How to Test a Voltage Regulator (Guide)

Voltage regulation is crucial in any electrical system. Without voltage regulation or the presence of a voltage regulator, the input voltage (high) will overwhelm the electrical systems. The voltage regulators work just like linear regulators.

They ensure the alternator output controls the charging voltage within the set voltage range. Therefore, they prevent voltage surges in an electrical system like that of a car.

With that in mind, it is necessary to check the condition of your car’s voltage regulator often.

In this guide, I will show you the whole process stepwise. Please read it to the end and you will know how to test your voltage regulator, using a multimeter.

In general, to test your voltage regulator, set your multimeter to measure volts and connect it to a battery – to check its voltage. Make sure your car is off when verifying the battery’s voltage. Note the multimeter reading, that is your battery’s voltage – the voltage should exceed 12V otherwise your battery is failing. Now turn on your car’s engine. The voltage reading should increase to above 13V. If it drops below 13V then the voltage regulator of your car has technical issues.

Tools for Testing a Car’s Voltage Regulator

You require the following tools to test the voltage regulator of your car:

  • Car battery
  • A digital multimeter with probes
  • Battery clips
  • A volunteer (1)

Method 1: Testing the Voltage Regulator of a Car

Now let’s check the status of your car’s voltage regulator by testing it with a multimeter. To perform this action, you need to first set your multimeter.

Step 1: Set your Multimeter

mechanic setting up Klein multimeter for testing

  • Twist the selection knob dial to voltage settings – that section is often labeled “∆V or V”. The V label may have a few lines on its top.
  • Next, set your multimeter to 20V. You can damage your voltage regulator if your multimeter is in the ohms Amps setting.
  • Plug the red probe into the port that’s labeled as V, and the black probe into the port marked COM.
  • Now adjust your multimeter by pinging the probe leads. The multimeter will beep if it is working properly.

Step 2: Now, Connect the Multimeter Probes to the Car Battery

mechanic connecting multimeter probes to car battery
Video | ehowauto

Now turn off your car’s engine and connect the multimeter probes accordingly. The black probe goes to the black battery terminal and the red probe to the red terminal.

It is necessary to obtain the voltage reading of your battery. It will tell you if your battery is failing or if it is in optimal condition.

After connecting the probes, read the multimeter display unit. The value you obtain should conventionally exceed 12V with your engine being off. The 12v means your battery is okay. However, lower values mean your battery is faulty. Replace it with a new or better battery.

Step 3: Turn on the Engine

mechanic turning the engine on for testing
Video | ehowauto

Set your car to “park or neutral” mode. Engage the emergency brakes and turn on the car engine. While doing this, the multimeter probes should stay pegged on the car battery, you may use the battery clips to do this.

Now check the multimeter display unit. The voltage values should increase from the noted voltage (while the car was off – battery voltage) to about 13.8 volts. A value of about 13.8V is an indicator of a properly functioning alternator voltage regulator. Any value appreciably below 13.8 means your voltage regulator is not working properly.

Another thing to observe is a steady or changing high or low output voltage. This also means your voltage regulator is not working as it should.

Step 4: Rev the Car Engine

You will need someone else to help you out here. They will rev the engine while you monitor the multimeter readings. Your partner should gradually increase the revs up to between 1,500 and 2,000 RPM.

Note the multimeter reading. A voltage regulator in good condition should have about 14.5 volts. And any reading above 14.5 volts means your voltage regulator is not okay.

Method 2: Testing a 3-terminal Voltage Regulator

A 3-phase voltage rectifier works by charging up the battery to replace the voltage consumed by an electrical system. It has the input, common, and output units. It converts the AC to DC – commonly found in motorcycles. Follow the below-mentioned steps to test your 3-phase terminal voltage rectifier.

mechanic testing 3-terminal voltage regulator with multimeter

  • Make sure your multimeter is still set.
  • Now, take the multimeter probes and measure the voltage of your 3-phase voltage regulator.
  • A 3-phase regulator has 3 “legs”, check each phase.
  • Insert your probes into the legs as follows: measure the 1st leg with the 2nd one, the 1st leg with the 3rd, and finally the 2nd leg with the 3rd leg.

multimeter probes and 3-terminal voltage regulator

  • Note the readings of the multimeter in each step. You should get the same readings for all the 3 phases. However, if the difference in voltage readings is considerable, go for a repair. That means your 3-phase voltage rectifier is not functioning as required.
  • Now proceed and check each phase to the ground. In this step, just make sure there is a reading, no reading means there is an open link. (2)

Take a look at some of our related articles below.

(1) volunteer –
(2) reading –

Video References

Philippine Life


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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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