to act like a "super advance" at low rpm's.
> The 20ms can be increased by increasing the value of C2. It wouldn't matter if C2 were increased in value to provide something as crazy as one second of time-out. It's just there as a safety circuit to protect the coil.
> BUT
> Personally I would leave the 20ms time-out as it is. The engine will soon start and be up to a reasonable running speed and a bit of extra advance while cranking should pose no problem.
> Don't forget you should adjust the timing of the engine with a timing light and the timing marks of the  engine.
> 
> Sage



Greetings sir,

I'm down to mostly polluting rather than contributing at this point, but just for completeness:

I'm interested in mostly single, a few 2-cylinder, and occasionally 4-cylinder engines, that generally produce up to around 20HP, with operational speeds typically in the range 600-2200 RPM.

And I apologize for my somewhat rambling writing.  You're both plagued by my tendency to write fables rather than technical documentation, and by the fact that I already had about half the answers I wanted.  As such I was partly writing just to record some of the thoughts, because I find this to be one of the best-documented online discussions on DIY electronic ignition designs/conversions, and having made some mis-assumptions coming into it from the direction of using it as a "points eliminator" in "real" engines, I figured I might save someone else a headache if I moved some of those assumptions and the corrected thinking into the light of day.

With respect to whether the 20ms timeout is safe, I think I've convinced myself not to find out.  Running the numbers more carefully, with where many of my engines try to put the cranking timing, and the average points dwell angle, the 20ms timeout would put the spark dangerously before TDC.  Since it's easy enough to push that delay out considerably, and the coil has plenty of thermal mass to occasionally absorb being stuck with the "points closed" for a reasonable fraction of a second, I think I'll save my fingers and push the timeout up to something more like 250ms.

Thanks for all your work on this design!
Will


----------



## Lakc

willray said:


> Umm, not to be contrary, but the physics magic is slightly backwards of that...  The current builds in the coil and reaches its maximum once the field saturates.  Back-EMF is produced by the changing field while the field is building, and this limits the in-rush current.  The ballast resistor is there to cap the current through the coil, once the field is saturated and the back-EMF has reduced to zero.


Nothing really contrary in that statement. Once the magnetic field reaches its full strength, the extra current just builds heat, whereas a tiny current can keep the magnetic field from collapsing. The ballast resistor or resistance wire also limits the current inrush as well, increasing the necessary dwell time. This is why it disappeared after the first generation (5 pin) automotive ignition systems. 


> Depending on who you ask, a typical automotive coil takes on the order of 5ms to reach saturation, maximum current, and therefore maximum stored energy.  If the hall sensor in this ignition "sees the magnet" for less time than that, then the spark energy will be affected.


I have no data that states otherwise, but modern automotive coil design has almost certainly pushed that figure down, and overall efficiency up. 



> Ideally Dsage and Jgedde could design a circuit that could provide power to the coil uniformly 10ms or so before the magnet _leaves_ the hall sensor, but this would require them to either design a psychic circuit that knows that the hall sensor will open in 10ms, even though the hall sensor (at higher RPMs) hasn't closed yet, or, (as far as my circuit design skills allow) would require including a microprocessor to predict when the sensor will next see the magnet based on the last revolution.


Such a design would be far enough removed from this circuits intended purpose that it becomes a bit apples and oranges. He has designed a simple ignition circuit that appears very robust, commendably so in fact. 



> Neither of those seem particularly likely, or appealing solutions, so it looks like you're left tuning this circuit both with respect to the rotational position of the hall sensor for timing, and with respect to the radial position of the sensor towards or away from the rotating magnet, and the size of the magnet, for dwell.


Both are rather easily implementable solutions for the homebrew IC engine market. 



> The next option would be to switch to a rotating optical slit-disk and optical sensor for the timing detector.  Dwell could easily be set in that system by controlling the (arc angle subtended) length of the slits.


Optics are very sensitive to dirt, and the optical shutter disc on the old Mitsubishi 2.6l full size engine could only be produced by photoetching. So unless your very good with your index, and can mill a .015 slot in .010 stainless disc, I would avoid that method. 

There are other ignition systems out there that utilize microprocessors as counters and delay a triggered signal (about 45 btdc) based on rpm maps for variable advance.


----------



## willray

Lakc said:


> Nothing really contrary in that statement. Once the magnetic field reaches its full strength, the extra current just builds heat, whereas a tiny current can keep the magnetic field from collapsing. The ballast resistor or resistance wire also limits the current inrush as well, increasing the necessary dwell time. This is why it disappeared after the first generation (5 pin) automotive ignition systems.



I guess I'm still being contrary, or perhaps it's a matter of semantics, but, the magnetic field is directly proportional to the current.   As a result, all of the current is necessary to sustain the field.  On the other hand, once the magnetic field has stabilized, very little (theoretically none) of the electrical energy dissipated goes into the field, so yes, what energy is being dissipated is going into heat.



> (regarding minimum dwell) I have no data that states otherwise, but modern automotive coil design has almost certainly pushed that figure down, and overall efficiency up.



