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Re: Repost: NST VA Rating and Power Factor

Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

>  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.
If you do the math (15000V*0.06A) you get 900VA - which is what it should be
for all 15/60 NSTs. I have no idea how you have got just under half that for
the franceformer ones... it is technically impossible :) I'd recheck the
labels, and if you are still lost measure the Vout of the secondary, then
short out the secondary and measure the current flow, and also measure the
current out of the mains socket. I think that the xfmr must be labeled
incorrectly. I dont know what the High Power Factor means - i'd check with
the company (or wait for other replies from the list

>  Does this mean that I will have little to gain by adding PFC caps to
> the
>  supply?
I always add PFC caps to the power supply - it makes the capacitors happier
when there are slight surges/dropouts. I just use them as standard things,
like a line filter.

>  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?
I think that would be ok - if the NSTs are out of phase though (which im
sure they arent) it might blow the caps. Also, you dont want too many caps
because they can cause surges

>  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).
If you didnt already get a reply to this...
If you have a 240V supply and step down to 120V you will get more current
provided your step down tranny can handle it. That way you can use american
NSTs on a british supply, and more of them to boot. However if you use a
british NST with a Vin of 240, you will get half the voltage out of the
secondary but no more current (they are current limited). Same, if you plug
a 120V tranny into 240V then for a short while you will get double the Vout
from the secondary. However 2 things could happen... 1) the primary core
saturates and the Vout of the secondary drops drastically as the primary
stops conducting. 2) the insulation on the secondary would break down due to
corona from the wires.

Good luck, sorry aobut the l8ness of my reply