Ignition circuit help

[canadianhorsepower]

This is the circuit I built. I did not see the point in trying the circuit if the coil won't spark without it. I used this circuit with a 66 caddy coil and it worked just fine.

with out having any part number no one can help you.the voltage divider between 47k and 680 is not enought to saturate the transistor itself

 

[canadianhorsepower]

you must also take into consideration coils in 1966 and now are not quite the same
at that time 12KV was hight now 50KV is almost the standard

 

[stevehuckss396]

with out having any part number no one can help you.the voltage divider between 47k and 680 is not enought to saturate the transistor itself

Works fine with the other coil. Here is what I used.

View attachment ignitionDevice.pdf

View attachment ignitionPNPDevice.pdf

View attachment ignitionDeviceHallSensor.pdf

 

[canadianhorsepower]

thanks I'll get back to you soon got to chat with my calculator
do you have any resistance value of the coil you were using with this ???
thanks

 

[stevehuckss396]

thanks I'll get back to you soon got to chat with my calculator
do you have any resistance value of the coil you were using with this ???
thanks

Look back at reply #34. I posted a pic with the coil readings. Keep in mind there is no connection between primary and secondary windings.

 

[Mosey]

Strong opinions, here.
Wonder?

 

[Lakc]

No, If the coil wont spark with the battery it isn't going to spark with the transistor in series with it. I would like to get the coil figured out before I hook up the electronics. I hooked up the caddy coil to the battery and it sparked fine.

Not exactly, if the coil draws more amperage then the caddy coil it will be more prone to arcing when you break the connection. Arcing slows down the collapse of the magnetic field which produces a weaker spark. It might actually work.

Whats the depth of your enclosure?

 

[stevehuckss396]

The current enclosure has .625 from the cover to the board mounts. Back of the board to the cover = .625

I can cut down the mounts to give .750 if need be.

 

[dsage]

Steve:

A couple of things:

The output of those dual output coils is between the two high voltage leads - not from either lead to ground. The high voltage travels from one HV lead to the first spark plug, jumps the gap, travels through the engine block to the other spark plug, jumps that gap and returns to the coil through the other HV lead.

Both spark plugs fire at the same time. The one plug fires when there is no compression so it's easy to jump that gap leaving all the energy for the other plug. It's called a waste spark ignition. Because the spark is sort of wasted on one cylinder at a time. Makes for a simple ignition though.


To test this simply - on the bench - put a spark plug on the one HV lead and use a clip lead to join the other HV lead to the threads of the plug.
I'll bet it works then.
The engine block is just a current path with this setup. It need not be grounded. (but it can be). It is not required.

As for your circuit the 680 ohms and 47k is fine on the input transistor but the other 680 ohm resistor on the power transistor is not sufficient to drive the power transistor with the coil you are using.

I didn't look up the actualy specs for the transistors you are using but generally speaking signal transistors and general purpose power transistors are similar.

The calculations go (roughly) like this.
For the input transistor:
12v/680 ohms = 17ma
The input transistor probably has a gain of about 150 so the transistor will be driven hard enough to supply 150 x 17ma = 2.6A but it will never need to do that nor could it. Suffice to say that that part of the circuit is fine.


For the power output transistor you still have the other 680ohms and 12V which is 17ma. The power transistor probably only has a gain of at best 50.
So 17ma x 50 = 0.85A.
Therefore the output transistor only has enough drive to supply 0.85A on its output collector.

Your coil you said was 0.8ohms so it will be trying to draw 12v. / 0.8 = 15amps. So you are way short of drive on that transistor.

You could substitute a darlington power transistor for the one you are using. A darlington will have a higher gain and will be able to drive the coil with the 680 ohm resistor. (if it is already then your fine)

If you need more help I can re-design the circuit for you.

As mentioned before an IGBT power transistor would be a better choice for all the reasons I mentioned previously and it would also work in the existing circuit.


BTW, you should not drive a coil directly across a 12V battery. In a car (back in the day) there was a ballast resistor of maybe .5 ohms to limit the current to the coil should the points stop in the closed condition.
I mentioned all of this before. It is possible for your engine to stop with the hall effect activated and therefore the coil will be stuck ON ans will likely burn out the coil and / or the transistor.
This is the one thing wrong with all the original TIM circuits.
Be careful!! or use my circuit. It's better in a lot of ways.

Sage
(Electronic Technologist - retired)

 

[canadianhorsepower]

[/Look back at reply #34. I posted a pic with the coil readings. Keep in mind there is no connection between primary and secondary windings. QUOTE]

Hi Steve, I did a few test and calls today and I have a few good answers.
1 even if it works you should fire your coil thrue ground and not live.
thats an easy fix replace both transistor with the oposite ( from NPN to PNP)
2 the output trans your using is on the limit as far as suplying the need of this coil
that is really more a "step up transformer" then an "inductor"
3 I called one of my buddy at BRP in Valcour reguarding the testting of these dual coil.
His answer was pretty straight forward, "you have a sparks it's fine" reason beeing because
it is fired simultaniously it has a vector effect on how mutch will go when. the fatter side will get
it all and leaner side will get nothing. He told me that they took them out of the market for two reasons.
Number one they were confusing to check and were very hard on the module.
I hope it's of any help. BTW what CAD did you use for these drawingscratch.gif

cheers

 

[stevehuckss396]

The electronic circuits were drawn in paint. The distributor and board were done in Alibre.

 

[canadianhorsepower]

is this the BEST you can do:shrug:

 

[stevehuckss396]

So what you are saying is to connect the 2 ground straps and the circuit is complete.

Alot of info up there. I must have read it 5 times.

