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Blowing up an ignition coil

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thedarklord

Wed Mar 07 2007, 09:33AM

Registered Member #569 Joined: Wed Mar 07 2007, 08:29AM
Location:
Posts: 3

I've got this old can type ignition coil. It has never realy worked well for me. Secondary shorting out??? maybe.

Seeming I don't have a use for it, I was wondering what sort of power it would take to blow this thing up. Are ignition coils shunted? If they are could I open it up and knock any shunts out of the core.

To drive it I have built the old 555 switching circuit but instead of using a 2n3055 I have replaced it with three paralelled mj15003's. That should manage aroud 750 watts. The whole unit normally runs off a 12v deep cycle battery.

I've run ignition coils at 50 watts for short periods. At that sort of power the insulating oil starts to boil. I wonder what 750 watts would do...

I know at 12volts I can run maybe 45watts~ max. At 50volts (max supply voltage of mj15003) I might manage 200watts. What dort of damage do you reckon this might do.

I'm a beginner so if you can see any obvious floors with my logic please let me know.

Download

Wed Mar 07 2007, 09:36AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

no shunts on an igcoil

ragnar

Wed Mar 07 2007, 12:56PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

For actual some impressive arcs and carbon blasting (as opposed to damage to the ignition coil from overcurrent; Bzzzz.-tic- -- much less impressive), build a 'proper' driver circuit...

Try an MJ10012 -- you'll only need the one, and you can run it at 48V, so long as you use a big zener clamp on it.

You'll need something other than the 555 to drive it; try to drive the base with a BC327 (errr, or is that a 337, I forget).

See my old "Bastard ignition coil driver from hell"
www.http://whiteplasma.com/matt/bicdfh2/
http://www.whiteplasma.com/matt/bicdfh/
http://www.whiteplasma.com/matt/bicdfh/sparkler.gif
(Which wasn't all that evil, but impressed me at the time)

Don't forget zener diodes on the 555 supply, a 1N4007 in series, bit of protection on the timer circuit always stops those disappointing failures when you have an audience

Electroholic

Wed Mar 07 2007, 02:37PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

what is that u shape thingy?
is that ur big zener clamp?
3V 5W each?

ragnar

Wed Mar 07 2007, 11:22PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Yes, that's the zener clamp. Those are 15V 5W zener diodes in series. I curled them into a spring and put them underwater for longer runs. =P

thedarklord

Thu Mar 08 2007, 07:44AM

Registered Member #569 Joined: Wed Mar 07 2007, 08:29AM
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Posts: 3

thanks for your suggestions I will probably give the bastard coil driver a go as soon as I get hold of a few mj10012.

so your driver basicly consists of an mj10012 switching darlington with its base being driven by a bc337 which is in turn connected to the 555 signal generator.
I understand you are using a 48v zener to clamp the vcc to 48volts.

Do you have any idea of how much the zeners will be disipating?
Also do you have a link to the schematic? if so please post it.

Finally how long do the coils last in this setup?

Thanks for all your help

ragnar

Thu Mar 08 2007, 09:47AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Almost right:

I have the 555 running off 12V, and the MJ10012 feeding 48V into the ignition coil primary. I have a 225V zener clamp (composed of 15 * 15V 5W zener diodes) across the MJ10012, as recommended in the datasheet. For lower powers, you could use 3 x 75V zener clamps instead.

MJ10012 is pricey, but a very nice transistor, especially designed for this application.

Ronnie

Thu Mar 22 2007, 08:54PM

Registered Member #600 Joined: Thu Mar 22 2007, 08:41PM
Location:
Posts: 10

Does anyone have any experience of how much energy an ignition coil can take in a pulse? I am planning on using 350 volt electrolytic capacitor(s). I'm aware that this isn't ideal because of the inductive kickback, but I already have some electrolytic capacitors, and a suitable diode to protect them would be cheaper than getting the same energy in non-electrolyics. I have my eyes on a 600v 100 amp rated diode sampled from ST.

Electroholic

Thu Mar 22 2007, 10:40PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

you can try, but lytic are generally slow for pulse transformers.

Ronnie

Thu Mar 22 2007, 11:34PM

Registered Member #600 Joined: Thu Mar 22 2007, 08:41PM
Location:
Posts: 10

So far I have tried a 4.7uf, without a diode as I have plenty of those to destroy, that worked surprisingly well, I have almost a kilojoule electrolytics, I suspect that would be way too much for a standard ignition coil. Most designs I have seen have used about 2uF pulsed repeatedly. My guess is that it could withstand about 200uF, the problem is that I only have one coil to experiment with at the moment. I plan to increment the power while watching out for any problems with the coil, perhaps overheating. It may just fail without warning.

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