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Ever since alternators became commonplace in cars in the late 1960s, engineers have been refining the basic design in subtle but significant ways. The result is that the latest alternators are more efficient and more compact, yet more powerful, more reliable and quieter-running than ever before.
They will provide power for the vehicle's electrical accessories and keep the battery charged for many years, often lasting as long as the engines on which they were originally fitted. But that doesn't mean they are immune to neglect or abuse. By following some simple maintenance guidelines and safety precautions, we can ensure an alternator's life will be long and trouble-free.
The alternator's biggest natural enemies are excessive heat and dirt. Heat is generated in the diode pack of the built-in rectifier and to a lesser extent also in the electronic components of the voltage regulator.
If it isn't dissipated effectively, these components will soon expire. For this reason, the diodes are mounted on a "heat sink", usually a piece of aluminium, a good conductor of heat with a large surface area from which the heat can be removed by radiation and airflow.
The rectifier and the voltage regulator are usually found at the rear of the alternator - the opposite end from the drive pulley - and it is, therefore, important to keep that surface free of any build-up of grime, which will impair the cooling function of the heat sinks.
In addition to heat sinks, a fan is provided to draw cool air through the innards of the alternator. On older designs, the fan was directly behind the drive pulley. On the newer, more compact models, you often find two fans mounted on the rotor shaft inside the casing. The cooling slots in the casing through which the air circulates should never be obstructed in any way.
n some modern engines the alternator is tucked away down the side of the engine under a maze of tubing and wiring and it's not easy to even see it, let alone wipe it clean. But still, it's a good idea to peer in there occasionally to check for any obvious danger signs.
We cannot do much about dirt getting into the alternator if the vehicle is used on gravel roads, except to be aware that inside the unit there are two spring-loaded carbon rods or "brushes" riding on the outside of rotating copper strips or "slip rings."
Dirt on these strips will make them and carbon rods wear faster and can also cause the rods to stick in their guides and lose contact with the strips. If this happens, the alternator warning light on the dashboard will tell you that your alternator has stopped working.
Something we can do a lot about is the element of human error when working on parts of the vehicle's electrical system that might affect the alternator. Human error is probably by far the biggest cause of premature deaths of alternators. First and foremost, it is important that the wiring connections at the back of the alternator are clean and tight. The wires themselves should be undamaged, the end-fittings secure and free of corrosion.
The same goes for the heavy wires from both battery terminals and the wire connecting engine and body. The attachment points on all these wires should be solid and clean.
The reason for the insistence on tight connections is that these wires carry heavy currents and an intermittent make-and-break connection on one of them can cause voltage spikes, which are bad news for the electronics in the alternator.
By the same token, it is folly to disconnect the battery, or the alternator, while the engine is running. Without the moderating influence of the battery, there will be spikes to make your hair stand on end.