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Magnetic resistance in generator, constant?

  1. May 20, 2012 #1
    Is the resistance of the turning shaft equal in both cases where the output induction circuit is closed and broken. Or to put it another way, if the electrons are permitted to flow via induction does it make any difference to the magnetic resistance?

    I'm hoping and expect the answer is that it doesn't matter i.e. constant magnetic resistance.

    Though if it is different, how significant is it?

    I'm getting confused thinking about the energy equation.

    If current does flow then kinetic energy was transformed into electrical energy.

    If current doesn't flow then where is the energy that was otherwise induced? Maybe the resistance has to change to account for that? Say if I'm hand cranking the generator then I will work harder to turn it at the same speed and more of my muscular energy will be used = to the induced current when the circuit is closed. Just musing, doubt that is right.
    Last edited: May 20, 2012
  2. jcsd
  3. May 20, 2012 #2
    I am not exactly sure what you mean by "output induction circuit is closed and open". I think you just mean if the output is connected to a load and because the output is the coils of the generator which are essentially inductors, that's what you meant by "output induction circuit".

    In that case then to answer your question, yes the magnetic resistance you could say does differ.

    The reason is simple, the more you load the generator, the higher the current in the windings (output), obviously greater current means bigger magnetic field and because the induced voltage from the turning of the shaft is induced in such a way as to create a current that will oppose that movement of the shaft. When the output is unloaded, then no current flows and thus no opposition created by the windings, you will still have a voltage induced but no current.
  4. May 20, 2012 #3
    I changed my terminology, but yes connected or not. Current flowing and not flowing.

    As you can see I'm far from an expert on this topic, hence the question.

    Is this saying the resistance at the shaft increases when current flows?

    Edit: I believe the answer is yes, and that makes sense now. The induced current creates a field which opposes the fixed field hence more energy is consumed rotating the shaft when current is allowed to flow. (if rotated at same speed)
    Last edited: May 20, 2012
  5. May 20, 2012 #4
    yes that is correct. It's all conservation of energy, lol. If it did create that Resistance to the turning of the shaft then you could create huge amounts of energy for very little effort.
  6. May 20, 2012 #5
    Yes conservation of energy ;-)

    The question pertains to this invention here,

    'Chinese Farmer Fights Smog With Fan Power'

    (I need 10 posts to link)

    I still think it's feasible as an energy recovery device, if a turbine can act as an efficient (aerodynamic) air displacer and rotate as well.

    Wonder what others think?

    One problem. If an air particle contributes to the turbine rotation then it has less energy transferred to it, so it won't (in most cases) displace out of the vehicle's way as well as the alternative. Perhaps an optimal design does both and recovers energy.
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