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Car Care Advice

The Car Voltage Regulator (How It Works + How To Test It)

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The car voltage regulator plays an essential role in your car’s charging system. 

But what is it, and how does it work? 

In this article, we’ll answer those questions, show you how to test your voltage regulator, and cover some frequently asked questions

This Article Contains: 

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Let’s get started.

What Is A Car Voltage Regulator?

As its name suggests, your car voltage regulator, or switching regulator, controls the voltage produced by the alternator (generator in older cars or starter generator in tractors). 

Without the alternator voltage regulator, the input voltage would be too great and overload the electrical systems in your vehicle. 

To prevent that, the voltage regulator functions much like a linear regulator in that it ensures the alternator output maintains a steady charging voltage of between 13.5V and 14.5V. 

That’s enough constant voltage to recharge the battery without overloading your car’s electrical components and circuits, like the instrument cluster, car battery, headlights, motors, and so on. 

If the charging voltage drops below 13.5V, the regulator supplies additional current to the field winding to charge the alternator. If the voltage level rises above 14.5V, the regulator will stop delivering the power supply to the field winding and prevent the alternator from charging.

So how does the voltage regulator ensure constant voltage?

How Does A Car Voltage Regulator Work?

The process begins when you turn the ignition switch. 

Voltage runs from the car battery to the starter motor, which brings the engine to life through combustion. 

Once the engine is running, a drive belt spins a rotor inside the alternator, electrifying the field coil and generating DC voltage to charge the battery. However, before the power supply can reach the battery, it has to pass through the electronic voltage regulator. 

The power supply flows through the alternator regulator, which contains diodes like a Zener diode, a transistor, and several other components. 

Together, these diodes turn the alternator on and off as the voltage output from the field circuit fluctuates, effectively controlling the duty cycle. 

The field coil within the alternator or generator connects to the switching regulator, which operates as fast as 2,000 times a second, opening and closing the connection.

If the voltage output drops below 13.5V, the power supply is low so the regulator’s sensors close the circuit to the alternator. This causes the alternator to switch on, increasing the magnetic field and delivering power to the battery. 

Then, once the voltage output in the battery reaches 14.5V, the regulator disconnects the alternator output or generator, weakening the magnetic field and preventing it from charging the battery. This makes sure the battery doesn’t overcharge and potentially explode or burn out. 

These days, your electronic voltage regulator hardly suffers any issues and is difficult to repair. As a result, when they start acting up, it’s easier to install a replacement than try and fix a faulty alternator regulator.

Many cars also have an engine control module (ECM) regulating the alternator’s voltage level through a specialized circuit. These are considerably more advanced and, as part of the fail-safe circuit, offer the ability to diagnose and describe potential problems. 

With that said, how do you test your alternator voltage regulator to make sure it’s providing solid voltage regulation? 

How To Test A Car Voltage Regulator 

If you’ve noticed problems with your car’s electrical system, testing the electronic voltage regulator can help you determine which part of your car’s electrical system is causing the problem. 

Fortunately, testing a voltage regulator is pretty straightforward, but it does require a multimeter. 

Note: This test is for cars that don’t have computerized voltage regulation. 

Follow these steps to test your voltage regulator:

Step 1: Set The Multimeter To Voltage 

Ensure your multimeter is on the voltage setting
The voltage setting often looks like ∆V or a V with a few lines above it. 

Set it to 20V. Testing an alternator regulator with your multimeter set to Ohm or Amp can damage your device. 

Step 2: Connect The Multimeter To Your Battery

To check an alternator regulator, we need to check the battery voltage. 

With your car off, connect the multimeter’s black lead to the black (negative) battery terminal and the red lead to the red (positive) battery terminal.

Step 3: Check The Multimeter

The multimeter should be displaying a little over 12 volts with the engine off if your battery is working correctly. If your battery voltage is below  12 volts, it could mean your battery is failing and you may need a replacement soon. 

Step 4: Turn Your Vehicle On

With your car in park or neutral and the emergency brake engaged, turn the engine on. Have a look at the multimeter and you should see the reading increase to around 13.8V while the car idles. 

