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Alternator voltage drop test

Alternator voltage drop test — How to

What does an alternator voltage drop test prove?

An alternator voltage drop test is done to prove the connections between the alternator B+ out and the positive battery terminal and the alterantor’s case grounding to the battery – terminal

You’ll need a multimeter set to DC volts to perform an alternator voltage drop test

Step 1: Test for voltage drop on the positive side of the alternator circuit

Touch one lead to the B+ terminal on the back of the alternator and the other lead to the + battery terminal. Record the value. Then move the battery probe to the positive battery post and record the value.

The voltage drop should not exceed 0.25-volts. If the result is higher than 0.25 when you touch the probe to the battery terminal but lower when you touch the probe to the battery + post, the terminal/post have corrosion and high resistance. Clean both and repeat the test. If the result is still high, check for corrosion between the cable and the terminal.

Step 2: Test for voltage drop on the ground side of the alternator circuit

Touch one lead to the alternator case and the other lead to the – battery terminal. Record the value. Then move the battery probe to the positive battery post and record the value.

The voltage drop should not exceed 0.25-volts. If the result is higher than 0.25 when you touch the probe to the battery terminal but lower when you touch the probe to the battery – post, the terminal/post have corrosion and high resistance. Clean both and repeat the test. If the result is still high, check for corrosion between the cable and the terminal.alternator voltage drop test

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Posted on by Rick Muscoplat



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