Model engine CDI easy and cheap

[Foketry]

It works
Thanks for all

 

[paulc]

It works
Thanks for all

View attachment 128275

Well done

 

[paulc]

Tachometer and Kill switch.
Using an electronic tachometer I connected the tach input to the trigger terminal on the CDI. This is the same terminal the booster induction coil is on.
The kill switch I ground the same wire. Seems to work fine in tests.

 

[paulc]

Here are some pictures of the completed item. Re potting the extra component added about 6 mm to the over all thickness of the CDI. FYI the potting mix is just some regular epoxy resin mixed with about 4% acrylic house paint
I pushed the terminal locking tabs in then using a heat gun softened the potting epoxy and the green plastic plug socket cam out easily. Then changed all the plugs to suit my needs and soldered my harness directly to the terminals which were cut short and bent over to form soldering pads. The unit has a tachometer output and a grounding kill option (blue ended wire).
I have tested the unit to 18,000 spark per minute on an exaggerated plug gap with no issues.
I'm please with how it came out. Now to test on a running engine.

NOTE: In the diagram we are only using the coil from the reed relay as an induction booster for the CDI trigger. The contacts from the reed can be trimmed off.

 

[Claudio Masetto]

Looks good.

 

[bluejets]

Good to see you have it sorted.

I did suggest a possible fix along those lines but haven't had time to scratch myself lately.
https://www.homemodelenginemachinis...park-fellow-aussie.100883/#convMessage-105350

Just noticed the fix in my email........

Now if you need a water temperature gauge to go with it, there is one on my youtube .
If you want I can link here on a new topic.
Yeah, it works no worries.

 

[paulc]

Good to see you have it sorted.

I did suggest a possible fix along those lines but haven't had time to scratch myself lately.
https://www.homemodelenginemachinis...park-fellow-aussie.100883/#convMessage-105350

Just noticed the fix in my email........

Now if you need a water temperature gauge to go with it, there is one on my youtube .
If you want I can link here on a new topic.
Yeah, it works no worries.

Hi Bluejets, still makes me think we need to test some other units on your set up. To see why your CDI works on your original circuit and why others dont. If you plug one of my spare CDI into your set up and it works I will faint!!! If you email me your addy I'll be happy to send you a couple to try out. It would be good to know.

 

[dsage]

Paul:
Do you have a proper schematic of your finished circuit - rather than the interconnection diagram or parts laid out on a piece of paper. I'm having trouble figuring out exactly how everything is connected.
Nice work. Seems a pretty simple solution to the problem.
Thanks

 

[bluejets]

PaulC,
Had a few minutes tonight so I dragged out the original drawing and modified it for you to your new design and specs.
You might want to check it out......
BTW..... most hall effect are open collector and require some kind of circuit to the positive rail be it either a resistor or an LED/resistor otherwise they simply just won't work.
It's just signal level stuff so 1k0 is ok.
I have shown it with a 680R as i calculated it out with a red LED @ 20mA. Good for setting the timing.
The original KY-003 already has a pullup so the 680R and the LED in this instance if using that module , is unnecessary.
If using a bare hall effect such as the 3144, always good idea to wack a small (0.1uf) cap right on the switch terminal legs power rails.
Not my idea, rather Allegro.
For others, just take note the order of the pinout on the KY-003 will be different to that shown above so don't blow it.

It might be an improvement to add a small series capacitor in the signal lead between the signal output of the Hall Effect and the BC558 base resistor. That way, the transistor only turns on during the pulse from the hall effect rather than being on all the time when the hall effect is on. (e.g. engine stops)
One of those suck it and see things I guess, might be unnecessary as KISS is best in many instances.

Finally a link to your reed switch.....
12V SPST Low Cost Reed Relay | Jaycar Electronics

dsage..hope this helps....

Cheers Jorgo

 

[dsage]

Yes. That's great.
I've been looking at schematics for 55 years so interconnection diagrams just don't completely do it for me.

Your suggestion of the series capacitor would normally be a good one but if I understand the CDI unit operation it might mess with the advance feature since the capacitor would charge up and "time out" releasing the drive to the transistor early at low rpms. I haven't analyzed it fully though.
Even if the transistor drive stayed on (engine stopped) there would only be 12ma or so of current draw. Of course I don't know what the CDI unit itself would draw. I assume not much since it appears it's looking for a HV pulse for a trigger. One would have to measure the current draw with the drive stuck on.

 

[paulc]

Yes. That's great.
I've been looking at schematics for 55 years so interconnection diagrams just don't completely do it for me.

Your suggestion of the series capacitor would normally be a good one but if I understand the CDI unit operation it might mess with the advance feature since the capacitor would charge up and "time out" releasing the drive to the transistor early at low rpms. I haven't analyzed it fully though.
Even if the transistor drive stayed on (engine stopped) there would only be 12ma or so of current draw. Of course I don't know what the CDI unit itself would draw. I assume not much since it appears it's looking for a HV pulse for a trigger. One would have to measure the current draw with the drive stuck on.

