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Re: NST Max Ratings and Mains Resonance (fwd)



---------- Forwarded message ----------
Date: Fri, 13 Feb 1998 06:26:18 -0800
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: NST Max Ratings and Mains Resonance (fwd)

Tesla List wrote:
> 
> ---------- Forwarded message ----------
> Date: Thu, 12 Feb 1998 15:54:09 -0500
> From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
> Cc: MALCOLM-at-directorate.wnp.ac.nz, Wysock-at-courier8.aero-dot-org
> Subject: NST Max Ratings and Mains Resonance
> 
> Bill, Malcolm, and other interested coilers,
> Besides the resonant rise that Malcolm mentions, there is also
> the fact that when the main cap and the transformer are set to
> resonate at the mains frequency, the transformer is capable
> of providing current levels that are several times the usual
> 'current-limited' value. If the wire in the secondary is too
> thin, then you can actually burn out the secondary winding
> under these mains-resonant conditions.
> 
> Thus, with the proper resonant conditions a 15KV 60 MA
> NST can charge the mains cap up to voltages in excess of
> 40KV, and at a rate that is much greater than the 60 MA
> rating would suggest. Note that both the extra voltage and
> extra current can contribute to the NST failing prematurely.
> 
> Hope this helps.
> Fr. Tom McGahee
> 
> ----------
> > From: Tesla List <tesla-at-pupman-dot-com>
> > To: 'Tesla List' <tesla-at-pupman-dot-com>
> > Subject: capacitor energy vs pwr factor
> > Date: Thursday, February 12, 1998 12:55 AM
> >
> >
> > ----------
> > From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
> > Sent:  Wednesday, February 11, 1998 5:10 PM
> > To:  Tesla List
> > Subject:  Re: capacitor energy vs pwr factor
> >
> > Hi Bill,
> >
> > > From:  Wysock, William C. [SMTP:Wysock-at-courier8.aero-dot-org]
> > > Sent:  Tuesday, February 10, 1998 12:57 PM
> > > To:  Tesla List
> > > Cc:  ttr
> > > Subject:  RE: capacitor energy vs pwr factor
> > >
> > >
> > > To all working with NST's as a power source.
> > >
> > > With any NST (containing a magnetic leakage shunt in its core;
> > > whether it be "stock" or "modified" for higher current) and
> > > irrespective of using external a.c. electrolytic power factor
> > > correction capacitors, there seems to be something
> > > fundamental missing in everyone's calculations.  Remember,
> > > you can hard-wire short the secondary terminals on an NST
> > > without burning the thing up.  If your NST was rated for example,
> > > at 60 ma., you will have 60 ma. flowing in the short circuit.  BUT,
> > > you will have "0" volts.  The voltage output of an NST is
> > > inversely proportional to the amount of current being drawn.
> > > The only time you have say, 15 KV rms at the output terminals
> > > is when NO current is being drawn.  The bottom line is that
> > > at no point do you have 15 KV *and* 60 ma., at the same time.
> >
> > I think that only applies to a resistive load. I've seen a
> > transformer ringing up with a capacitive load. I've seen Q's in the
> > vicinity of 6 at mains frequency with one combination I checked.
> >
> > ?
> > Malcolm
> >
> > > The load voltage and current will be less (for the point where
> > > the current sine wave phase angle crosses the voltage sine
> > > wave phase angle,) to yield maximum usable power.
> > >
> > > Bill Wysock
> > >  -------------------------------------------
> > > Tesla Technology Research
> > <snip>
> >

All,

Fr. Tom is definately correct. The good news is that you'll get more
"bangs per half-cycle"... the bad nes is that your neon's secondary may
be stressed to 2-3X it's normal current rating. From a practical
standpoint, 60 mA transformers seem to withstand this abuse much better
than 30 mA ones, probably because of their significantly larger wire
size and the relatively larger thermal mass.

Safe coilin' to you!

-- Bert --