What an Alternator does
One scenario of an alternator going bad; you are driving along when the radio starts to cut out. Just a few minutes later, you notice the dash lights dimming. Soon after, the warm air coming from the heater is replaced by cold outdoor air. If you have not made it home before this happens, trouble is afoot. Next, the heater, lights, and radio stop all together and you are forced to coast off to the side of the road. At a time like this, many may think the battery is the culprit, but it is the alternator. Although the battery and the alternator are related, they do have separate functions.
The charging system of a car is made up of the alternator, the battery and the voltage regulator. It is the alternator which channels the energy into the battery to run the interior and exterior lights, the radio, the heater, and other power using equipment. There are two types of regulators; a grounded regulator controls the amount of negative ground. Then there is the grounded field type which controls the amount of battery positive. Alternators are found near the front of the engine and are driven via the crankshaft.
Alternators are very lightweight, relatively small (about the size of a coconut) and are found in most passenger cars and lightweight trucks. The outer core is usually made of aluminum to dissipate the heat it generates, and also because aluminum does not magnetize. The vents on either side of an alternator also help dissipate the heat. Older models of alternators have the exterior fan blades, where the new ones have cooling fans built in. Inside the alternator is the voltage regulator. The regulator distributes the power to the battery. You would also see, inside, a diode rectifier, slip rings, and brushes.
There are finger poles fixed at a staggered angle around the alternator. These poles alternately north and south poles. This alternating pattern creates the magnetism that induces voltage into what is called the strator. The diodes convert AC power to DC power. All of these things work together to create and distribute the power needed to send to the battery to run the electrical equipment in our cars. Normally, all of these parts work in perfect harmony to keep our battery happy and our car running. However, sometimes the unthinkable happens.
Because there are so many moving parts in an alternator, it is common for them to become dirty and they also suffer stress from extreme heat and cold. The most common failure is with the bearings. Needle bearings enable the spinning of the rotor. Dirt and heat are normally the cause for the bearings to fail.
One quick and easy way to tell if the alternator is malfunctioning is to check and make sure your battery light glows when you start the car. If it does not, chances are the alternator is not working. You may get the car started because the battery will be holding enough juice, but it will die, probably in route to where you are headed.