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DC transformer

  1. Feb 12, 2013 #1
    Hello, so I was looking at some dc to ac mechanical generators when a dc motor is used to drive a generator which in turn induced ac as was used for power conversion back in the day when semiconductor devices were not around yet.Well they had some drawbacks as the mechanical wear and etc.

    So I came up with a strange idea and wanted to ask some expert opinion about could such a device work at all and how efficiently?
    In the attached picture you can see a toroidal ring with a empty middle.around the ring there are 4 primary windings and 4 secondary windings.The windings could be switched in parallel or series operation based on the ring size wire turn ratio etc.But to get a theoretical understanding that is not so important right now.
    In the middle of the toroidal ring there is a magnetic fluid the fluid is separated in three or four parts let's say and the separation is made by a dielectric fluid with no magnetic properties, the inside magnet could be made out of solid magnet with solid dielectric between and flowing into a fluid or whatnot.But that is again "semantics" this is just a theoretical device.
    So applying the DC current to the primary coils would start to push and create magnetic field in the rotating ring magnet which would then while rotating pass the secondary coils that are just after the primary ones and induce a current in them hence a moving magnetic field cutting the secondary wire perpendicularly.
    The question then is how fast could the magnetic fluid be able to spin if the ring would be in vacuum from inside?
    Also could mounting a electrically charged plate right between each of the primary and secondary windings help to make the field of the liquid fluid stronger as it now would have a opposing electrical field to the one in the primary wires just like in a dc brushed motor where the rotor has winding with current passing through them too which make the magnetic field between the stator and rotor stronger.

    Basically this is a linear motor bent around into a toroid shape ring , for the toroidal ring to work the inner flowing magnets should be separated in parts I guess otherwise because of the uniform field on the DC the magnets would not spin at all but when they are separated each of them feels a pull when passing through each of the DC primary windings shown in the picture , the secondary windings are colored pink.
    Also what difference would it make if the toroid ring itself the outer part of it would be made if a dielectric material like plastic or metal like copper?wouldn't metal outer shell distribute the magnetic field created by the DC primary windings evenly and hence stop the chance of the inner flowing magnet to start moving ?

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    Last edited: Feb 12, 2013
  2. jcsd
  3. Feb 13, 2013 #2
    My wording may be a bit misleading or should be rephrased but can someone shed his light on this principle?
  4. Feb 13, 2013 #3


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    Having just cut a hedge I'm somewhat too tired to be answering this question but...

    Why would the thing rotate? There appears to be no equivalent to a commutator?

    Do you understand how ordinary DC motors work? For example suppose we take that DC permanant magnet motor you mentioned and replaced it's ferrite magnets with stronger rare earth magnets. If we change nothing else (eg same battery voltage, same number of windings on the rotor)... would it spin faster or slower?
  5. Feb 13, 2013 #4
    Well basically if the inner rotating magnet would be electrically/magnetically connected throughout the ring or if the ring would be made out of some kind of metal rather than plastic I guess it surely wouldn't rotate as the field would distribute itself around the ring uniformly and the inner magnet would just spin to the nearest N S position and stay there but the thing is the ring is made out of non magnetic material so that all the field produced by the primary dc coil goes through into whatever is inserted in the ring.
    Now the inner ring consists of 4 separated liquid or solid magnets the thing is they are separated and if you cut out only 1/4 of the ring for example you get one primary dc coil and one secondary the primary has a field and when you put a magnet in it the field will repel that magnet in one or the other way pushing it right by the secondary coil and inducing current in it.
    This is basically a linear magnet motor just twisted around into a toroid shape and the inner magnets are separated so that when one coil has accelerated one of the magnets it can fly around and with a short gap the next one is coming in to be again pushed by the field of the primary coil to again circle around.Like a maglev train only put in a circle with the train being the magnet and the coil field accelerating it.

    Well if the magnet would be of a some kind liquid type and then separated I could insert a conductor plate between each of the primary and secondary coils so that when each of the 4 magnets are being pushed by the primary coil they would have and electric field in them too while passing by the secondary coil to make the induced current stronger.
    But that is just an option it doesn't change the basic principle.

    Why do you think it would need a commutator, linear motors don't have commutators too, maglevs either when their running on track instead they completely rely on the linear motor principle when a static magnetic field is pushing a magnet in either one or the other direction depending on the field poles/current polarity in the wires.

    @CWatters increasing the magnet strength will increase the field strength electrical or permanent magnet doesn't matter increase the field strength and the rotor field now has a stronger field to push itself against to so in a dc motor it would result in increase of rpm and torque I think.
  6. Feb 13, 2013 #5


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    Overall it appears to be similar to a brushless motor of the type that has the windings on the outside and magnets on the rotor. These are also essentially linear motors rolled up.


    They need an electronic commutator usually integrated into the speed controller. Sometimes this is done using a hall effect device to sense the position of the rotor but modern controllers sometimes use a signal from an un powered winding. For example on a three pole motor two of the poles are normally powered at any one time. The backemf from the unpowered winding can be used to work out when to comutate the field on the powered windings.

    In a DC permanant magnet motor increasing the field strength reduces the rpm. From a standing start this type of motor accelerates until the back emf equals the applied voltage. If you increase the strength of the magnets this occurs at a lower rpm.

    To compensate you normally reduce the number of turns in the windings. This reduces the back emf and increases the rpm at which the back emf equals the supply voltage. One advantage of using rare earth magnets is that fewer turns have less resistance so the "copper losses" are lower. Modern brushles motors can be >95% efficient so there is very little room for improvement in their design. Things like eddy current losses and friction (bearings and air drag on the rotor) can be significant.
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