How To Test An Alternator: Necessary Steps And Recommendations!

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Do you want to know if your alternator is in good condition? To know how to test an alternator to find out if it works is hard or not, if you don’t know what to look for. The easiest way to test it is by using a voltmeter.

If you are well in tune with your car, there are a few other methods you can try as well. This test is used to determine the general condition of the alternator and battery.

How to test an alternator

Some newer vehicles may have computer controlled charging systems and would require additional testing. The methods for testing an alternator are as follows:

The alternator of a vehicle
The alternator of a vehicle

1- Using a Voltmeter, Tester or Multimeter

This is a well-known technique to test an alternator, these devices are very important and it is good that you have a multimeter available.

you can buy a voltmeter

You can find one at any store that sells auto parts or electronics for less than $20. Don’t worry about getting an expensive one; a cheap voltmeter will do for this purpose. If you want you can also choose to buy one on Amazon.

If you have a multimeter, you can use that instead. A multimeter measures voltage as well as other electrical properties such as current and resistance. You will need to measure the voltage when you are checking your alternator.

Check the battery first

The battery is needed to start the car, and the battery in turn causes the alternator to spin fast enough to keep the battery charged. This means that if the battery has a low charge, it will not be able to start the car and, therefore, you will also not be able to test the alternator, so any additional tester tests will be totally useless.

If the weather is cold or your battery is old, your battery could be the problem and your alternator could be fine. For that reason it is convenient do a battery test before you get ready to check the alternator. This is how it’s done:

  • Turn off the car and make sure the engine is off before making the tester connection.
  • Open the hood.
  • Connect the multimeter to the battery and place the red lead of the tester on the positive terminal of the battery, then proceed to put the black lead on the negative terminal. Avoid touching the drums with your skin.
  • Read the voltmeter. If the battery reads above 12.2 volts, it has enough power to start the alternator, which can then be tested with the voltmeter.
  • If the battery may not have the required voltage, charge the battery and retest it or try a different technique to test the alternator.

Start the vehicle and crank the engine at 2,000 RPM

This will draw power from the battery, which should cause the voltage regulator to kick the alternator into high gear.

Keep the engine running and retest the battery with the voltmeter. When you read the voltmeter this time, the voltage should go up to at least 13. If the voltage fluctuates between 13 and 14.5 volts when you vary the revolutions, your alternator is good; if, on the other hand, the voltage remains the same or decreases, then your alternator is not working properly.

Repeat this process with the lights, also the stereo and air conditioning on. The alternator will be in a state of charge if the battery voltage is maintained above 13 volts, this with the engine at 2,000 rpm. You should also have all accessories turned on.

2- Monitoring your alternator

Regarding how to test an alternator, keep in mind that there are empirical methods that many people have developed, such as: test an alternator with a lamp. Such a lamp is used as a tester.

Check alternator pressure gauge

If you have a volt/amp meter, it will read the alternator output for you. Run the engine at 2,000 rpm for testing and turn on the AC fan or heater, headlights, and any other accessories that force the alternator, and watch the gauge to see if the voltage or amps drop.

As a rule of thumb, if the voltmeter is higher when the engine is running than when the engine is not, it can be safely assumed that the alternator is charging.

Listen to the alternator while the engine is running

If there is a problem with the bearings, you may hear a grinding noise coming from the front of the vehicle, which becomes louder with more electrical accessories eating up power in parallel.

Turn on the stereo and rev the engine

He tunes his radio to a low number on the AM band with no music. If you ever hear the radio whining or becoming inaccurate every time you hit the throttle, there’s a good chance it’s the alternator.

Find a place where they test alternators for free

Since every store would love for you to buy your new alternator from them, many will try to get the upper hand on their competitors by offering free trials. Disassemble your alternator and bring it in to be safe. This is how you can test an alternator for free.

