Re: Best cap size for a sync gap

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

Original poster: "john couture" <johncouture-at-bellsouth-dot-net> 

Gary -

It is always interesting to read the presently rare posts from coilers who
are researching the classical Tesla coil circuits. There are still a lot of
unknowns regarding the operation of this type of TC.

With your tests I would recommend measuring the input to determine if the
input is varying with changes in the output. I made similar tests in the
past and found many surprises including that the VA output could be greater
than the VA input under certain conditions.

John Couture

-------------------

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, April 28, 2004 10:57 PM
Subject: Best cap size for a sync gap


 > Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
 >
 > I finally "got around to it" to an experiment that's been nagging me for a
 > very long time.  I wanted to determine the optimum cap size for a coil, in
 > terms of maximizing the power pulled from the NST.  Tank frequency issues
 > come later.
 >
 > With a newly constructed sync RSG and a dummy load consisting of three
500W
 > halogen lamps in series in place of the primary inductor, I scoped the gap
 > voltage.  As is typical with sync gaps, I adjusted the phase such that the
 > bang occurs somewhat after the peak charging voltage.  The later I phased
 > it, the brighter the lamps and the higher the bang voltage. If the timing
 > is too late, the gap stops firing altogether, so I brought it just to the
 > brink of this point.
 >
 > To measure the voltage, I use Terry's fiber optic probe, which sadly, I
 > have yet to accurately calibrate.  But for the purposes of finding the
best
 > cap size, even a qualitative measurement is adequate.
 >
 > I use an unmodified 15/60 NST, cranked up to 144VAC.  I had available two
 > .02uF caps, and one .01uF cap.  With these I measured the bang voltages
 > using .02, .03, .04, and .05uF.  The peak-to-peak bang voltages measured
 > were 688, 618, 552, and 482 mV respectively, as directly indicated on the
 > scope.  FWIW, if I scope just the unloaded NST secondary -at-120VAC input, I
 > get 598mV p-p.
 >
 > If I calculate the relative bang size with a simple scale-less formula of
 > C*V*V (mV*uF*uF), I get
 > .02   9,467
 > .03  11,478
 > .04  12,188
 > .05  11,616
 >
 >  >From this I conclude that using a .04uF cap with my 15/60 NST will
result
 > in the highest power throughput.
 >
 > Has anyone else performed such an experiment?  Just trying to understand
 > why my result is so at odds with the widely suggested value of .028uF for
 > the same power supply.  Hmmm, wonder what I'd have gotten if I had tested
 > at 120VAC?
 >
 > Regards, Gary Lau
 > MA, USA
 >
 >
 >