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Re: [TCML] variac


You should put an ammeter on the unit to see how much you are pulling. You have to adjust your load so that it doesn't draw more than 20 amps. Kinda like having a car that theoretically could go 120, even though you can't legally drive it above 65 in most places.

A big Variac like this can sometimes trip the breaker immediately upon being powered up, even with no load on it. This is due to a residual magnetic state left occasionally in the core from the last time it was turned off. A way to prevent these nuisance trips is to wire a beefy 10 ohm power resistor in series with the Variac primary which is then shorted out by a suitably rated contactor (power relay) driven by the same power switch as the Variac. The inherent mechanical delay on the contactor armature gives a few AC cycles at restricted current through the Variac and allows the magnetic state of the Variac core to normalize without tripping the breaker.

jhowson4@xxxxxxxxxxx wrote:
Hey guys i just got my 22.5 amp 0-140v variac in the mail. I thought that the power here in my dorm was 30 amp but no its 20 so needless to say I had to get maintnence to come flip my breaker back on. grr
 Is there a way I can limit the current going into it so that it would be take  10-15 amps from the wall.  With out taking away my ability to go from 0-140 volts.

Jay H.
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