Variable voltage charging system and method for a vehicle

A method of controlling a variable voltage charging system on a vehicle, the variable voltage charging system comprising an alternator configured to alternately output at least a low charge voltage to charge a low voltage storage device and a high charge voltage to charge a high voltage storage device and a switch configured to switch between at least a first switch position connecting the alternator to the low voltage storage device and a second switch position connecting the alternator to the high voltage storage device, the method comprising:

• operating the alternator and the switch in a low voltage mode to charge the low voltage storage device, wherein the alternator outputs the low charge voltage and the switch is in the first position;
• identifying a high voltage mode condition based on an alternator temperature and then:
• changing the switch position from the first switch position to the second switch position;
• changing a regulation setpoint of the alternator from a low voltage setpoint to a high voltage setpoint;
• and
• operating the alternator and the switch in a high voltage mode wherein the alternator outputs the high charge voltage to charge the high voltage storage device.