I'm sure some gains in efficiency have been realized, but, a coil ignition is a fairly fundamental resistive/inductive/capacitive circuit, and even antique LRC circuits perform fairly close to their theoretical/idealized optimums.  Essentially they're limited in terms of how fast they can store energy in the magnetic field, by the fundamental physics of resistors and inductors, and other than small changes that can be brought about by things like slightly decreased resistance through optimized metallurgy, there's not a bunch that can be done to dramatically change their performance.

In addition to eliminating the need for a distributor, one of the big advantages realized by multi-coil-pack ignitions for modern engines, was that the dwell for each cylinder could be made longer than the duration between successive cylinder firings.  This helped eliminate problems with weak spark at high RPM, that could not be overcome by coil optimization with the physically limited dwell duration inherent to single coil designs.

Of course, this is all just idle chatter here, since I'm running engines that, at the most modern, have 1960s ignition components.



> Such a design would be far enough removed from this circuits intended purpose that it becomes a bit apples and oranges. He has designed a simple ignition circuit that appears very robust, commendably so in fact.



Absolutely.  Which is why I thought it worth extending the discussion to practical aspects of applying the circuit to "real" engines as well as the model engines for which it was designed.  It is, as far as I can tell, the nicest, most robust, and most carefully thought-out points-replacement ignition circuit to be found on the internet.  It just has some implementation details that need to be considered before use, to eliminate "gotcha"s in real-engine drop-in-replacement applications.



> Optics are very sensitive to dirt, and the optical shutter disc on the old Mitsubishi 2.6l full size engine could only be produced by photoetching. So unless your very good with your index, and can mill a .015 slot in .010 stainless disc, I would avoid that method. :roll eyes:



I have no personal experience with trying to implement such a thing (only, amusingly, with that particular ignition ceasing to function), but, I suspect there's a big difference between "could only be produced (to adequate tolerances to make their EFI and spark control computer happy)", and what would be necessary to run an engine that's used to a crappy points ignition, on a crappy worn distributor, better than what the points could do.

Realistically, the tolerances required are no harder to maintain than the tolerances required for the magnet and hall-effect sensor, with the primary difference being that one could adjust the "points closing" timing (which inherently doesn't require much precision) much more easily than can be done with magnets.

The optical-dirty problem does concern me, but maybe I'll make one just for gits and shiggles.  Bet I can maintain adequate tolerances to run a 1 or 2 cylinder engine with just a hand-file and jeweler's saw.

Will


----------



## Lakc

willray said:


> I guess I'm still being contrary, or perhaps it's a matter of semantics, but, the magnetic field is directly proportional to the current.   As a result, all of the current is necessary to sustain the field.



That part is not semantics, it takes very little current to maintain a magnetic field created by a larger current. Modern ignitions have done this ever since the demise of the round oil filled coil.


----------



## dsage

Will et.al.

As with any circuit there were compromises made for simplicity, ease of construction, typical rpm's and cylinder count of model engines. And the ability to energize a coil for at least several times the time it takes to fully energize many of the existing small model coils (which require much more time than a full size car coil BTW). While at the same time being a protection device against continuous activation.
 Most model engines idle at more than 1000rpm, are cranked by things like electric drills that run at about that speed and run at several thousand rpm. The 20ms timeout was probably reasonable. But, for a full sized SINGLE cylinder engine that might have a maximum few hundred rpm then by all means do some basic calculation or measurement of the dwell TIME produced by the points at cranking speed (if that's what you want to use) and change C2 to give a longer time-out to suit the application. There is no harm in making the timeout many times longer as long as it still protects your coil. But don't get crazy with it since other circuit values may come in to play and a much larger capacitor may affect the normal operation.

BTW, to address another issue that was pointed out. The apparent intermittent  triggering when using low battery voltage and waving a magnet manually over the sensor had nothing to do with the speed of the magnet moving past the sensor per se. It had to do with the small transistor not having enough drive current (with low batteries) to turn it on quickly. The coil was firing in most cases but the transistor was switching too slowly (and hence the field was collapsing too slowly) for the coil to produce it's full output. Hence the resistor R6 was changed to 22k to drive the transistor harder (and faster). But that's all history as long as you use the most current schematic values and it works ok now with weak dry cells of 6v and a full sized car coil.


Sage


----------



## willray

Lakc said:


> That part is not semantics, it takes very little current to maintain a magnetic field created by a larger current. Modern ignitions have done this ever since the demise of the round oil filled coil.



Nope, that's not semantics, and I apologize for pointing it out, but modern ignition or not, you can't beat Ampere's law.  The magnetic field is not something that gets "built up" by a big current, and then "kept trapped" in the coil by a small current.  The current is why the field is there, and the field exists because, and only because, the current is flowing, with the magnitude of the current dictating the magnitude of the field.  Reduce the current and the magnetic field collapses.  This is why coils work, and it's simple physics.

At this point this has gotten wildly off the topic of this wonderful circuit, and I'll bow out here, both because it's off topic, and because you're not arguing with me, you're arguing with almost 200 years of extremely-well characterized physics.

