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Toroidal coil rotating magnet

  1. Aug 8, 2015 #1
    there is a toroidal coil , a magnet rotates in the middle of the coil , I wonder what happens when first the magnet that rotates is a permanent magnet , second case if the magnet that rotates is a electromagnet supplied with a certain frequency AC current?

    I wonder what kind of output we see on the toroid coil, in the case of the permanent magnet i'm not sure in the case of the electromagnet i think we should see the input ac frequency of the rotating magnet + some additional power from the rotation.?
     
  2. jcsd
  3. Aug 8, 2015 #2

    Hesch

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    It depends on the shape of the rotating magnet and how the toroid coil is wound.

    Please attach a drawing.
     
  4. Aug 9, 2015 #3
    well it's really hard for me to drawn anything that you could understand better than my words but for simplicity we can assume the toroid being a round tube , and the magnet a sphere rotating inside that tube.
     
  5. Aug 9, 2015 #4
    well the same thing just from another perspective would be a linear coil with an endless stream of magnets seperated each by a distance running through that coil, in once case the magnets are all permanent magnets in other case assume they are electromagnets which are fed with a certain frequency and waveform AC. say 50hz.
    in both cases what kind of waveform and frequency i would see if i attached an oscilloscope to the coils terminals?
     
  6. Aug 9, 2015 #5

    jim hardy

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    Have you looked into magnetic amplifiers ?
    i think you need to draw it then apply right hand rule
    see hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

    Does flux inside the toroid change ?
     
  7. Aug 10, 2015 #6

    Hesch

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    Also the width of the coil is important: Will the coil cover 30° or 360° of the toroid ?
    How is that sphere magnetized? Something like this:



    with the poles: N-S-N-S (two pole pairs), or what?
     
  8. Aug 10, 2015 #7
    thank you Jim , yes i have looked into magnetic amplifiers and I have to say this thing im trying to work out is kinda different.
    the flux changes along the path of the coil contantly.


    well we could say that coil covers almoust all 360° of the toroid.basically there are two cases , one case (more a theoretical than practical one) were the magnets travels inside the very core of the toroid , not the window in the middle but the very core , which in normal transformers is filled with iron laminations.as the magnet travels in the core the flux engulfs the loop fully.

    the physical idea of a generator was this, the same toroid with a coil on it , but in the middle window which is normally empty , there is rotor shaft, from the toroid core there come say two extensions attached to the toroid core at one end and an airgap wth the rotor at the other end.field coils are located on those extensions.the field coils are arranged such that one pole always points into the toroid core while the other into the rotor, the rotor has two blades at each side of the toroid those blades have an airgap facing the sides of the toroid. in other words the flux from the field coils goes into the rotor where via the blades it is directed back into the stator of the toroid were the other pole is. as the rotor moves this flux passing out the blades through the wire into the core is dragged around the toroid so the high density flux area travels around the coil.
    since the flux goes into the core from both sides the direction of flux is opposite at each side of the toroid , co the induced curent doesnt cancel out.

    i was talking about this elsewere but the poeple said that it wouldnt work because the flux isnt the same and doesnt go through the whole loop of the coil.
     
  9. Aug 10, 2015 #8

    Hesch

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    If the coil covers 360°, and the flux is symmetric in the toroid, no emf will be induced in the coil.

    But if the coil covers 180°, and the magnet has one pole pair, the shape of the emf will be . . . . . .

    Well, sketch a curve of the flux passing through the windings ( the Ψn - value ) when the magnet rotates. Emf = dΨn/dt.

    Be careful with the signs.
     
  10. Aug 10, 2015 #9

    jim hardy

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    all i see is symmetry cancelling out any voltage

    Salvador1png.png

    there's a reason they say a picture is worth 103 words
     
  11. Aug 11, 2015 #10
    Ok then I will try my best attempt at a drawing a bit later on.
     
  12. Aug 11, 2015 #11

    Hesch

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    Only if the coil covers 360° of the toroid, as shown in the attached image in #9.

    Say it covers only 180° ( the right half of the toroid ) the magnetic field will still be symmetric, but the left half of the magnetic field will not pass through any windings.
     
