OT? DIY Powerstat Wiper Button

You might get away with a fettled motor brush actually. A battery carbon may not be tough enough.

Graham

You need graphite, not just a carbon rod from a battery.

Motor brushes are graphite.

Hi, Mark. Variac wipers are just about the most difficult commutation problem for their current rating. Generally, these variable autotransformers will use a sandich-type carbon brush to achieve a relatively high cross resistance in relation to the resistance going the length of the brush from contact to wire.

Some motor brushes have a higher cross-resistance characteristic, too, but your getting one that will happen to work well seems to be pretty much a matter of chance. A regular carbon is, of course, out of the question.

It happens that replacement brushes for Powerstats are available, but you'll have to pay a few bucks. This was the first source I googled:

They show a replacement brush available for $23.00 USD. I'm sure your yard sale Powerstat will still be a good deal, even with the purchased replacement part. I'd buy it if I was in your shoes, instead of cobbling together a replacement that probably won't work well under rated load.

When you replace the brush, be sure to go over the lapped contact surface of the winds with a lint-free cloth dampened with alcohol, to remove any dust or dirt. Also check to make sure the wiper seats evenly on the surface, and rotates freely. Poor alignment will kill your brush or burn the wire surface quickly. Also, when you finish, slide the contact across the entire surface, and check for any sparking or discontinuities while it's sliding.

Good luck Chris

use the yeller pages, find a place that does motor rewinds, if they don't have one they'll have a source, or the ability to manufacture one most likely.

Bye. Jasen

I just did a quick google, and some guy says he bought a motor brush and ground it to size, but that was only a 2.5A variac. Just be sure and grind the nose down to a flat:

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