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Have problems with your car’s alternator but don’t know how to test alternator with multimeter? Then you’re in the right place.
We know how tedious and complex troubleshooting can be. But with the correct information, you can get this job done quickly.
That’s why we want to share all the information you need to know before testing an alternator with a multimeter and a few pro tips on how to fix it.
How Do I Know If My Alternator Went Bad?
Before testing your alternator with a multimeter, please consider the following symptoms:
Typically, you wouldn’t overthink if your battery stopped working — especially if you’ve never replaced it before. However, this problem could be related to your alternator.
If you have a faulty alternator, it probably damaged your battery. In this case, you will have to replace the alternator and battery.
Battery Warning Light
Did your battery warning light come on as you were driving? Well, it means that the alternator is no longer charging the battery, meaning there is a problem with your alternator.
While some car noises are harmless to some extent, some of them can be pretty scary and often mean trouble.
If your car makes weird noises and they all seem to come from under the hood, you might want to check your alternator.
How to Test your Alternator & Battery with a Multimeter
To test an alternator, you have to test the battery. For more on how to test alternator with multimeter, check this out:
1. Plug the Leads
First, take your black lead, connect it to the COM jack, then grab the red one and plug it where it says “VΩ.”
2. Set the Multimeter to Volts DC
To start, turn your multimeter to 20 volts DC. As long as it’s above 15 volts, you’re good to go.
3. Connect the Leads to the Battery
Before connecting the leads to your car’s battery, make sure to clean the terminals. That said, grab your red lead and put it on the positive terminal on your battery. Next, connect the black lead to the negative terminal.
4. How to Test Battery and Alternator with Multimeter
After connecting the leads to the battery, you should get close to 12.6 volts. That’s the number you want to shoot for when testing the battery.
Next up, start up the car. When running the vehicle, your multimeter should display anywhere from 14.2-14.7 volts. This means that your alternator is running correctly.
However, if you get anything above 14.7, your alternator is overcharging the battery, and there’s something wrong with it. And if it’s below 14.2, it means your alternator is not working anymore.
5. Increase the Power Going Into the Alternator
To make sure everything is working, we’ll put a load on the alternator by turning on several accessories, like your radio and lights. When running all these accessories, make sure that your reading does not go below 12.7 volts.
When you get the first reading, shut off the car. You should now get anything around 12.6 or higher. This means that the alternator is working as intended and is charging the battery.
How to Run a Voltage Drop test
We’ve done a lot of work so far, but we still need to run a voltage drop test to make sure the alternator is working.
1. How to Test Car Alternator with Multimeter
Touch the black lead to your battery’s negative terminal, and then put the red lead on the alternator’s case. Next, start up your car and turn on all your accessories to load the alternator.
The reading should be -0.05. Now raise the RPMs to 1,500. Your reading shouldn’t change significantly. As long as it’s not -0.1 or -0.2, you’re good to go.
2. Test the Engine Block
To make sure the alternator is working, grab your red lead and connect it to the engine block. Once again, your reading should be close to -0.05. If your voltage dropped significantly, clean the connection between the mounting block and engine block.
3. Test the Chassis Ground
Once again, grab your red lead and put it on the ground. If the connection is bad, clean it until it works again. For more information about this broad topic, watch this YouTube video:
Frequently Asked Questions (FAQs)
If you need more information on how to check for bad alternator with multimeter, check this out:
How can I test my alternator at home?
- Yes! You can test an alternator at home. All you need is a multimeter. In many cases, you might find that your alternator is still in great shape, and you just needed to clean the connection to the alternator.
How do you check if your alternator is bad?
- Take your red lead and put it on the positive terminal of your battery, then put the black one on the negative terminal. You should get 12.6 volts. Next, start up the engine to make sure the alternator is working. If you’re getting less than 14.2 or 14.7, it means the alternator is no longer working.
Will a car run with a faulty alternator?
- Yes, you can drive a car with a faulty alternator. However, your radio will shut off, your lights will dim, and then your vehicle will die as it doesn’t have enough power to run smoothly.
Can a bad alternator destroy a new battery?
- If your alternator stopped working, there’s a high chance it’ll destroy your battery. Therefore, replace the alternator to prevent further damage.
There is a lot to do when learning how to test alternator with multimeter. But only then can you test a damaged alternator.
And as we noted before, test the alternator yourself before taking it to a professional. Sometimes cleaning the connections going into the alternator is more than enough to get your vehicle back on the road.
It takes a little bit of time, but you’ll save yourself a lot of money if you take some time off.