Horsepower rating of generator

[503engi]

I'm in the process of purchasing a generator, but I need some clarification on the horsepower rating. The majority of brushless AC generators I have found say that they require x horsepower. Is it possible to run the motor at its rated RPM, but only has a fraction of the horsepower requirement?

My assumption is that if you have a generator rated for x horsepower, and you can drive it with a x/2 motor, you can only get half the rated power output from that generator. Is this true? Or am I completely off and the generator will not spin at all?

 

[eeprom]

I'm guessing that you are buying a generator without a prime mover. There is no rule that says the prime mover power has to be greater than the generator capacity.

The biggest issue you will have with this is speed/voltage control. If you use an underpowered motor, and you controlled the speed well, you could still get the generator to produce power at the proper voltage. But you would be limited to maybe 75% of the power rating of the prime mover.

 

[503engi]

So in a sense, if I mated a 1HP prime mover to a 2HP generator, the generator would only be capable of 1HP (~745W) assuming ideal conditions? With assumed inefficiencies, I'm probably looking at about 500W out of the generator in this case?

 

[waross]

You could still get about 1500 KVA.
You could rate the set for 33% power factor.
Generally, motor driven gen-sets from a few KW up into the MW range and above are rated for 80% PF
Some of the exceptions are prime rated vs. standby rated, deliberately over-sized prime movers to allow extende3d service between overhauls and three phase to single phase conversions.

Bill
--------------------
"Why not the best?"
Jimmy Carter