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Why won't a permanent Magnet Motor work?
I was talking with a friend of mine the other day about being able to replace electro magnets in a motor with permanent magnets, with the intent of driving a generator to produce electricity. He was quick to say that it was impossible (He's an engineer) to produce over parity. I asked why and he answered because it defies physics. I took a pencil and four magnet's off of his desk taped 3 magnets to the pencil and set it on his tape dispenser and held the fourth magnet to it and the pencil began to spin. I asked him "if I can do this in 3 minutes with stuff off of your desk, do you really think people with the intelligence and resources of say M.I.T. couldn't produce a spinning shaft with enough magnetic force to turn a generator shaft?" Also I saw a demonstration of the Meissner effect that looks very close to what I am talking about on a smaller scale. And here is a link to a patented permanent Magnet motor I found. So what do you think?
Old Prof- You are correct I did move my hand, should have included that , however it seems like multiple magnets in the correct array around the shaft would produce the same effect. Thanks for your input.
3 Answers
- oldprofLv 71 decade agoFavorite Answer
If you are talking about a motor with nothing but permanent magnets, your friend the engineer is correct. It can't be done. And I doubt very much your recount of the pencil motor experiment.
Once one of the three magnets on the pencil aligned with the fourth in your hand, it would stay there. There is nothing to move the next magnet on the pencil to align with the stator magnet and concurrently pull the aligned pencil, rotor magnet off the fourth stator magnet in your hand.
Unless, of course, you moved your hand and the stator magnet. That would move the rotor, but only so far as you moved the stator magnet. Perhaps a fairer experiment, to preclude moving the stator magnet, is to find a way to fix it above the pencil without holding it in your hand.
Electric motors work because they provide a change in electro-magnetic flux. In a simple DC motor, for example, the rotor starts to align with the stator coils on either side.
Then, just as the rotor is aligned, so it would stay there without a change in polarity, the stator changes polarity so the rotor passes on through and is propelled to align in the opposite direction. That cycle continues with each half rotation of the rotor; and that's what propels it and makes it a motor.
So, what I think, you need to go back to the drawing board.
- Anonymous5 years ago
A permanent-magnet motor does not have a field winding on the stator frame, instead relying on permanent magnets to provide the magnetic field against which the rotor field interacts to produce torque. Compensating windings in series with the armature may be used on large motors to improve commuation under load. Because this field is fixed, it cannot be adjusted for speed control. Permanent-magnet motors are convenient in miniature motors to eliminate the power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which requires current to flow in field windings to provide the stator magnetic field. To minimize overall weight and size, miniature permanent-magnet motors may use high energy magnets made with neodymium or other strategic elements. With the higher flux density provided, electric machines with high energy permanent magnets are at least competitive with all optimally designed singly-fed synchronous and induction electric machines.happy to answer you!!!!!