Will


----------



## willray

dsage said:


> Will et.al.
> 
> As with any circuit there were compromises made for simplicity, ease of construction, typical rpm's and cylinder count of model engines. And the ability to energize a coil for at least several times the time it takes to fully energize many of the existing small model coils (which require much more time than a full size car coil BTW). While at the same time being a protection device against continuous activation.
> Most model engines idle at more than 1000rpm, are cranked by things like electric drills that run at about that speed and run at several thousand rpm.
> 
> ...
> 
> Sage



Thank you sir.  These are exactly the kind of considerations that I hadn't, umm, considered, when I first started thinking about using your circuit as a way of improving the ignition reliability on my assortment of antique rust.

I really do appreciate all the work that you and Jgedde have done on this circuit, and now that I understand the practical considerations of applying it to real engines, I think it'll be immensely valuable for my rust collection, as well as to others who collect and restore rust.

Someday, maybe I'll have the time to get my shop in order, and get around to making a model engine or two, too.  It's on my list for when I finally get the new shop finished.

I do think I'll make an optically-triggered version of your circuit just as a joke.  A bit of digging says that both Panasonic and Omron make nice slot sensors with dark-on outputs, which will make adjusting the timing pretty easy.  I'm thinking I can get perfectly adequate timing control out of a scrap from a soda can, and tin-snips


----------



## dsage

Will:

Re: >>> Omron make nice slot sensors with dark-on outputs,

Not sure exactly how you are going to arrange the mentioned sensor but, as with the Hall sensors and original ignition points you will need the input to our ignition circuit to be normally High (i.e. 12v) and then drop low for several milliseconds (at least) and then go back high again until the next spark is required.
 It may actually work in reverse but you would be racing the timeout circuit every time if the input was normally low.

Sage


----------



## willray

dsage said:


> Will:
> 
> Re: >>> Omron make nice slot sensors with dark-on outputs,
> 
> Not sure exactly how you are going to arrange the mentioned sensor but, as with the Hall sensors and original ignition points you will need the input to our ignition circuit to be normally High (i.e. 12v) and then drop low for several milliseconds (at least) and then go back high again until the next spark is required.
> It may actually work in reverse but you would be racing the timeout circuit every time if the input was normally low.
> 
> Sage



Yup - that's doable with the slot photo-sensor.  Hooked up properly they're much like a hall sensor, with an output that sinks current to ground when "on", and that floats when "off".  Give it a pull-up resistor, and it should be good to go.

With a Dark-on output, the trigger can be just a flying tab, with a leading edge "wherever", so long as it provides adequate dwell, and the trailing edge at the intended "points opening" trigger point.  I can't see any reason that the tab can't be simply attached to the outside of the flywheel - any reason other than safety at least, but for a proof of concept it should do.  Easy peasy.

Will


----------



## willray

jgedde said:


> I ended up changing the 1 uF capacitor in my circuit to 6.8 uF. This increased the lock-out inhibit time and makes the delay much more obvious along with when the plug will fire under normal conditions. 6.8 uF is a standard value but is less common. That said, a 4.7 uF capacitor would be a reasonable choice as well and much easier to get. Most 4.7uF caps you can readily get will be polarized. IN this circuit, the (-) pin goes to the hall sensor input side.
> 
> Cheers!
> John



So, can anyone give me rough numbers on how much the timeout changes, going to, say 4.7, 6.8, or 10uF?  Alternatively, roughly how much capacitance would you estimate would be needed, to push the timeout up into the 100+ms range?

Thanks,
Will


----------



## dsage

It'll probably be close to doubling if you double the capacitance. It's 1uf for 20ms now (I think) so 5x that or 5uf should get you close to 100ms. But that's only rough figuring. Trial and error would be the best approach But don't go crazy with it. Like I said before other issues may arise.
Also heed the advise about polarity of the capacitor (quoted above).

John has a spice simulation of the circuit and can probably tell you better what's required for 100ms.

You really need to do the math (or measurements) on how long your points are actually closed at cranking speed if you are worried about artificial advance. You might be surprised how fast you are actually flipping it past TDC by hand or foot or whatever you're planning. The points may not actually be closed very long. I wouldn't get too paranoid about a bit of advance. And don't forget you can adjust the timing (usually).

Sage


----------



## willray

dsage said:


> It'll probably be close to doubling if you double the capacitance. It's 1uf for 20ms now (I think) so 5x that or 5uf should get you close to 100ms. But that's only rough figuring. Trial and error would be the best approach But don't go crazy with it. Like I said before other issues may arise.
> Also heed the advise about polarity of the capacitor (quoted above).



Excellent.  I wasn't sure the timeout was likely to roughly scale with the capacitance, and didn't want to poke around blindly.

I'll just grab some film caps in roughly the right range, and we'll see what we see.



> John has a spice simulation of the circuit and can probably tell you better what's required for 100ms.



You mean there's someone else out there who's obsessive-compulsive enough to build simulations for trivialities?   I'm pretty sure this is some kind of disease...



