Warren wrote:Running a motor through a gear reduction, means I can use a lower wind/higher rpm motor at the same battery voltage, just geared down more, for the same power/speed. This should allow lower motor current for the same output wattage, and greater electrical efficiency...correct?
Warren wrote:I know that both motors are designed to run on 36-48 volts. My question is, at the same input voltage, if they are both geared to produce the same bike speed/output wattage, will the faster turning motor have lower electrical loses?
If you run a motor faster, it will have the ability to output more power - you can get more power at the same torque level. Parasitic losses will increase, though, so the peak efficiency point will occur at a higher power level. For power levels below the new peak efficiency point, the efficiency will be worse than before. Direct drive hub motors are designed for low rpm, so not much attention is given to mitigating eddy current losses - hysteresis losses are the dominant parasitic loss. Eddy current losses go up as the square of the rpm however so, with the high pole count and thick laminations, there will be a limit to the speed that you can run a direct drive hub motor efficiently. For any motor, the eddy current losses depend, principally, on pole count and rpm (flux frequency), lamination thickness (losses increase as the square of lamination thickness) and core material.Warren wrote:Yes, "run the motor at a higher speed and gear it down more". I will still be spinning at my 80 rpm cadence, putting in my 100-150 watts, but this bigger motor will be spinning 40-50% faster than my current one, and hopefully putting out 2-2.5 times the power.
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