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Reuseful energy

  1. Aug 29, 2008 #1
    Dear all,

    I have querey regarding reuseful energy from system.
    Our system is big cylinder (1000mmφ x 1000mm width) having mass of 500kg is rotating 500rpm to do function.It consumes power 4kw continiously
    My curiosity is since cylinder is constantly rotating can we attach some dynamo accessories to generate power?
    Wheather attachment and generating power is possible?
    Can it we significant magnitude ?

    any case studies in this field ?sites?

  2. jcsd
  3. Aug 29, 2008 #2


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    Gold Member

    If you want to attach a dynamo to get 1kW out, then you'd need to uprate your motor to put an extra 1kW in (plus some more for losses).

    You won't get more energy out of this device than you put in.
  4. Aug 29, 2008 #3
    that 4kW is consumed against the losses, ie friction losses, viscous drag etc, it is not driving it, if you attach a power producing device, it ll increase the load on your system, then you need to increase the input to keep the shaft rotating at 500rpm.
  5. Aug 29, 2008 #4


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    Staff: Mentor

    This principle is called Conservation of Energy.
  6. Aug 30, 2008 #5

    Thanks for your comments.But still i am not clear.
    Of course you might be correct but i am not getting fully.
    I will brief about my system.A big cylinder fitted with shaft (in central) and this rotates 500 rpm.Cotton is fed over one half quadrant in the outer periphery,my doubt is how power consumes? to rotate that much cylinder(wt 500kg) to overcome inertial resistance or to get over the cotton resistance (cotton is pass thro big cylinder and another rotary system) or to both.

    Also if we attach in coils over outer periphery of the central shaft one end, while rotating this shaft flux will not create? and cant the power will produce?cant it generate even 0.5kw?why the input load is increased?

    If we consider motor rotor assumption is not correct?
  7. Aug 30, 2008 #6


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    Staff: Mentor

    What does it matter how the power is dissipated by the machine? Heck, leave the machine out of this, then all you are left with is a motor driving a generator.

    It takes power to drive a generator because a generator is converting mechanical power to electrical power. Magnets push electrons around, and that requires physical force.

    If this were not so, we'd already have perpetual motion machines generating all of our power. Again, conservation of energy prevents this.
  8. Aug 30, 2008 #7


    Yes i am agree that if we get around coil over shaft it will restrict and this will proportionately increase the input.

    But while rotating mass of 500kg any flywheel effect can we get?
    Also this flywheel effect cannot useful energy out?

  9. Aug 30, 2008 #8


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    Staff: Mentor

    No, the flywheel effect stores energy, it doesn't continuously generate it. You only get energy out of a flywheel when you slow it down.
  10. Aug 31, 2008 #9
    Thank you for your guidance.
  11. Sep 3, 2008 #10
    Therefore, you could possibly get some energy out of the system when you switch the machine off and slow down the "flywheel" if it could be connected to a dynamo. You would probably need a clutch so that you could engage the dynamo as soon as you switch off the machine. I doubt that the amount of power received would be very much in comparison to what you put in over a day of the machine being on, but you may be able to use it to power some lights or store it in a battery to be used in the starting of the machine the next day.

    Hope that helps.
  12. Sep 3, 2008 #11
    Thanks for your comments.Hands of to your idea.
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