How to Test a Car Alternator with a Multimeter

Test a Car Alternator with a Multimeter

Are you suspecting that your car alternator is not working correctly? Test a car alternator with a multimeter is a simple and efficient way to diagnose any issues. This guide will walk you through the process of using a multimeter to check voltage and amperage, troubleshoot common alternator problems, and ensure your car is running smoothly. With the right tools and knowledge, you can quickly test your car alternator in no time.

The alternator of an automobile manages the amount of direct voltage reaching the car’s battery. When you are driving the car, the alternator helps the car battery to keep charged so that you do not have to face any problems on your way. But if any fault has occurred in the car alternator, you have to face some difficulties while running your car.

It is essential to know how you can check your car’s alternator because if your engine starts giving you jerks or your car stops on the way, it will be difficult for you to get out of the situation.

Here you will understand how this alternator works and the procedure for testing the car alternator using the digital multimeter. The digital multimeter can easily access the alternator. It will not take much time to do its task, so using this miracle gadget will always benefit you.

Components of the car alternator:Components of the car alternator

There are two primary components of the car alternator. One is the moving component, and the other is the stationery component.

  • Rotor
  • Armature coils


When power is supplied to the engine, it rotates the rotor coils. In response, the flux is produced, which keeps rotating along with the rotor.

So it is clear that the rotor is the moving component of the car alternator.

Armature coils:

Armature coils don’t move. As the flux in the rotor keeps rotating, electricity starts to be produced in these armature coils.

Armature coils are said to be the stationary component of the car alternator.

Working principle of the Car alternator:

This all is a matter of voltage. So it is clear from the components of the car alternator that a car alternator works when a rotating coil produces a magnetic flux that rotates around the stationary iron coil of the alternator and produces the voltage.

The mechanism upon which this alternator works is to compensate for the level of voltage supplied to the car engine. When the car engine is not working, the voltage level of the car battery is called the resting voltage level. Most of the time, the vehicles have this resting voltage level between 12.4 to 12.6 volts.

When we start the car engine, the whole car system uses voltage, so the alternator’s voltage drops suddenly. The alternator then starts producing a higher voltage to compensate for the voltage requirement of the engine. In this way, the alternator performs its basic role in running the engine.

Signs that indicate the damaged car alternator:Signs that indicate the damaged car alternator

Following is the list of signs indicating a faulty and damaged car alternator. If any of the following symptoms in your car show, you immediately have to check on your car alternator.

  • If your car battery is working well but it is still difficult to start the car engine, then the alternator might be the reason for this condition.
  • If your engine takes much time to crank, it can be the faulty car alternator.
  • Check your car’s headlights; if they are dim, it is also a sign of a bad car alternator.
  • If you feel a burnt smell while driving the car, it might occur because of the burning of any alternator wire.
  • If your car’s alternator produces some strange sounds, then this is the time to stop and test the alternator now.

How to test a car alternator with a multimeter?How to test a car alternator with a multimeter

After learning about some major symptoms that show that your car alternator is causing some trouble, you have to test your car alternator properly.

Material required:

  • Digital Multimeter
  • Hand Gloves

Here are the quick steps to test a car alternator with a multimeter

  • Turn on the digital multimeter
  • Set the multimeter to check the voltage
  • Set the voltage range
  • Connect the probes of the multimeter with the correct alternator terminals.
  • Take the readings
  • Turn the car engine on
  • Note the voltage readings
  • Turn ON all electrical the equipments in the car
  • Note the voltage readings
  • Turn off the car engine
  • Note the voltage readings
  • Compare the results

Let’s move to the detailed step-by-step guide below:

Turn on the digital multimeter:

It is necessary to turn on the digital multimeter whenever you are going to test anything by using it. So turn on the digital multimeter and move forward toward the next step.

Set the multimeter to check voltage:

As of now, you are going to test a car alternator, so you have to set the digital multimeter to the Direct Current Voltage settings. For this, turn the selection knob of the digital multimeter toward the V– symbol. Now your digital multimeter is ready to take the test.

Set the voltage range:

Now you have to set the range of the DC at your digital multimeter. Most car alternators have a voltage between 12 to 14 volts. So you can range the digital multimeter at 15 volts.

Connect the probes of the multimeter:

Now you have to make a proper connection between the digital multimeter and the car alternator. So for this, you can use the probes of the digital multimeter. A multimeter has two probes. You have to connect them with accurate terminals.

So now, take the red probe of the digital multimeter and connect it with the car’s alternator’s positive terminal. Similarly, take the black probe of the digital multimeter and connect it with the car’s alternator’s negative terminal.

Make sure to keep the settings the same. Follow these guidelines precisely as they are mentioned here.

Take the readings:

After connecting the digital multimeter with the car alternator, you will see the resulting direct voltage readings on the display screen. Note this reading.

If the readings you get are close to 12.4 to 12.6 volts, then it means that your car alternator is working well. If readings are a significant difference, then it indicates some problem there.

Turn the car engine ON:

Now you have to turn ON the car engine to make the condition of your car alternator clear in front of you.

Note the voltage readings:

Take a look at the voltage readings on the display screen this time. The car alternator is good if the results are around 14 to 14.2 volts. If it is not, then the car alternator is causing the trouble.

Turn ON all the electrical equipments:

Now you have to turn on your car’s electrical equipment, including the headlights, fog lights, radio, electronics, fan and all other equipments that run on a power supply.

Note the voltage readings:

Note the voltage readings from the digital screen of the multimeter. If the readings are above 13 volts, then it means the alternator is performing well, but if the voltage drops down from 13 volts, it is confirmed that there is an issue with your car alternator.

Turn off the car engine:

After testing it in running condition, you have to test it by turning it off. After turning off the car engine, you have to check the voltage.

Note the voltage readings:

Congratulations if the voltage readings are around 12 to 13 volts. Your alternator has no problems.

Compare the results:

Compare all the voltage results with the normal readings given in this article. If the readings are close enough to the normal readings, the issue might be in any other car components.

Still, if the readings are in great difference from each other, then you have to make your car alternator checked by a professional car mechanic.

Final verdict:

The car alternators perform their major role by providing enough voltage to the engine. If it starts causing a problem, it needs an immediate check; otherwise, your engine may get severely damaged. For this, you are advised not to let everyone operate your car system.

Let it drive only by the person who knows how to use it, and if you feel any burping sound coming off your car engine and alternator, give it a check without wasting time.

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