An alternator is a generator of electric power device in your car and is a major component of your vehicle's charging system. Whenever your engine is running, the alternator charges your battery and supplies additional electric power for the vehicle's electrical systems. An alternator is attached to the engine and is driven by a drive belt (also known as a serpentine belt).
An alternator is a maintenance-free unit. Averagely, an alternator can last for 8-12 years without any repairs. If an alternator fails, the car may still run on battery power alone for a short time, but will die as soon as the battery charge is depleted.

Symptoms

The most frequent symptom of a problem with your vehicle's charging system is a battery-shaped warning light or the "CHARGE" icon that comes on while driving. Normally this warning light should come on when you turn the ignition, but should disappears as soon as the engine is started. If it stays on, there is a problem with your charging system. The charging system warning light doesn't point directly to a failed alternator, although alternator problems are very common. You mechanic will need to do further testing to pinpoint the defective part.
Sometimes when the alternator becomes weak, you may notice that your car's headlights and dash lights become dim at idle.

Testing Of Alternator

Your mechanic can test the state of your charging system with the battery and charging system tester. The test can show if the charging system is weak or not working at all. It also can detect if one of the diodes inside the alternator has failed. If the charging system failed the test, your mechanic will need to do further diagnostic to see if it's the alternator or something else causing the problem. Other charging system problems include a loose drive belt, faulty wiring or blown fuse, defective ignition switch, etc.

If no charging system tester is available, your mechanic can do a simple voltage test with multi-meter. The test involves checking the battery voltage with the engine off and with the engine running. The battery voltage should increase at 14.5vdc once the engine is started, as the alternator supplies additional power. If the battery voltage does not increase from 12vdc once the engine is started, there is a problem with the charging system.

How to make your alternator to last longer

Often an alternator can fail prematurely when a protective engine undercover or shield is damaged or missing. This is happens because sand and water from the road can get inside the alternator and cause it to wear faster. If your engine under shield is damaged, have it replaced to keep the engine compartment clean and dry. A coolant or oil leak can also damage the alternator. Similarly, if you have to shampoo the engine compartment, the alternator must be protected from water and detergent.

The Principle operation of Alternator and the common Problem

A typical AC car alternator has two wingdings: A stater (stationary outside winding) and a rotor (rotating inner winding). A voltage supplied through the voltage regulator to the rotor winding energizes the rotor and turns it into a magnet. The rotor is rotated by the engine via a drive belt. The magnetic field produced by the rotating rotor induces AC electric current in the stationary stater winding. Diodes are used to convert AC current into DC current used in the vehicle's electric system. The output voltage is controlled by the voltage regulator. Typically, a voltage regulator is built-in into the alternator.

The most common alternator problems include; Worn carbon brushes has two legs, worn contact rings has two copper cylinders at the back of the rotor and a failed voltage regulator. Bad outer and inner alternator bearings large and small silver cylinders can produce a whining noise. When the alternator is rebuilt, the bearings, voltage regulator, brushes and some other parts are typically replaced with new ones.