Re: Power factor correction capacitors for MOTs

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

Original poster: "Virtualgod" <mike.marcum-at-zoomtown-dot-com> 

Measure primary current loaded. Ideally you should come close (~90-95% or
so, depending on the efficiency of the mot) to the unloaded current draw
when the pfc cap is the right size.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, November 11, 2004 9:45 AM
Subject: Re: Power factor correction capacitors for MOTs


 > Original poster: "Borislav Trifonov" <bdt-at-shaw.ca>
 >
 > Does the load of the transformer matter?  I'm bridge rectifying and
 > filtering for DC output.  Should measuring the current draw be done with
 > the transformer loaded or not (I know it's drawing a good deal even
unloaded)?
 >
 >
 > Tesla list wrote:
 > >Original poster: "Virtualgod" <mike.marcum-at-zoomtown-dot-com>
 > >Here's a starting formula:  uF =        10^9             where F if line
 > >freq, V is line voltage, and C is the corrected kVA
 > >                                                 ------------- (C)
 > >                                                   2(pi)FV^2
 > >rating of the transfornmer (50% of VA rating for unmodded nst's). Since
you
 > >don't know and have no way to measure the uncorrected mots output VA
under
 > >load, probably be best to assume 50% efficiency for a ballpark figure,
use
 > >the previous formula, and then adjust the pfc by adding/removing
microwave
 > >oven caps in parallel, measuring the current drawn with a DMM. Whatever
uF
 > >draws the least current under load is what you need. I did this with a
 > >modded  7.5/32 (originally 7.5/20) nst and found about 40uF works best,
tho
 > >TC's are hardly sinusoidal loads, so the pfc will only help so much.
 > >Mike
 >
 >
 >