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RE: What size PFC should i use with my 15/30 NST?

This equation is incorrect. The Vo and Io are in volt amps. This PFC
equation is on several web sites and I am amazed it is still being shown.
You need to find the reactive volt amps (VAR). I showed how to do this in a
past post that I cannot find now. This is why manufacturers rate their PFC
caps in VARs.

John Couture


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, August 30, 2000 8:24 PM
To: tesla-at-pupman-dot-com
Subject: Re: What size PFC should i use with my 15/30 NST?

Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net>

Hi John M., Terry,

Tesla list wrote:
> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> At 10:50 PM 8/29/00 -0500, you wrote:
> >
> >Hi again,
> >
> >I do have another question.  I would like to put a PFC on my NST but
> >know what size cap to use.  It is a 15/30 stock NST.  I'm using a 13nf
> >with a 120 bps SRGS (if that makes any differenc).  Any recomendations
> >there?  If so, is there a formula or rule of thumb to use to determine
> >size PFC to use?
> >
> >Thanks in advance,
> >John M.
> >
> I think this is correct.  It was posted awhile back and needed about three
> typo corrections but this should be right.
> Cpfc = ( Vo x Io ) / ( 2 x pi x f x Vi^2 )

This is correct. I posted a few days ago as Cpfc(uF) = (KVA *
That was wrong. The 10^9 should be 10^6. Anyway, the value is uF. PFC's due
their size are typically rated in uF.

Just wanted to correct my previous blunder.

>  Where
>         Cpfc = Power factor cap value in Farads
>         Vo = Rated NST output voltage in volts
>         Io = Rated NST output current in amps
>         pi = 3.14159...
>         f = AC line frequency (50 or 60Hz)
>         Vi = AC input voltage (120 VAC)
> Cheers,
>         Terry