Edmunds Answers

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  • avatar karjunkie 07/13/09 5:33 pm PST

    In modern alternators, the voltage regulator and diode pack are inside the alternator and are not serviceable by most DIY's and mechanics. If any one of these parts goes bad, the whole alternator assembly needs to be replaced. Testing the alternator is simple and basic. You need to check the voltage and amperage output. The voltage is easy enough to check with a voltmeter. If the voltage is between 13.5 and 14.5 as in your case, it's a good bet the alternator is good. To check the amperage output, you'll need some special equipment. You'll need an ammeter and a load tester to check the amperage. When the alternator is load tested, a simulated load, usually ½ the Cold Cranking Amperage rating of the battery is applied to the charging system. Then the engine is run at 2200 to 2500 rpm and the amperage is read on the ammeter. The reading should be close to or at the rated amperage of the alternator. If it is, then it's good. If it's substantially lower, then it is weak and should be replaced. The variation you noted is perfectly normal.

Answers

  • karjunkie 07/13/09 5:33 pm PST

    In modern alternators, the voltage regulator and diode pack are inside the alternator and are not serviceable by most DIY's and mechanics. If any one of these parts goes bad, the whole alternator assembly needs to be replaced. Testing the alternator is simple and basic. You need to check the voltage and amperage output. The voltage is easy enough to check with a voltmeter. If the voltage is between 13.5 and 14.5 as in your case, it's a good bet the alternator is good. To check the amperage output, you'll need some special equipment. You'll need an ammeter and a load tester to check the amperage. When the alternator is load tested, a simulated load, usually ½ the Cold Cranking Amperage rating of the battery is applied to the charging system. Then the engine is run at 2200 to 2500 rpm and the amperage is read on the ammeter. The reading should be close to or at the rated amperage of the alternator. If it is, then it's good. If it's substantially lower, then it is weak and should be replaced. The variation you noted is perfectly normal.

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