How to Test Vehicle Alternator with Multimeter!

Vehicle Alternator's are a major part of having a safe and normal functioning vehicle. Over time your Alternator may begin to fail and need to be tested. This video shows you how to test a Vehicle Alternator using a Multimeter to be sure it’s working properly.

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[powerfulsun]

Another easy method: first check voltage of battery with engine off then recheck the battery with engine on, if the voltage increases that means the alternator is working and charging. So your method tells you there is power to the alternator but doesn't tell you that the actual alternator is working. By doing the method mentioned above, you will hit two birds with one stone. Thank you

[rawalbikash]

If my car doesn't start then how could I test alternator?

[obiwanrazzy]

Perfect. This is exactly what I was looking for. And straight to the point too! Thanks.

[jermainejones]

Finally a straight to the point video thanks

[marty]

Thanks mate! I can now pin point whether it's the alternator or a break in the wires along the way to the battery. I was never taught that you can check this way only at the battery site. Awesome vid! Very helpful. These days it's too expensive to take to mechanics, they said it was my battery and I bought a new Bosch from them for $300 dollars plus their charge to look at it $185. Didn't fix the problem so I'm not going back for more problems. Thanks again. I'll continue to educate myself and figure it out. It's too expensive to have these problems these days even though I'm a worker.

[Velofire_]

Thank u I've always had a hard time understanding how to use one for testing

[raulescobar]

Thanks brother! Excellent video! I need to do this test quickly because a storm is coming and my tractor is in the field and won’t start. I just put in a new battery and it started just fine throughout the day. Thanks for the quick and to the point video!!!

[RJAV]

Thank you for this quick straight to the point video! 👍👍

[JourneyMN]

Quick and strait to the point. Thank you.

[globally]

I'm learning tonnes from your channel.
Cheers from the U.K.

[edwardedward]

When checking the alternator output voltage make sure everything is off especially the automatic switch on the vw cc ! If anything is on the alternator voltage will be less than 14 volts .Cheers Eddie

[rasgum]

Just what I was looking for. Thank you, sir.

[mobilehomelife]

Thanks for the help, will be testing my alternator shortly.

[MLife]

Thank you for a simple short and to the point video 💯🙏

[humrod]

Short and to the point. Sweet! Thanks!

[lindarpel]

Very good job explaining. How do I check the connection from the alternator and battery?

[richardlisiura]

This is what I was looking for. The engine noise was a bit much but otherwise a good video indeed. Thanks...

[jefffoust]

Thank you! Great video...simple and to the point 👍

[StarClay]

I find that my alternator has the same voltage as the battery (about 12.6), would that mean that I can disregard bad connectors and such as a problem and that the problem simply must be that I have to replace the alternator? Or can there still be other possible reasons for it?

[ButterfatFarms]

Just confirming the alternator is putting out DC voltage above that of the battery voltage is a very basic test for an alternator. You also need to check the AC Ripple voltage. Cut and paste FYI... ( I would suggest measuring AC Ripple directly at the alternator between the case and the positive terminal)

How to Test for Alternator AC Ripple
Testing for AC ripple is a straightforward process, you just need a multimeter with a low AC setting.

Testing Procedure:

1) Set Up the Multimeter— Set your digital multimeter to the AC voltage setting. The scale should be set to a range that can detect low voltages, such as 0-2 volts.

2) Connect the Multimeter— Connect the multimeter’s positive lead to the positive terminal of the battery and the negative lead to the negative terminal of the battery. This setup allows you to measure the AC voltage present across the battery terminals.

3) Start the Engine— Start the vehicle and let it idle. Observe the multimeter reading. In a healthy system, you should see a very low AC voltage—ideally below 50 mV.

4) Rev the Engine— Slowly rev the engine to about 1, 500 RPM. The AC voltage should remain relatively low and stable. If the AC ripple increases significantly with engine speed, this could indicate an alternator issue.

5) Evaluate the Results— If the AC voltage exceeds 100 mV or fluctuates wildly, it’s a sign that there may be a problem with the alternator, such as worn diodes or stator windings. In such a case, further inspection or alternator replacement may be necessary.

What to do if your AC ripple is too high
High or irregular AC ripple can be caused by one or more open diodes in the rectifier bridge or by a fault in the stator windings. Since it doesn’t really make sense these days to replace internal components, replace the alternator with a new unit.