Alternator

[Six_Shooter]

Alternators, while they do take power to turn, electrically speaking a considerably larger alternator (amperage wise) will not take a lot more (horse) power to run.

Lets take a 140 amp alternator.

In a perfect world, it would always charge at 14.4V, regardless of actual load, so lets use that number for the time being.

Watts = E (Volts) * A(mps)

So 14.4 * 140 = 2016 Watts

1 HP = 756 Watts (745.699872 actual)

To find HP, we take the Watts and divide by 756.

So 2016 / 756 = 2.667 HP.

Now alternators aren't 100% efficient, so lets assume worst case at 50% efficient, which means that we need to multiply the HP figure we just found by 2.

2.667 * 2 = 5.334 HP.

This would only be if you actually pulled a full 140 amps out of the alternator, which would only happen at higher RPM anyway, where most of our cars wouldn't miss the 5 or HP.

This also doesn't take into account mechanical losses, but they are usually less than the electrical load anyway.

There's also something to be said about being about to produce full power from the engine, from having a solid and stable charging system as well. I have known of many cars that pick up power by putting a larger alternator that is capable of actually supplying the needed current.