When I sent my nine-year old car for servicing, the workshop mechanic mentioned that the alternator may need to be replaced. How does he know this?

In all likelihood, your mechanic's suggestion was based on his knowledge of your car and its age.

There is no way of assessing the condition of a car's alternator just by looking at the unit or listening to the engine.

The alternator is a belt-driven "electricity generator" that charges up the vehicle's 12-volt battery when the engine is running.

Among the parts which make up the alternator is a "voltage-regulator" that maintains the charging voltage supplied to the car's battery regardless of engine speed.

When the battery does not receive the charge, a warning light on the car's instrument cluster, usually a red symbol of a battery with the "+" and "-" signs, will light up.

Because the alternator is belt driven, a slipping or broken drive-belt will obviously affect its performance.

Not long ago, specialist mechanics could rebuild an alternator. But these days, because of high manpower cost and shortage of skilled mechanics, the quickest fix is to replace a faulty alternator.

Most workshops can quite easily check if an alternator is in good condition by checking the voltage when the engine is idling and with lights and air-conditioner turned on.

The battery voltage under such conditions should always read between 14.1V and 14.6V. A significantly lower reading means the alternator is nearing its end of life and must be replaced.

It is common for alternators to start showing wear from the sixth year.

Shreejit Changaroth