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Re: Power Factor Capacitor -- Was -- RE: schematics...Adam Smith's



Hi Mark,

> Original Poster: "Mark Broker" <broker-at-uwplatt.edu> 
<snip>
> > a PFC cap is a capacitor that is normally used before the load ( NST
> > etc) it is wired in paralell with the 120V system  altho most PFC caps
> > are of low values ( uF wise)  you end up having to parallel several
> > together to get a hi enuf value to be effective
> >
> > if you are looking for PFC caps   be sure to look for "Motor Run"  caps
> > ...  the "motor start" caps are cheaper for the amount of uF but...
> > they dont hold up well in extended usage ( motor start caps are used for
> > a brief moment when the motor starts, then they switch off)(( they just
> > offer a surge to help out starting torque))
> >
> > most motor run caps are  oval shaped and about 2 times taller than they
> > are wide  usually they are in a metal case too ...
> >
> > Scot D
> 
> Actually, I've been told that Aluminum Electrolytic will work for a 120VAC
> PFC cap.  These are inexpensive and very common.  And to head off criticism
> that Aluminum electrolytic caps shouldn't be used in an AC circuit, I was
> told by an Electrical Engineer (Technician?) who runs all the electrical
> labs here at school.  He said that electrolytics can take the AC, just not a
> constant negative DC bias.

They are terribly lossy when momentarily reverse-polarised. And 
when reverse polarised for any length of time are apt to explode. I 
wouldn't take that advice. Back-to-back is OK if leakage currents are 
close to identical.

Another technician.