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I now have an ignition coil.

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LAN_403

Platinum

Wed Dec 28 2011, 07:08PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

My friend gave me an ignition coil from a chainsaw today, here it is.

How do I drive it? (light dimmer? :)...) It's a very small cute (lol) coil, so hard to get...

Is it ok to leave the light dimmer out, as I don;t have one, or use something else? Also which I think is odd the coil does not have a complete iron core, underneath (not in photo) it's just a U of iron core, and it isn't full, so like it's like a C or U, not full as in mains transformer.

Also I'm trying to power it to see if it works, so I put 20vDC into it to see if it even sparks and none. It has two outputs, one HV, and one bare tab, so I thought the core was the other connection and it was, but there are no sparks from the HV out, it did spark when I pulled the starter in the chainsaw?

Marko

Wed Dec 28 2011, 07:52PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Some people tend to have fun by charging a few-uf cap to mains voltage over a diode and a resistor, or whatever, and then dumping it with an SCR or large switch into the ignition coil (a chicken stick works in necessity too!). Can't be simpler than that, for some pulsed sparks (I'm afraid your small coil could be easily killed by this though).

Or, have a relay based oscillator drive it (hard on relay though)!

Marko

Platinum

Wed Dec 28 2011, 07:57PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I have a small relay from a big TV, but when I put 12v into it, it just clicks, and I think it do not oscillate (if it did, wouldn't it buzz, and not click?)

So I can drive this coil current limited with 60w bulb then a retifier and a few 250/275Vac caps for sparks?

Also can't it work on mains alone?

Thank you. Thumbs you to you ^^

Steve Conner

Wed Dec 28 2011, 08:30PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Does the coil even have a primary winding? The open core suggests that it's a magneto, energised by a permanent magnet on the engine flywheel.

A magneto ignition might still have a primary winding on the coil, even if it's just for the kill switch to short out.

Don't use the light dimmer circuit without the dimmer, you'll get no sparks and a burnt coil.

Platinum

Wed Dec 28 2011, 08:46PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Dr. Watt The Fork wrote ...

Does the coil even have a primary winding? The open core suggests that it's a magneto, energised by a permanent magnet on the engine flywheel.

A magneto ignition might still have a primary winding on the coil, even if it's just for the kill switch to short out.

Don't use the light dimmer circuit without the dimmer, you'll get no sparks and a burnt coil.

Yeah it's a magneto I think :(, so I won't get sparks/arcs from this?

Steve Conner

Wed Dec 28 2011, 09:07PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If it has a primary, you can dump pulses into it and get sparks. If it doesn't (unlikely) then you might have to get creative

Try your hookup with the 20v supply again, but flick the low voltage wire against the tab, quickly making and breaking the circuit, and try to get little sparks there. You should get much bigger ones at the output terminal. Remember that transformers only work with changes in current, a steady DC current will do nothing.

Platinum

Wed Dec 28 2011, 09:29PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

It's very obvious transformers cannot work off steady DC, I may seem stupid but I have some knowledge.

I've tried pulsing DC with my hand just flicking it on and off, so it acts as a HV induction coil, but nothing.

When I use the core and tab as input they spark, and it does not set my PSU off (so there is resistance in there, so it must have a coil) but no spark from HV side.

Steve Conner

Wed Dec 28 2011, 09:35PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Try moving the high voltage lead closer to the core so it doesn't have so far to jump, still nothing?

Sorry, but when someone says they're testing a transformer by hooking it up to a DC supply, I fear the worst.

The secret of the relay oscillator is to connect the relay's coil in series with its own normally open contacts. So when it turns on, it turns itself back off again, then it's off so it turns back on, etc... If it doesn't have any NO contacts, you can't make an oscillator.

Platinum

Wed Dec 28 2011, 09:42PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Yes I've made the spark gaps tiny, I've tried to spark it to the tab and core. Nothing, so, I cannot get any sparks?

I'm thinking about trying to knock the iron core out and try to get ferrite in there, flyback made from a magneto lol.

Also where I said the laminations make a C or U, it is where the flywheel spins to generate the HV.

Marko

Wed Dec 28 2011, 10:30PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hm, the coil looks like a closed core type to me, though a magneto would be expected from a chainsaw unless it has a battery on it which I doubt!

A magneto or not it should have a low voltage winding which goes to contact breaker and a snubber cap; the only difference is that the magneto builds it's energy up from a moving magnet instead of current in the primary winding; the breaker keeps the primary shorted until it's ignition time when it opens and creates a desired flyback pulse.

Just prodding the ignition coil with 12V won't work without a snubber cap. Not completely sure why, but it seems that big arc that otherwise appears in the contacts eats up most of the energy.

If you don't have an original capacitor, try connecting one in range 0.1 - 1uF between the contacts of your "switch", and report results.

Of course, charging it to 200-300V later and dumping it into the coil might produce even more interesting effects...

Marko

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