I ran a test and thought I would pass it along to help troubleshoot charging problems. This was on a 55 amp alternator with a external solid state regulator.

RPM Bat V Field term V With head lights on Bat Field

idle 14 9.5 13.4 11.4

fast idle 14 5 14 7

cruise 14 3.5 14 5.4


This shows that at idle with the lights on, the regulator is putting the highest voltage into the field winding but still can't reach the regulator setting of 14 volts. At the high speed test with no lights, it only takes 3.5 volts to maintain the battery at 14 volts. The current thru the field winding is typically 3 amps max at 12 volts. This goes thru the slip rings to the rotor.