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Author: Subject: Ignition coil drivers
Eclectic
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[*] posted on 14-2-2005 at 16:26


On the circuit above, the ground for the spark should be whichever coil terminal is connected to the secondary winding.
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Twospoons
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[*] posted on 14-2-2005 at 19:03


If you kill the back EMF with a diode you wont get anywhere near as much output volts. Adding a 100V Zener in series with the diode means your primary voltage is now effectively 100V, not 12V, so your're output will be correspondingly higher.
The zener will get hot, so use a stud mount type, and give it a heatsink.

The 2N3055 has the collector connected to the body, base and emitter on the two pins. You will not be able to solder a wire to the body as it is usually made of aluminium or stainless steel. Use a bolt, ring terminal, and star washer.
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Pommie
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[*] posted on 14-2-2005 at 19:16


Quote:
Originally posted by Twospoons
If you kill the back EMF with a diode you wont get anywhere near as much output volts. Adding a 100V Zener in series with the diode means your primary voltage is now effectively 100V, not 12V, so your're output will be correspondingly higher.
The zener will get hot, so use a stud mount type, and give it a heatsink.


I think you'll find that the output voltage is proportional to the rate of change of the primary current and therefore, killing the back EMF is the best course of action.

Also the 2N3055 has a max Vce of 60v, so it would simply melt with a 100V zener and, the 100V produced would also fry the 555.

A better (more energetic spark) could be produced by putting a capacitor between the collecter and emitter of the transistor, making a resonant circuit. But this would also fry the other bits.

Mike.

[Edited on 15-2-2005 by Pommie]
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[*] posted on 14-2-2005 at 20:59


Quote:
Originally posted by Pommie
I think you'll find that the output voltage is proportional to the rate of change of the primary current and therefore, killing the back EMF is the best course of action.


[Edited on 15-2-2005 by Pommie]


I think I know how a flyback converter works.

Vce of 60V? OK, so lets use something with a bit more muscle, like a MJ15003, which will do 140V, 20A.

Adding a resonating cap can work really well, but is much harder to design, and really requires a switchmode controller chip.

There's also nothing wrong with the old fashioned trembler/points arrangement. The points are set up with a bit of iron in the magnetic path of the induction coil, so that the points open when the coil energises. I built one using an old magneto coil many years ago, used to light petrol in a paint can with it. I could get 2cm spark in air from it.
There may not be enough stray field from a modern ignition coil though.
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