Some common causes of alternator problems include wear and tear, a bad battery, a lost ground and a slipping belt. Indicators that warn of an impending alternator problem can include the dashboard warning lights, a growling or whining noise from the engine compartment, and the smell of burning rubber or electrical wires.
An alternator is a fairly simple piece of equipment with just a few parts that can fail. The plates that generate the electricity, the bearings that allow the pulley shaft to rotate and the pulley itself can all wear out over time. The alternator is turning at up to three times the speed of the crankshaft that drives it in order to maintain a stable electrical current output a lower speeds. So it is making many more rotations than the mileage on the car.
A weak or failing battery can put additional stress on the alternator to keep it charged. This turns the battery into a load instead of an energy bank and causes the alternator to increase output which can make it fail prematurely.
Manufacturers typically ground alternators to the frames of automobiles. If a loose bolt breaks the connection, the alternator's voltage regulator can overcharge the battery and destroy the entire electrical system.
Damage or wear to the belt that drives the alternator can cause it to slip and not turn fast enough. This can make the alternator undercharge the battery and damage both of them.