car battery care

How to check if your alternator is in good condition

Not sure if your alternator is in good condition? If you don’t know exactly where to look it can be quite difficult to determine if an alternator is still working properly. If you have a voltage meter handy, this is certainly the easiest way to test. If you are familiar with car mechanics and know your way around, there are also a few other ways to properly test your alternator. Just keep reading and you will find out which way is the best for you.

Method One: Use a strain gauge

Buy a voltage meter.

You can buy this device in almost every car parts store for about 15 to 20 euros. Don’t buy the most expensive voltage tester, a cheaper one will suffice for this purpose. If you already have a multimeter, you can use that as well. A multimeter measures voltage and other electrical values ​​such as current and resistance. To check the alternator, you must set your device to voltage.

First, check your battery.

You need the battery to start the alternator. Once the engine is running, the alternator then charges the car battery. This means that if your car battery is not well charged, it cannot supply the alternator with power. In this case, you can measure the alternator, but the values ​​will not tell you anything because the empty battery falsifies the information. If it is very cold at the moment or your battery is a bit older, your alternator could be working perfectly, the cause is the battery. That’s exactly why you have to check the battery before you take care of the alternator.

Here’s how to do it: Turn off your car. Make sure the car is completely off before measuring the alternator voltage. Open the hood. Connect the voltmeter to your battery. Connect the battery’s red lead to the red end of the voltmeter, then do the same to the black leads. Be careful not to touch the battery with your skin. Read the readings from the voltmeter. If the voltmeter shows you a value of over 12.2 volts, the battery is fine and will provide you with enough energy to start the alternator. You can now test the alternator with the voltmeter. If the battery is no longer strong enough, i.e. it shows you a value below 12.2 volts, you have two options. You can either have the battery charged and then test it again, or test the alternator in a different way.

Start the engine and accelerate until you reach 2000 rpm.

This should result in power being supplied to your battery. Your alternator should therefore get a nudge from your regulator, which will then put it into high gear.

Run the engine and test your battery again with the voltmeter.

The reading on your voltmeter should now read at least 13. If the engine RPMs vary the reading may be between 13 and 14.5 volts, if this is the case then your alternator is fine. However, if the display does not go up or even goes down, then your alternator has a defect. Repeat this process with the lights, radio, and A/C on. The alternator is charging when the battery voltmeter reads more than 13 volts with a machine running at 2000 RPM and the accessories turned on.


Method Two: Watch your alternator gauge

Check the alternator gauge.

If you have a volt/ampere display, you can use it to read your alternator. Turn on all your electronic devices in the car. Air conditioning fans or heater fans, headlights, etc. Now look at your display and check if it is losing voltage or amps. As a rule, remember this: if the voltmeter is higher when the engine is running and lower when it’s off, it means the alternator is charging.

Listen for alternator noise while the engine is running.

If you have a problem with the bearings, you can hear a squeaking noise coming from the engine compartment, which gets louder as you turn on more or all of the electrical devices in your car at the same time.

Turn on the radio and go into reverse.

If the radio makes a whining noise or the gauges blur as soon as you step on the gas pedal, these signs are also very likely related to the alternator.

Find a car parts shop and have your alternator tested for free.

Since almost any auto parts store would be more than happy to sell you an alternator, owners are happy to offer free tests to outperform the competition. To be on the safe side, remove your alternator and bring it to the shop.



If you come to the conclusion during your test that your alternator is defective, this does not necessarily have to be true. Sometimes the cause lies elsewhere. For example, you may have a blown fuse, a relay is defective or your voltage regulator is damaged.


Some people advise testing the alternator by starting the engine, disconnecting the negative cable from the battery, and then waiting for the engine to stall. don’t do that! This method can damage the voltage regulator, alternator, and/or other electronic equipment. Make sure you keep your hands, loose clothing, and jewelry away from the moving parts under the hood while the engine is running.

About the Author

Dylan Roberge

Dylan Roberge is a San Francisco-based writer and editor with over a decade of experience covering money saving and deal hunting. Before going freelance, he got his start as an editor at Yahoo Finance. These days he writes about mobile, tech gadgets, and lifestyle subjects for a variety of publications.