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Variac current and VA rating
Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>
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?
I have a possible way to test this with the little equipment that I have. I
could measure the input current and the output current for a particular
setup with this variac and a resistive load. Then run the hot input wire
through a current transformer with the hot output wire going through the
current transformer in the same direction. If the currents add or cancel
would indicate in-phase or out-of-phase respectively. I have a 5 amp ac
meter with a face reading 0-30aac and a 30/5 current transformer. I think
this test would work and I'll try it as soon as I can.