What is the alternator/what does it do?

The alternator is a small unit that resembles a stubby electric motor. It consists of an aluminium casing with a central shaft, supported by two bearings one at the front and one at the rear of the housing, a magnetic rotor, wire windings, a pulley wheel, a fan blade, a set of diodes, housed in the rectifier, this controls the electrical output, and a set of brushes.

It is attached to and driven by the engine and a rubber belt via pulley wheels. As the central core rotates within the wire windings an electromagnetic charge is created and is transferred via the brushes and the diodes in the rectifier which manages the power supply to the battery and electrical systems in the vehicle. The fan blade positioned just behind the pulley wheel sucks air into the unit to cool it. The belt can be seen, depending on the type of vehicle in the array of belts and pulleys driving the engine's timing belt, cooling system pump, sometimes, the engine cooling fan, normally this is electric and not belt driven, and the alternator. The alternator has two pivotal fixings and a sliding belt tensioning fixing.

The function of the alternator is to generate the electrical power required to run the engine and all the vehicle's electrical equipment. When the engine is running the alternator also keeps the battery fully charged.

What if something goes wrong with the alternator?

On average an alternator has a normal life of approximately 10 years. The unit can suffer damage from running the vehicle with a faulty battery, loose electrical connections or a loose belt, which causes slipping on the pulleys. After long service the alternator parts wear out, the bearings, the central core, the rotor or the brushes. The failure of the alternator is usually a gradual process slowly generating less and less power over a period of time. Signs that there is a problem with the unit can include dim headlights and problems with low power from the battery which can cause problems with starting the engine, as the battery is supplying power that the alternator is failing to supply in sufficient amounts and is not fully charging the battery. The alternator is usually a sealed unit and is not serviceable and when required needs a replacement unit.