During my experiments I found leaving the 0.1 cap on the base leg of the transistor caused the spark to break down at an earlier rpm. The cap gives a short pulse but at high rpm this is not allowing the reed coil time to saturate.
Removing the cap I can push past 18,000 sparks per min!
The current draw even if the hall is stuck on is very small, the cdi quickly fills the 400v cap and stops taking. Even if the reed booster coil draws current its nothing, I suspect you could leave it stuck on all day. I’ll do some current draw tests in various situations including hall on while stationary.

Bluejets good work on schematic! Is the role of the LED across the Hall just for indication or plus protection purposes ?

 

[bluejets]

BTW..... most hall effect are open collector and require some kind of circuit to the positive rail be it either a resistor or an LED/resistor otherwise they simply just won't work.
It's just signal level stuff so 1k0 is ok.
I have shown it with a 680R as i calculated it out with a red LED @ 20mA. Good for setting the timing.
The original KY-003 already has a pullup so the 680R and the LED in this instance if using that module , is unnecessary.

 

[paulc]

BTW..... most hall effect are open collector and require some kind of circuit to the positive rail be it either a resistor or an LED/resistor otherwise they simply just won't work.

But Im using a bare bones Hall sensor with no pull-up resistor or LED across the Hall pins and it works fine?

 

[paulc]

 

[bluejets]

you're probably getting bias through the pnp transistor.....fine by me if you don't want to listen.
Just thought I'd tell you as it will trip you up one day.

 

[paulc]

you're probably getting bias through the pnp transistor.....fine by me if you don't want to listen.
Just thought I'd tell you as it will trip you up one day.

Hey Bluejets, please dont think Im being defiant, Im just trying to understand the reasons for why my Hall sensor is working in the absence of a resistor and LED and in response to you saying "simply just won't work".

Do you think back EMF from the reed coil could be an issue for the Hall sensor? Can the Hall sensor be further protected from spikes. I know first hand how easy they are to damage

 

[74Sprint]

The data sheet for the 3144 states that when it is off it can handle 28 volts on it's output.

 

[paulc]

MORE INFO:
Hi all, well I can 100% confirm that , as I suspected there are indeed variations of this so called 4 PIN 12 VDC CDI. So far I have received two of these units from two separate eBay suppliers. The units are packaged the same but each performed differently. These differences below.

1. Supplier "A" and unit "A" would not work on member Bluejet's modification, but would work using the modified circuit with booster induction coil in series with the trigger terminal.
2. Unit A would spark on the LED going out.
3. Unit A does have a crude retard feature on start up RPM (below approx 700).

4. Supplier "B" and unit "B"works fine with the above circuit with NO booster coil. But does have a hotter spark with the booster coil.
5. Unit B has no timing advance or retard, its fixed at all RPM.
6. Unit "B" with the booster coil sparks when the LED first comes on.
7.Unit "B" with no booster coil sparks when the LED goes out! ( go figure)?

Conclusion: Based on my practical experiments unit B with booster coil, no advance, and sparking when Hall LED first comes on is the preferred unit IMO. It has a stronger spark as determined by the ever increasing gap it could jump at 18,000 spark / min without breaking down.

Now how does one know which one they are buying?

Cheers Paul

 

[bluejets]

Bit of free time so whipped up a mod circuit using PaulC idea but different bias arrangement and also dc block cap.
If one needs to use a remote Hall effect 3144 type to reduce size of the pickup hall as apposed to the KY-003 module, one could simply remove it from the KY-003 module or use a descete part and add any indicators themselves.
If using the module, it has all the necessary components on board except for the 0.1uF capacitor.
Relay i used was a small 12v unit, details on the drawing but just about any small coil would suffice.
This particular one was chosen due to coil resistance of around 700 ohm.
I cut a small hole in the top of the case and filled it with epoxy, probably not necessary but did it all the same.
My opinion would be that this type of coil would produce a better pulse due to it's inbuilt core whereas the reed coil has an air core.
As best I could tell with my little DS150 scope, trigger pulse is around 8-10V.

 

[Eccentric]

Can the CDI drive two coils simultaneously? I am looking for an ignition system for a inline twin cylinder engine with a single hall sensor pickup and wasted spark. The pistons move in unison, one is on the power stroke while the other is on the exhaust stroke. An ignition system that has a magnet on the crankshaft and a hall sensor that fires a CDI unit once a crankshaft revolution that could drive two coils would produce a spark to the two cylinders simultaneously. One would fire the power stroke and the other would be wasted.

I really like the idea of using the inexpensive 12DV CDI units for skooters and mopeds. But could one fire two coils instead of one? Without knowing the inside circuitry of the CDI unit, the switching transistor driving the coils in parallel would see half the resistance and be required to drive twice the current. Don't know if it could handle that.

there are six cylinder car engines that use this technique, firing two of the six cylinders simultaneously, one with wasted spark. I have not been able to find one of the CDI units as inexpensive as the moped variety.

Any other suggestions? Using a wasted spark ignition would eliminate the distributor.

Thanks