If you see 13.8V on your multimeter, you can rule out your car’s alternator as the cause of your electrical issues. 13.8V suggests everything is working correctly and the alternator is charging your battery as it should.

If your output voltage drops below 13V right after starting the engine, you may have a problem with your electrical system. Consider performing a voltage drop test.

Lastly, if you notice a steady or intermittent high or low voltage output, it suggests your alternator voltage regulator is the problem.

Step 5: Rev The Engine

You’ll need an extra set of hands here. Have someone rev the engine while you keep an eye on the multimeter. Slowly build up the car’s revs until it reaches 1,500 – 2,000 RPM.

Step 6: Check The Multimeter Again

If your alternator voltage regulator is working correctly, your battery’s voltage output should cap around 14.5V. If the reading is above 14.5V, you likely have a faulty voltage regulator. If the reading is below 13.8V, your battery is weak and will probably need a replacement.

Now, let’s go over some regulator FAQs:

5 Car Voltage Regulator FAQs

Here are a few common voltage regulator questions and their answers:

1. Where Can I Find The Voltage Regulator?

You can often find the voltage regulator mounted inside or outside of the alternator housing. If it’s mounted outside, you should see a wire harness connecting the regulator to the car’s alternator. 

2. Can A Bad Voltage Regulator Ruin A Battery?

Yes, a bad voltage regulator can definitely ruin your car battery. 

If too much voltage is flowing to the battery, it can warp the platers and destroy your battery. Alternatively, if there’s low voltage, the battery won’t be able to charge fully and you may struggle to turn your car on. 

If the voltage regulator fails completely, the battery power will deep-discharge. While your standard 12 volt lead-acid car battery is supposed to discharge, discharging too far can cause irreversible damage to the plates within the battery, significantly reducing its lifespan.  

3. Can I Drive With A Faulty Voltage Regulator?

Technically, you can drive with a faulty voltage regulator, but doing so is risky. 

You might be fine and nothing happens, but you run the risk of blowing some expensive electrical components without constant voltage. If you have a faulty voltage regulator, you should have it replaced as soon as possible.

4. How Much Does A Voltage Regulator Cost To Replace?

An alternator voltage regulator replacement is quite an expensive job. 

Your car’s make and model will have the greatest impact on the cost of a new voltage regulator. For the part itself, though, you can expect to pay anything between $40 and $140. 

However, labor costs also play a big role here. 

This is because most voltage regulators sit inside the car’s alternator, making it difficult to access. As a result, labor costs should be somewhere between $140 and $240.

You might pay a little less if you have an external voltage regulator (i.e., your voltage regulator is mounted outside the alternator).

Having said all that, the total cost of replacing a voltage regulator should be somewhere between $180 and $380. Of course, if the faulty regulator damages any other electrical components, the cost will be higher. 

5. What Should I Do If I Need A Voltage Regulator Replacement?

If you need a voltage regulator replacement, don’t drive your car to a repair shop as doing so can damage expensive parts. 

When looking for a mechanic to perform a replacement, always call for a mechanic to come over and double-check they’re: 

Fortunately you don’t need to panic; RepairSmith ticks all the above boxes. 

They can sort out any hassles with your car’s electrical system, including replacing the voltage regulator. 

What’s RepairSmith
RepairSmith is a convenient mobile vehicle repair and maintenance solution. 

Here’s what RepairSmith offers:

The cost of replacing the voltage regulator will vary depending on the make and model of your car. For an accurate cost estimate, fill out this form

Final Thoughts 

There are several components in your car’s charging system, and the voltage regulator ensures that they continue working by monitoring the output voltage. 

However, with time, the voltage regulator could start acting up. 
The best way to determine if it’s working correctly is to test it. 

If the test reveals the issue is with your voltage regulator, your best bet is to replace it as soon as possible. 

And when the time comes for a replacement, don’t worry. 
Simply contact RepairSmith for professional help and advice! 

Their ASE-certified technicians will come to your driveway and handle all of your car’s repair and maintenance needs.