When to Change Alternators in Cars

Iskandar Blogger 11:30 PM

The heart of the charging system in your car is the alternator. After the engine starts, the alternator works to replace the power supplied by the battery during cranking, as well as to provide all of the power requirements for the car's electrical system. Diagnosing a faulty alternator accurately is accomplished by a process of testing and eliminating possible causes of a failure in the charging system. This troubleshooting procedure is well within the average home mechanic's skill level and will take just a few minutes to accomplish.

Instructions

    1

    Visually inspect the battery terminals and external wiring on the alternator. Clean the terminal ends with baking soda and water to remove corrosion, and tighten the terminal ends securely. Repair the wiring and connections on the back of the alternator, if they appear damaged, loose or corroded.

    2

    Test the battery with the engine off. Touch the positive and negative leads of a digital volt/ohm meter set to read the D/C volts to the positive and negative battery terminals. Charge the battery before continuing the test if it gives a reading below 12.5 volts. Low battery voltage in most computer-controlled cars will prevent the engine from spinning fast enough to start, and may cause the computer to shut down, as well.

    3

    Test the power wire to the back of the alternator, using the circuit tester. Attach the tester cables to the battery terminals and touch the probe end of the tester to the large power terminal on the back of the alternator. Repair the fuseable link, or replace the main fuse if power is not found at the power terminal of the alternator.

    4

    Start the engine and check voltage at the battery again, using the digital volt/ohm meter. With the engine running, voltage at the battery should be above 13.5 volts, but not more than 15 volts. Replace the alternator if the voltage is below 13.5 volts or above 15 volts.

    5

    Turn on the headlights, heater and radio to load the electrical system. Voltage should not drop below 13 volts at the battery with an electrical load. Replace the alternator if voltage drops below 13 volts while under a load.