On 29/07/14 16:51, John Williamson wrote:
You get *all* the energy back, less the hysteresis losses in the iron
core. There are no such losses in the copper windings, and air cored
transformers don't suffer them either, they're just not very practical
at 50Hz or so due to the size they'd have to be.

And because they'd be so enormous, there'd probably be losses in
anything for some distance in the form of eddy currents