Re: PFC for my NST_2

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Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Nathan,

On 23 Apr 01, at 16:27, Tesla list wrote:

> Original poster: "Nathan Morris by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <themfam-at-home-dot-com>
> 
> Cool people out there,
> 
> I was looking at the 'Computer Study of NST Charging Circuits'
> <http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm>http://
> hot-s treamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm  that Terry
> posted over the weekend and it made me think of something.  My 40 HV
> Russian Military caps finally made it in from Lithuania and I have
> been working on getting my cap situation squared away.  I have also
> been running calculations for the correct PFC cap size to use with my
> 12/30 NST.  The plate rated VA is 360 for my NST. The calculation I
> found for figuring ballpark PFC size produced a 66uf for my PFC.  
> 
> Observation 1: I noticed (at the above link) that the PFC values for
> the listed 12/30's were not the same.  

There might well be differences in primary inductance depending on 
who manufactured the transformer. That would affect the PFC value.
 
> Observation 2: All of these tranneys had different tank cap sizes and
> drew different amounts of line current.  

Reasonable.
 
> Observation 3: The listed VA rating on the NST's in my group (12/30)
> STARTED at 423 and went up to nearly double the Volt Amp rating on my
> tranny.

Are we talking about ratings or VA drawn from the mains? (I didn't 
check on the website).
 
> Question 1:  Unless these NST's have been modified, shouldn't the VA
> rating be the same on all of them?

The ratings should be the same.
 
> Question 2: Does the primary cap have any effect on the PFC cap? 
> (NO.. Right?)

It may do. I notice the typical equations for calculating the PFC cap 
don't take it into account but the amount of correction must surely 
depend upon the real vs reactive load presented to the mains. 
Speculation on my part. Comments?
 
> Question 3:  Does a PFC cap of 66uf sound correct for my NST with a
> 120v input at 60Hz?

Sounds ballpark.
 
> Question 4: Other than setting up a phase offset between the E and the
> I prior to running into the transformer for a more balanced, phase
> corrected secondary output on my tranny, what is the MAIN benefit of
> using a PFC.

The PFC cap doesn't affect the secondary at all. It is connected hard 
across the mains which has near zero source impedance. It is there to 
present a resistive load to the mains (provides a conjugate match for 
the transformer). It affects only the load that the mains wiring 
sees. That includes switches, breakers and fuses. The benefit is to 
reduce mains current to that of a pure resistive load which in turn 
reduces stresses on the above components.

Malcolm