DC Motor to run an Alternator

[bikram]

Is it possible/meaningful to use a 12V DC motor to run a 120 amps. Alternator at 2100 rpm ? If yes, what kind of DC Motor should be used (RPM/Watts/HorsePower)

[russ_watters]

Sure it is possible, but I don't know why you would do it. The motor just needs to be about 20% larger than the alternator to account for inefficiency losses. You didn't say what the voltage of the alternator was, but if it is a 120 A, 12V AC alternator, then what you are doing is converting 12V DC to 12V AC with a 20% loss. So figure on a 150A motor to run it (1800W).