Mark L. Fergerson wrote:
> I got a Powerstat type 10B cheap at a yard sale and discovered later
> that the wiper button was missing. I've been advised that whittling a
> replacement out of battery carbons, motor brushes, etc. is a Bad Idea.
> Finding a proper (i. e. factory) replacement is simply not possible
> as They Don't Make 'Em Anymore.
> So, any suggestions what to use?
> Mark L. Fergerson
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
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
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.