140 amps

How Many Watts Does A 200 Amp Alternator Produce? A large alternator can be 200 amps or more. 14.4 volts x 200 amps = 2880 watts. How big of an alternator do I need for 3000 watts? 3000 watt / 12V is equal to 250A. A 250A alternator is needed to keep up with it.