Small Ignition Coil Drive Question

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scottyp

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Nice complete setup.

I used to love Hobbyking, way back when their website was basic and easy to use, lots of fun items, their prices were super cheap, and you knew how much shipping was going to be, etc. It may have taken an while to get to you, you would almost forget what you ordered and it showed as a surprise. I'm not into RC like I used to be, I am glad to be spending my time here instead.
 

earlwb

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One thing to note is that one should not try creating sparks with a gap larger than the spark plug gap. The super high voltages actually damage the varnish insulation on the wire inside of the ignition coil. Once you do it, the coil is on borrowed time as it now has pinhole shorts in the insulation. How long it lasts depends on luck mostly. Many of the modern car ignition coils only work one time when you try to see how long of a spark you can get out of them. You get that great two inch spark once and then its dead.
 

doc1955

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One thing to note is that one should not try creating sparks with a gap larger than the spark plug gap. The super high voltages actually damage the varnish insulation on the wire inside of the ignition coil. Once you do it, the coil is on borrowed time as it now has pinhole shorts in the insulation. How long it lasts depends on luck mostly. Many of the modern car ignition coils only work one time when you try to see how long of a spark you can get out of them. You get that great two inch spark once and then its dead.
Yep you are correct I did this with a cheap coil that I had a few just to see. It lasted a lot longer than I expected matter fact I ran an engine with this coil for several years before it pooped out on me. Worse is not giving the coil a place to discharge the secondary windings will eventually short out. The spark in the video I posted was very wide and I wouldn't have believed it could jump that far if I didn't see it. Like I said I was just playing and was not concerned with ruining the coil. I use the same type coil on a few of my engines 2 of them on my Mini Hog engine. On some I use the el-cheapo driver and others I use the tm6 with a ballast to raise the resistance of the coil to protect the driver that is being used. Most of them I run on 5V (a USB wall wart) and almost every one of them I use a hall sensor.
 

earlwb

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I can't blame you, as I did the same thing with some old coils years ago. But I thought I would mention it in case someone bought a new coil and tried it before they used the engine on their project.
 

bluejets

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Plus $10.50 delivery.....................................................

Closer to my quote than yours...;)
 

earlwb

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Yes, I agree, the motorcycle/scooter.moped ignition sets are a great deal at present. But the spark plug may be too big for small model engines. You may need to replace the spark plug cap. Such as using for a 1/4x32 size spark plug or a NGK CM6. We are lucky and can get free shipping here.

Screen Shot 2020-09-29 at 8.16.29 AM.jpg
 

tornitore45

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One thing to note is that one should not try creating sparks with a gap larger than the spark plug gap.
When the plug fires inside an operating engine the pressure is several time the atmospheric pressure and so is the gap breakdown voltage compared to the same plug being fired in open air.
If your ignition system can't make a 1/4" spark in open air, when you are testing, it may not work well in a running engine if at all.

Testing on a much wider gap than a 1/4" is asking for trouble. The voltage will rise until it find the weakest spot, usually inside the coil.
 

bluejets

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Yes, I agree, the motorcycle/scooter.moped ignition sets are a great deal at present. But the spark plug may be too big for small model engines. You may need to replace the spark plug cap. Such as using for a 1/4x32 size spark plug or a NGK CM6. We are lucky and can get free shipping here.
Fairly certain I explained the replacement of the ht cable with a Belden cable, more scale appearance.
Some others here had scale appearance caps as well for the 1/4" plugs.
 

rutzen

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Hi Earlwb, I bought a complete ignition set up on ebay that looks the same as the one you pictured on your previous post. I can't see how to get it to work though. I think i've got the AC set up as you show in the ebay listing. As far as I know it needs an AC supply which would be from a flywheel generator. Should I have got the DC version? I only paid £7.50 for it so I haven't lost much if it is scrap.
 

earlwb

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Yes I think that you should have gotten a DC version instead. I am trying to remember what one can do in using the AC version. Not enough coffee in me yet. One of the forum members posted a link to a thread he started on the subject at the beginning of this in post number 5. it might help.
here it it Model engine CDI easy and cheap
You can check the article in the PDF file and see if you have a AC or DC version ignition unit.

Hi Earlwb, I bought a complete ignition set up on ebay that looks the same as the one you pictured on your previous post. I can't see how to get it to work though. I think i've got the AC set up as you show in the ebay listing. As far as I know it needs an AC supply which would be from a flywheel generator. Should I have got the DC version? I only paid £7.50 for it so I haven't lost much if it is scrap.
 
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doc1955

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If you have some diodes you could build a full bridge rectifier just need 4 diodes then you could change it t a dc current.
 

rutzen

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Thank you for the replies. The engine is one I am making for a model of a Rumely Oil Pull single cylinder so I am having to design it from scratch. Whatever ignition system I use it has to be small to fit in the space available. I've never made an IC engine before being a steam loco man usually. I've thought about using Jan Ridders design but some people say they can't get it to work. I only need low rpm.
 
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