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Starting and Charging SystemStarting and Charging System Components > Alternator 

Function: Provides power to the vehicle's electrical systems and charges the battery while the engine is running.


Signs of Wear: Engine doesn't turn over, loss of battery power, some loss of electrical power (dimming headlights, etc.), alternator warning light illuminates.















The alternator provides electrical power to the vehicle when it is running. The main components of the alternator are the voltage regulator, diode bridge rectifier, stator, rotor, and the case. 

The rotor is made up of two pole pieces with interlacing fingers and a core of field windings. When current flows through the windings, the rotor becomes a rotating electromagnet that induces voltage into the stator winding as it rotates. The strength of the rotor's magnetic field depends on the amount of current flowing through windings. This current is controlled by the voltage regulator. If the vehicle demands a higher voltage, more current is allowed through the rotor windings by the voltage regulator. Current flow through the rotating rotor is made possible by a set of slip rings and brushes. The stator consists of three wire windings surrounded by a stator frame. When voltage is induced into the stator, it needs to be converted from AC voltage to DC voltage in order to be useful to the vehicle. The rectifier converts the AC voltage to DC voltage by means of a special arrangement of diodes, which allow current flow in only one direction. After the current has been converted, it flows from the alternator to charge the battery and to power the electrical components of the vehicle. The alternator usually produces a slightly higher voltage than normal battery voltage.

When a diode or multiple diodes fail, the rectifier is unable to convert AC voltage to DC voltage completely. This results in a lower DC output voltage from the alternator that may be insufficient to charge the battery. Low voltage can cause electrical devices on the car to malfunction and may cause the vehicle to become inoperable.

When the alternator is not providing sufficient voltage to the electrical system of the car, the battery light usually illuminates. If this light is illuminated, the car should be serviced immediately. 

The alternator turns mechanical power from the engine into electrical power for the car's components.

A failed diode in the alternator can cause lowered alternator voltage. 

Starting & Charging System: Replace Alternator  

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