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Ho-Made Variac
Hi All,
IMHO, home brewing a variac is totally crazy. You can buy one used for
around $30, and they are very easy to find. In order to build one you
would need a source of silicon steel core material, no, "sheet metal" wont
work, unless you make the core 5 or 6 times bigger than it would be with
high grade core material. Variacs are toroids, and a toroidal core is not
that easy for the home brewer to build. You need to come up with a roll of
core material (easier said, than done) and roll the core to your specs,
however you arrive at those. The steel must be insulated with a thin coat
of varnish and wound tightly and precisely, then secured. Thats the "easy"
part. Next the core must be insulated and wound, again tightly, uniformly
and precisely. Winding a toroid without the proper machinery is a real
challenge. Even a 1.5 kVA variac has a couple hundred turns of wire on it,
and can become a can of worms real quick. After the core and coil assembly
is completed you have to rig a wiper assembly. If you're lucky and planned
ahead, maybe you can adapt one from an old variac. The question then
becomes, if you had an old variac, why didnt you opt to try and rebuild it
instead of home brewing one? My advice: save yourself the frustration and
search for a used one. Hope this helps. Happy coiling.
P.S. Forget the straight core idea. An open magnetic circuit will
saturate far too easily, unless your core is the size of a tree trunk.
Eric
edavidson-at-icva.gov