Alternator

An alternator is a machine that converts mechanical energy into electrical energy in the form of alternating current (AC). In most applications, the AC is rectified to direct current (DC) to charge batteries and power DC electrical systems.

A typical automotive alternator consists of a rotor (field winding) that is driven by the engine via a belt, a stator with three-phase windings, a rectifier bridge of diodes, and a voltage regulator. The rotor field is excited with a small current, creating a changing magnetic flux that induces AC in the stator. The diodes convert this to DC, which is regulated to a target voltage.

The regulator monitors output voltage and adjusts the field current to keep the system stable as engine speed, load, and battery state change. Most car alternators use brush contacts to feed current to the rotor, and are designed to dissipate heat with a built-in or external cooling system.

In larger power systems, synchronous alternators supply AC directly to the grid and are controlled by governors and automatic voltage regulators to manage voltage and reactive power. Industrial and marine alternators vary widely in size and design but share the same basic principle.

The term alternator originated in early AC generators; in automobiles, alternators began to replace DC generators in the mid-20th century because they are lighter and more efficient at varying engine speeds.