> You really need to do the math (or measurements) on how long your points are actually closed at cranking speed if you are worried about artificial advance. You might be surprised how fast you are actually flipping it past TDC by hand or foot or whatever you're planning. The points may not actually be closed very long. I wouldn't get too paranoid about a bit of advance. And don't forget you can adjust the timing (usually).
> Sage



I get the feeling you've never been holding the crank of a 20HP engine when it kicks back 

It's true I haven't measured (when I get a chance, I will do so and report back), but based on the cam profile, on some of my engines the points are closed for well over 180deg of crankshaft rotation.  I estimate I hit about 1 revolution per second hand-cranking, maybe even 2 or 3, but that still leaves the points closed for an awfully long time!

Don't worry, I'll figure it out.


----------



## willray

willray said:


> ...
> Don't worry, I'll figure it out.



Ok, I'm back with some data.  Been working pretty much non-stop on the framing for our new shop, so I haven't torn into any of the engines to get real-live points-dwell times, but I did scare up a batch of caps and test the circuit timeout with a handful of the likely suspects:

C2 value  ::  dwell time before timeout

1uF    :: 18ms
1.5uF :: 28ms
2.2uF :: 40ms
2.7uF :: 55ms
3.3uF :: 60ms
4.7uF :: 85ms
5.6uF :: 95ms
6.8uF :: 120ms
8.2uF :: 140ms

Not quite linear (and of course, these were +/- 10% caps), but close enough.

As a side note, just in case this saves anyone else hair-pulling, don't try to test this thing with a soft power supply, and expect anything resembling useful numbers or performance.  I recently "upgraded" one of my bench supplies in the lab, and stupidly used the new one while testing this circuit.  Unfortunately the new one apparently doesn't react to changing load conditions particularly well, and the output droops precipitously before the regulation catches up and stabilizes things when presented with a suddenly increased load.  Undoubtedly the result of new modern digital wizardry and optimization (nor did it flag an overcurrent condition, which at least would have been acceptable.  BAD HAMEG!).   The results, with a low-ohm load in place of the coil, were between confusing and useless.

Will


----------



## dsage

Just a couple of notes on your testing.
First off thanks for the results.
A conventional ignition circuit requires a high wattage ballast resistor in series with the coil. Usually a couple of ohms or so to limit the current. A full sized car coil by itself is only a few tenths of an ohm and on 12v you could have at least 24amp pulses trying to be produced by your supply. (~ 12v /0.5 ohms). Probably more. For that reason a power supply is not usually a good thing to test with. 
   Having said that -  you can THANK your power supply for saving your coil, the driver circuit and probably your wiring. Had you been using a good battery you might have smoked it up (with no ballast resistor).
 You mentioned a few posts ago that you thought your point closed time (dwell time) on your "old iron" engine was REALLY REALLY long. A full sized coil and even the small model coils never require more than 20ms to be fully saturated. Any more time energizing it than that and you're just wasting power heating the coil, the ballast resistor and the driver transistor and stressing your points (on a standard ignition). Also killing your battery prematurely. This is where the 20ms came from in the original timing values. No point in powering the coil any longer than it takes to saturate it. Your just wasting power.
 So if you want my opinion you should spend some time looking at adjusting your points dwell (closed time) to 20ms (or so) at cranking / idle speed for a low revving engine. It's probably just a screw on the points set.
  Yes that time will become less as the engine speeds up but a full sized coil will produce a good spark at less than 1ms dwell time. 
 The forgoing are all typical values and user results may vary. But this is why ignition circuits are different on different cars - because manufacturers choose values that work for their coil, expected rpm, etc. etc.
 Using the ignition circuit was not intended to be "plug and play". Some pre-work needs to be done to tailor your trigger signal for the intended usage.
 i.e. points adjustment, magnet size, expected rpm etc etc.

BTW. The capacitor size vs time values you came up with from your testing are pretty close to expected. As I mentioned in another post I expected 5x the capacitance would give you 5x the time. Given component tolerances that's  pretty much what you got. (18ms for 1 uf and about 90ms for 5us). Give or take.

Sage


----------



## willray

dsage said:


> Just a couple of notes on your testing.
> First off thanks for the results.
> A conventional ignition circuit requires a high wattage ballast resistor in series with the coil. Usually a couple of ohms or so to limit the current. A full sized car coil by itself is only a few tenths of an ohm and on 12v you could have at least 24amp pulses trying to be produced by your supply. (~ 12v /0.5 ohms). Probably more. For that reason a power supply is not usually a good thing to test with.
> Having said that -  you can THANK your power supply for saving your coil, the driver circuit and probably your wiring. Had you been using a good battery you might have smoked it up (with no ballast resistor).



Ah, I used a low-ohm dummy load, not a no-ohm dummy load... I'm not that much of a dummy     This power supply isn't capable of enough current to do much damage regardless, but in this case it was definitely not helping.

And yes, I expected that the timeouts with different caps would end up where you predicted them to. I just wanted to confirm that it really was so, and perhaps save someone else the trouble of doing the math if they wanted to select a longer timeout.


