A dual voltage supply system supplies high and low voltage electrical power to separate high and low voltage loads. The system includes an AC alternator and first and second rectifier circuits, each connected to the alternator and a corresponding high and low voltage load. The first rectifier circuit commutates the alternator voltage to the high voltage load when the alternator voltage is higher than a voltage of the high voltage load. The second rectifier circuit commutates the alternator voltage to the low voltage load when the alternator voltage is higher than a voltage of the low voltage load and less than some maximum voltage which is less than the maximum voltage that can be tolerated by the low voltage load(s). The second rectifier circuit is turned off whenever the first rectifier circuit is turned on.