Re: NST Resonant Charging?

To: tesla-at-pupman-dot-com
Subject: Re: NST Resonant Charging?
From: Greg Leyh <lod-at-pacbell-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 15 Oct 1998 18:35:33 -0600
Approved: terryf-at-verinet-dot-com

> Original Poster: Bert Hickman <bert.hickman-at-aquila-dot-com>

> > Here's the results from the simulation: (Qchg ~10)
> >
> > Break Rate  Overcharge
> >
> > 240BPS  -    18%
> > 120BPS  -    25%
> >  60BPS  -   103%
> >  30BPS  -   181%
> >  15BPS  -   230%
> >
> > As I understand it, NST's are not designed to withstand
> > even their own open ckt voltage indefinitely, let alone
> > a voltage rise due to resonant charging.
> >
> > This suggests that perhaps a static gap which is firing
> > erratically (thus producing a low BPS and a high overshoot)
> > may be the silent killer of marginalized NST's.
> >
> > IMO, resonant charging seems more a bug then a feature,
> > especially if it cannot be used in the 200-plus BPS range.
> > --
> >
> > -GL
> > www.lod-dot-org
> 
> Greg,
> 
> Can you simulate a voltage-controlled switch for the main gap instead of
> forcing the breaks to more closely approximate a static gap? My freebie
> version didn't give me this capability. :^)

My freebie has a 'voltage controlled break' that seems to work well.
Note that it has an R'on' of 1 ohm.


> Also, does the PSpice model show any increase in capacitor recharge
> current between breaks as we get closer to mains resonance? I'm seeing
> breakrates between 360 and 480 BPS from a pair of 15-50's with a total
> gap of over 0.5" (I know, I'm really overstressing the NST's...).

The simulation shows that the NST current stays relatively 
sinusoidal at 60Hz if the break dwell is small. The RMS value 
increases by an amount roughly equal to the overcharge, 
that is about 20% for 240BPS and 240% for 15BPS, at 60Hz.

This makes sense, given that the current in the NST
cannot increase beyond its short circuit current until 
the resonant charger has gone through enough swings to 
build up the tank voltage past 15kV RMS.
-- 


-GL
www.lod-dot-org