Alternator

The alternator is a vital component of a vehicle's charging system. While the engine is running, the alternator generates electricity to power the vehicle's electrical components—such as the lights, radio, and climate control—and to continuously recharge the starter battery. It is driven by the engine's serpentine belt or accessory belt.

Inside the alternator, an electromagnet (rotor) spins inside a set of stationary copper coils (stator), creating alternating current (AC). Because automotive systems run on direct current (DC), a built-in rectifier converts the AC to DC. A voltage regulator monitors the battery's state of charge and adjusts the alternator's output, typically maintaining a steady voltage of 13.5 to 14.5 volts.

When an alternator fails, the vehicle relies entirely on battery power, which quickly drains. Common signs of alternator failure include dimming or flickering headlights, a dead battery, a dashboard warning light (often shaped like a battery or labeled ALT/GEN), slow power windows, and whining or growling noises caused by worn internal bearings.

If you experience starting or electrical issues, a mechanic can perform a charging system test to determine whether the problem lies with the battery, the alternator, or the starter motor. Replacing a failing alternator prevents unexpected breakdowns and electrical damage.