Permanent magnet motors are well fit for use where response time is a factor. Their speed characteristics are similar to those of shunt wound motors. Built with a conventional armature, they use permanent magnets rather than windings in the field section. DC power is supplied only to the armature.
Permanent magnet motors are not expensive to operate since they require no
field supply. The magnets, however, lose their magnetic properties over time, and
this effects less than rated torque production. Some motors have windings
built into the field magnets that re-magnetize the cores and prevent this from
happening.
Automobiles have installed DC permanent magnet motors that control power seats, windows, and windshield wipers. DC permanent magnet motors produce high torque at low speed, and are self-braking upon disconnection of electrical power. Permanent magnet motors cannot endure continuous operation because they overheat rapidly, destroying the permanent magnets.
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