RE: Variac capacitors

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-Compaq-dot-com>

Whether a transformer or variac would benefit from a PFC cap depends
entirely upon the load.  If you have a purely resistive load, then no
PFC is necessary.  I've never heard of a variac coming pre-wired with a
PFC cap, since the variac maker has no knowledge of what kind of load it
will drive.  If there was a cap across the input, I would guess it is
for EMI suppression, or, it could be a MOV for transient suppression.
If it looks like a disk capacitor in *series* with the AC input, it
could even be a Positive Temperature Coefficient thermistor to reduce
turn-on current surges.  It would be helpful if the type/size of this
cap was mentioned...

Gary Lau
MA, USA

 -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent:	Saturday, December 08, 2001 1:12 PM
To:	tesla-at-pupman-dot-com
Subject:	Re: Variac capacitors

Original poster: "Jason Petrou by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Jonathan,

It is possible that some variacs may need PFC, so in that case it would
be a
PFC cap for the variac... I would expect this if the cap was between 1
and
5uF, which is small PFC. However I am just speculating... it may be to
stop
phase shift or something... if you have a dual trace scope then hook up
a
current shunt and measure the V/I and see if there is an offset
with/without
the cap... that will tell you if it is a PFC cap or not.

Best R,
Jason
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, December 08, 2001 3:37 AM
Subject: Variac capacitors


> Original poster: "Jonathan Peakall by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jpeakall-at-mcn-dot-org>
>
> Howdy All,
>
> The variacs I have came with (meaning were slavaged with) a capacitor
which was
> across the input lines. I'm assuming that I want these there. Can
anyone
> confirm/deny?
>
> Thanks!
>
> Jonathan Peakall
>
>
>