Treat it like a Pot (volume adjustment) - don't put it in series.

It is a transformer that has an input winding that one end is common
to the output. Often the input is not across the 100% winding but
a few turns short. That gives you the 120% more than the input because
the wiper sees ''120 windings'' when the input is press across ''100 windings''.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Grant Erwin wrote:
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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