External screen heats up tranformer rapidly

Last night I added an electrostatic screen (3M copper tape) on the outside of my filament transformers. And soldered the outside screen to the internal electrostatic screen that runs between primary and secondary. To my suprise the transformer got warm real fast????

I don't understand why that would happen. So I removed the extrernal screen and voila..did not get warm anymore. I realize now after typing this that I should have just disconnected the external from the internal screen first...

Anyway..anyone have an explanation?
Seems to me that if you wrap copper tape around a transformer you have effectively added another scondary winding of one turn.
So now your primary is pushing current around this new short circuited secondary thus getting loaded and hot.
Wrap one turn of tape but keep the ends insulated from each other where they overlap so you don't have a current loop and you would be OK.
Did you put it around the WINDINGS, or around the whole TRANSFORMER? Big difference ;)

Flux goes one way up through the center limb (which the windings are wrapped around), then goes back down the two outside pieces (or just one in a C core). 2 - 1 - 1 = 0 so a "shorted turn" around the outside of it all will only squash leakage, while the majority of the field happily circulates inside the core where it belongs.

I had it on the windings :xeye:

like in the pic


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