Re: NST Resonant Charging?

To: tesla-at-pupman-dot-com
Subject: Re: NST Resonant Charging?
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Wed, 14 Oct 1998 19:34:33 -0600
Approved: terryf-at-verinet-dot-com

Hi Greg,

> 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.

Agreed and it shows in practice. Charging effectively occurs over a 
half cycle if the gap fires on each peak. The cap certainly can 
charge beyond Vo/c in a half cycle in my experience. It partially 
recharges after quench as the NST secondary voltage is going back 
down and then swings on through to the opposite polarity on the next 
1/4 cycle.

> What is really going on?  Does anyone have voltage waveforms 
> of a NST resonant charge cycle in action?

Next time I borrow the storage scope I'll get a divider onto it and 
take some photos.

Malcolm

** If it's under 10 Amps it's Leakage Current **