Zenith variac type 100r - carbon brushes

[Mike Watterson]

I wonder would a carpenter's pencil do?

I was given a small variac which also inconveniently was missing the brush and was for 110V.

I did wonder about the shorted turns scenario because the turns are quite close.

[joebog1]

Pencils are graphite NOT carbon !! I wouldnt be going that way then ( said my friend Spike ) .
A dry cell carbon rod is hard carbon, even the cheaper versions. Its easy to find out out. If you file a bit of carbon rod,
with a decent quality file, the carbon brush of a Variac ( or equivelents ) is "hardish " .
That means it makes small carbon granules, NOT soft carbon dust as is a motor or generator brush.
A "good " file will make zing, not grind noise.
Nope!! I havent been smokin any tschidt !!.
My experience,

Joe

[ppppenguin]

Graphite IS carbon. So is diamond. So is graphene. All different forms or allotropes of carbon.

I'm guessing here but carbon rods for batteries and variac brushes are probably sintered granules of graphite.

[joebog1]

I am sorry for ignorance Mr Borinsky,
 I DO know the difference, but I am not, have never been, nor will I become a chemist or materials engineer.

I did have the "gist " of the question though, and still stand by a plebs view of the question.

Motor brushes are soft carbon.
Battery carbon rods are hardish carbon.
I dont have any diamonds large enough to file down to do an amateur hardness test apon.
In fact I dont have ANY diamonds at all, AND "there are no diamonds in the mine. " 
with apologies the Lenny.

Joe

[PerdioPal]

I have one diamond, it is on the end of my grinding wheel dresser, even the carborundum doesn't wear it down so a file will have no impact at all. Back on topic, variac brushes are anisotropic as said before, I have seen dynamo brushes made of many leaves of brass to do a similar thing.

[ppppenguin]

According to this article (and many others), graphite is naturally anisotropic: https://asbury.com/resources/education/g...nisotropy/ If you think of the layer structure in graphite, this is hardly surprising.

The makers of carbon brushes probably use quite a lot of knowhow to get the right combination of electrical and mechanical properties for different applications.

[joebog1]

I lied !! :-(.
I have two diamonds. One is fitted into my Shure V15, the other is still in its "packet " in case I break the one I use to play my vinyl.


Sorry PPPenguin.

Joe