How to Test Alternator By Disconnecting Battery – Do and Don’t ?

Last Updated on May 25, 2023 by admin

The alternator is a key part of the car’s electrical system. It creates power for the car to run, and it also recharges the battery. If there’s something wrong with your alternator, it can cause all sorts of problems.

When your car’s battery is drained, the first thing you likely think to do is charge it up. But if your car won’t start and you’re not sure why, testing the alternator should be your next step.

You want to know “How to Test Alternator By Disconnecting Battery ” but should you use this method ?

In this post, we’ll show you how to test the alternator with the right method . Stay tuned for more tips on troubleshooting your car’s electrical system.

How to Test Alternator By Disconnecting Battery – Not Recommend Use This Method

Here is the way you should not use :

  1. Turn on the vehicle.
  2. While it is running, carefully remove one of the 12V battery leads.
  3. See if the vehicle continues to run. If the vehicle keeps running, the alternator is working. If the vehicle stops running, the alternator is not working.

Why Test Alternator By Disconnecting Battery Is Not Safe ?

Testing your alternator is an important part of car maintenance. But testing the alternator by disconnecting the battery is not safe and can damage your car’s electrical system , you will run the risk of killing the regulator.

The alternator is therefore not designed to run the engine directly, and running it without a battery to handle burst current draw could fry the regulator.

What is an alternator and why would you need to test it?

An alternator is a device that generates alternating current (AC) by electromagnetic induction. It is typically used in automobiles and other vehicles to charge the battery and power the electrical system.

You might need to test your alternator if your car is having problems starting, the battery isn’t holding a charge, or the electrical system is acting up. Testing the alternator is relatively simple and can be done with a multimeter.

How To Test An Alternator With A Multimeter ? Step by step guide

If your car’s battery is not charging, it could be because the alternator is not working properly. To test whether or not your alternator is functioning correctly, you can use a multimeter to measure the voltage at the battery. If the voltage is low, then the alternator is likely not working correctly.

Step 1 : Open your car’s hood and locate the battery.

Step 2 : Using the red lead on your multimeter, touch the positive (+) terminal on the battery.

Step3 : Touch the black lead on your multimeter to the negative (-) terminal on the battery.

Step4 : Set your multimeter to read DC volts.

Step5 : Start the car and let it run for a few minutes.

Step6 : Observe the reading on the multimeter. If the voltage is below 12 volts, then the alternator is not working properly.

Step7 : With the car on but all accessories off, read the voltage between the battery terminals (a healthy alternator will read about 14V)

Step8 : With the car on and all electrical accessories on, read the voltage again (a healthy alternator will read about 13V)

How can you test my alternator without voltmeter or multimeter ?

If you don’t have a voltmeter or multimeter, you can still check an alternator.

Step1 : Start the car and turn on the engine. Rev it to 2000 RPM. Observe the ampere or voltage gauge (if your car has one) on the instrument panel. Turn on all of the car’s electrical accessories. A high reading on the gauge while the car is idling indicates that the alternator is charging the battery.

Step2: Open the hood of the car and listen to the alternator while the engine is idling. A squealing or screeching sound might mean that there is a problem, like a loose belt. The sound becomes more noticeable when you turn on accessories.

Step3: Turn your car radio to the lowest frequency on the AM band. Turn the volume down low. While stepping on the accelerator, try to listen to the sound coming from the speakers. If it’s a whining or buzzing sound, it’s also a sign that something is wrong with the alternator.

Common Symptoms of a Bad Alternator

If your car is starting to act up, it might be time to get your alternator checked. Here are some common symptoms of a bad alternator:

-Your car won’t start

-Your headlights are dim

-Your car is making strange noises

-You notice a burning smell coming from your car

-Your battery dies quickly

Your car won’t start

One of the most common signs of a bad alternator is when your car won’t start. If your battery is working but your car still won’t start, it could be because the alternator isn’t charging the battery.

Your headlights are dim

Another sign of a problem with the alternator is dim headlights. If the alternator isn’t working properly, it can’t provide enough power to run all the electrical components in your car, including the headlights.

Your car is making strange noises

Strange noises coming from under the hood could also be a sign of a bad alternator. If you hear a grinding or squealing noise, it could be an indication that the alternator bearings are failing.

You notice a burning smell coming from your car

If you notice a burning smell coming from your car, it could be because the alternator is overheating.

Your battery dies quickly

If you find that your battery dies quickly, even after being fully charged, it could be a sign that the alternator isn’t working properly. The alternator is responsible for keeping the battery charged, so if it’s not doing its job, the battery will drain quickly.

What should you do if your car has a bad alternator?

If your car has a bad alternator, it’s important to have it checked and replaced as soon as possible. A bad alternator can cause a number of problems, and if left unchecked, it can eventually lead to your car not starting or running properly. If you notice any of the symptoms of a bad alternator, be sure to take your car to a professional mechanic or auto technician for diagnosis and repair.

How to replace an alternator in your car?

1. Park your car and turn it off.

2. Pop the hood and locate the alternator.

3. Disconnect the negative (-) terminal from the battery.

4. Disconnect the wires from the alternator.

5. Remove the bolts that hold the alternator in place.

6. Install the new alternator and tighten the bolts.

7. Reconnect the wires to the alternator.

8. Reconnect the negative (-) terminal to the battery.

9. Close the hood of your car.

10. Start your car and let it run for a few minutes to make sure that the new alternator is working properly.

If you notice any problems with your car’s alternator, it is important to have it checked by a qualified mechanic as soon as possible. Replacing an alternator is a fairly simple process that most mechanics will be able to do in a few hours. However, if you are not comfortable doing it yourself, it is always best to leave it to the professionals.

Tips for prolonging the life of your car’s alternator

Avoid using electrical accessories when your engine is not running. This includes things like cell phone chargers, laptop chargers, and even cigarette lighters. These can all draw power from your alternator, causing it to work harder than necessary and potentially shorten its lifespan.

If you must use electrical accessories while your engine is off, make sure to disconnect them when you’re finished so they don’t continue drawing power needlessly.

Keep an eye on your car’s battery health. A healthy battery will put less strain on your alternator, allowing it to last longer. You can check your battery’s health by testing its voltage with a voltmeter.

Make sure your car’s belts are in good condition. A loose or worn belt can cause your alternator to work harder than necessary, potentially damaging it.

Have your alternator checked regularly by a qualified mechanic. This will help ensure that it is working properly and catch any potential problems before they cause damage.


We hope this article was helpful in showing you how to test alternator . If you found this information useful, please share it with others who may also find it helpful. Alternators can be tricky things to diagnose and repair, so we want to make sure as many people as possible have access to this valuable information.

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How To Know If Car Battery Is Dead ?