Repair Toroid Enamel

[ravix]

I was modifying a toroid power transformer from center tapped to dual secondary when I got careless and damaged some of the enamel on the secondary wires. There are a few very small spots where the coating is off -- maybe 5-6 locations total. I am not very concerned because there don't appear to be any shorts and the secondary voltage is only 15V so I don't have to worry about arcing, but I still want to repair them. Some of them are on wires next to each other so they could shift around over time and cause shorts in the future.

Does anyone have any ideas? I have thought about using glue or something like nail polish to touch up the enamel. Alternatively I can unwind the toroid and use some heat shrink at each of the nicks, but I would prefer not to do this! It is a 150VA transformer so I expect it to get warm.

[AEIOU]

Originally Posted by ravix

I was modifying a toroid power transformer from center tapped to dual secondary when I got careless and damaged some of the enamel on the secondary wires. There are a few very small spots where the coating is off -- maybe 5-6 locations total. I am not very concerned because there don't appear to be any shorts and the secondary voltage is only 15V so I don't have to worry about arcing, but I still want to repair them. Some of them are on wires next to each other so they could shift around over time and cause shorts in the future.

Does anyone have any ideas? I have thought about using glue or something like nail polish to touch up the enamel. Alternatively I can unwind the toroid and use some heat shrink at each of the nicks, but I would prefer not to do this! It is a 150VA transformer so I expect it to get warm.

Fingernail polish is what came to my mind too! You can pick any color you want or get clear. Thin the paint if it's too thick.

[johnferrier]

At Fry's Electronics, I've seen enamel polish (for transformers). Comes in a small bottle with a brush. Not far from the printed circuit board etching kits.


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[johnferrier]

Turns out it's a varnish. This stuff . . .


Red Insulating Varnish



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[ravix]

Sounds great. The closest Frys is a 40 minute drive, but I might try to find some varnish like that locally. Thanks for the info!

[geraldfryjr]

use a clear nail polish is fine.
as long as the winding is not to badly nicked.

I did that to one of mine but the nicks are quite deep and nearly cut the wire compleatly through.
This causes a higher resistance in that spot and can cause it to fuse open but since it is on the top layer it can be fixed.
luckly I have another use for it and I don't need that winding.
no need for any expensive varnish for 15 volts. jer

[AndrewT]

I have "repaired" the enamel with nail varnish. It worked.

I was splitting a 70+70Vac pair of windings into four windings of 35Vac each.
I needed to scrape off some enamel to measure the voltages on the secondary to find the midpoints of the windings. Snip and connect in 4 extra leadouts. Worked a charm and saved having to unwind and rewind the secondaries.

[M1EUF]

Ordinary household polyurethane varnish works well for me and sets harder than nail varnish. I have used a low oven (50 deg.C) to speed up the drying time, it then sets in 10 to 15 mins.