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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.

Follow these steps to test your voltage regulator:

Step 1: Set The Multimeter To Voltage Ensure your multimeter is on the voltage setting. 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.

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