----------



## tightwadracer

Hi 
Firstly I must congratulate you on doing so much fine work and for sharing it.

I am a Technology teacher in Australia and 2 of my students are building engines which will require this ignition system, I have been building a proto.
However I was wondering if you have a PCB layout available to share as I see more of these motors will be built in the future.


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## dsage

How do you plan to fabricate the boards?
Model Engine Builder Magazine Issue 34 had an article with pdf files you could use for the toner transfer method of both sides of the board. Component lists, schematic and stuffing diagram was also in the article.
There was also info on how to calculate magnet size etc. for your particular engine to properly trigger the unit.

Sage


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## tightwadracer

I have contacted the magazine in relation to the purchase of issue 34 and have had very immediate and positive response.
We have a few options for manufacturing PCB, including toner transfer.
we may even be able to use our four axis hartford machine centre to engrave them.
When I get time i will upload some photos of our fantastic workshops.

Thanks again


----------



## canadianhorsepower

Ok so if i go this way 

7) IF A HALL SENSOR IS NOT BEING USED, R2, C1 AND E6 CAN BE DELETED

I assume R6!!
what do I do with D3 ?????
and R3 goes directly to the base of Q2
thanks


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## dsage

Refer to the diagram in post #47
If a hall sensor is not being used you can delete R3 and C1. (but IMHO for all they're worth you might as well keep them in case you want to switch to a hall sensor).

Everything else must stay.
If your using points then they must switch to ground when closed and then they can be connected to E6 connection (Labelled HED IN which goes to R7).
For easy connection (rather than finding a ground elsewhere) you can connect the points across E6 and E7
Don't use a condenser across the points (like in a car).

Hope that helps.

Sage


----------



## paulc

Hi Guys, I'd like to give this design a shot.  Is there a basic vero board layout or similar available?


----------



## dsage

EDIT:
See message 211 Below for update.

Here is a circuit board layout that you can translate to a vero board. It's double sided but you should be able to work that out on vero board. Also attached is the simpler schematic. It's electronically the same as the original but simplified to reduce the board complexity. You might want to check with the Editor of Model Engine Builder Magazine. I gave him all the circuit board files and he was investigating getting some made. I'm not sure if he followed through.
I don't have any circuit boards to offer.
A complete write up and the files to make your own circuit boards with toner transfer was featured in Model Engine Builder Magazine #34 for the original (more complicated) circuit You might want to ask the Editor about a copy of that edition.


----------



## paulc

dsage,
That is very kind of you, perfect!
I went ahead and ordered back issue #34 MEBM.
But in the mean time........
The PCB pdf you attached the top side traces, in red are understood but the bottom side of the board (blue traces) is partially obscured.Would you by any chance have the layout of the bottom side to share here too?

I will post my results here.  I  actually have a 7 cylinder (350cc) radial that I scratch built in 97' it uses a kettering system (12 volt TIM Bosch module off an old VW Golf) and my own hall sensor picking up sesing 7 rotating magnets, it runs well, once I get her running again I will post here.  This is this engine I want to convert to this system.  I would like to retain a 12 volt supply.

Paul




dsage said:


> Here is a circuit board layout that you can translate to a vero board. It's double sided but you should be able to work that out on vero board. Also attached is the simpler schematic. It's electronically the same as the original but simplified to reduce the board complexity. You might want to check with the Editor of Model Engine Builder Magazine. I gave him all the circuit board files and he was investigating getting some made. I'm not sure if he followed through.
> I don't have any circuit boards to offer.
> A complete write up and the files to make your own circuit boards with toner transfer was featured in Model Engine Builder Magazine #34 for the original (more complicated) circuit You might want to ask the Editor about a copy of that edition.


----------



## dsage

Here are the top and bottom separately and the schematic. Please double check the connections and the part numbers vs the schematic. I have several versions of the board and although they are all functionally the same the board layouts and part numbers may have changed.


----------



## paulc

I think you may forget to attach your files?

Here is what I interpret the bottom (blue) traces would look like if seen from the TOP through a transparent board with the red traces on the top side deleted for clarity.  But Im not overly confident.





dsage said:


> Here are the top and bottom separately. Please double check the connections and the part numbers vs the schematic. I have a few versions of this and although they are functionally the same the part numbers may vary depending on the version.


----------



## paulc

David,  This is how I interpret the tracks for both faces of the PCB.  ALL seen from the TOP.  Can you confirm I have the bottom face blue correct?


----------



## dsage

BTW. If you are using a 12v supply you should use a ballast resistor or a coil that has one built in. Just like a car does.
You will notice there is a bit of space left around the IGBT power transistor on the circuit board. This is to allow a small TO-220 heatsink to be fastened under the transistor. You might find you need the heatsink with high spark rates - which your 7 cylinder will have.


----------



## dsage

paulc said:


> David,  This is how I interpret the tracks for both faces of the PCB.  ALL seen from the TOP.  Can you confirm I have the bottom face blue correct?



