Re: OT variac brushes ( operation )

Don Black <donald_black@...>

Carbon brushes aren't what they at first seem. They have different resistivity in different directions so they conduct well from the face to the rear connection but poorly across the face to minimize the current flowing from turn to turn (or segment to segment in a commutator). I'm sure others who work with them will be able to add more to this. Also, I believe the brush material differs depending on the voltage and current they operate at.

Don Black.

On 05-Jun-13 11:33 PM, Bert Haskins wrote:

While doing my spring cleaning I ran across a GI model W variac that is
missing it's
brush and brush holder assembly.
It would not be much of a trick to fab up a new assembly but that raises
a question:
What happens when the brush connects more than one turn on the core?
This would seem to be a fault condition ( as in a shorted turn ) but it
looks like that is
just what happens on my other variacs.
Does it matter?

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