On Monday, 30 April 2018 13:50:53 UTC+1, wrote:
Got this nice 0-140 5 amp variac that started arcing. Iunplugged it immediately of course.

It had been repaired before. When I first got it the wire feeding from the AC input had pulled the turn of the winding off, soldering took care of that. There was a little catch right at that point but it wasn't bad. Months, maybe about a year ago that "catch" got worse and I reworked it, tightening up the winding and making sure it was smooth. It was fine.

Then about last week I was using it to boost voltage to a car battery charger to feed something a tad over its usual output, which was working fine. And no overload at all, the drain was about 2.5 amps at 16 volts or so, so that was well within spec for the variac. Later I turned it down because it was time to test the UUT with lower voltage. (this is an intermittent overheating problem in the DC/DC convertor of an AC/DC version of the Tek 422)

Then I noticed that at the end, above where the line goes in, it was arcing between the windings.

I don't have nor want to find the magnet wire to rewind or partially rewind this thing. Is there a chemical solution to this problem ? (pun intended)

Perhaps our resident thaumaturge Jeff Lieberman has some idea, or anyone. I don't use it enough to buy another one but when I need variable AC I need variable AC. I might have to add some boost/buck transformers to my newly kludged bohungus isolation transformer. It even has a fan.

http://usr.audioasylum.com/images/7/...badazzis01.jpg

As you can see there is plenty of room for a few smaller transformers, but I would need them to be able to handle the current of the main one, right ? Otherwise an overload could be a catastrophe, and I have had enough of those in my life.

But is there a way to fix the variac ? I'm thinking a solvent, then enamel, then filing it down for the wiper to contact and ??? Maybe. I don't know if I can find such chemicals, or if they even exist. And how would I keep the windings on place once they're stripped ?

Any ideas ?

Also, I am not all that worried about the boost end of it, ans I am not concerned with ground faults because I can just always run it off isolation. It will almost fit n that cabinet but not with the knob in front, and I don't want it on top. But then it might be ready for the dump anyway.

Thanks in advance.

Variacs are never ready for the dump.
If you can get all traces of the carbon out from the gap, you're most of the way there. If not, and I expect you won't, I'd cut the wire and unwind half a turn each side. Put a turn of new wire on & solder its ends to the old ends where they're not in the way. With 2 half turns out the way it should be easier to remove any carbon.


NT