I think we were typing at the same time and I had deleted the files until all was correct. See the update - post 211 and my comments in post 214.
Sorry for the confusion.


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## paulc

Got it!  and thank you,
I read in an earlier post in this thread, that there was a component change (a resistor) if one intends to run on 12 volts over 6 volts?

Regarding heat , I intend to make a decent sized aluminum base pate that is bolted to the heavy transistor, the whole show will be potted on top of this plate, the plate will extend past the ends a little as tabs to allow for two small mounting holes. The "module" in this package, will then be mounted to a larger heat-sink via heat transfer compound on its rear metal face, then be placed in ventilated area in the prop wash.

Im ordering the parts now!


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## dsage

There is no need to go overboard with the heat sinking. One of the small TO-220 sinks that fit under the transistor right on the circuit board is sufficient. The transistor runs pretty cool even on a V-8 with normal rpm. The heatsink will be live. So keeping it small and isolated will avoid a lot of issues with it touching something. See attached. The 273 version fits on the board.
It's by Wakefield and if you order from Digikey it is part number 345-1022-ND.
Link here


			https://www.digikey.ca/en/products/detail/wakefield-vette/273-AB/340320?s=N4IgTCBcDaIMwBYCsBaAjABjGFA7AJiALoC%2BQA
		


Concerning component changes, there was some discussion of the circuit self-triggering when used on a large single cylinder hit-miss engine at low  hand cranking speeds. In which case increasing C2 might help. But you wont have that problem with 7 cylinders. I don't recall any other issues. It works fine on all my engines as-is.
Let me know if you find otherwise.


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## paulc

dsage said:


> . The heatsink will be live.



Oh.... the heat sink if connected to the ear of the transistor will be VCC +? 
So the heat sink can NOT be mounted on an earthed chassis?


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## dsage

Correct. The transistor tab is live.
There is no need for that much heat sinking. But if you must, you could purchase a TO-220 insulating add-on with a mica washer, and insulator for the screw. The small heatsink I showed fits on the board and should be sufficient. Even more so if you can arrange for a bit of air flow.
Keep the whole circuit as compact as possible. Don't use long wires anywhere or you will likely have issues.
Attached is the connection diagram. Again - keep all the wires as short as possible. Especially keep the battery close with a direct (and short and heavy gauge) ground from the engine block direct to the battery negative.
All of the issues I have seen using any coil driver (not just this one) is from folks spreading things out. The whole coil driver board is only a couple of inches square. Keep it that way and connect it with short heavy and direct connections. (Yup I can't stress it enough - four times now)


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## paulc

Thanks for the advice, I'll do all that.  I'm working on the circuit board print now,  going to etch the board using the laser printer transfer method.  This will be perfect for this job.  Once I have all the bits I'll post some pics to show others how I went.

Also what are the ramifications for having longer leads, what issues does this cause?

And lastly the components you listed on the PCB are ordered with some spares. But what is the difference between the 6 volt and 12 volt set up? Is it just the ballast resistor on the 12 volt version that differs between them?

When I test the 12 volt automotive  coil what should I look for and how many amps should this circuit be kept to?


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## dsage

Long leads cause all kinds of havoc with radiated interference being picked up by the wiring and sneak paths for high energy back to the battery. It usually results in the hall sensor blowing. Also, connect things exactly as the diagram shows (short and direct) There must be a direct lead from the engine block (spark plugs) back to the battery. Do not assume that a round-about ground connection will suffice. Also the hall sensor should have all three wires shown tightly twisted together and connected directly back to the circuit. Again - don't assume that because a wire eventually finds it's way to where it needs to go that that will suffice.
The high energy spark current / voltage will be looking for any path it can find back to the battery so it must be directed properly so it doesn't try to follow say your hall sensor wiring back to the battery.
I'm not sure what coil you plan to use. If it's a standard automotive coil of 12v then you'll need a ballast resistor of maybe 2 ohms and 25 watts. The current should probably be limited to 5 or six amps. There is no real need for a high power ignition system on a model. It's just a waste of power.
I (and many others) use four AA Nimh rechargeable batteries (approx 6v) in a holder and a Ford 12v COP coil (small). I don't use a ballast resistor because the batteries themselves limit the current. So this makes a nice compact arrangement.
BUT something must limit the current. It depends on what coil you're using how much it will try to draw.
Don't run the system on a power supply. Power supplies will not supply the pulse current reliably and it will likely give poor results.


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## paulc

Very good!
Is there a possible change to the PCB component list that would allow me run on 12 volts without the need for an external ballast resistor?


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## dsage

No. The board is just a driver. It's up to you to limit the current. It was made that way to keep it small. The ballast resistor value can vary and in general are very large and can dissipate some heat. Also some model coils don't require ballast resistors. It was just easier to make it that way.
There are car coils that have the ballast resistor inside. You'd have to research a vehicle where one of those was used.
What is your reason for insisting on 12v?
The previously mentioned AA battery solution is a nice small arrangement and easy to hide.


