How to test Alternator with Multimeter

What is an Alternator?

Alternator is actually a generator that converts mechanical energy into electrical one to recharge your vehicle battery. In cars, we could find it near engines. Its main purpose is to charge the battery all the time when the vehicle is in a running state for the stability of battery voltage.

In case of a malfunctioning alternator car’s battery may go out of charge, turning into a serious issue for you. Don’t worry here we’ll tell you how to test alternator with multimeter. It’s a quite simple procedure that didn’t actually require electrical skills.

Follow these steps to check alternator with help of automotive multimeters,

Checking Battery Condition

Before testing alternator directly, this is mandatory test to verify whether car battery is working or not. To check battery follow steps given below,

How to test alternator with multimeter
  1. First of all turn on your multimeter, make sure that it has a fully charged battery.
  2. Now put black probe into com jack and red into volt-ohm terminal.
  3. Set multimeter’s range to dc 20 volts or more.
  4. For testing alternator you should test vehicle’s battery first, for this connect meter probes to battery terminals respectively.
  5. If meter is giving somewhat 12.5 to 13.5 volts that probably means that battery is in good condition, also the alternator.

Testing Realtime Alternator’s Performance.

  1. For this, you’ll need another participant who will start the car, while you’ll observe readings.
  2. Now tell one of your companions to start the car to check alternator’s real time performance.
  3. Once the car engine has been started, observe the current and voltage level of battery.
  4. If it’s in between 14 to 14.8, it will indicate that alternator is in working condition.
  5. If it’s above 14.8 that means alternator is overcharging the battery.
  6. Same as below 14 voltage will be an indication that the alternator is not charging battery.

How to test Alternator with Multimeter

There is another process to check the condition of car alternators frequently applied by pro automotive electricians. If you can easily reach your car alternator then connect the red probe of the multimeter to the alternator positive terminal and the black probe to any metal part near it, it may a bolt or other thing. You may also connect the black probe with the negative terminal of battery.

car alternator

Now check readings on the meter screen, it should be 14 or nearby to make sure that the alternator is doing well. If you’re getting a low reading like 13 or more that may be due to low rpm speed, verify it by increasing engine’s rpm to 1500- 2000. Voltage level should be improved after this, if it’s still giving low volts then check alternator belt and pulley whether they are working well or not.

There may be numerous reasons for a bad alternator’s voltage, from low rpm to belt or pulley issues. It may also be due to the alternator’s voltage regulator problems. If you checked everything and found them well then it’s time to replace your car’s alternator.

Read also, Best fluke Multimeter for Automotive

What are the signs of a faulty Alternator?

A malfunctioning alternator gives many signs before its complete failure. For example, early battery drainage may be a sign of a weak alternator along with battery issues as well. Your vehicle’s weak cranking/starting power may be also an indication of it or dim headlights may refer to the slow performance of the alternator. Any abnormal noise from the engine side is also a sign to check your car’s alternator.

Another Classic method to test alternator

This is an old method used by auto electricians to test alternators. In this simple method, we’ll teach you how to test an alternator of the car. Connect the multimeter’s black probe with the negative terminal of the battery and black probe to alternator’s body after starting the engine. After that turn on all electric accessories like audio systems, lights to put a load on alternator.

how to test alternator with multimeter

Now check readings on multimeter that should be somewhat between -0.04 to -0.05. Give race to a car engine to increase rpm and observe the change. The reading should not change abruptly, if this results in a minor change of readings that’s proof that the alternator is in a good position.

How a bad Alternator may affect my Car?

If a car is running with a faulty alternator it may result in many harmful effects on the car. Like a bad alternator can destroy battery performance, even resulting in total damage. An alternator with a weak or spinning belt may damage other engine parts anytime in case of sudden breakage. Due to the poor performance of alternator, you may face a low voltage output of battery which is a risk for vehicle’s headlights, ignition system, audio/video systems, and other accessories.

Final Verdict

Till now you’ve learned how to test the alternator with multimeter thoroughly. Although it’s a technical matter that may require professional technicians, still you may do a self test easily after learning these skills and solving minor issues. We recommend you do not try to make major changes by yourself if you’ve no proper training for it.

These self troubleshooting techniques are actually for first aid and minor faults. As sometimes even bad connections or wear and tear may lead to underperformance of machinery parts.