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RE: Repost: NST VA Rating and Power Factor
Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>
Connect 240V to variac terminal 1 and variac terminal 4. Now you will get 0V
to 120V by turning the wheel clockwise from variac terminal 1 to variac
terminal 3. You can also get 0V to 120 V by turning the wheel
counterclockwise from variac terminal 4 to variac terminal 3. Using an
inexpensive voltmeters from a hardware store, you can mark the 120V location
on the variac. You don't want to just leave the variac at the 50% (120V)
location. Throwing your tesla coil suddenly on at 120V to your NST bank can
cause a current surge that can pop your service main breakers, and transient
high voltages can damage one of your NST. You want the feature of being able
to slowly bring up the voltage from 0V to 120V. Your variac is a single
phase outfit that was removed from a huge three phase powerstat used to
power an x-ray machine. I would say that your variac can easily handle up to
80 amps. Don't worry about applying 240V across a 250V variac. The General
Electric power supply from which your variac was removed used voltages they
had set up for their own purposes. Just as long as you don't pass the
boundary of good judgment, you can configure your variac to do whatever job
I might be sinking in water here, but I think that the curious ratings you
see on some of your NSTs are estimates for loading the transformers with
neon tubing. Loading your NSTs with a tesla coil is quite a different
matter. I would go ahead and use the 900VA for each of your NSTs. For pfc I
am assuming that each of your NSTs are 60Hz. My calculation gives 165.8uF of
power factor correction for each of your NSTs. This give a total pfc of
497uF to be adding in parallel with primaries of your NSTs. To answer your
question, there is no point in placing pfc on each NST individually. You
don't have to hit precisly on 497uF, but some amount close by. All you want
to do is lower the current draw from the service mains.
> -----Original Message-----
> From: Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent: Saturday, May 19, 2001 11:27 AM
> To: tesla-at-pupman-dot-com
> Subject: Repost: NST VA Rating and Power Factor
> Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> First, is the reposting of unanswered questions a problem for the list?
> I'm sure this is a simple question for the experts here, but it seems to
> have sunk below visibility in the endless flow of posts.
> Anyway, again, my main question has to do with the "high power factor"
> label, and 495 VA rating on Franceformer 15/60 NST's, as opposed to 900
> VA rating on Jefferson 15/60's. I've depotted a Franceformer in the
> past, and it didn't contain a PFC cap (do any NST's?), but I don't
> recall if it was labelled the same as these other two are.
> Why such different VA ratings on different 15/60 NST's, and does this
> have any bearing on whether anything is to be gained by using PFC caps?
> Thanks again,
> Bill Vanyo
> Original post was:
> My power supply consists of three 15/60 NST's. Two are Franceformers,
> and are marked 495 VA, and also have "High Power Factor" on the label.
> The other is a Magnatek/Jefferson, marked 900 VA.
> Does this mean that I will have little to gain by adding PFC caps to
> When adding PFC caps, is there any point in placing them on each NST?
> Since they're in parallel, I can just put the PFC caps in one place,
> hooked in parallel, no?
> Also, regarding the problem of tripping the house breaker (It was on a
> 15amp breaker, but there is a 20amp available that I'll try next time):
> I've got a 240 volt line in my garage (20 amp breaker). If I use my
> variac to step this down to 120 volts, will I be able to draw more
> amperage? The variac is 240 volt 50 amp, and has multiple terminals,
> and I think there's a way to use it as a stepdown (other than just
> leaving the dial at 50%), though I'm not sure how to do this (asking in
> another post).
> Bill Vanyo