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Power curve of Generator

  1. Mar 3, 2008 #1
    I'm designing a power assisted bicycle for my senior project in mechanical engineering and I have a few questions about the electric side of the design. I want to attach a small motor to be driven by the rear wheel to generate electricity to recharge the battery. The specs of the motor I was looking at are as follows
    American Bosch Motor/Generator
    -1/3 HP
    -24 volt DC
    -No-load speed 7800 RPM
    -No load amps 1.5
    -Full load speed 5900 RPM
    -Full load torque 60 oz-in
    -Full load amps 15
    -Motor body: 2.5" diameter x 4.5" long
    -Shaft: .25” diameter x .75”
    -flatted on two sides.
    -Two 10-32 mounting studs on front, .7” long, on 1.94” centers.
    -self-resetting bi-metal thermal protection.

    Now my question is, is there a way for me to calculate what kind of current is being generated at a certain rpm? I'm hoping there is a generic formula and its not totally dependent on the motor.
  2. jcsd
  3. Mar 3, 2008 #2


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    Gold Member

    Manufacturers often times have a torque vs. rpm graph to describe the motor's performance. If you are looking for a power vs. rpm graph for the motor, it can be calculated using a torque vs. rpm graph.

    [tex]P = \tau * \omega[/tex]

    [tex]P[/tex] is power (Watts)
    [tex]\tau[/tex] is the torque (N-m)
    [tex]\omega[/tex] is the angular speed (rad / second)

    So say a motor is developing 20 N-m of torque, and is spinning at 20 rad/s; that means it is developing 400W of power.
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