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Motor generator

  1. Jan 15, 2010 #1
    Dear Experts,

    I tried using a small dc motor to generate electricity.
    Assuming a 9v motor turns at say 2000 rpm and draws a current of say 200mA.
    If used as a generator will this generator produce exactly the same 200mA if the generator spins at 2000 rpm?

    I tried spinning the generator as fast as i could but seems that the current is very much lower than 200 mA (for discussion purpose). So, i wish to confirm the above.

  2. jcsd
  3. Jan 15, 2010 #2
    Small brush-type dc motors with a permanent magnet stator are at best 60% or 70% efficient (at optimum RPM and torque) in converting electrical energy into mechanical power. The same can be said for converting mechanical power to electrical. To confirm this, you could take two identical motors, back to back (axle to axle), and measure the electrical-to-mechanical-to-electrical conversion efficiency as a function of the input RPM AND the electrical load (I2R) on the output motor. This will give you a family of curves, a different curve for each RPM.
    Bob S
  4. Jan 16, 2010 #3
    Dear Bob S,
    Thanks for your answer.

    To confirm, you mean the electricity needed to convert electric-mechanical energy for at a fixed rpm is the same as that produced by the process of mechanical-electrical energy conversion?

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