toroids are much "faster and cheaper" to manufacture, these are reasons for their wider use, why even John Curl will choose EI's over toroids anytime, if the accountants do not overrule him...
It's about 20 years old, bought from Maplin, made by Antrim Transformers, it doesn't "look" to be impregnated.
this is how i do it in my traffos...i completely submerge in varnish and soak for 30 minutes...
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Tony, my transformers (toroids) are wrapped in clear tape, silly question I guess, but should I remove it?
Varnishing is done to the industrial transformers, exposed to humidity etc. For in-house conditions with near constant temperature due to HVAC there is no point of doing it. It will not render IP20 part into IP40 one. Moreover varnish dissolves wire insulation and if the x_former of yours was not designed to be impregnated then so be it. Film wrap is PET. It provides some insulation as well as mechanical protection. DIYers often use paraffin or wax which could help with heat removal but do not bet on insulation enhancement - both may contain water and procedure is questionable at best without vacuum.
Stated like this it is blanket.
Risk of dissolving wire insulation depends on the properties of the varnish (polyurethane-, epoxy- or whatever based) and the properties of the wire unsulation (there are many different types each with their own specific properties).
You need more specialist equipment for toroids.
I’ve wound plenty of HF SMPS transformers (Pot core) in a former life which is pretty much about the same level of difficulty as an EI transformer. You can use a hand winder.
For the same output power torroids are
Smaller - so more space efficient
More electrically efficient (electrical conversion efficiency and thus temperature rise)
Quieter - very small radiated mag fields.
They do suffer from higher in-rush surges than EI’s but that’s an easy problem to solve.
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i used air drying polyurethane varnish, electrical grade, the same type varnish used on floorings are actually more expensive though of the same material...
i hung the traffos out in the sun to dry..
never had any problem with magnet wire insulation coming off...not once...been doing traffos for more than 40 years now...
sorry, you have to use line filters, dipping in varnish will not help, even if you remove the outer wrap, there are still plastic wrappings on top of the primary winding...
Where did I say bout insulation coming off? Wire is coated with lacquer and you impregnating it with the same. Even if it's not the case, varnish contains solvent which does damage the insulation, period. A lot of transformers are wound without interlayer insulation, especially toroidal.
In case of cherry picking: insulation can be different and there could be safe combinations. However industrial wires often have wrapped around insulation.
P.S. Doing power electronics for 42 years does not automatically mean that I am right or wrong.
reason why i never recycled copper wires, the moment i dismantle a traffo, the copper is scrapped and sold, end of wire journey...