[Frank Lee]

Originally Posted by NiHaoMike

A 120kRPM, 8 pole alternator is only 8kHz. Common silicon steel would be quite lossy at those frequencies, but it can easily be handled with powdered iron or ferrite. Switching power supplies, the most common application of those magnetic materials, operate at tens to hundreds of kHz.

A friend of mine has built a hybrid A/C that uses a centrifugal compressor operating at 75kRPMs, driven by a switched reluctance motor. I don't know about the compressor efficiency but the overall system efficiency is about 40 SEER equivalent. (It started in the low 30s, but optimization brought it up, with no changes to the compressor.)

Good, stick 'em on turbos too!