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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.
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).
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
Registered Member #569
Joined: Wed Mar 07 2007, 08:29AM
Location:
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.
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.
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.
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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