  13. Aug 11, 2015 #12

    jim hardy

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    aha i missed that, thanks
     
  14. Aug 11, 2015 #13
    suuuds.png so here is my crude drawing , well first of all if i made the coil just half the toroid and rotated a bar shaped magnet inside the toroid window I would have just an oridnary generator and in fact not the best efficiency.

    so the idea was like this there is a toroid with a coil wrapped on it spanning the whole length of the toroid. then there are field coils placed on the pink attachments which are fixed or the same material as the toroid core on which the coils sits, as you feed ac current into the field windings they are arranged such that both alike poles will point into the core of the toroid and the other two alike poles will face the airgap with the rotor , the rotor has blades or whatever you call them on it and is a low reluctance path for a amgnetic field so the opposite poles seek to find each other to establish flux and the flux should go from the field coil into the core through the windings into the blade back into the rotor and into the other end of the field coil, in other words i need the rotor to have a flux at the right angle with the toroid core so that once the rotor rotates the flux from the blades would cut the coil wire on the toroid core and induce current.
    I don't know what do you think.
     
  15. Aug 13, 2015 #14

    jim hardy

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    you need to lead people's thoughts
    not flood them with a run-on sentence that's a disjointed heap of thoughts with no flow from one to the next
    Might it be easier to read like this ? my questions in blue
    Draw the flux on your diagram, then show how that flux changes as the rotor turns.
     
  16. Aug 14, 2015 #15
    the two field windings are wound such that both N poles for example face into the torus core and both S poles point into the rotor.

    the airgap with the rotor is because the field coils are stationary together with the stator torus. the only thing that turns is the rotor which is made up of a shaft and two blades at each end so that the blades move past the sides of the torus as the rotor turns.

    the field flux from the field coils is such that it travels through the core which is stationary as the field coils but then to complete the magnetic loop the flux travels through the blades and through the rotor back to the field coils. since the rotor is a low reluctance path for the field lines.
    but since the rotor with the blades rotates the blades change their position contantly as they are gragged around the torus the high flux area between the core and the blades cuts the wire sitting on the torus.which is the output coil.
    the field current in the field windings is AC. suuds 2.png
     
  17. Aug 14, 2015 #16

    jim hardy

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    Ahhhh much better !

    Hmmm will think on it

    meantime

    what if

    you tapped your coil at three places
    and energized the rotor with ac
    would there be voltage between the taps ?

    salvador2.jpg

    What would happen if you made two such apparati
    connected their stators in parallel
    and their rotors in parallel
    ?

    I honstly don't know
    but you might look up "selsyn"

    .
     
  18. Aug 15, 2015 #17
    as to the image you posted I think there will be no induced current nor between the taps not in overall, because the whole coil is one big coil and the magnet has two sides of flux direction both of them cutting the same coil just at different parts.so the total current will cancel out.well thats my take on it.

    my picture with the blades has only one way flux direction at any part opf the coil so there shouldn't be cancelling currents.the flux itself changes direction as the AC field current does but at any given moment both blades or whatever the blade count all have the sam flux direction either from the rotor to stator or vice versa.
     
  19. Aug 18, 2015 #18

    jim hardy

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    i re-drew my diagram so the col is divided into three equal sections of six turns.

    Salvador3.jpg

    Magnetic flux that passes through loop of wire is said to link it.

    Do you understand that induction in a loop of wire causes voltage in proportion to the rate at which magnetic flux linking those loops of wire i changes?

    Does it look as if the flux through the individual loops of wire might change ?

    As Hesch pointed out above, induction around the whole toroid will sum to zero
    but around just a segment it will not.

    Please read up on Faraday's Law.
    I think you'd benefit from simple experimenting, for example
    http://amasci.com/coilgen/generator_2.html

    upload_2015-8-17_23-53-55.png
     
  20. Aug 18, 2015 #19
    Ok yes I agree if the coil would be split in different parts then each of those parts would see induced current beacuse the poles of the magnet traveling by that coil would change respectively.
    But my ideas was a bit different.not to go into long explanations in simple terms take the same drawing you attached, but this time the magnet has one pole at a time on both ends , the other pole at a time is located in the torus core itself.so the rotating magnet is one pole at any given time and the torus itsel os the other, the poles switch with some given frequency, the magnet rotates, now what happens is the flux path is in the same direction at both ends of the magnet , so now there are no cancelling currents induced.yet the flux passing the coil changes.
     
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