Reading Alternator Output graph

From a 1972 dodge van manual; there are 4 alternators listed. 26A, 35A, 45A, and 51A. This is how the part's stores would know what alternator you have. The higher amperage alternators have a double belt pulley. The ratings are based on 1250 ENGINE RPM @ 115 volts.

I replaced the alternator on my late 1980's truck. The specs that came with the rebuilt Nippo alternator stated the maximum output current is 90 amps and the 'idle speed RPM output' is 28 amps.

Problems occur when a larger amperage alternator is swapped into a car designed for a smaller amperage system. Chrysler charging systems worked well for many years, then corrosion came along. And tinkering.