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What Are the Most Common Alternator Problems?

The alternator supplies a car's electrical system with power.
The alternator charges the car battery.
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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 03 July 2014
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Alternators are devices that charge the battery of an automobile and supply its electrical systems with power when the engine is running. Most common alternator problems may be divided into two basic categories: electrical and mechanical. Mechanical faults include collapsed or seized rotor bearings, broken housings or mountings, and faulty pulleys. Electrical problems include faulty rectifiers or regulators, worn brushes and slip rings, and damaged windings. Potential alternator failure is often indicated by intermittent illumination of the charge lamp on the instrument cluster, occasional dead batteries, or unusual noises and odors.

Automobile electrical systems are powered by a battery when the engine is not running and an alternator when it is. The battery is also charged by the alternator during running cycles, thereby making it one of the most important parts in any vehicle. Although modern alternators are generally robust and reliable, they may experience occasional failures. Mechanical breakdowns and the failure of electrical components generally first manifest themselves in the illumination of the charge light while driving and eventually in dead or partially charged batteries.

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Mechanical problems in the alternator typically involve the physical driving of the part rotor by the engine. The most common of these problems are rotor bearing failures. These typically result from over- or under-tensioned fan belts or simple wear and tear, and generally cause overheating of the rotor and eventual bearing collapse. Worn rotor bearings almost always start to become noisy before they fail completely and produce unusual grinding sounds from the alternator area of the engine. If this occurs, the bearings should be replaced as soon as possible.

Broken casings and mounting studs are other common mechanical issues. Alternator casings are generally light alloy parts, and the mounting points are particularly susceptible to breakages. If these parts break or crack, the alternator may move out of position slightly and no longer be driven correctly by the engine. This results in low power output and potential rotor bearing damage. This type of problem usually shows up as intermittent illumination of the charge light on the dashboard while driving. Two part pulleys can also separate and cause similar rotor drive problems, although this is very rare.

Electrical alternator problems almost always involve either the rectifier or the voltage regulator. These electronic components are responsible for producing direct current (DC) power from the alternator's alternating current (AC) output and controlling the amount of power delivered to the vehicle's electrical and battery charging systems. A breakdown of these parts will sometimes produce a characteristic burning smell from the engine compartment and eventually result in poor charge rates or total alternator failure. In these cases, the charge lamp may illuminate while driving but the first indication is usually a poorly charged battery. Other, less common, electrical problems include damaged windings, broken or worn slip rings, and brushes or loose connections that manifest themselves in the same way as rectifier and regulator problems.

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