Abstract: An engine-driven alternator assembly includes an output winding having an internal impedance characteristic similar to a separate stationary ballast for high intensity discharge lamps. The output winding is direct connected to lamps in a mobile light tower application having four HID lamps. The alternator assembly includes four separate alternator units each having an output winding wound to establish the inherent internal impedance to provide a ballast source for the connected lamp. Each alternator unit has its rotor mounted on a common shaft connected to the shaft of the engine. Each alternator unit establishes an open circuit voltage to strike an arc across the HID lamp and then a sustaining voltage to maintain current flow as well as limiting the current to the lamp. The alternator unit has a high frequency output, preferably within 200 to 600 hertz. The alternator unit is a permanent magnet alternator, a switched reluctance alternator, an induction alternator, or a wound synchronous alternator.