Quote:
Originally Posted by elhigh
Then you're the guy who could answer this: don't rare earth magnets have a really sharp drop off of effectiveness at some critical temperature? And that critical temperature isn't all that hot.
Just as a f'rinstance, like a not-too-exotic N45 neodymium, the critical temp is...what?
[looks up "Curie temperature"]
Okay, never mind. Inside the engine is hot, but not THAT hot.
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It's more complicated than that. Things like "temperature coefficient of coercivity" that the electrical engineer in the next office understood far better than I did. Which is why he chose samarium cobalt magnets for use in a liquid cooled electric motor operating at 250 deg F. My electromagnets ran at slightly above room temperature, so I chose neodymium magnets for the higher energy product.
The temperatures of a piston pretty much rule out any permanent magnet.
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