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 switch position;
• identifying a high voltage mode condition based on at least one of an engine RPM of an engine and a temperature, wherein identification of the high voltage mode condition includes identifying that the engine RPM exceeds a threshold RPM for a predetermined time and a charge level of the low voltage storage device is at least a threshold charge level, and then:
• changing the switch 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.

A charging system for a vehicle, the system comprising:

• an alternator configured to generate electric power from a rotation output of an engine, wherein the alternator is 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;
• 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;
• a controller configured to control operation of the alternator and the switch between at least a low voltage mode and a high voltage mode based on at least one of an engine RPM of the engine and a temperature, wherein in the low voltage mode the alternator outputs the low charge voltage and the switch is in the first switch position and in the high voltage mode the alternator outputs the high charge voltage and the switch is in the second switch position;
• and
• wherein the controller is configured to operate the alternator and the switch in the low voltage mode when the engine RPM is less than a threshold RPM for a predetermined time and to operate the alternator and the switch in the high voltage mode when the engine RPM exceeds the threshold RPM for the predetermined time.