Car Alternator Guide

How Car Alternators Work

A car alternator supplies power to keep the battery charged and run all the electric accessories. Problem in the charging system while you're driving, the alternator light will begin to glow.

The alternator's output capacity is directly proportional to the RPM of the engine and alternator temperature.

Charging systems are normally sized by the car manufacturers to provide at least 125% [when operating at high RPM] of the worst-case OEM electrical load, so that the car battery can be recharged.

Short trips at night or in cold weather might not keep the battery fully recharged, especially when the electrical load is increased with high power audio equipment or full beam lights.

Vehicle charging systems are not designed to recharge fully discharged batteries and doing so may damage the stator or diodes from overheating.

Charging System Components

High-output is demanded of alternators in modern vehicles to heat seats, drive high-amp stereos and HID headlights etc. 100+ amp alternators are becoming more and more common.

Other components of the charging system include:

• The alternator belt
• Voltage regulator (where required)
• Battery cables and associated wiring

Voltage Regulator

Some times, apparent problems with the alternator, are actually the voltage generator. If the voltage generator is not working correctly, too much power or insufficient power may be sent to an electrical component, causing poor function, trigger the fuse or burn out the component.

The voltage regulator is cohoused inside the car computer or in some models, the alternator.

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