What material should you use to re-insulate a chipped/burnt toroid ... when replacement is not an option?

Here are pics of said toroid - http://imgur.com/a/Z0hC8 - I'm planning to replace the wrapped wire, just need advice on what to use to cover up the broken insulation on the actual toroid?  I've tried nail polish, however it heated up and smoked against the bare wire (hadn't yet rewired it when tested).

The toroid is on a Power Supply.  Replacing the entire PSU is not an option.

sort by: active | newest | oldest
orksecurity6 years ago
The toroid is wrapped with enameled wire, where the enamel coating provides the insulation. Purchase the correct wire -- appropriate gauge, appropriate insulation. And make sure you exactly replicate the number of turns.
cowpuck (author)  orksecurity6 years ago
Thanks for the guidance; ended up following both points: using Shellac and getting new wire. I used the Shellac to coat (dunked it entirely) the toroid (donut part) and re-wrapped it with the new wire.

The problem that I'm facing now is that it appears that the Shellac is being heated up by either the toroid or its new insulated wire (not really sure which). Once it gets heated enough it starts smoking. At that point, I've disconnected the power. Without a load on the PSU, it doesn't heat up enough to smoke; it's only once the PSU is plugged in the Mother Board that the smoke occurs. Note, none of the other components show any signs of stress/being broken/etc.

I realize that the initial concerns dealt with the wire's insulation and not the toroid itself. Perhaps I was a bit overzealous and applied too much Shellac?

Given this information, would you say that it's normal for a toroid to become hot enough to burn off the Shellac? How should I now proceed?
Sounds like you're putting more power through the coil than that wire thickness was designed to carry. Which may be why it failed in the first place. If so, the question is what else is broken to cause that problem.
cowpuck (author)  orksecurity6 years ago
Initially there were bad (bulged) capacitors in the PSU; you can see pics here - http://imgur.com/a/MATUf - you can see from these pics that the toroid was initially fine; though I just noticed the green resistor next to the toroid looks a bit burnt as well, but not broken - might be related; not sure.

I didn't realize (at first) that this PCB had such a huge ground plane ... after a failed attempt to remove the first cap, I bought this Chip Quik flux that made the removal job a breeze (highly recommend using it).

The problem occurred with that first attempt to remove the cap - that attempt (via the soldering iron) burnt up the toroid.

Any insight?
Sounds like a general meltdown. Good luck, but when you start frying multiple parts it's usually a losing battle -- if you don't find ALL the bad parts (which may include ones not obviously bad), it risks wasting all your time and money by blowing up again.

You might want to punt this, scavenge what good parts remain, and get another PSU.
cowpuck (author)  orksecurity6 years ago
Good points. Thanks for your time and guidance.
Re-design6 years ago
You could carefully unwind it and count the turns. Then reinsulate the wire using shellac. Do three coats then rewind the toroid when it's dry.
cowpuck (author)  Re-design6 years ago
Aside from the wire, is it also advised to also put the shellac on the donut portion of the toroid that is slightly chipped/burnt (at about 11 o'clock in the pics)? or would the repairing the insulation on the wire be enough?

In other words, is the wire's insulation the most important part of the repair? The assumption being - as long as there is insulation on the wire, then the donut's chipped/burnt insulation isn't a big deal?

Thanks for the guidance.
It would be a good idea to paint the chipped edge to soften it and protect the wiring insulation.
Worth a try...