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Motor for flywheel

  1. Jul 12, 2012 #1

    Me and my friend is starting a project to building a flywheel system with aim for energy storage. This is a small budget experiment to see how long flywheel can hold energy with our design. One problem we face is finding a suitable motor, we plan to use induction motor to avoid eddy current lose, but most of the induction motor under 1kW has max rpm around 3500, a bit low for our purpose.

    Is there cheap induction motor that can deliver 6000rpm or above?
    provided we can ignore bearing friction, can we ramp up rpm by increasing drive frequency?

    Also, we plan to rip out original bearing of the motor and connect the motor rotor to flywheel rotor with a shaft, both inside a vacuum. Would there be a heat dissipation problem to this approach?

    Since I'm new to all this, any help would be appreciated.
  2. jcsd
  3. Jul 12, 2012 #2

    Simon Bridge

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    You can "overclock" motors of course:

    running in a vacuum will create heat dissipation problems.

    details will depend on your requirements - which are sparce right now. eg. if your flywheel is a millstone then you probably won't get a cheap motor to your specs but if it is a dime then it's probably easy.

    To get a flywheel to store energy for a long time, you want to have it heavy with as much mass around the rim as you can get and minimize friction in the bearings: magnetic bearings for favorite.

    Then you worry about spinning it up.
    If you are having trouble fitting a motor to your design you can always fit the design to your motor. (Since this seems to be your biggest constraint.)
  4. Jul 12, 2012 #3
    A lot of the parameters are not fixed yet, the only thing we're sure about it is its going to be low budget.

    Yes, magnetic bearing is needed.

    Another option I'm thinking is put the motor outside, then use magnetic coupling to drive the rotor, once the flywheel is spun up, we pull the motor away. But this could introduce a bigger problem that part of the vacuum wall would have to be non metal.
  5. Jul 12, 2012 #4
    I don't wish to rain on your parade, but cheap and magnetic couplings don't go together.


    At low speeds like 6000 rpm, you don't need magnetic bearings or vacuum sealing or a magnetic coupling. It's just not worth it. Don't kid yourself that because it's not touching there is no losses. Magnetic bearings cause 'friction' by hysteresis.

    Good oiled deep groove ball bearings and a well balanced flywheel are all you really need.
    Last edited: Jul 12, 2012
  6. Jul 13, 2012 #5

    Simon Bridge

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    There's also fancy ceramics and polymers...
    On the whole - the method you use to spin it up can wait until you have the rest of your design sorted out. You just have to allow for an interface. If your method has too-low rpm, you can gear it ... in principle you can rig any kind of motor provided it can turn the crank. But until you sort out the basic design the variables are too ... um ... variable.
  7. Jul 13, 2012 #6
    Thanks for the replies guys, and those links are really helpful. I managed to find NEMA documents for "overclock"ing AC induction motor.

    The current low rpm is just due to motor and material constraint, at this stage we just want to test if our magnetic bearing works (low energy lost for a period of time), hence all the fancy requirements about vacuum and motor, only when we eliminate other lose mechanisms can we determine the performance of the bearing.

    Ceramic/steel bearings would be used as well, but only as backup when magnetic levitation is not stable.
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