How powerful of a motor do you need to run an alternator? Answered
From questions I have read and step by step’s I have read a question came to my mind.
How powerful of a motor do you need to run an alternator?
I checked the Delco Remy alternator series from 10SI in 37 Amps, to the 40SI durable brushless model, in 240, 275, and 300 Amps.
All their performance charts show rpm’s at the alternator not the motor.
The pulley on the crankshaft is considerably larger than the pulley on the alternator, giving you more rpm’s at the alternator than at the motor.
All their performance charts show rpm’s from 1200 to 8000 rpm’s.
All their performance charts show at 3000 rpm’s you get 13/16ths of max power.
The last 5000 rpm’s only gaining 3/16ths of power.
The thing is none of the performance charts say the horsepower to drive the alternator.
I decided to approach the problem from a different direction
Typical alternator efficiencies are in the 54%-60% range.
Brushless alternator efficiencies are in the 60% 70% range.
A typical 12v 60 Amp alternator produces 720 watts at 55% efficiency.
It needs just 1310 watts to drive it or a little under two horsepower at 1492 watts.
This does not account for mechanical efficiency of connecting the alternator to the motor.
With this in mind a three horsepower motor should drive a 12v 60 Amp alternator.
This is just an educated guess but I would like a horsepower chart.
720 watts would do well at charging a battery bank while you sleep; however I could not run my microwave and charge batteries at the same time.