How to test an Alternator – Complete Guide (+ VIDEO)
Published : 12 / 11 / 2018
What if You turn the key and instead of starting the engine You hear some clicking noise? Maybe Your battery is dead or Your alternator is failing. Read this article and learn How to test an alternator and fix it
BY YOUR SELF.
How an Alternator Works?
The battery starts the vehicle, and therefore it spins the alternator at sufficient speed to keep the battery charged. Because Your battery is too low Your car won’t be able to start running. On the other hand You can’t test the alternator with multitmeter. For instance in cold weather an old battery may be the cause of unsuccessful start.
First check Your battery
To check if the battery is still good turn off the engine and before attaching the voltmeter. Open the hood and connect the voltmeter to the battery. Place the red lead of the voltmeter to the positive battery terminal and the black lead to the negative terminal. Avoid touching the battery with Your skin.
Set Your voltmeter to DCV above 15 V, which is 20 V. Read the voltmeter. Your battery is good if the number is above 12.2 volts. If it shows under this number it indicates low battery. So charge it before You go to the next step.
How to test an alternator:
Leave the multimeter at same place and start Your car . Now it should be in the range of 13 to 14.5 V which means Your alternator is doing it’s job and it is charging Your battery. Above 14 V indicates Your alternator is overcharging which can cause damage to the battery. This indicates that You have an issue with voltage regulator. It regulates voltage sent from alternator to the battery.
Low reading on the multimeter
If the reading are lower than 13 V Your alternator will still charge your battery, but with accessories (stereo, lights, AC) it won’t be enough. Perform the same test with light on, stereo, AC on and see if the number is still in the same range.
However, if the numbers are still low You have to check the connections to the battery, since it could be the problem. Just sand them down with sandpaper to ensure better connections. After that, inspect the back of the alternator to see if all wires are properly connected. Check for any damage on the wires that could indicate a bad connection. Also, check the belt of the alternator, because it might be not tight enough to spin correctly.
If You are not a “reading” person skip to the end of the article and watch very detailed video about How to test an alternator
Voltage drop test for positive and negative sides of the battery
Connect the black lead to the negative side of the battery. To perform the test start Your car and turn on additional element such as light, AC, stereo. Grab the read lead and touch it to the alternator case. While doing the test, every time You check different connections, raise accelerator up to 1500 to see are there any changes.
Good: The numbers should be 0.05 or around it.
Bad: If You read 0.1 or 0.2 You have a problem. To check a bad connection on the alternator case; put the red line on the alternator case bracket. When You see significant drop it means the connections between the case and bracket should be cleaned. If that’s not the problem, You want to check the engine block to see if there is the correct range.
In case You find an incorrect range, clean the connections between engine block and mounting bracket. Last thing to check is the chassis ground connections. In conclusion, the goal is to look for the ground connections that are causing the problem, clean them up and reconnected it properly.
Keep the car on, as well as the lights, AC and stereo. Place the red lead to the positive side of the battery and black side of it on the B+ post on the alternator on the end of the bolt.
Good: If the reading is 0.2 You have a good connection. Above 0.3
Bad: If the readings are 0.3 or above, check the connection on the nut (not the end of it) and the direct connection from the alternator and nut. If You find problems in these spots, clean them up and reconnect it.
For more detailed instructions watch this amazing video from very professional ChrisFix and learn much more!
Please comment below and give us a feedback, so We can help other car enthusiasts with useful informations!
Also read other articles on our website about electrical problems, such as airbag light on, and other useful staff.
Your Automotive Fixing Team
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