How to Test an Alternator with a Multimeter

An alternator is one of the most fundamental parts of the electrical system of any vehicle. It gives power to the engine; as a result, the engine and other electrical accessories start. However, this important part can become bad due to multiple reasons. If it happens, your car’s engine will fail to start, or it may start but turn off after some time.

In this article, we have given a step-by-step guide to testing an alternator with a multimeterOpens in a new tab. so that you can check it on your own.

A brief introduction to the alternator

An alternator is one of the main parts of an automatic charging system. Its function is to convert mechanical energy into electrical energy that powers the electrical components of a vehicle. Alternators produce alternative current (AC) through a mechanism called electromagnetism. This alternating current is converted into direct current with the help of a rectifier. DC further activates the electrical system of your car.

Alternators usually have a lifespan of 10 to 15 years, but that is not always the case. They can get damaged due to overuse, water exposure, heat buildup, frayed wires, and some other reasons. If your alternator has failed, your car will not start, or if it starts, it will stay on for only a few minutes. If that is the case, you will have to replace or rebuild the alternator.

It is important to keep an eye on your car’s performance so that you can identify if there is something wrong with your car’s internal system or not. Below are the common signs of a bad alternator.

How do you check if your alternator is bad?

Lights are either very bright or very dim

A healthy alternator provides the required amount of voltage to run electrical accessories. If it is providing more or less than the required amount, it means there is an issue with it. Your car’s lights may become overly lit or dim. They may also flicker, which is another sign of a bad alternator.

The battery is not getting fully charged

The function of an alternator is to support the battery. A vehicle’s battery can be dead if it has been overused or its expiration time has been reached. It can also become dead if the alternator is not providing sufficient power.

You can check whether the issue is in the battery or in the alternator through a simple experiment. Jumpstart your vehicle; if it stays on, it means the issue is in the battery. On the contrary, if it dies after a short time, it means the alternator is not performing well.

Car is producing growling noises

A car may produce different sorts of noises. Some are harmless, while others indicate that there is an issue with the internal system. A bad alternator can make growling noises. It usually takes place when the belt that turns the pulley of the alternator gets misaligned.

Slow electronic accessories or system

As the electronic accessories of a car run on the power supplied by the alternator, when the alternator fails to produce power, the electronic accessories either do not work or take too long to perform their function.

If AC is not cooling the car, windows are taking a lot of time to move up or down, and other instruments are also not working, it could be due to a bad alternator. Most of the modern cars come with a priority list. It tells which accessories will first lose the power if the alternator becomes bad.

The engine does not start properly

A lot of times, if alternators lose their activity, engines start creating trouble while starting. Frequent stalling is another indicator of the same problem.

The foul smell of burning wires

If your engine is producing a foul smell of burning wires, then the car’s alternator may have some issue. This smell is often produced when the belt that pulls the pulley of the alternator heats up or starts wearing out. Alternator’s pulley will also produce the same smell if it has been seized. An overworked alternator also produces the same smell.

Tools required

The most helpful tool for testing an alternator is the multimeter. A multimeter is a handheld device that is used to measure different quantities like voltage, current, resistance, etc. This is why it is one of the must-have tools that electricians have. A variety of multimeters are available online and the local auto parts or tools stores.

You may also need sockets and wrenches if you have to remove the battery from your car. That is why it is better to have a basic tool kit with you so that you have access to all the basic tools.

How do I test a car alternator?

Below is the step-by-step guide to checking whether your car’s alternator is producing enough power or not.

  • Get a multimeter and connect it to the terminals of the battery. This battery should be in good condition, and it should be fully charged before starting the test. While connecting the multimeter, make sure you connect the red probe with the red terminal of the battery and the black probe with the black terminal of the battery.
  • Keep the engine and electrical system (AC, radio, heater, lights, etc.) off and then check voltage.
  • If it is around 12.6 volts, then it means the battery is alive, not dead.
  • Now turn the engine on and check the voltage again. The voltage value should be around 14.2 volts to 14.7 volts, indicating that the battery and alternator are in good condition.
  • Turn on the electrical system of your vehicle, including radio, lights, and AC. A healthy battery and alternator will have a voltage higher than 13. If it is below 13, it indicates the alternator is not supporting the battery with the required voltage.
  • If this is the case, take your vehicle to an expert and let him identify the true cause of this condition of the alternator. He will also suggest you suitable solutions.

The bottom line

The procedure of testing an alternator is quite easy. All you need to have is a multimeter to get started. If you have identified that your car’s alternator has gone bad, then take it to a mechanic so that he can provide a timely solution. In a separate post, we have explained how you can test a capacitor with a multimeter.Opens in a new tab.