Re: NST Resonant Charging?

To: tesla-at-pupman-dot-com
Subject: Re: NST Resonant Charging?
From: Ed Phillips <evp-at-pacbell-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Wed, 14 Oct 1998 19:36:38 -0600
Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: Greg Leyh <lod-at-pacbell-dot-net>
> 
> Hi All,
> 
> I still don't understand how resonant charging could possibly
> work in a practical NST-powered TC.
> 
> Assume the cap is set to Xl of the NST's leakage inductance,
> which gives 0.011uF for a 15kV 60mA NST (this seems to be the
> most popular method of choosing Cpri).
> Then the cap resonates with the NST at 60Hz, and the voltage
> will build with each cycle -- and if the gap is set to not fire,
> the voltage buildup will ultimately be limited by the Q (and the
> breakdown strength) of the charging circuit.
> 
> But what if the gap fires at each peak, at 120BPS?
> Then the energy is stolen from the cap every 8.3 mS, preventing
> any significant resonant rise!  Remember, this charging circuit
> resonates at 60Hz, and therefore requires a significant portion
> of the 60Hz cycle to build past even the normal open ckt voltage!
> 
> The charging slope could of course be speeded up by using a smaller
> capacitor, but at the expense of ultimately limiting the available
> primary energy.  The other important point here is that the firing
> rate *must* be 60BPS or a multiple thereof, in order to get any
> decent performance out of a 60Hz-fed resonant charger.
> 
> What is really going on?  Does anyone have voltage waveforms
> of a NST resonant charge cycle in action?
> --
> 
> -GL
> www.lod-dot-org

	Everything you have said is true as stated.  I have a number of
simulated waveforms of resonant charging, with the variable parameter
being the breakdown voltage of the gap.  If the gap is set wide enough,
it will not break down on every cycle, but can "count down" and fire at
submultiples of the line frequency.  I have tried that experimentally
here by lowering the primary voltage of my transformer and keeping the
gap fixed in order to protect the insulation.  I have gotten a spark
rate of less than 10/second and so can you.  The actual waveforms can
show much more complex behavior, and I'll try to resurrect some of them
and offer them in JPEG format.

Ed