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## TonyM

Hi Guys 
Have the specs for the 3040P changed. The datasheet looks a lot different to the one shown on the schematics. https://www.mouser.com/datasheet/2/308/ISL9V3040P3-1306581.pdf Does it make any difference if they have. I am about to order some.


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## dsage

I just checked the link you gave to my original saved spec sheet and it's the same.
I'm not sure what schematic you are using. I went back to post #144 to the schematic that John Gedde (who was collaborating on this design) and he used the correct symbol that looks pretty much like the spec sheet. Symbols vary a bit.
I know very early on I used the incorrect symbol for an IGBT because I couldn't find one in Eagle PCB. But the connections have always been correct.

Anyway - just pay attention to the connections and you'll be fine. If you're using the PCB layouts I posted a while back it should take care of itself.


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## TonyM

Thanks. I missed that as I was just looking at the later posts.


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## TonyM

Hi Guys. One more question please.    The 2N4124 transostor is no longer available and Farnell have offered me this as an alternative. Will it work OK in this circuit.

https://cz.farnell.com/on-semicondu...r-bipol-npn-45v-to-92/dp/2453791?ost=bc547cbu

Thanks Tony


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## dsage

I guess time moves on. Yes it appears the 2N4124 has gone obsolete. Very strange.
It's a pretty much bread and butter transistor.
The substitute should work.

BUT

That particular substitute has a difference in the pinout. The legs are situated looking at the flat face left to right:
CBE (collector base emitter)
The 2N4124 pinout is
EBC (emitter base collector)

You can use the substitute. You will just have to turn the transistor facing the other way leaving the center lead in the same place.

Double check my work. I'm pressed for time at the moment.

Download the data sheet for both transistors and you'll see the difference in orientation of the legs.
For some reason this issue crops up a lot with these transistor packages. But it's easily corrected as above.
Actually I'm surprised they recommended it as a direct replacement. Electrically it's suitable but physically if you inserted it in an existing circuit as a replacement for an original it would not work.

BTW. The link you supplied asks for cookies. I didn't allow it so I had to get the part number and go to Digikey to observe both transistors. 
So again - check my work.


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## TonyM

As long as it's OK spec wise I will sort the orientation using the datasheet. I just wanted to be sure it works with your circuit. 

Many thanks.


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## dsage

TonyM said:


> As long as it's OK spec wise I will sort the orientation using the datasheet. I just wanted to be sure it works with your circuit.
> 
> Many thanks.



Odd. I just checked Digikey again for the BC547 Farnell recommended. They list the BC547 as obsolete as well.
So use what you can get I guess. I'll have to find a replacement with a more stable supply.

Spec-wise the BC547 looks like it should be ok. Nothing special is required there. It's used as a switch. Either on or off.

I'll have to check my stock of parts. Maybe I have a BC547. If so I'll try it in an existing finished board for you.
I won't be able to do that for a bit.

But for the cost of them. I'd say go ahead and give the BC547 a try.


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## dsage

Update:

You're in luck !
I rummaged around through my never used parts and found a dozen or so BC547 transistors. Surprised me.
The BC547 works fine to replace the 2N4124.
BUT
You just have to reverse the collector emitter orientation as mentioned before.


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## cds4byu

This link shows the 2N3904 as a replacement for the 2N4124.  DigiKey has no 2N3904 in stock, but suggests a 2N4401BU as a replacement.  They have 41,000 in stock at a price of $0.35 each.

Order page is here

Carl


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## Rocket Man

WHERE is the circuit drawing?  I buy 2N3904 in packs of 100 for $3 free postage.


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## dsage

Schematic and board layout are in Post 211.

What are the boards in your picture??


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## Rocket Man

dsage said:


> Schematic and board layout are in Post 211.
> 
> What are the boards in your picture??



WHERE is post 211 ???  I see random numbers on the left.


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## dsage

This is post #236. (in the top right corner of this box).
Scroll up the page to the top and click on page 11. and down to #211.
Basic stuff navigating this forum.


(you can also scroll down to the bottom and select page 11 too).


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## TonyM

I did my version for the non electronics guys amongst us who may want to try.  I would be happy for someone to check and critique please.


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## dsage

Quick glance. It looks good. The proof is in the pudding they say. Give it a go and see how you make out.
The only minor suggestion is to fatten up the traces from the battery to the coil and from the coil to the transistor. i.e the path the coil current will take.
If it's pcb material your using add a heavy layer of solder on the board or if it's wire use maybe #18 or so. You want minimal resistance in that path.
Also be sure to ground your engine block DIRECTLY back to the battery negative with a separate wire for spark current to return.
Also don't forget a ballast resistor in series with your coil if it requires one.


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## Oldiron

Is there any way to modify this circuit to fire the plug when the circuit *opens* if using conventional points? I have an old model made by someone of some skill quite a while ago using contacts on the exhaust valve push rod that used a condenser and coil. Conventional ignition fires when the points open and the field in the coil collapses. If the engine stops with the contacts closed the coil will get very hot or burn up so I want to use this circuit as a kind of one shot. I really don't want to make any visible modifications to the engine. Ideas please. Bob


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## dsage

If you build the driver according to the circuit diagram it DOES by design fire the plug when the points OPEN.
In fact the nice thing about this design is that it will not remain on and burn up your coil. If the engine stops with the points closed it will "time out" and stop driving the coil after a period of time.

