How conductive? There are epoxies filled with Ag powder that may work. Depends how much power it has to pass.

Stay away from silicone conductives, because they loose conductivity as they get hot.

I think you're better off looking for a replacement part.

Good luck,

LL

The variac is old one" OHMITE MFG, CAT NO. VT4N 120V input / 4.75 AMP output " if some one can guide me to a place to find a replacement carbon brush.

Some useful info perhaps.......

http://sci.tech-archive.net/pdf/Archive/sci.electronics.repair/2007-01/msg00198.pdf

I have faced the same type of problem. But the solution is very much simple. Just take a plastic adhesive, Mix some carbon powder readily available inside a used battery, Use this mixed adhesive for your purpose. I have used it for broken carbon brushes & having no problem. To get better result, make a small hole by hand on the surface where the wire to be connected with a small watchmaker screwdriver before pasting the wire with this mixed adhesive. When the arrangement dried, check the resistance with a multimeter & you shall find very minimum resistance of the adhesive junction.

Inform me about the result at yes_iamin2000@yahoo.com.

D C Satpathi.

Glueing carbon brushes ???

Why don't you just buy a brush that is a little larger, and make it the right size with a file and/or sandpaper ?

I did this a thousand times, and it always works !

Good luck !

If you have access to a lathe you can make a new one from a larger carbon brush. I did so.

Yes answers given MAY return unit to service- reliability is a problem in my experience- I simplt take old brush & shape a new brush out of say a larger brush taking into account orig comp-eg carbon, bronze, sintered copper etc- the carbon rod from a 1.5v drycell has sufficed in the past- simply use a rough file to shape, then finer to get final good sliding fit. The embedded wire some brushes have is not essential for made up brush to work reliably in my extended experience.

Solder ? As far as I know only (most) NON FERRO METALS can be soldered ...

But carbon is not a metal and does not solder. If you could solder it there would be many applications doing just that.

It is just conceivable you could plate it with copper and solder that. But I think you would be better off taking the advice of those that have carried out repairs in other ways.

JayGeeBSE

Buy or get epoxy silver or polymeric silver glue. I do not know your location but if it is in USA than you can get this from any electronic out fits like Dupont, Ferro, Able stick, Lord etc. If you are in India you can contact Global Applied Materials in Chennai, India and they will provide you .

Go to your local tool supply, and look for a brush similar in size and composition, preferable a little larger/thicker.Use Flint Paper to hone it down to the proper size.Do not use Emery cloth for this, because it is conductive and may imbed into the brush and cause erratic behavior.

Glue it? Nope.

Good solution if it cost less than glue and guyis rich enough to buy brush that will be our first suggestion and second will be glue and I was going to say how to make glue also if he needed with starting materials available in market radiely. But your solution is better than mine so I will not say any more

The brush replacement is the best solution, but unfortunately it is hard to find in the market, so we have to go with the glue solution.

I used to work for a company that manufactured carbon brushes and commutators.The brushes are made from powdered carbon/copper powder, and are formed under high temp and pressure.Glueing will not succeed.

Send me some dimensions, I may have a few old ones lying around that can be modified.

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I will help you our with the glue formulation as long as you can send me the details what strength, use temperature requiremnts are. This should not be issue you can make out of copper -polymer ink which will bond both side

A carbon brush for your application can easily be made or modified from a DC motor brush or a Generator brush. A dremmel tool and a Volkswagen generator brush (because it's a big block of carbon) can be carved to fit. The one that I have used was plated with copper(at one end) and had a flexable wire already attached. Worked well. A variac brush is usually supported by a BeCu arm that spring loads it to the Xformer windings. Good Luck!

I think the glue made of copper- polymer ink is a good idea, but where we can find the polymer ink - is it easy to find ?

In USA there is company call Nano Adhesive makes copper ink. If you want to make your self I can explain you how to do that. I dol not want some one to make business out of this. My email is Masyood@gmail.com send me your email and I will provide you both way.

What is the amp rating/voltage range of the variac?I have a few old ones around that are collecting dust.----SSB----------------

I explained at the beginning of this article about my variac , it is a small one:

120v input

4.75 Amp output

Sorry I overlooked that.I'll check and get back with you.

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