Toroidal coil and magnet question

Discussion in 'General Electronics Chat' started by cmartinez, Jan 19, 2015.

  1. cmartinez

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    If I were to spin a diametrical magnet inside a toroidal coil, as shown in the figure below. What would happen?

    Capture.JPG

    My intuition tells me that the whole thing would just heat up (even if both sides of the wire are left unconnected), since one side of the magnet would induct current in the opposite direction as the other side of the magnet. But of course I could be wrong and I'd like to know what others have to say. Also, I wonder if there's an easy way to simulate this.
     
  2. wayneh

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    I think you're right; you'd see heating in the coil, and a drag on whatever motive force was spinning the magnet. Imperfections might allow for an emf appearing at the poles of the coil, but just a fraction of the applied motive force.

    How in the world did this come up?
     
  3. MaxHeadRoom

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    That appears to me to be the same as an induction motor when the rotor bars are open, i.e. no rotor current, only rotor current when the ends are connected?
    Max.
     
  4. cmartinez

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    Say we short circuited the coil... I was wondering if this could be a good way of translating motion directly into heat... Maybe place it in a heat exchanger directly coupled to a wind turbine or water mill or something like that, and use it to heat water (or some other fluid) in places where solar exposure is scarce but wind is readily available...
     
    Last edited: Jan 19, 2015
  5. MaxHeadRoom

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    Maybe make a good dynamic brake?!!
    Max.
     
  6. cmartinez

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    A dynamic brake... maybe... too bad it wouldn't be a regenerative one...
     
  7. GopherT

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    The magnetic lines of flux of the torroidal core will be all inside the core. There is no magnetic field to bother other components (or your dial) outside of the core. And by outside, I mean, not within the windings. This is why torroids are so famious for low-noise amplifiers. The power supply transformer does not cause any interference with other devices.

    With your core shown and assuming the magnet is connected to some axle concentric to the torroid, I doubt anything will happen.
     
  8. cmartinez

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    The coil is an air-core type... and I'm assuming that the magnetic field lines don't extend as far as the coil's outer diameter... You don't even think that some heat would be produced?
     
  9. GopherT

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  10. cmartinez

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    Interesting... but there must be a difference between the magnet's field lines cutting both through the inner and outer diameters of the coil, and cutting only the inner diameter... mustn't it?
     
  11. wayneh

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    You wouldn't need a fancy coil - you could just spin the magnet near a metal plate. Eddy currents in the plate would heat it up.
     
  12. t_n_k

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    Even given a different flux density cutting the inner and outer coil "faces" the effective emf generated due to either magnetic pole face would be countered by that generated by the other opposite magnetic pole face.
    If current could flow in any part of the open ended conductive coil geometry, one would expect a resulting partial opposing flux to either of the generating pole fluxes. This would require current to circulate within the very small vertical wire filament dimensions as tightly constricted loops. In theory this would be possible so there would be some (albeit small) Joule heating loss due to said currents.
     
    Last edited: Jan 20, 2015
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  13. cmartinez

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    And what if the coil were short circuited? What do you think would happen? I think that the current would then be far higher... but I'm not an expert on this field...
     
  14. t_n_k

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    I wouldn't expect there to be any difference.
     
  15. cmartinez

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    This is interesting... seeing that there are discrepancies of opinion among people that know more about the subject than me... What this means is that the only way to solve it is to either simulate it, or build it... and since I don't have a simulator with this capability, I'm going to build this thing and do some experimenting... I'll even probe various parts of the coil with my scope, see what's going on in there. It won't be today of course... But I'll get on with it in a few weeks, God willing. Then I'll get back here with the results.
     
  16. alfacliff

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    it has already been done. magnetic dields and torodial coils. there is no magic here.
     
  17. cmartinez

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    I'm quite sure it has, but I googled it thoroughly before posting this thread... couldn't find something similar... what I saw was that the magnetic field was contained inside the toroid's ring, and I couldn't find anything related to a magnetic field acting radially ... do you know of a link where I could look this up?
     
  18. cmartinez

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    OMG... I just did a search again using slightly different wording on toroidal coils... and I was pointed to "free energy", "zero point energy extraction" and "overunity" sites! ... the net is definitely full of quacks!
     
  19. GopherT

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    I would guess that it all depends on how strong your magnet is, and how close your magnet is to the copper. I would be interested to see what kind of current flow you will actually see between any two points. My first guess would say that there is too much symmetry and restricted current paths and high conductivity to see significant eddy current heating or any net current flow.

    If any current can be induced to flow, completing the circuit in your coil will likely slow the spinning magnet. I assume from the image in your first post, that the two leads on the coil are not connected as the initial state.

    What software will you use to simulate this?
     
  20. GopherT

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    Careful, the simple mention of those words and phrases can cause the mighty hand to close this thread.
     
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