Re: PFC for my NST_2

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Nate,

At 04:16 PM 4/23/2001 -0500, you wrote: 
>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  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.  

Calculating PFC cap values is not an exact science ;-)  In this case, the
computer was doing real time nonlinear calculations to find the PFC value.
Most formulas are probably linear and not taking into account the switching
nature of the primary circuit.  60 - 100uF is fine for a PFC value.  Most
of the good comes from the first 50uF and the rest is not a big deal.  I
"think" the computer calculation is probably closer than the equation you
used, but the values will all work well.

> 
>Observation 2: All of these tranneys had different tank cap sizes and drew 
>different amounts of line current.  

That is because they are different :-)  Each particular voltage and current
of NST needs different cap values for a particular matching.  These should
match all the standard equations well.

> 
>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.

NSTs in Tesla coil use will easily exceed the rated VA rating.  This is
because we are driving a capacitor that tends to resonate with the NSTs
output allowing higher power throughput.

> 
>Question 1:  Unless these NST's have been modified, shouldn't the VA rating 
>be the same on all of them?

The "actual real" VA rating is very dependant on the primary capacitor
size.  The "rated" VA is when the NST is used for neon signs and other dull
resistive loads.

> 
>Question 2: Does the primary cap have any effect on the PFC cap?  (NO..
Right?)

Big effect!  If the cap is small, the NST will draw little power if just a
cap is across the output.  However, hit the resonant size at say 6.6nF and
the voltage and current will skyrocket to destructive levels.

> 
>Question 3:  Does a PFC cap of 66uf sound correct for my NST with a 120v 
>input at 60Hz?

That is fine.  The difference between 66uF and the perhaps more accurate
value of say 90uF is small.  any cap in that general range will do the job
well.  It is much better to us lower values rather than higher values.

> 
>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.

PFC caps drastically lower the current needed from the AC line.  My big
coil draws 16 amps without PFC and about 9 amps with PFC.  When the sync
motor is also running at about 5 amps, I can't run it on most 120VAC
circuits without popping breaker at 21 amps.  However, with the PFC caps I
only draw 14 amps so no breakers trip.  Also, the AC source line loss is
less (do to lower current) so the power is a bit better.

Thanks for the great questions!  Hopefully I have answered them ;-)

Cheers,

	Terry


> 
> 
> 
>--Nate
>