How much power is required to turn an alternator/generator?

Question

I just want a rough estimate of the amount of horsepower required to actually spin just an alternator. I'm guessing it's very low but I could be wrong....the application would be for 4-6 fairly high output alternators run off one engine.

Answer 1

It's totally a function of the actual output of the generator and it's efficiency. Figure you lose 10% in the belt, and another 10% to friction in the bearings, the efficiency of the alternator/generator. then there is the actually load on the generator....not it's rating maximum output. 1 kilowatt is about 1.34 horsepower. At 12 volts, 100 amps would be 1.2 KW which is about 1 1/2 HP. Add in the efficiency loses and figure about 2 1/2 HP for 100 amps out. For real world applications and continous use double that as everything gets more and more inefficient as things heat up. A high output generator might put out 200 amps at 14 volts. or 2.8KW . Take 5 of them and you have 14KW. Add in the 100% factor for losses and inefficienty and you've got to put out 28KW. That equals about 40HP.

Answer 2

I have set up a 100amp alternator and found that a 3 1/2 hp struggled. I have now fitted it to a 5.5 hp honda . It is bisect coupled and spins at aprox 3000 rpm.

Answer 3

If you have a bunch of accessories turned on (A/C, Sound, lights and so forth) it takes MORE H/P to turn it, as the alternator is doing two jobs at once. Powering all those accessories AND trying to recharge the battery.

Answer 4

Depends on the load.

Answer 5

ya your right it is about 4to6 hp.