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Re: Variac current and VA rating

Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net>

Hello Pete,

I the poor guy trying to unpot a MagneTeK Jefferson NST...    :^(((
while still waiting to see if I can reserect this soggy transformer I have
some answers for your variac question.

Well,   Power in must = power out   which is almost the same as the VA (volt
amps) rating.  Power (resistive load) & VARs (reactive load ... inductive/
capacitive) load.  so it would seem this is a posibility but, there is a
current limit for the wire (which I have exceeded in the past ... gives
smoke signals   :-0  ).  The 180 degree phase shift is the same as swapping
the output wires.  If your not already aware,  the Variac is an
autotransformer, meaning it's one continuous length of wire rapped around a
toroidial core of iron.  The connections to it are taps on this coil (single
layer as you see).  The wipper connected to center(variable) terminal wipes
across the top of the toroidial transformer / coil and you can get different
voltages.    Check to see if a current maximum is listed .. that would be
the indicator.  otherwise it shound work   if within VA and current limits
.... I wouldn't interconnect windings though !
VA=    /    power(watts)^2 + reactance(VAR's)^2

~^~^~^~^~^~^~^~^ MAY THE ARCS BE WITH YOU^~^~^~^~^~^~^~^~^~^~

Shaun Epp
Winnipeg, Manitoba
>Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>I have an old variac rated at 9 amps with taps for 120vac and 240vac input.
>I have read that the output current of a variac autotransformer is 180
>degrees out of phase with the input current and therefore tend to cancel
>each other out.  Is it possible to set the output for 120vac and draw 18
>amps when the input is 240vac at 9 amps without overloading any of the
>windings?  If the output current is out of phase with the input is it true
>for 120vac in and 120vac out?