A basic question regarding transformer laminations

[KT]

Hello, Can anyone tell me if a transformer relies on electrical contact between the laminations for proper operation or not? My concern is that I have some small output transformers that seem to be susceptible to rust. If I coated them with a varnish, should I be concerned about the varnish seeping in between the laminations and insulating them from one another? Or does this not matter? Thanks, KT

[Tim__x]

Quite the opposite, the whole point of the laminations is to reduce conductivity The laminations must be insulated from each other to reduce eddy current losses.

[zigzagflux]

As well, if the rust has started, it may not be possible to stop it.

Of course, oxygen is needed to propogate rust, which your varnish may help somewhat.
However, the very fact that you have rust says the xfmrs were either stored in a poor environment, or were not manufactured proprerly.

[KT]

Thank you. That sheds some light on things. Well, the rust has not started, but the lams are made of a metal that seems likely to rust at some point. I may be wrong, but I just wanted to take precautions. Thank you, again, for the insight. Best, KT

[richwalters]

Originally posted by Tim__x
Quite the opposite, the whole point of the laminations is to reduce conductivity The laminations must be insulated from each other to reduce eddy current losses.

Anyone who has magnetics knowledge will immediately recognise a horrible habit that many manufacturers are adopting to save assembly costs and that is welding the laminations.. welding relies on to some extent that the laminations aren't short ciruited on the other end....this hardly appears in practise and a temp rise is expected from eddy current motor effect. The obvious stray leakage inductance and construction assembly from such a grotty method is only applicable for non-audio applications. A choke may perhaps be exception where a calculated gap is permitted.

It's fair to mention that I recently asked a quotation for a custom low power mains tranny specifically for an audio application with lower Bmax and insisted that laminations be strictly E&I interleaved. The pending manufacturer (who claimed had years of Xformer experience) said this wasn't possible. Rubbish ! No deal and total lack of applications experience. Are universities producing overqualified who know nothing about practical physics ?
The irony is the same time I also applied the same spec to a UK transformer manufacturer and got a reply within hours, " size, Bmax, regulation factor no problem". Accepted offer.

For others after a custom transformer for a specific project, carefully tabulate a specification exactly what you are after. These days everyone cuts corners.

richj