| MadSci Network: Engineering |
Simple DC motors have an efficiency of about 50% based on some brief looks at motor data. I recently saw an ad for a brushless DC motor that advertised an efficiency of 60% as though it was higher than normal.
To get an idea of what efficiency you'll get from a given motor, divide the ouput torque and speed by the input voltage and current. For example:
efficiency = (Torque in in-oz)*(speed in rev/sec)/((current in amps)*(voltage in volts)*22.5)
The 22.5 is the conversion from watts to ft lb with the appropriate conversion factors for in, oz, etc thrown in.
When run as a generator, it is hard to predict an efficiency. The motor is optimized for use as a motor. You might get 50% efficiency, but probably less. The efficency of the generator would be the output watts divided by the input energy. The formula above is just flipped upside down.
For an example of typical DC motor
data, see the website below:
http://www.globe-motors.com/ss_in.p
df
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