by Arne » Fri Mar 19, 2010 4:33 pm
Since I fly model airplanes, I will offer up some information. First, they are air cooled, with an airspeed of any where between 20 and 70 mph to keep them from freezing up... Second, they are lightly built and really don't get a lot of hours of wear on them before they are tossed.
One big enough would cost you more than a briggs and stratton 'real' engine. The fuel is about $10.00/gallon on sale.
Weedy engines operate at high speeds to get hp/torque, around 8.000 rpm. and usually more. At 3,000 rpm you won't get much bang for the buck. They are 2 stroke, mostly, though the new ones are 4 stroke. They are small and don't have much power.....
I can't think of any reason to try any of the above except as a fun toy.
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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.