Most Helpful Member
I know many people, who use Microwave as defrost / preheat... And they run it for tens of minutes (try defrost 2kg of meat, it will run nearly hour or more...). By your posts all of them should have fried transformers. Is there no safety and every microwave producer is sure, that nobody runs it for more than few minutes? Are you really sure about your posts?
Obviously with extended use they get quite hot, but they are designed to do so - maximum heat is probably reached in 10-15 minutes?.
However, I wouldn't suggest that a microwave oven transformer is a good choice to rewind, as the laminations are welded.