The Typical Alternator Voltage

Automotive voltages can be read with a multimeter.

An automotive alternator is an electrical generator that creates energy to run the vehicle and charge the battery. A vehicle's alternator that does not put out enough voltage to complete both of these tasks requires repair or replacement.

Output Voltage

Alternator output will vary, but the alternator output should range between 13.8 and 15 volts. To determine output, connect the positive and negative leads of a multimeter to the positive and negative terminals of the car battery. Measure alternator output with the engine idling and all electronic accessories (headlights, radio, etc.) turned off.

Alternator Failure Signs

A low alternator output may a sign of a failing alternator. The alternator pulley spins on an internal bearing. These bearings and other internal components may begin to fail and reduce the alternator output. To test, remove the belt and turn the pulley by hand. The pulley should turn smoothly. Uneven resistance or roughness when turning the alternator's pulley is an indication of wear that will likely require alternator replacement.

Other Causes

Alternator output may also be reduced due to belt and wiring problems. Inspect belts for proper tension and signs of wear or damage. Belts that show cracks or uneven wear will need to be replaced. Inspect wiring to the alternator and battery for damage, corrosion, or loose connections.

References

• AA1Car: Alternator & Charging System Checks
• 2CARPROS: How to Check a Car Alternator