How many watts of elec. does a electric car motor take to run it at 75 mph? How many volts etc.

Question

If I wanted to charge the electric cars battery while driving it, how much electricity would the generator have to produce? In Watts, Amps, Volts? How big would the generator have to be?

Answer 1

Depends on the air resistance of the body, the rolling resistance of the tires, and a few other things.  You could probably do it with 40 horsepower, which comes out to 40 hp x 746 watts/hp = 14,920 watts.

Divide that result by the motor's voltage to find the motor current.  The power produced by the generator would be equal to the power used by the motor plus whatever losses are incurred in the conversion process.  

Note that these are not particularly friendly numbers, which is why there are no electric cars that can go 75 mph.