Here is a question hopefully Jon or some of you other engrs can answer. Does an alternator require more shaft work when there is a higher electrical load? Like a loud stereo or headlights?? My thinking tells me yes. To me its common sense but maybe I'm missing something. Its been a while since I was in circuits 101... - I'm in a heated debate on my race forum here in Tx and I was wondering if I could get some insight. Plus the extra knowledge would be great-

If by shaft work you mean it takes more power to turn at higher electrical loads, than yes, it does require more. This is basic physics. You're taking mechanical energy and converting it to electrical energy. The conversion is not and can never be 100% efficent. MOre load on the alternator means more energy is being produced, which means more load on the engine.

That said, to produce 250W, you will need .26 (yes, that's about 1/4HP) at 100% efficency. At 80% efficency (which is actually kind of low for a decent alternator) that goes up to about .32 (~1/3HP).

To go furthur, 1 HP is about 746W. Then use 80% as a conservative efficency.

Thank you... I appreciate the feedback-