The purpose of an alternator is to keep a vehicle’s battery at full charge while the engine is running. This vehicle may be a car, a farm tractor, a semi-truck or any other piece of equipment which needs a constant charging source. The alternator is belt driven and converts alternating current to direct current. Most often, the reason an alternator stops producing a current is worn out components, such as bearings, brushes and the slip ring. There are cases where the regulator stops regulating the charge going to the battery or the rectifier stops converting AC to DC. The less common component failures are the rotor and stator. If the alternator is forced to constantly be charging at a high rate due to a weak battery or high resistance in the power circuit, it gets very hot and the stator and rotor can burn. A cutaway look at what is inside an alternator is below.