Has there ever been a dyno comparrison done of running with and without the alternator? the rotor is a heavy lump of rotating mass on an already flimsy crank at high rpm. I imagine it would eat some hp when loaded with the ignition, lighting and charging requirements.
Total loss system
- Thread starter brxpb
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Power loss(consumption) from alternator is likely a fart in a wind storm.
745 watts per horsepower so let us say an alternator at full tilt is 180 watts/745 watts or about 0.26 HP. If you know your actual power consumption then you can take that wattage and divide by 745 to get HP consumed.
745 watts per horsepower so let us say an alternator at full tilt is 180 watts/745 watts or about 0.26 HP. If you know your actual power consumption then you can take that wattage and divide by 745 to get HP consumed.
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Dances with Shrapnel said:
With a shunt regulator the alternator is always running at full load. So .26 horse times two for the 50% average efficiency of a permanent magnet alternator and you get about 1/2 horse. That is about what I have seen on the dyno. Jim
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Does crankshaft mass change power output ? I would have thought it would only alter throttle response time. Also the crankshaft mass is pretty irrelevant if you are using a close enough box which helps you stay near the revs for max torque. I have a theory that due to the heavy crank the standard 850 Commando tends to spin up at a fixed rate which is less unaffected by the gear ratio than on other bikes. To my mind it is a major advantage as long as you have the close box. With the standard box, it is horrible - especially on the down-shifts. On a road bike it probably does not matter.
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comnoz said:
So I revise my estimate from one to two farts in a wind storm.
Good stuff Jim, didn't realize PMAs had such dismal efficiencies.
These are mightily efficient alternators then :!: , I remember Ford cars asking Lucas for 100 watt output alternators but they refused, so they went to Bosch.
A 100 watt Bosch car alternator I took in for repair once the workman told me that his tester which consists of a 5 HP electrical motor would not turn it on full load :!:
A 100 watt Bosch car alternator I took in for repair once the workman told me that his tester which consists of a 5 HP electrical motor would not turn it on full load :!:
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So are we saying the modern 100 amp/1200watt alternators available for cars only use less than 2 hp? I have been amazed at the load they seem to put on the engine after start up or on a low battery. My 65 GTO that runs the 100 amp alt and power steering with the same belt ,with minimal alternator pulley contact, will squeal like crazy unless the belt is really tight. The original spec was for a 37 amp alternator. I note the same loading of the engine on an El Camino with a 100 amp alternator. So, I would like to know the calculation used. Is it 1hp for 745 watts? Reality for me does not mesh with 1 or 2 hp.
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comnoz said:
So that indicates a 27% to 32% efficiency. Add to that a belt drive or a slipping belt drive and it adds up for a car.
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