I knew that both plugs fire at the same time. That is fine with me.

I know the gain is more like 300 not 50. Would that be acceptable?

I'm not worried about the coil being left on. The starter box I use has a switch on it. The motors get started and after they run I cut the power to shut them down. The ignition would never have power on it unless the motor is running.


I could always use more help. If you redesign the circuit do you think you could get this thing sparking or am I wasting my time with this thing? I know they are a pain but it looks so good on the motor.

Lakc is looking into a CDI circuit. Would the CDI circuit be a better driver for the coil and give a stronger spark?


Well thanks for looking into this thing for me. I know how time consuming it can be diving into something like this.

 

[stevehuckss396]

is this the BEST you can do:shrug:

Whats wrong with paint? Makes good drawings and it's free.

 

[dsage]

Candianhorsepower:

You are completely wrong !!

You cannot correct Steves circuit by simply swapping NPN and PNP devices. It will NOT work.

Steve:

Sorry I didn't check your component PDF's first. Your output transistor is an excellent choice. It has a gain (hfe in the specs) of 300, so with the 680 ohm resistor should have enough drive to supply 5amps to the coil. This is more than enough (even though the coil will be trying to draw 15amps. It also has a high breakdown voltage so it won't be supressing the primary kickback. (That;s why it's designed for ignition circuits).

You need to make a couple of small changes to your circuit though...

1. Move the coil to be in the collector circuit - between the collector and 12V. The way it is it will be difficult for the drive to the output transistor to fully turn it on.

2. Ground the emitter (the one with the arrow - where the coil is in your diagram now).

3. Add a 1k resistor from the base of the power transistor (also where the 680 connects) to ground. This will ensure the transistor turns off properly.

4. For safety please also add a low value high wattage resistor in series with the coil. I'd say 1ohm 10watt wire wound ceramic part should do it. (like the old school cars had - ballast resistor)


Sorry I don't have the ability to redraw your circuit at the moment.

For the benefit of others please redraw it like I mention here. (so I can see and doule check it too)

Also go back a couple of posts and see my note about how the coil needs to be connected to the plug(s) and how to test it on the bench.

Let me know if you need further help or don't understand my instructions.

Thanks


Sage

 

[dsage]

Steve:

Sorry I didn't see your post #53 asking about the plug wiring.

I'm pretty sure what you have is a dual output coil used for waste spark ignition. I hope I'm right on this and haven't wasted a lot of effort typing this.

There are no grounds necessary on the spark plug side of things.
I recommend you test it as suggested on the bench to be sure and so you can see the spark energy Sorry for the crude diagrams below.


With one plug connect like this:

HV --plug -------jumper wire-------HV

IF you want to test with two plugs:

HV --plug------jumper wire -----plug---HV

The jumper wire will need to be clipped to the threads of the two plugs and the HV leads connected as normal to the tops of the plugs.

In the engine, screw in the plugs into the heads and connect a HV lead to each. The plugs will be connected together because they are both screwed into the metal heads. The block / heads do not need to be grounded (although it won't hurt anything it is not necessary).
The spark is looking for a path between the two HV leads. NOT to ground. What it sees is two spark plug gaps in series between the HV leads. The heads / block is just the connection between the plugs.
(obviously the heads must be electrically connected and not insulated by head gaskets - very unlikely as bolts will make the connection).

I know it sounds odd but you have to get your head around the fact that the heads / block are not supplying a ground for the spark, just an electrical connection between the two plugs.

Hope this helps.

If I missed answering anything let me know.

BTW. Now that I see the nice job you have done, (as usual) I would recommend continuing with what you have. If the coil is good, the arrangement will be fine. No sense starting over. Using a CDI unit with a conventional car coil will result in excessive HV which may cause you problems on a model sized engine. 7kv is plenty on our small plugs. 60kv on the other hand will be looking for all kinds of places to jump.


Sage

 

[Lakc]

So what you are saying is to connect the 2 ground straps and the circuit is complete.

As long as both plugs are screwed into the same motor your fine

Lakc is looking into a CDI circuit. Would the CDI circuit be a better driver for the coil and give a stronger spark?

I have one, needs some tweaking I think we can even cram it into the space you have as well. I actually had originally programmed in a pinswap so it would fire a transistor instead of an SCR for the CDI. As to which is better, that debate is similar to the Apple-PC one and we wont go there

 

[canadianhorsepower]

Whats wrong with paint? Makes good drawings and it's free.

Sorry I was trying to joke a little. it's funny with all your knowledge and programs seeing you using paint really surprise me

 

[canadianhorsepower]

Sage, [QUOTE]Candianhorsepower:

You are completely wrong !!

You cannot correct Steves circuit by simply swapping NPN and PNP devices. It will NOT work[/QUOTE]

Hold on a minute before doing bold comments like this one. I know damm well that a "SIMPLE SWAP" would not work that's
what I teach. Instead of trying to look like a smart ass and add a full page of infor that are not neede at this time I pointed out
some change that could be done. If you read the complete post you would realize that even if it doesn't satify you it's a working circuit.
I'm trying to give Steve as many info as I possibly can and from there he can decide what to do.

are you the same one that wrote on post #30 I DIGRESS JUST ORDER ONE OF THE CDI AND BE DONE WITH ALL THAT TIM STUFF
IT WOULD HAVE BEEN NICE IF YOU WOULD HAVE STICK TO YOUR WORDS INSTEAD OF BLASTING ME OFF FOR NO REASON

 

[stevehuckss396]

Sorry I was trying to joke a little. it's funny with all your knowledge and programs seeing you using paint really surprise me

I drew that circuit along time ago before I had access to any of the fancy drawing programs.