Re: Power factor correction capacitors for MOTs

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

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