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Re: Variac current and VA rating

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <broker-at-uwplatt.edu>


A variac can be run intermittently for roughly double the current.  I run about
16-17A through my 10A variac for several minutes at a time with little
heating.  All manufacturers tend to put a decent safety factor (usually around
2) into their calcs.  If you find that the variac is getting excessively warm,
put a muffin fan on it to aid cooling.

Mark Broker
G-5 Geek #10

Tesla list wrote:

> Original poster: "Pete Komen by way of Terry Fritz
> <mailto:pkomen-at-zianet-dot-com><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