Re: OT? how much horsepower to produce 60kw


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Posted by David Sherman on Thursday, November 18, 2004 at 10:13PM :

In Reply to: OT? how much horsepower to produce 60kw posted by mike a on Thursday, November 18, 2004 at 3:59PM :

The theoretical conversion is 746 watts equals 1 hp, but since electrical motors and generators are generally about 75%-80% efficient, 1 hp per kW is a pretty good rule-of-thumb conversion factor for electric motors. Going in the other direction, it gives you roughly half a kW per hp out of a generator (or .746 * 0.80 = .6kW if you're an optimist). When you figure that the flywheel HP of the engine may not be what's on the engine's spec sheets if they didn't include the power required to drive the engine accessories, or the engine is getting tired, and you figure that the generator has windage losses (due to its own fan and the rotor spinning in air) of its own, I'd go with the .5 kW per hp (2 hp per kW) figure.

With a generator that big, remember that it's hard on engines to run at high RPM and light load for a long time. If your load will make the engine work pretty hard most of the time, you'll be okay, but if not, better to use a smaller generator and smaller engine. The military did an experiment with some medium-sized diesel gensets that ran continuously on some island somewhere and found that putting load banks on the generators significantly increased the engine lifetime between overhauls. Of course it also increased the fuel consumption, but they concluded that overall keeping at least 50% load on the gensets saved more money in maintenance than it cost in increased fuel consumption. I'm not quite clear on what all the problems are with running a diesel at high speed and light load, but as I recall one of them was a buildup of carbon in the combustion chambers.



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