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Alternator Check and Replacement
By Mike Bumbeck/
Printable version
Degree of DifficultyModerate
Estimated Time120 minutes
120 minutes
Taking charge of your vehicle's electrical system

The electrical system in an automobile is comprised of three parts that must all function individually for the system to operate in balance. The battery is the first part. The battery stores electricity to spin the starter and start the engine when the ignition key is turned. The alternator is next in line.
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The alternator produces electricity once the engine is running. It gets its juice for making juice from a belt-and-pulley system driven by engine power. As well as producing electricity for heated seats, turn signals, and the four in-seat DVD players, the alternator also sends extra electricity to the battery for storage. The battery can also help out during times of heavy electrical demand. The third component is the voltage regulator. The aptly named component tells the alternator how hard to work depending on electrical demand, and regulates the flow of electricity coming from the alternator and going to the battery and accessories.

If all goes well, there will be electricity in wait when the key is turned, as well as when the engine is running. If any one of these parts wears out or fails, the symbiotic relationship of the automotive electrical system goes pell-mell. A number of unwanted things can happen to you by way of an out-of-commission electrical system, from having no radio to absolutely no electrical power to get the engine going again.
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The trick to determining whether or not a new alternator is required lies in testing. When the electricity stops flowing, a common error is to assume that the battery is dead, replace it with a new one, only to have it quickly discharge because the alternator had already breathed its last breath and is no longer making electricity to charge up the battery. Conversely, one could replace a perfectly good alternator when in fact it is the battery that has lost its ability to store electricity. A finicky voltage regulator can also cause problems. The classic symptoms of a dead or dying alternator are lights getting dimmer and sluggish electrical accessories while driving around after dark.
This situation occurs because the alternator is no longer making enough electricity to run the show and the vehicle is drawing power off the slowly dying battery. If driven around long enough, the vehicle will use up all the battery's electricity and everything will come to a halt. Since getting stranded at night is not the world's best motoring experience, it pays off in the long run to maintain and check batteries, belts, voltage regulators, and alternators.
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