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Ignition coil abuse



    Hi all (again!) :))

Well, the rotary idea is simmering as I dig up info on converting a
motor to sync operation.  Till I have the info, I'm content with a
simple low-powered static gap on that 4kv30ma nst (love that
thing!)  Anywho, I got adventurous and set it up like I'm driving a
normal TC primary, but instead substituted an old ignition coil I
got lying around.  Yowza.  It hasn't died yet, but it gets a bit
warm to the touch (no oil bubblin' yet, but I know the insulation
inside is taking a pounding from the HV more than the heat).  The
problems and questions...

I'm running a 4kv30ma nst, using 15nf of 17.6kv MMC (trying to
avoid resonance for the moment), across a single static gap.  The
gap 'trodes are copper pipe (2", all I had!), set the width of a
hacksaw blade.  The system runs beautiful, not TC like, but gives
*very* pretty and intense white-hot sparks. I don't assume it to
have a very long life in this kind of service tho...I'll be a
little sad when it dies on me. *sniff*

Now, the nst is 120watts (4kv*30ma).  The gap is around .75-1mm
(measured at 1 side, and the spark jumps all over the entire width,
so it's parallel I assume).  What is the firing voltage, and
knowing the firing voltage, how do I find out how much bang I'm
dumping into the ignition coil?

Also, I can't get a good "spark to grounded wire" going here,
because the sparks will crawl over the nose of the HV output to the
terminals (not too good for my caps and NST), so I'm trying to
eliminate that. But no matter what I've tried, as soon as the
distance to the grounded wire approaches the distance from the
inner electrode in the HV out of the coil to either terminal, it
arcs over on me.
Also, when it's running and arcing to the terminals, I'll get a
really loud *pop* every once in a while.  I always kill it and
check for damage to the caps, but find none.  The sound originates
from the arc from the HV on the coil to the terminal.  Is it
dumping the cap energy *there* as well as across the normal spark
gap? (this only happens when the arc is hitting both input
terminals on the coil) :(  All in all, it's fun as heck! And
*really* good for the ozone layer ;)  Fans on over here to air it
out.
    Do I need to epoxy a HV bushing to the top of this thing so the
arc will have longer to creep?  I'm also scrambling to dig up good
HV diodes to charge a DC system.  :)  Think of this as scrambling
to follow the rather steep learning curve to become competetive in
the GMHEICSLR.

Thanks for your time & info
                                            Shad (aka Sundog)