The alternator in the foreground
The alternator in the foreground

Don’t forget to read: How to loosen the alternator belt

Do you want to know if your alternator is in good condition? To know how to test an alternator to find out if it works is hard or not, if you don’t know what to look for. The easiest way to test it is by using a voltmeter.

If you are well in tune with your car, there are a few other methods you can try as well. This test is used to determine the general condition of the alternator and battery.

How to test an alternator

Some newer vehicles may have computer controlled charging systems and would require additional testing. The methods for testing an alternator are as follows:

The alternator of a vehicle
The alternator of a vehicle

1- Using a Voltmeter, Tester or Multimeter

This is a well-known technique to test an alternator, these devices are very important and it is good that you have a multimeter available.

you can buy a voltmeter

You can find one at any store that sells auto parts or electronics for less than $20. Don’t worry about getting an expensive one; a cheap voltmeter will do for this purpose. If you want you can also choose to buy one on Amazon.

If you have a multimeter, you can use that instead. A multimeter measures voltage as well as other electrical properties such as current and resistance. You will need to measure the voltage when you are checking your alternator.

Check the battery first

The battery is needed to start the car, and the battery in turn causes the alternator to spin fast enough to keep the battery charged. This means that if the battery has a low charge, it will not be able to start the car and, therefore, you will also not be able to test the alternator, so any additional tester tests will be totally useless.

If the weather is cold or your battery is old, your battery could be the problem and your alternator could be fine. For that reason it is convenient do a battery test before you get ready to check the alternator. This is how it’s done:

  • Turn off the car and make sure the engine is off before making the tester connection.
  • Open the hood.
  • Connect the multimeter to the battery and place the red lead of the tester on the positive terminal of the battery, then proceed to put the black lead on the negative terminal. Avoid touching the drums with your skin.
  • Read the voltmeter. If the battery reads above 12.2 volts, it has enough power to start the alternator, which can then be tested with the voltmeter.
  • If the battery may not have the required voltage, charge the battery and retest it or try a different technique to test the alternator.

Start the vehicle and crank the engine at 2,000 RPM

This will draw power from the battery, which should cause the voltage regulator to kick the alternator into high gear.

Keep the engine running and retest the battery with the voltmeter. When you read the voltmeter this time, the voltage should go up to at least 13. If the voltage fluctuates between 13 and 14.5 volts when you vary the revolutions, your alternator is good; if, on the other hand, the voltage remains the same or decreases, then your alternator is not working properly.

Repeat this process with the lights, also the stereo and air conditioning on. The alternator will be in a state of charge if the battery voltage is maintained above 13 volts, this with the engine at 2,000 rpm. You should also have all accessories turned on.

2- Monitoring your alternator

Regarding how to test an alternator, keep in mind that there are empirical methods that many people have developed, such as: test an alternator with a lamp. Such a lamp is used as a tester.

Check alternator pressure gauge

If you have a volt/amp meter, it will read the alternator output for you. Run the engine at 2,000 rpm for testing and turn on the AC fan or heater, headlights, and any other accessories that force the alternator, and watch the gauge to see if the voltage or amps drop.

As a rule of thumb, if the voltmeter is higher when the engine is running than when the engine is not, it can be safely assumed that the alternator is charging.

Listen to the alternator while the engine is running

If there is a problem with the bearings, you may hear a grinding noise coming from the front of the vehicle, which becomes louder with more electrical accessories eating up power in parallel.

Turn on the stereo and rev the engine

He tunes his radio to a low number on the AM band with no music. If you ever hear the radio whining or becoming inaccurate every time you hit the throttle, there’s a good chance it’s the alternator.

Find a place where they test alternators for free

Since every store would love for you to buy your new alternator from them, many will try to get the upper hand on their competitors by offering free trials. Disassemble your alternator and bring it in to be safe. This is how you can test an alternator for free.

The alternator in the foreground
The alternator in the foreground

Don’t forget to read: How to loosen the alternator belt

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