Capacitor discharge spark gap trigger test --SUCCESS!!

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

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>

Gentlemen and Ladies,

I finally finished up my capacitor discharge spark gap trigger and got in a
short test of it.  It doesn't draw much current, probably less than 1 amp
(out of the wall socket).  I haven't tried for maximum arc length from the
GM HEI coil, but at about an inch, it puts out solid blue-white arcs, with a
120 Hz buzz.  I'll put up a schematic when I draw one somewhat more neatly.

It has a high-voltage section using a 480V transformer rectified to a large
capacitor.  An SCR controls the charging of a small capacitor (1.5uF).
Another SCR controls the discharge of the small capacitor through the coil
primary.

The low voltage section contains an 18v transformer rectified, regulated via
a 7815 voltage regulator (a large filter cap and various smaller caps).  An
LM339 differential comparator detects zero crossing and its output starts
two 555 timers.  One timer generates a pulse passed through an SCR pulse
transformer (for HV isolation) to the charging SCR.  The other timer is
adjustable through most of the half cycle.  When its output goes low, it
signals another 555 which generates a pulse which drives the discharge SCR
(again through an SCR pulse transformer).

Lots more details, but that is a sketch of the concept.

Checking things with my oscilloscope (recently acquired), it is easy to see
the discharge pulse vary across most of the half cycle.

The reason I fire the charge SCR at zero crossing is I don't want it
turned-on when the other SCR is turned on.  The pulses are around 220 uS.
The delay to the earliest discharge pulse is 1.7 mS. The largest delay to
discharge is about 7.2 mS (all these are from the zero-crossing signal (in
reality the signal comes somewhat before zero crossing.

I haven't measured all these times and some of them may be off somewhat.
I'll get them exact when I have time.

Tesla Coil: a generator of large arcs which burns money.

Pete Komen