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Farmall & IHC Tractors Discussion Board |
Re: Re: Re: Re: Re: Re: Farmall H Electrical System
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Posted by Andy Martin on September 26, 2000 at 20:32:05 from (38.31.74.106):
In Reply to: Re: Re: Re: Re: Re: Farmall H Electrical System posted by ltf in nc on September 26, 2000 at 19:31:03:
Yeah but, amperage and wattage of a motor are also based on the horsepower being consumed. I have to believe that the 12v setup will take more horsepower out of the starter than the 6v because the engine is turned faster. So the load does change, the requirements on the starter change. If you put fewer teeth on the bendix for the 12v case to turn the engine at the same speed as the 6v, then the amperage should be roughly half. If the torque required to keep the engine turning at cranking speed is independent of cranking speed, and the 12v supply turns the starter under load at twice the speed of a 6v source, then the wattage or horsepower would double for the 12v case: double the hp and double the voltage so the amperage remains the same. I can't see that the torque required to spin the engine twice as fast would be only half the torque required for the slower speed. As I said before, the bearing drag probably is relatively independent of speed, but the engine compression components (valves, rings) probably work better at higher speed, so the torque may go up. I think it takes no more than 50# pull on a 9.5 inch radius crank to turn over an H fast enough to start, and that is only 40 ft-lbs. If it takes you 1/4 second to pull up 1/4 turn (a good snap), you are cranking at 1 rev/sec. So your manual cranking hp is only 40/550=.073 hp. My recollection is that a strong man can put out 1/6 hp, and .073 is roughly 1/12, so it seems reasonable. 885ft-lbs/sec would equal 1,118 lbs pull on a 9.5 inch crank at 60 rpm (1/sec), or 280 lbs if you could spin it at 4 rev/sec. A strong man indeed. But both the man and the starter can start the engine. The man, however, is not in danger of moving the tractor if it is left in gear: the starter is much more powerful. For sure we agree that 12v is not bad for a 6v starter! And please don't take offense by my discussion, I guess it's my 4 cents worth
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