RE: Input power measurement

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

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

I don't think that the cap being mains-resonant results in the maximum 
current draw.  With my 15/60 NST, I've noted OK performance with a 
mains-resonant 0.01uF cap, better-still performance (and comparably higher 
mains current) with a 0.02uF cap, and unstable performance with 
breaker-popping current draw with a 0.03uF cap.

It appears that when driving a Tesla Coil load, the faceplate rating on an 
NST is irrelevant, grossly understating the maximum possible VA draw.  I 
"think" it has to do with a near-resonant mains condition of the NST 
secondary and the tank cap.  If you have a LTR cap trading energy to the 
NST, a larger cap will dump more energy into the NST, resulting in a higher 
secondary current, saturating the current shunts.

Gary Lau
MA, USA

  -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com]
Sent:	Sunday, March 09, 2003 1:32 PM
To:	tesla-at-pupman-dot-com
Subject:	Re: Input power measurement

Original poster: "Barton B. Anderson by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Skip,

Resonant mode running is causing the high charging current. The cap value
is designed to be resonant with the transformer at mains frequency
(charging frequency). At resonance, LC reactances are ideally removed and
leave only the winding resistance in the circuit. Thus, a maximum current
characteristic is achieved (which is the purpose of running in a resonant
mode). Richie Burnett has a good write up of this (sometimes ok, sometimes
not).

http://www.richieburnett.co.uk/resonant.html#resonant

Take care,
Bart

Tesla list wrote:

 >Original poster: "Skip Greiner by way of Terry Fritz
 ><teslalist-at-qwest-dot-net>" <sgreiner-at-wwnet-dot-com>
 >
 >Hi all
 >I am using a 9kv at 120ma NST. In operation I use an iron vane ammeter
 >(known to be within 5% accuracy) to monitor current. My mains voltage is
 >nominally 117V. Interestingly the current into the NST is about 17A when
 >running in resonant mode. It is my understanding that an iron vane meter
 >reads true input current regardless of waveform. Therefore my input power to
 >the NST is nearly 2000 watts.
 >
 >I would appreciate comments from anyone who can help explain the discrepancy
 >between the 1080va rating of the "current limited NST and the measured input
 >in resonant mode operation.
 >Skip
 >
 >
 >
 >