Quote:
Originally Posted by tqlspec
Fitz - I'm just curious where this information came from. The alternator puts X amount of load on the engine, as it is always "on." The engine is always loaded by the alternator. This would be true on new vehicles with load controllers. Just my 2 cw.
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The alternator load on the drive belt is not a constant. It varies directly with the current draw on the alternator. The output power of the alternator in watts is the product of the output voltage and load current. My fans draw 25 amps when both run. At a constant 14V output this gives 350 watts. 746 watts is one horsepower so it takes about 0.5 hp to run my electric fans. According to Delco Remy the power conversion efficiency of my alternator is 65% which means for every 1 hp input at the pulley I get 0.65* 746 watts (484 ) out or just divide the power needed to drive a load like my fans by the decimal equivalent of the power conversion effiency of the alternator. In my case, 0.5 HP/0.65 = 0.75 HP from the engine. As you can see, the changes are small, but cannot be ignored if you're going to do an apples to apples comparison. Most drag racers prefer the electric fan and pump because the battery acts like a flywheel by smoothing out the load currents and spreading the fan and pump loads over a time period LONGER than the time required to do a 1/4 mile pass and there is no chance of damaging the engine by throwing a belt and losing circulation in the cooling system.
This information came from two sources. AC Delco provided the specs on my 105 amp alternator and the conversion factors came from my Thermodynamics text. Without bragging, I need to introduce myself. I am the Technical Director of Special Systems at Raytheon Missile Systems Company in Tucson. I have a Masters degree in Electrical Engineering from USC and I did Graduate level work at Stanford in Aerospace Engineering. So, that makes me a rocket scientist that likes to play with old trucks!