The incredible inedible ignition coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

  Hi All,

	Yes, hokey subject, but it's been stuck in my head all day, just figured
I'd pass it on! ;)
  Had myself an idea yesterday at work.

    Basically, I figured an oil-cannister type ignition coil is a mini
1-eared polepig.  So I grabbed my 2 coils (leftovers, cost me $26 each new),
my "bargain bin" dimmer from home depot ($1), and a couple of runcaps
salvaged from an AC unit.

  I hooked up the auto coils anti-parallel (hook the negative terminals
together, that's where the secondarys are grounded to), and put that in
series with the runcap and dimmer.  I added 2 bent coathangers for a mini
jacob's ladder.

  At 5uf, power draw was less than 1A (didn't register on my analog
amp-clamp).  thin purple sparks, didn't climb
 at 25uf power draw was around 2.2A, nice yellow NST type arc with a
blue-purple core and raspy sound. climbed to be about 1.5" long
 at 50 uf power draw was around 4.6A, good thick yellow arc, still raspy.
with the purple core.  climbed to be about 2"
 at 150uf (couldn't help myself), power draw was ~9-10A (a bit jumpy), good
thick 2.5" arc (the widest point in the JL).  Still raspy, with the purple
core.

  at 5uf, there was no detectable heating
 at 25uf, there was noticeable heating after 5 min of cont. runtime, and the
cans were fairly hot after 10 min of cont. use
 at 50uf there was noticeable heating after 2 min of use, and the cans got
hot in about 4-5 min (too hot for my tastes, i don't want a pair of
oil-filled cannisters popping on my workbench)
 at 150uf the cans got hot in about 1 min.  Cool offs after each run were by
slapping the coils (these have metal cannisters) in the fridge for 1/2 hour.

 So at ~200 watts, they run *very* well.  at ~500 watts they run well for
short runs, and at 1kva they buzz loudly, vibrate around on the table
(they're surely saturated at that point) and generally manage freakish
output for a car coil.   I don't know how well the scr based dimmer will
hold up in TC service.  Mine is a cheapie 200 watt unit I think (horribly
overdriven, but it survived).
  My thoughts are to run the coil at a much higher freq (a V8 running
3000RPM fires 400x a second, so I know for a fact the coils cores work well
at higher frequencies).  The problem is that an alternator (Oh NO!! That 3
phase thing again!!!) will literally stall a 5hp gas motor trying to run a
heavy load (and I blew up an alternator, this was long ago).  A beefy DC
supply with either a mechanical points system (noisy) or a SCR setup (will
probably fry from the backlash of the tank circuit) seems to be a good
answer, allowing me to set my pulse frequency.

   So, given some time (or if someone will test it) to see how the SCR in
the dimmer handles tesla duty, the anti-parallel ignition coils were a very
stable power source.  I'd put the voltage about 15+kv (it'd jump ~1/2"), and
enough current to push an arc to about 1.5" at ~200w input.  The coils
survived the 1kva pounding with flying colors.  internal construction-wise,
the base of the secondary (looks like 40ga wire) is connected to the
negative terminal of the primary (22ga).  oil-impregnated kraft paper
insulating the windings, and a thin steel laminate core. The core floats at
HV in the coils I have (?!), but it's insulated against it and it's given me
no problems in actual auto service, so it must be fine.  So for the "NST
Challenged", this may end up being a viable tank tranny for low powered
coils (and intermittent medium duty).  The weakest link I can see is the
SCR.

 Hope this helps someone, I welcome comments!
												Shad