Having to use higher output alternators to run the new electronic doodads on our cars makes me wonder how much engine hp is used.
I thought this was an interesting question. A little digging, and I was shocked to learn that most automotive alternators are lucky if they are 50% efficient. I found a site with some good info on the topic:
Alternator Efficiency If you use a 100 amp alternator:
Watts = Volts x Amps. If we assume the alternator when charging puts out 14 volts, then 100 amps times 14 volts is 1,400 watts. Double that to 2,800 watts of power needed from the engine to make 100 amps (because the alternator is only 50% efficient).
1 horsepower equals 745.7 watts. If 2,800 watts from engine is needed to make 100 amps, divided by 745.7 watts per horsepower gives you 3.75 horsepower.
I think I got my math right...
