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 (60oC)). Test voltages are set at 13.5V (for 12V units). Engine-to-alternator drive ratios vary by engine, but a conversion factor of 2 is shown here for simplicity.