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Not An Overunity Question

  1. Jun 15, 2010 #1
    If electromagnets in an electric motor were replaced with permanent magnets, would it make a significant difference in the amount of energy required from the motors power source?
     
    Last edited: Jun 15, 2010
  2. jcsd
  3. Jun 15, 2010 #2

    russ_watters

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    Please note: the title of the thread is basically saying the opposite of what it says. No one ever says "not an overunity question" if a question is really not an overunity question. And people looking for overunity and trying to skirt our rules say it all the time. By saying it, you are acknowledging that you already think it is an overunity question. Please keep that in mind the next time you pick a thread title.

    But since you say it isn't overunity, you should have all the information already at your disposal to answer the question yourself. So take a crack at the answer yourself. Bear in mind that good electric motors already exceed 95% efficiency. And keep in mind the first law of thermodynamics, which I referred to in another thread of yours. Look it up in wiki if you need to.

    [edit] While permanent magnet motors already exist (you can look them up on wiki too), it sounds like you are looking for a motor that produces output power without input power. Is that correct? If yes, please explain how that jives with what I said in the previous paragraph - and your thread title.
     
    Last edited: Jun 15, 2010
  4. Jun 16, 2010 #3

    Redbelly98

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    Not sure I understand what you are thinking. With no electromagnets the motor would simply come to a stop, with the N pole of the stator magnet near the S pole of the rotor magnet and vice versa.

    Moreover, with no electromagnets there is nothing for the power source to connect to!
     
  5. Jun 16, 2010 #4
    I'm not sure what kind of motor you're referring to. In the simple DC motor, to the rotor it makes no difference whether the static magnetic field there was produced by electromagnets, or by permanent magnets, in the stator. So by using the latter you save the energy that would be lost to resistance in the wire of the stator electromagnets. Effectively, I guess permanent magnets give the advantages of superconducting electromagnets without the difficulty of cryogenics.

    I like to see people given the benefit of the doubt. In this case I assume deanbo has anticipated a comment like yours and explicitly specified that such is not correct.

    (Unless, perhaps, the OP really means the exact opposite of what the OP wrote.. but then, maybe russ also means something entirely different from everything russ wrote... :confused: how complicated!)
     
    Last edited: Jun 16, 2010
  6. Jun 17, 2010 #5
    Is a battery powered generator with permanent magnets likely to place less load on the battery than a battery powered generator with electromagnets all other things constant?
     
  7. Jun 17, 2010 #6
    Surely.
     
  8. Jun 17, 2010 #7
    A battery powered generator???

    If you have a battery, why do you need a generator?
     
  9. Jun 17, 2010 #8
    Deanbo, the magnets in a motor have to be able to reverse polarity, or be switched on and off. Below is a picture of a simple electric motor. The outer magnets are permanent magnets, and the inner magnets are electromagnets. The arrows represent repulsive forces between the inner and outer magnets.
    Electric_motor_cycle_2.png
    The repulsive forces turn the motor clockwise.
    Electric_motor_cycle_3.png
    Once the inner electromagnets are horizontal, completely aligned with the outer permanent magnets, the polarity of the electromagnets has to switch in order for them to be pushed around for another 180°. If the inner magnets were permanent magnets, their polarity could not be controlled. They would turn only until they were aligned with the outer magnets, at which point they would wobble to a stop.
     
  10. Jun 17, 2010 #9

    DaveC426913

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    Parroting Archosaur: the reason electromagnets are an integral components is so that the polarity can be switched with each half-cycle. Permanent magnets will not do this.
     
  11. Jun 17, 2010 #10
    Umm. I believe deanbo is talking about replacing the field magnets, shown in Archosaur's picture, with wound magnets.
     
  12. Jun 17, 2010 #11

    DaveC426913

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    ?? Do you mean replacing the permanent magnets with electromagnets? That's exactly opposite to what he said.
     
  13. Jun 17, 2010 #12
    Yeah, nevermind. Nothing like adding to the confusion.
     
  14. Jun 17, 2010 #13
    Permanant magnet motors have some desireable characteristics like high starting torque and small size. They are not the most efficient motors. The record for motor efficiency is held by induction motors with active electronics on both the rotor and stator. In this way patasitic losses can be minimized.

    Edit: I can't find a reference now to this but I'll try to find it and post it.
     
    Last edited: Jun 17, 2010
  15. Jun 17, 2010 #14
    This is counter-intuitive. What type of induction motor, and which parasitic losses?
     
  16. Jun 17, 2010 #15

    Redbelly98

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    Glad we are in agreement. :smile:

    It's still not clear to me just what type of motor the OP was thinking of, or if he was wondering about replacing all coils with permanent magnets or just some of them.
     
  17. Jun 17, 2010 #16
    So is deanbo talking motors or generators?
     
  18. Jun 17, 2010 #17

    russ_watters

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    The phrase is, of course, self-contradictary and nonsensical....
     
  19. Jun 17, 2010 #18

    russ_watters

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    I'll bet you a beer the OP is talking about an all-permanent magnet perpetual motion machine: http://www.lhup.edu/~dsimanek/museum/unwork.htm#cheng
     
  20. Jun 17, 2010 #19

    Redbelly98

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    I think more along the lines of Archosaur's post. The OP is not completely versed in how motors work -- in particular that at least one magnet in the motor must switch polarity, necessitating an electromagnetic.
     
  21. Jun 17, 2010 #20
    Right, I don't get the sense from the OP that he's one of the "heretics". I think this was just genuine confusion.
     
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