Homer J Simpson said:
About 0%. What makes you think they'll lose magnetism? It isn't 1940 any
more.
I think most modern magnets, especially the powerful rare earth variety,
will hold their magnetism almost indefinitely, and even older magnets do
not deteriorate very much when they have a complete magnetic path (like the
"keepers" on old horseshoe magnets. The iron in the rotor of a DC motor
serves the same function. However, I have heard that magnets can lose their
field when overheated, as may happen in electric vehicles when you subject
the motor to overload conditions. I believe this happens at the "Curie
Point", and I don't know if it is a permanent loss or if magnetism returns
when cooled.
I am convinced that three phase AC induction motors are the best choice for
vehicles, and they are increasingly being used in locomotives. They are
very rugged and inexpensive, requiring very little maintenance, and have
very impressive power to size and weight ratios if you use PWM VF drives
and push the frequency to 150 Hz, or even beyond 400 Hz with special
laminations. The drive electronics are more complex, but the technology is
well understood and controllers are often quite inexpensive.
Paul