To that point: If you are using the circuit on a full sized hit-miss engine running at typically very low rpms the time-out feature might become a problem especially on starting. The engine might kick back when you pull it over by hand. If so let me know. It's easily fixed by increasing the value of C2.
This has never been a problem with models.


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## dsage

BTW. 
Perhaps it wasn't clear, but you can connect your points to the input instead of the hall sensor. The hall sensor and magnet works like points i.e. normally high input going to ground when active.
Eliminate the capacitor / condenser that it typically across the points on your engine. It is not necessary and will cause issues.


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## Oldiron

I have bult 3 of these but this is the first one I've used with points. No condenser used. The led comes on and it fired when the points close for sure and went out but didn't fire when the points openied when I was trying to set the timing last night. You have to barely turn it to set the timing so the lock out may be the problem but how do you get around that. The parts are as specified and built on the same PCB  board as the others so I dought wiring is the problem but I will build another today just in case. BTW thanks to everyone involved in designing this. Bob


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## dsage

When you turn the engine over by hand it may "appear" that the spark is occurring when the points close (the LED lights). In fact when it is operated so slowly the timeout is triggering every time. The timeout is only about 15 mill-seconds (I think) after the points close (the LED turns on).
So what you see is the LED go on, the timeout happens and the timeout will issue one spark before you can turn it enough for the LED to go out. Once triggered (by timeout or otherwise) it will not generate another spark until the cycle repeats.

You can set your initial timing using the LED. The led follows your points operation.
Use a degree wheel or degrees marked on the flywheel with a TDC mark reference. A timing light will be of no use turning by hand because of the timeout spark triggering it
  Turn the engine over by hand and watch the LED go ON. Ignore the spark and keep turning until the LED goes OFF. Set your timing according to the marks.
Just set it roughly. You can use a timing light once the engine is running.
The 15ms timeout is a non-issue when the engine is running.
Unless like I said, you have a very slow running single cylinder engine. Typically a full sized hit-miss.
You should also check and adjust the dwell degrees of the points. Most hit-miss engines have excessively large dwell time (points closed time). This is just a waste of power and overheats the coil keeping the coil charged for more than the 6ms or so it takes to fully charge it.


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## dsage

I never envisioned the timeout being an issue. And it hasn't been. The circuit could have been designed for a several second (or longer) timeout. Something more in line with times that might actually damage a coil should it stay energized.
But that would require more circuitry than the driver itself. The point was to keep the circuit as simple as possible. Tradeoffs are always in play with circuitry.
As mentioned C2 can be increased a bit if you get kick-back from a large single cylinder engine when pulling it over by hand. But the LED starts to act funny if it gets to be more than a few microfarads.
Decreasing the dwell is an all round better solution.
You can do the math for your engine minimum rpm / dwell time etc.


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## Oldiron

Ahh, so the spark occurs when the LED goes off if running at speed. Time to fire when the led goes off and disregard the false spark. Thanks. Bob


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## Oldiron

It worked out great. The engine runs. Thanks. Bob


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## dsage

Great. Another happy customer.


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## dsage

TonyM:
Back in post 237 you posted a perf board layout for the ignition circuit. Did that work out? 
If you made any changes that resulted in a finished product would be willing to post them? 
Your solution would be easier for folks to build than the pcb's I posted and would help get more made.
Perhaps a picture of the finished product too - Thanks


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## TonyM

dsage said:


> TonyM:
> Back in post 237 you posted a perf board layout for the ignition circuit. Did that work out?
> If you made any changes that resulted in a finished product would be willing to post them?
> Your solution would be easier for folks to build than the pcb's I posted and would help get more made.
> Perhaps a picture of the finished product too - Thanks


Hi Dave. 
I didn't make it yet. Hobbies have been on a back burner because I have been rebuilding part of the house.(out of necessity) 
What little time I have had is trying to make a 1/4 scale 'electronic' magneto. The printed body containing the circuit, coil, battery and reed switch trigger using the parts from the 'Ridders' type ignition.
I was hoping to discuss alternative circuits with you when I restart. Probably in a month or two.


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## dsage

Ok. Let me know.
Thanks


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## peterl95124

DSage, hope you're still reading this thread,

question, why not a "free wheeling diode" in the primary LC circuit ?

Peter.


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## dsage

Sorry a poor explanation but in short you really don't want a free wheeling diode per se. It will dampen the coil output.
If you use a regular transistor it actually breaks down when the reverse energy from the coil is created. Sort of like what a free wheeling diode would do.
It doesn't really hurt the transistor but it can be as low as say 100v which limits the coil energy output.
When you use an IGBT the reverse breakdown is several hundred volts because of the zener etc inside the as shown below. So you can get a higher energy output from the coil.
Maybe I've misinterpreted your question.


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