Easy to follow step by step guide on how an automotive alternator works, this information pertains to most vehicles.

An alternator is designed to supply electrical power (13.6 to 14.6 volts) to a vehicle when the engine is operating while charging the battery for future use.

Typical Automotive Alternator (Appearances Vary)

A serpentine belt is used to deliver rotation from the engine via the main drive pulley.

Serpentine Belt

A large power terminal is used as the main voltage feed to the electrical system which is usually connected to the positive battery post or power distribution center (PDC), most alternators are designed with a built in voltage regulator which helps stabilize the voltage output.

Main Power Output

This main power feed is used to power circuits throughout the vehicle.

Power Distribution Center

A wiring harness connector is used by the computer PCM to control and monitor the alternator and voltage regulator during variable engine speeds (RPM's) and voltage demands.

Computer Connector

The alternator works on the principle of electromagnetism, by turning the magnetic armature inside a wire field which has been electrified to produce AC (alternating current) voltage. A series of diodes (6) convert AC to DC voltage which is needed for the electrical system. An armature is supported by two roller bearings on either end of the alternator housing, voltage is transferred to terminals at the rear of the housing via a spring loaded brush set.

Alternator Expanded View

Helpful Information

A common alternator problem is undercharging, this condition is often accompanied by symptoms such as a battery warning light, low state of battery charge, poor or erratic performance from electrical components.

Common Problems

  • Alternator will overheat due to extreme usage causing a failure.
  • Poor battery condition can cause alternator failure.
  • Weak alternator can cause the battery to slowly drain.
Best Practices

  • Once jump started a severely discharged battery can cause the alternator to overload and fail internally, if this occurs replace or charge the battery before replacing the alternator.
  • A serpentine belt must be in good condition
  • Clean battery terminals regularly


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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