Alternator

An engine-driven electrical generator that provides alternating current (converted to direct current) to power the aircraft electrical system and charge the battery during flight. The alternator is driven by a belt connected to the engine and produces electrical power proportional to engine RPM. If the alternator fails, the battery alone must supply all electrical loads, and its capacity is limited to roughly 30 minutes depending on the electrical load. An alternator failure is indicated by a discharge on the ammeter or illumination of a low-voltage warning light, and the pilot should reduce electrical load and plan to land as soon as practical.