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Re: Power Factor Capacitor -- Was -- RE: schematics...Adam Smith's
Tesla List wrote:
>
> Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
>
> Tesla List wrote:
>
> > Original Poster: "Bunnykiller" <bigfoo39-at-idt-dot-net>
> >
> > Tesla List wrote:
> > >
> > > Original Poster: "William Parn" <parn-at-fgm-dot-com>
> > > >
> > >
> > > What is a power factor capacitor, and where does it go?
> >
> > Hi William..
> >
> > 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.
>
> Mark
Mark,
Don't you believe it! :^)
While it is possible to briefly run back-to-back electrolytics on AC (as
in motor-starting applications), you never want to apply AC directly to
a single electrolytic capacitor or even an AC motor starting capacitor
for any length of time. Under the reverse polarity half-cycles, the
capacitor's thin dielectric layer (thin aluminum or tantalum oxide) is
eroded and then rebuilt on the next half-cycle. This results in
excessive internal heating and can result in actual dielectric
breakdown. Severe internal heating inside the capacitor roll will
typically rupture the capacitor's safety vent (if you're lucky), or
cause it to explode (if you're not so lucky). I've seen epoxy-bodied
tantalum "bullet" capacitors explode with the force of a firecracker due
to internal buildup of gas and/or steam during accidental application of
reverse biasing.
For Tesla Coiling Power Factor Correction, only use film-type caps!
Trust me on this one, Mark... :^)
-- Bert --