If Scott stops by I am sure he can tell us about a whole lot of things that affect "loss" in a transformer. I have bumped around the edges of this stuff but just enough to understand this is more than 2 coils of wire and a core when you get down to the nitty gritty of the difference between the "goesinna" and the "comesoutta". The only thing I know is the loss ends up being mostly heat so the temp this thing runs at is a pretty good clue about the efficiency.
