Alternator Output Curves

Alternator output is dependent on a number of factors:  battery condition and capacity, wire size, engine horsepower and engine RPM, battery temperature and alternator temperature.  Of these factors, alternator speed and temperature are the most important.

The following chart describes alternator output based on two temperature levels (ambient (26oC) and hot (90oC)).  Engine-to-alternator drive ratios vary by engine, but a conversion factor of 2 is shown here for simplicity.