Re: Rotary Sparkgap

In a message dated 96-02-16 15:12:56 EST, tesla-at-grendel.objinc-dot-com writes:

>Subject: Rotary Sparkgap
> have seen recently that it is preferred to have a high rpm spark gap. How
>breaks per second does a 7500 or 10000 rpm motor usually make? I have build
>but not implemented yet, one based on a 24V 1HP DC motor (about 1ft dia
>long, strong!). I have atttached a 18" diameter FR4 (flame retardent G10
>3/4" thick disc. I have placed 16 1.25" long tungston rods about 1" in from
>the edge
>and secured them with screws and loctite. I then have on the outside of this
>tungston rods imbedded in heatsinks that are moveable for adjustment of
>length. this spins at 2000 RPM (low speed, lots of mass though!) This gives
>me 533
>breaks per sec.
>Is this enough?
>All I have had to go on are books about tesla and patent wrappers and such.
>The ones I see Tesla use seem to be attached to a combination xfmr/motor (in
>Should I work on this gap, or work on something better that you guys have
>                                          Kevin M. Conkey


It sounds like a great rotary gap to me.  I would definitely fire it up and
try it.  What are you using for primary capacitor and transformer?  If the
transformer will put out several hundred milliamps, you can crank the break
rate way up and get much more power out of the coil.  Might as well fire the
gap as soon as the capacitor is fully charged.

This would be a great question for Mark Rzeszotarski who seems to be our
resident scientist/mathamatician.  With say 14,400 volts in at 500 ma how
long does it take to fully charge a .025 mfd capacitor?  And how long after
the gap fires do we want to wait for the primary to ring down a ways (10
cycles?) before we fire the gap again?  If I remember the math on this, one
time constant would be about 1ms so to fully charge the cap we would need
about 5ms.  This means we should not fire the gap any faster than every 5 ms.
 If I calculate my gap speed correctly, I am firing the gap (at least
bringing the electrodes in a position to fire) every .75 ms.  Something is
wrong here, maybe Mark can figure it out.  

I know I was running my rotary at 667 bps and increased the performance quite
a bit by going up to 1333 bps (16 electrodes running at 5000 rpm).

Ed Sonderman