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Re: coil running of car battery(s)?

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

"I am thinking of doing somthing like this myself.this is what I am
of, a 555 timer ckt. @ around 60-100 hz driving a HEI auto coil (or 2).
possably use the 555 ckt to drive a 3055 fet for more current to the
Use this for the HV power supply to the coil?
don't know if this will work for sure but it sounds like it will. I will
let you know if I get more information on this, what does every one else

	The idea is generally OK but you'll certainly need a power transistor
to drive the primary of the coil, preferably one with a lot higher
voltage rating than the 3055.  I'm using an 800 volt IGBT for this
purpose and it works fine.  Also, you'll want a buffer transistor
between the 555 and the power transistor as otherwise the 555 may not
last long.  I also use a capacitor in series with a resistor across the
primary, with values determined experimentally.  Not too much help?

	As for the timer circuit, I have means for varying the width of the
turnon pulse to the output transistor and the time between pulses.  The
former sets the output voltage and there is a "saturation time" beyond
which you don't get any more output but the current goes way up.  The
timing between pulses varies the rep rate and hence the power input.

	As for coils, I've found that the GMHEI are not the best for charging
the primary capacitor of a TC - impedance kinda high.  I've had better
luck with an Exel coil.  With a setup like this and using a 4700 uufd
primary capacitor I've been able to get about 4" streamers from a small
coil with a 3.5" oblate on top of it.  No breakout however, had to start
the streamers by bring a screwdriver or something up close.  Does give a
very nice brush discharge visible in the dark.