Is it possible: Electric motor

BlazGr

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Could you create a motor thaht is powered only by magnets-the normal ones, not the electromagnets.
 

13thmonkey

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no. Conservation of energy, or if you can it would have very very little torque and the slightest load would gradually slow it down.

Also you'd need a monopole, as like poles repel, but the poles rotate you'll then put unlike poles together which attract, and would prevent the rotation from continuing.
 

Olle P

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If you use magnets only, in what way would the motor be "electric"?

... but that doesn't prevent the build of a magnetic motor the task of which is to keep the axle oriented in a single direction and revolve less than half a turn away in either direction.
If that limitation is acceptable then it's fine to do such a motor!

In fact, all electric motors that have permanent magnets function like that to a lesser degree. If you try to rotate the axle of a motor that's not connected to power you'll find that the axle has a finite number of stable positions.
 

13thmonkey

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that's only 2 poles, you'd need more than two poles to get a rotation going else you'd be expecting the one interaction with a pole to turn 180deg.
 

MU_Engineer

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Absolutely no, it's physically impossible. You need a rotating magnetic field to make a motor rotate and only an electromagnet with a variable poles that do not line up with the opposite poles of the stator will cause a rotating magnetic field. A (permanent) magnet has a fixed magnetic field that does not move. Putting permanent magnets in the rotor/armature would cause the rotor to align itself to the magnetic field of the stator and then be immobile. You would need a rotor with a brushes to alter its electromagnetic poles along its rotation to provide a rotating magnetic field with a permanent magnet stator.

This is also why only a squirrel cage AC induction motor with an odd number of evenly spatially offset phases of 3 or more can self-start. A single phase motor without something like a shaded coil, a start capacitor used in an LC circuit to pull the start winding 90 degrees out of phase, or a brushed rotor such as a universal motor or repulsion-induction motor will act like a motor with permanent magnets on both the rotor and stator and refuse to start. Witness how a single-phase AC motor with a dud capacitor or start relay won't start, it will only hum and act like its rotor is locked, the magnetic fields align and do not move, so the motor doesn't run. A 3 phase motor has magnetic fields 120 degrees out of phase so they never align, so a 3 phase motor will always start with simply applying current to its stator windings.

Also, a motor provides work to a load. You cannot have work be performed unless at least an equal amount of energy is fed into the system due to the law of Conservation of Energy. You can feed energy into an electromagnet but not a permanent magnet.
 

BFG-9000

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You could physically rotate the permanent magnets in the stator to alternate their polarity, which would then induce rotation into the rotor with its permanent magnets. But that wouldn't exactly be a useful motor as you'd need other motors to spin the magnets anyway, and it would be more useful to use their power directly.
 

Olle P

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I'm thinking "swing door".
If you rotate it off center the "motor" will act to push it back, and that's all it does.
 

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