Re: variac question?

Jeff Wisnia wrote:

Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington



Just a WAG, but maybe the sliding contact has worn "flat" and is touching too many turns of wire, creating a multiturn shorted winding when set at the 30% position, thus causing the problem.

You didn't say whether your variac is a 0-100% kind or the kind which can output more than 100% of the input voltage.

If it's the 100% kind, then maybe when it's set to 100% the contact arm is no longer resting on the winding but is on a broader piece of metal connected to the hot input.

More details please. If you plug it in at 100% and then lower it to 30% do things stay OK?

It doesn't pop the breaker at 100%, and at the moment it's turned down to
60% and doing an electrolytic derusting job. After that's done I'll be
able to experiment more.

Mine can be wired either to 0-100 or 0-120%, I believe. I've had it both
ways. I used to use it to overdrive hot air popcorn poppers to get more
power out of them when using them to roast coffee beans. But now it's
wired 0-100%. It's possible there's a wiring error, but I don't think so.

Grant
.

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