Thread: Alternators

Fairly simple calculation. 746W = 1 hp

But you have to make a few assumptions. First one is overall efficiency. At a guess I would think about 50% (automotive alternators are not designed for efficiency, and run quite hot at maximum output, despite having good cooling), although it is probably more like a fixed load equivalent to perhaps 50W from the load of the fan, belt losses and bearing losses plus a percentage efficiency with losses from the field current and resistive loss.

So for zero current, 50W is equivalent to about 0.07hp

With a current of 50A at 14V = 700W, factored for 50% efficiency = 1400W plus 50W = 1450W or close to 2hp.

John

Originally Posted by Zute

Just wondering how much horse power an alternator would use, ie on a small car no current draw to full charging.
Formula Vee's don't run an alternator because they had generators. But you can run with out any charging system. Ie a gutted gen. With the power just coming from the battery, which you than charge between races.
But me being a lazy bugger, I think a alternator that could be switch off during the race would work just as well.

The old Kent powered Formula Fords run a total loss system to save HP.
We just used to recharge the battery between races.

An old mechanic/engineer I knew ran his Group Nc Cortina alternator through a switch to save HP and reckoned it worked.

Just hook the regulator input to the brake light. Then the only time you get charge is during braking. Sorta like a cheap regenerative braking system.