Quote:
Originally Posted by SpEEdyBL
2. The equation for % efficiency of a motor is (VI - rI^2 - I0)/(VI) where V= volts, I = amps, r=resistance and I0 = amps at no load. So if you plot the graph as % efficiency vs. amps, you will see that if you use a higher voltage constant, you will get a higher max efficiency. But keep in mind this is only a theoretical equation and at some voltage, the efficiency starts to get worse. This voltage where peak efficiency is the highest is known as the sweet spot of the motor.
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That equation only models electrical losses -- not magnetic losses (magnetic losses are lumped in with the IO constant...) Keep in mind that magnetic losses are non-linear (especially at high power.) Also, the IO constant needs to be measured at the same RPM as the output -- because other losses (like windage) are also non-constant (windage losses are RPM cubed...)