Update - the Variac Went Up in Smoke!

[Cursitor Doom]

Astute readers will recall I was attempting to get an old variac up to modern safety standards. Well, it just spewed out a great deal of acrid smoke and is now reposing in the dustbin. The only thing I can think of that *might* have caused this was that I applied Servisol contact cleaner/lube to the brush and the windings at the edge around the circumference where they contact the brush. Could the Servisol have dissolved the varnish on the windings and shorted them out? I've checked everything else and it was wired correctly so I can't think of what else could have caused it to spontaneously combust.. Any thoughts?

[tabbypurr]

they're not too hard to rewind, I wouldn't bin it

NT

[Brian Gaff (Sofa]

Yes how old was the Servisol? I trashed a headphone socket using the older stuff, the glue holding the contacts melted. Brian

[Brian Gaff (Sofa]

Really? How do you get the contact area? Brian

[The Natural Philosopher]

Old windings are shellac insulated and that dissolves in ethyl alcohol. And almost anything else. It is apparently used to coat pills so they dissolve in the intestine and not the stomach.

So with shellac, the question is 'what will *not* dissolve it?'

[Andy Burns]

mechanically remove the shellac where the wiper needs to touch it, sander maybe?

[newshound]

Several different Servisols. The contact cleaner seems to be hydrocarbons but they also do an IPA one (which will dissolve lacquer, I think).

[tabbypurr]

sandpaper, scraper, solvent, whatever. Not a problem.

[Cursitor Doom]

The one now awaiting recycling was manufactured in the 1940s and insulated with whatever they used back then. As you say, shellac I guess back in those days.

That could well explain it then!

[tabbypurr]

There are probably people that would buy it as is. Variacs are hard to get now.

NT

[Cursitor Doom]

It would only be worth a fiver in the state it's in now - if that. Not worf the bovver.

[newshound]

Can't comment on the current market, but back in the 70's I worked in a large and well-equipped industrial research lab. We were always in trouble at the end of the FY if we hadn't spent our generous budgets. Rumour has it that some people would go to stores and sign out some large variacs, which got charged to the budget. In the new FY, you could take them back and the funds would magically be switched across the year boundary. (I've heard of other labs where the same trick was done with gold or platinum wire and mesh).

[tabbypurr]

The 3 faulty variacs for parts only on ebay now are priced at £60, £225 and £53.38, all plus postage.

NT