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Old 10-18-2012, 07:09 AM   #2 (permalink)
kennybobby
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Does it say if the 21 Hp is a continuous rating or for just a limited duration?

let's assume it is continuous. 21 Hp is about 15,700 watts, so the 120 VDC rating let's us calculate the current as 130 Amps continuous for the armature.

From your measurements at 12 VDC the field resistance is about 1.7 ohms, so at 120 VDC it will draw about 70 amps. i would not want to energize the field all the time, only when the pedal is pressed.

A brush-type DC motor has a fairly linear response, so scaling up the voltage to 120 from 12 will increase the no-load speed x10, so the motor voltage constant is 7700/120 ~ 64 rpm/volt. The motor torque constant is 1/7th of the voltage constant, or 9.2 amps per ft-lb. Dividing the 130 amps by the torque constant indicates that the motor would make about 14 ft-lbs of torque at 7700 rpm on a 120VDC power supply.

As the motor is loaded the current will increase and the speed will decrease. When the motor is stalled at 120 VDC the armature currents could go up to 2000 amps and generate 200 ft-lbs of torque. My guess is that it is an aircraft starter motor, not intended for continuous operation. As such it is probably not reversible, and probably not really suitable for an electric vehicle. Does it have any sort of cooling fans/vents/ducts--that would be another clue?

It may still be possible to run this motor in an EV by using lower voltages with high capacity batteries, e.g. Lithium cells, depending upon the transmission. Good luck to you.

Last edited by kennybobby; 10-18-2012 at 07:35 AM..
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