Zenith variac type 100r - carbon brushes

[Bushbaby]

Hi All,
A friend of mine has been in contact ask for help with his Zenith variac. He needs new brushes - does anyone know where he can get some or get alternatives that can be modified to fit?

Best Regards

Rob

[boater sam]

Variac carbons are a special type of carbon, motor or dynamo brushes are unlikely to work well.

Does this help? http://carbonbrush.com/variacbrush.htm

[joebog1]

Interesting post sam,
I got to the point where one brush costs 321 $. better order a couple of spares too. Might be a good time to start a new mortgage too.

Joe

[Refugee]

I made one from a washing machine brush and it has been working fine for quite a few years.

[Murphyv310]

A washing machine brush is too soft, it would work if the variac was stable and only adjusted when off, if its a meaty variac like my 2kw one then it's an absolute no no.

[Bushbaby]

Thanks all
He told me that his Variac is a Zenith Variac 100R thats the only info that I have.

[ppppenguin]

The 100RM is rated at 8A, approx 2kW. I don't know if there are other models that are also known as 100R.

[Murphyv310]

Hi
Might be a difficult part to obtain, mine is slightly worn but inside the casing there is a spare taped to it, a nice touch IMO.

[boater sam]

There are lots of articles on the net about this type of carbon, here is one,   https://sound-au.com/articles/variac.htm

another  https://www.eevblog.com/forum/reviews/va...-material/

The brush must short windings together as it traverses, ordinary carbon causes sparking which damages brush and winding.

There is a suggestion that the carbon rod from a dry cell may be more suitable material.

[ppppenguin]

That Australian article is really excellent, just about everything you needed to know about variacs. Though it doesn't tell you how to go about finding a replacement brush.