Time To Test a Voltage Regulator!

Are we holding a charge or dead as a doornail?

Time Needed: 5 Minutes, Difficulty: Beginner, Cost: $0-$15

If the alternator is the heart of your vehicle’s charging system, the voltage regulator is the brain. As the engine’s serpentine belt spins the alternator, it produces an electrical charge. Without the help of a voltage regulator, the voltage output would gradually increase, and seeing as most of the systems in your car are designed to operate on just 12 volts, 16, 18, or even 20 volts might become an issue.

You can generally tell that the voltage regulator is failing to do its job when you begin to notice inconsistencies in the vehicle’s electrical systems. Flickering gauges, an inoperable instrument cluster, and lights getting brighter as you increase engine speeds are all tell-tale signs of a bad voltage regulator.

Of course, just throwing parts at a car based on a hunch is no way to handle things unless you have a thing for gambling. But, if you’d like to keep as much of your money as possible, you’d better listen to Carbibles band of car nerds, cause we’ve got a few simple tricks to help you understand whether the voltage regulator is the problem.

The Safety Brief

Troubleshooting the voltage regulator is a quick job that requires minimal effort. Still, it can place you underneath the hood of your car as the engine is running, and you’ll want to practice proper safety techniques as you work.

No, we’re not spraying carb cleaner on anything or breaking out the torches. So, there’s no need to worry about losing that signature mustache. You just want to be mindful of where you place your digits as you work. Of course, a good pair of safety glasses and protective gloves are always a good idea.

The Tools & Parts You Need to Test a Voltage Regulator

The method we’re using to test a voltage regulator is a simple inspection of how much of a charge the alternator is putting off while the engine is running. We’re taking the readings we gather and comparing them to what the manufacturer of the vehicle or regulator tells us is acceptable. Naturally, that means a touch of homework is necessary on your end. 

In our case, we’re performing the test on a 1969 Dodge Charger that’s using a voltage regulator, which converts the charging system to a one-wire configuration. Voltage readings should be anywhere between 13.5 and 14 volts with the engine running on this application. Most cars and trucks should be calling for similar numbers, but you want to do your research and make sure. Also, keep in mind that we want to take our readings with the engine idling and under acceleration. So, calling a friend for help is a good idea. 

Aside from a computer or manual to get your numbers from, you will need one tool for the job—a multimeter.

Now, we won’t take the elitist stance and tell you that you need a high-end multimeter for this test. The cheapest one at the parts store should do just fine, that said, it really is worth investing in a good-quality multimeter you’ll have for decades. 

The How-To Test Your Voltage Regulator

Let’s get after it.

1. Start the Engine

Neither the alternator nor the voltage regulator will do their jobs without the engine running. So, fire that bad boy up. If you’re working with a carb, let it run until it reaches operating temperature and the idle smooths out.

Time To Test a Voltage Regulator!
Though the reading checks out, we still opted to continue testing.

2. Check the Voltmeter

If you have a voltmeter gauge in your car, you can check the reading to get a good idea of the charging system’s current output. In extreme cases, this will tell you right away if there’s an issue with the voltage regulator. However, many old gauges aren’t all that accurate, so you should still proceed in testing to make sure you’re in good shape.

3. Pop the Hood

It’s time to get dirty, pop the hood and break out your multimeter.

Time To Test a Voltage Regulator!
It’s best to familiarize yourself with all readings and make sure you set the multimeter to read DC voltage as that’s what cars operate on.

4. Set Multimeter to Read Voltage

Again, we’re taking a reading of the alternator’s voltage output. Set your multimeter to the appropriate setting and get ready to sweat.

Time To Test a Voltage Regulator!
I just hung the probes for this test. Don’t worry. That positive terminal is getting replaced.

5. Probe Battery Terminals

Simply connect the leads of your multimeter to the battery terminals—positive goes to positive and negative goes to negative.

Time To Test a Voltage Regulator!

6. Inspect Your Reading

Take a look at the voltage reading with the engine at idle. Take note of this number.

7. Inspect Readings With Engine Accelerating

Have an assistant bring the engine RPMs up. They don’t have to hit the rev limiter, but they should bring the engine speed up above 1,500 RPM. Remember, an alternator with no voltage regulator will continue to put out a higher charge as speed increases. You want to take note of any fluctuations in voltage output as engine speed increases.

8. Compare Results to Specs

Alright, the hard parts over. Now, all that’s left is to compare the voltage readings you got with what the manufacturer calls for. Anything outside of that range tells you that the voltage regulator is bunk. 

The Car Bibles Questionnaire

Car Bibles answers all your burning questions!

Q: What causes a voltage regulator to fail?

A:  Anything that causes a voltage spike can cause a voltage regulator to fail. Poor electrical connections, insufficient grounds, jump-starting the system, or overloading the alternator are all situations that can cause voltage spikes. Over time, the regulator can succumb to old age, but it’s usually triggered by some wiring issues or abuse of the system.

Q: Can you drive with a bad voltage regulator?

A: Technically, you can. However, there are some significant risks in doing so. For the most part, the lack of a functional voltage regulator will lead to overcharging of the system. A higher voltage output can lead to a number of electrical issues, which are always an extreme safety hazard. So, if your voltage regulator isn’t working correctly, you should have it switched immediately. Also, keep in mind that wiring issues often create voltage spikes that kill the regulator, meaning you should also find the root of the problem and that can be equally, if not more, dangerous.

Q:  How much does it cost to replace a voltage regulator?

A: The cost to replace a voltage regulator varies substantially by the model. For example, a replacement unit for an older application, like the Charger we’re using as a guinea pig, lists for about $50. In the case of modern cars, the regulator is a part of the alternator itself. If it’s serviceable, the price of the components is usually in the same ballpark. If the system is not serviceable, you’re subject to the price of a replacement alternator which can be a few hundred dollars.

Video Tutorial on Testing a Voltage Regulator

Testing a voltage regulator is extremely simple. But that doesn’t mean everyone finds the written word engaging enough to follow along. Don’t worry. We’ve got a short clip here to help get a visual guide of the testing procedure!

Best Places To Buy Tools and Parts to Test a Voltage Regulator?

Nope. We can’t check out your tool collection from here. But, we can say that you don’t need much to test your voltage regulator. Again, a super-affordable option like the WeePro Vpro850L Digital Multimeter should do just fine for this test. If you are going to dive head-on into the world of automotive repairs, it is wise to spend a little more money, though. The Fluke 87-V Digital Multimeter might be a more expensive model, but the accuracy and longevity of this model are sure to keep you probing away for decades.  

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