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Self exiting dynamo question

  1. Jun 19, 2010 #1
    self exciting dynamo question

    I was reading about dynamo's and there was one that the power it made was used to run the electromagnet that made the magnetic field that the induction coil spun in.
    This got me thinking if a generator can make enough electricity to power an electromagnet that is as strong as the magnet in he generator, could some one make a generator that did not move and instead of spinning the induction coil or the electromagnet you could simply turn a series of electromagnets on and off in order to induce current into a secondary coil?

    I keep thinking about these self exciting dynamo's and about 3 phase motors and thinking to myself that putting these two devices together should make electricity with no mechanical input. But that cannot be right can it?
    Last edited: Jun 19, 2010
  2. jcsd
  3. Jun 20, 2010 #2
    Sounds like you're re-inventing the transformer. :smile:
  4. Jun 20, 2010 #3
    I was actually thinking it would work more like a generator with out any moving parts
  5. Jun 26, 2010 #4
    1) In a steady electromagnetic field, the act of passing a wire through it to cut the flux will induce resistance in the wires generating the field as well. (Not an electrical engineer/did really badly in the course where I learned that/may be wrong). Similarly I believe the current running through the wire (which wouldn't actually exist since this doesn't work) would resist the current in the other wires generating the electric field, therefore the more power generated by the system, the more power required to run it, proportionally.

    2) A pseudo-rotating electric field, i.e. a bunch of stationary fields instantaneously moving angularly around a wire (instead of a single rotating field rotating angularly) won't generate electricity since there won't be any flux being cut.

    So that is why it will not work right?
    I would prefer an explanation not just some one shouting "you cannot get more energy out than what you put in" over and over again. so if I am correct with the flux lines not being cut then let me know, thank you
  6. Jun 27, 2010 #5


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    A generator can certainly generate enough power to supply its own magnet coils (provided there is some magnetism there to start the process).

    However, powering its own magnets is not the main function of a generator. It also has to supply power to the outside world, so that you can use it.

    It is easy to turn the rotor of a generator when there is no load on it and a little harder if it is supplying power to its own field coils and much harder to turn it if there is a serious outside load on the generator.
    This increasing difficulty in turning the generator translates into the use of more fuel in the driving engine.

    If you supplied the field coils from a battery, as is done in cars, you would avoid the initial situation of having no magnetic field to generate anything with, but eventually, the generator is used to charge the battery, so that power still comes from burning fuel in the engine.
  7. Jun 27, 2010 #6
    but that says nothing as to why not or how much power you could get out of a device that switches a series of magnets on and off like a 3 phase induction motor.

    In effect take a three phase induction motor and replace the rotor with a generator coil and bolt it in place so it cannot rotate, shouldn't electricity come out of that set up?
    If no is it because of the flux lines not being cut by the wires in the generator coil?
  8. Jun 27, 2010 #7


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    Without movement then all you've got is a transformer. Sure you'll get "electricity come out", but always less then you're putting in to create the field.
    Last edited: Jun 27, 2010
  9. Jun 27, 2010 #8


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    You want to switch current to the coils of a series of electromagnets? So, you must get this current from a battery? So you have some power being fed into the device.
    You may get some power induced in the other coils like this, but it is just the power from the battery. You can't get more power out than you put in.

    If no is it because of the flux lines not being cut by the wires in the generator coil
    This is right. You may get a small amount of power from the battery induced in the other coils, but you won't get new power being generated.

    You may not know this, but there is a prohibition on this Forum about discussing "free energy" and "perpetual motion machines". This is basically to avoid wasting time on pointless discussions.
  10. Jun 27, 2010 #9


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    But what is a generator for? Surely it is to produce electricity from something moving (a different energy source).
  11. Aug 7, 2010 #10
    This sounds like generating power from a motorized appliance and then after initial startup from the utility power the device becomes self generating. For example a motorized appliance of 220 volt 9 amp draw turning at 1100 rpm.
  12. Aug 7, 2010 #11


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    The device will grind to halt because of the inevitable losses involved. It will slow down faster, in fact, than if you just let it run with no 'internal' electrical connections and rely just on friction.

    General principle: if ever you think you're getting something for nothing - you're not.
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