How to Test Alternator by Disconnecting Battery

How to Test Alternator by Disconnecting Battery

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A vehicle resembles a human body in myriad ways. In humans, we refer to the brain as the most prominent organ. The same applies to vehicles, where mechanics refer to the alternator as the powerhouse or the brain of the vehicle.  Now, the alternator is tasked to power the various electrical components of the car while still charging the battery for later use. As a mechanical part, the alternator can sometimes fail due to one reason or another. In this case, you need to learn how to test alternator by disconnecting battery to save yourself from massive trouble.

Now, the alternator is designed to work in perfect harmony with the battery. The battery provides the voltage to start the engine while the alternator does the rest. So, in case the alternator fails, then it means the battery will not get sufficient charge and the car’s electrical components will not get power.

So, to save you the trouble, this short guide will discuss how to test your car’s alternator by disconnecting the battery. We’ll also discuss some common symptoms of a failing alternator and detail an alternative method of testing the alternator.


Which are Some Signs of a Failing Alternator?

Repairing the alternator is quite costly. So, before you point fingers at this component, it’s always wise to watch out for common symptoms that point to a failing or faulty alternator. You see, sometimes the problems might not be the alternator but rather other components such as the battery. So, with that said, here are 5 signs you should watch out for.


  • 1. Battery Indicator Light

The first obvious sign of a failing alternator is the battery indicator light on the dashboard. Depending on your car’s model, this indicator light will appear in the form of a battery or a “Check Engine” icon. You see, a normal alternator should run at 13 – 14.5 volts. So, in case the voltage drops or goes higher than this, then it means the alternator is faulty.


  • 2. Dead Battery

The second common symptom of a dying alternator is the battery losing charge too fast. You see, the purpose of the alternator is to charge the battery. In case the alternator is faulty, then the battery will get overly bored without being compensated. Eventually, the battery will die leaving you with a dead motionless vehicle.


  • 3. Dim Headlights

When you start the engine, the alternator kicks in by charging the battery and providing adequate voltage to the rest of the electrical components. Now, if you notice your car’s headlights, interior lights, and dashboard lights are flickering or struggling to stay alive, then there’s a possibility the alternator is not supplying sufficient power output.


  • 4. Strange Noises and Weird Smells

There are different types of noises you’re likely to hear when the alternator is going bad. The first one is a loud squealing sound that indicates the serpentine belt is either worn out due to age or it’s misaligned.

The second one is grinding or growling noises. This indicates worn-out inner bearings that cause the alternator to work slower than usual.


  • 5. Frequent Stalling

If you’re having problems starting the car, or what you’re seeing is frequent stalling, then it means the battery has an insufficient charge to start the engine. In fact, if what you’re hearing is clicking sounds when you start the engine, then it simply means you have a dead battery.

On the flip side, engine stalling and difficulty starting can be caused by issues in the ignition system. Since the spark plugs, distributors, and the injection system all require adequate power to work, a failing alternator will not supply sufficient power output to these components leading to failure.


How to Test Alternator by Disconnecting Battery Positive or Negative

Now that we’ve discussed some common symptoms of a failing alternator, how then do you test your alternator by disconnecting the battery? Well, let’s find out.

  • Step One: Park in a Safe Place

Before you commence with the testing process, you should note that such delicate tests should be conducted in a safe place. Therefore, it’s recommended that you park your auto in a safe location such as a parking lot or driveway.

  • Step Two: Inspect the Car’s Hood

Once you’ve parked on level ground away from kids and pets, you can now open the car’s hood to inspect the engine and the rest of the components. This is to ensure that everything is in stable condition.

  • Step Three: Start the Engine

Next, step into the driver’s seat and start the engine. Allow it to idle for some minutes to get enough time to identify symptoms that tell the alternator is indeed damaged.

  • Step Four: Disconnect the Battery’s Positive Terminal

Once the car starts, get out of the driver’s seat and inspect the battery. In case of any corrosion in the terminals, remove them immediately. When you’re done, disconnect the positive terminal of the battery while the engine idles. Try to identify any difference in the idle when the positive terminal is disconnected.

In case you don’t see or hear any changes, then it means the alternator is fine. On the other hand, if you hear any changes on how the engine idles or if the car runs for a while then stalls, then it means you have a faulty alternator.


Is this Method Safe?


To be honest, testing a faulty alternator by disconnecting the battery is very dangerous. You see, the alternator is tasked to charge the battery while supplying electricity flow to various electrical components in the car.

When the battery is disconnected, the alternator works as a backup power generator. The risky part with this maneuver is that the alternator might supply excess voltage that can potentially burn the fuses within the car’s fuse box.

This can lead to damage to multiple electrical components. Note that other than supplying power, the battery helps to stabilize the amount of electric current coming from the alternator.


An Alternative Method You Can Consider


As you can see, disconnecting the battery terminal to test a faulty alternator is quite dangerous as it can cause you to fry a few electrical components. So, to avoid suffering hefty costs of replacing your car’s electrical components, it’s better to try an alternative method such as testing the alternator by using a multimeter.

  • Step One: As usual, you’ll need to start by parking in a safe place such as a parking lot or a driveway. Make sure the ground is even to avoid any problems.
  • Step Two: Turn the engine on and turn off all the electrical components.
  • Step Three: Next, use a voltmeter to test the positive and negative terminals of the battery. Record the readings and move to the next step.
  • Step Four: In this step, you’ll be applying a heavy load on the battery when testing its health. So, turn on all the electrical components in the car and test the voltage readings again.

So, in the first test, the voltage reading should be around 14V while in the second test, the voltage reading should be 13V. Any reading that goes beyond or below the mentioned volts means that the alternator is faulty and needs a thorough inspection.


Final Thoughts


So, there you have it. In case you’ve been asking how to test the alternator by disconnecting the battery, then we’ve detailed a simple procedure you can follow. But, just as we’ve discussed, this method is not safe. Remember, other than testing the alternator, you need to ensure that your car’s electrical components are safe.

For that reason, you need to pick a much safer method, which is testing the alternator using a multimeter. Thankfully, we’ve added some steps you can follow meaning you don’t have to waste your time searching for any information.

Finally, yet importantly, the alternator is a vital component that heads the car’s electrical department. When coupled with the battery, these two components provide sufficient power to start the engine and run all the car’s electrical components. Therefore, the alternator and the battery demand regular checkups and maintenance to run smoothly.

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