I'm playing about with home made igns and have read all the info etc on here, there is a lot about the ign controllers but very little about coils. So from what I get so far:

Kettering needs about 200 turns primary, 20000 secondary, (100:1 ratio) draws about 1.5 amps on the low volt side and will work on 4.8 or 6v

CDI needs a lot less as its already at 2-300v primary, so 40 turns primary and 2000 secondary (50:1 ratio) is okay for 4.8v

BUT, it sems a lot of people just buy them from CH rather than make them, but I'm in the UK and there is no supplier for small ign coils here. I'm currently using a 6v motorbike coil but its a bit heavy. So, has anyone made a neat smallish coil and if so what turns, core shape/layout and wire gauge did you use, and what input voltage? I guess there are a few more out there who could use this info as it seems there are quite a few home ign builders.

Cheers in advance,
Rich

I just made 2 coils from some old transformers. It took some trial and error, but the end result was good.
The spark is just as good as on my CH ignition coils, and the weight is the same, about 40 grams.
The size is also about the same as my CH coil.
I have tested a lot of different ratios, and several ways to wind it, and this is my best results;
Primary: 100 turns of 0,8 mm wire
Secondary: A LOT of turns of very thin wire. I did not count, but the layer of wire was about 5 mm thick.

A short clip of it running is here: [link=http://home.online.no/~jon-mj/Coil.wmv]Coil clip[/link]

The images show the final coil, and a side by side comparison with a CH coil.

I will write a description of how to make the coil later.

Jon-Magne

C&H hasn't used those coils for many years...They're Modelectric coils, made for old time spark ignition engines, 3 volts max with a set of points...They work for a while but the insulation isn't good enough and will break down...Been there [8D]

Hi Jon,

Thats the kind of thing, and it looks like you are running it from the CDI circuit from the magazine too? I know the modelectric ones have known probs hence asking about making your own, like them, but better, and your small one sounds good. I look forward to some more info. If you know the wire dia for the secondary that would be useful too.

Thanks in advance,
Rich

I have made a page with details of the coil on my [link=http://home.online.no/~jon-mj/homemade_coil.htm]homepage[/link],
You should find all info you need there.

The CDI is from the design on my web.
It is an open source design, but i have not put the latest version on my page yet.
It has programmable delay, a nice test function, as you see on my cideo clip, and uses no special componens.

Jon-Magne

fantastic, thanks Jon. Nice website too, I have a seagull harrier as well. I'd be interested in any info for the new CDi circuit too with the programmable delay. I guess you mean it works as auto timing advance?

I'm off to search for a transformer now!

I had looked at the french website but to be honest designing circuits is beyond my knowledge at the moment. I can make one from a diagram and prototype board but not from scratch. When you put the circuits up for the new CDi system with programmable delay I'd be very interested (or by email if you already have the info but not done the web page yet). I'll PM you my email address.

Cheers,
Rich

I have sent you a mail with all the info needed. The CDI has auto adwance, and a programmable ignition curve.
It uses a PIC microcontroller, and the curve can be modifyed in a Excel sheet, and then put into the PIC program.

Jon-Magne

I just made another coil, this time from an 220v/9v transformer, used 50 turns on the primary.
It works, but seem a bit less powerful than the other two i made.

Jon-Magne

I made one last night from a 220v to 12v transformer with 100 primary but as I was soldering on the -ve wire t the two start ends I broke off the thin wire end[:@] no way to rescue it so its back to start again. I'll let you know how I get on.

Cheers,
Rich

I'm reading this tread, and a lot of all treads in Engine Conversion to. I'm buidling an ignition (CDI) based on the gas burner ignition. In original it works from 1xAA cell for a long time. I changed the step up coil from original (it delivered not enough current to charge the capacitor). I wired the coil on a standard ferro (7mm diameter and 40mm long) in a 3 layer (450 windings 0,2mm; 20 windings 0,57mm and 10 windings 0,2mm - just like the jmj). It provides me about 100-120V from a 5V supply. In the spark coil the important thing is the spacers between sections of the secondary. The standard isolation on the wire doesnt provide isolation above 1kV. My ignition does a standard spark without advance.

Sorry aobuot my english but it's my first post on the english language forum (before I only red).

Hi
for HV coil I am using Honda Transalp HV coil, on a Homelite 38 cc chainsaw engine, sorry only on a test stand , took a lot of abuse, no problems.
With this coil put in the air a Weedeater 18cc converted to CDI, small and low compression engine , but works, the only problems was the RFI, cured it and flown well.
But the Weedeater was very low in compression.
Any motorcycle HV coil will work, but must be CDI ignition.
Also experienced with the grey coil from a Echo 51 cc chainsaw, works , very small and light.This have two coils, magneto coil and HV coil (grey).
Good luck
Jose

Skazoo, which schematics are you using?
I have not seen one powered by a single cell.
I have not made my coils in sections, i know i probably should, but have no problem, yet..
One coil i made had wire with a very thin layer of insulation, it was no good, i could hear the spark inside the coil.
The other 3 i made is fine, so far.

Jon-Magne

Jmj now I'm using step up build just like the one from your homepage. The one cell ignition is made as a multivibrator trigered by a rising voltage on a output capacitor. It provides maybe 10 sparks per second so its not enought for our ignition systems. The first step up coil has about 100:1 ratio so it could work from even one cell. But it generates not enough current to speed up sparks so I change it.
The section isolator shouldnt be a layer isolation. We create in this option some capacitor between layers. For isolation we should use a parallel section wounded one by one besides.

I would sure like to hear how you fellows are doing with your ignition projects; ups. downs, successes, failures, etal.

Thanks, Tim

Does anyone knows the exact values for the resistors in the original low tension TIM 4 cdi module,for a continuous work with a 4.8 V power source?
..and eventually their values for a 6V continuous operation? (modelectric coil)
Engine on test is a O&R 23,year 1948.
Piero