AutoZone Starting & Charging guide - Alternator

An alternator charges the vehicle's battery and powers the electrical system when the engine is running. A belt connects the alternator and crankshaft pulley. While the engine is running, this spins the alternator rotor shaft, converting mechanical energy to electrical energy in the form of alternating current. This process provides electrical power to run a vehicle's electrical components and accessories.

Charging System Design

1. Alternator & Voltage Regulator: The alternator provides power to electronic components when the vehicle is running. The voltage regulator controls the voltage output to maintain a constant voltage within the system.

2. Battery: Provides power to electronic components when the vehicle is not running.

3. Belt: Transfers rotational force generated by the engine to the alternator and other accessories via a pulley system.

Note: A faulty alternator can be the cause of a dead battery. Before replacing a battery that consistently loses its charge, bring your alternator to AutoZone. We can test your starter or alternator for free.
*Service not available in California


Oil/Fluid Soaked: An alternator will fail when its internal components are damaged by petroleum products spilled into it.

Loose Mounting: On this alternator the pulley was installed incorrectly. Notice the shaft wear. This is an indication that the problem was improper installation.

Over Heating: Heat is a major cause of failure in alternators. The alternator has vent holes that allow heat to escape and help to prevent overheating. When vent holes are plugged by 60% or more, failure is likely to occur.

Arcing: Notice a loose electrical connection has caused arcing and burning. This burning is from the high temperatures created by the electrical current jumping from a power wire to a ground. This failure happened, because the alternator was not installed properly.

Broken Mount: Broken mounting ears indicate that the mounting bolts were over-tightened or the alternator was improperly mounted when installed, which caused the housing to crack. This can result in premature failure of the alternator.

Over-tightened: Over torqueing the alternator wire to the post can damage or break the post and destroy the alternator.

Burned Alternator: If the battery does not hold a charge of 12.4 volts or more, the alternator will constantly try to recharge a depleted battery. This constant charging can cause an alternator to overheat.

Missing Pulley: The nut on the alternator pulley needs to be tightened properly. If it is not, the pulley may fall off while the vehicle is running.

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