8 months ago

How To Easily Diagnose a Bad Alternator At Home

A significant part of your car’s operational mechanisms are powered by electricity rather than the fuel-powered engine. To run all the electronics in your car, it has an alternator. This can be thought of as an electric generator that converts engine power into electricity. 

There can be several situations where the alternators might not work like they’re supposed to and that can result in serious problems. You need to know how to check your car alternator so that you can diagnose it. 

Before that, it is important to understand how the mechanism of the alternator works. Only then will you know how to test the car alternator.

DISCLAIMER: All the information is provided in good faith to help you diagnose the issues with your car’s electrical system. Work on your car with care and if you need assistance, please seek help from a professional.

How does a car alternator work? 

The working principle of a car alternator is the same as that of the electricity generators in hydroelectric power plants, but it is considerably smaller. 

Here’s how this piece of machinery keeps the battery of your car juiced up: 

  • A drive belt or serpentine belt links the alternator to an engine pulley which rotates the alternator.
  • Inside the alternator, there is a coil that’s suspended in a magnetic field. 
  • The rotational motion of the coil produces an electrical current that charges the car battery.

That’s a pretty straightforward mechanism, on paper at least.

Now that we know what an alternator is in a car and how it works, let’s explore what can go wrong with an alternator.

What can go wrong with an alternator?

Like any other piece of machinery, there are a lot of things that can go wrong, rendering the alternator ineffective. Here’s a few of them: 

  • The serpentine belt can lose tension, failing to provide enough traction to the alternator pulley. 
  • The belt can break altogether, resulting in the alternator not spinning at all. 
  • The alternator bearings can get jammed, resulting in them not rotating as they should. 
  • The coil inside the alternator can get fried due to a surge of electricity, causing the alternator to produce insufficient or no current.

Those are some of the things that can go wrong with an alternator, but how do you know if the alternator is having a problem?

Tell-tale signs of alternator problems

As your car has a lot of electrical equipment in it, several signs can show up indicating that the alternator is not providing enough current. Here are some of the indications of a car alternator problem: 

  • The car does not start easily, especially when it is cold. 
  • The headlamps get increasingly dimmer as you drive.
  • The horn of your car does not sound like it normally does. 
  • The alternator serpentine belt creates squeaking sounds.
  • The air-conditioner’s blower does not blow air as it should.

These signs do point towards a faulty alternator but they cannot be definitive, because they are also the same symptoms that indicate a weak battery in your car. So, before you go for an expensive car alternator repair, you need to be sure that it is the alternator that’s bad and not the battery. 

If you start noticing any of these signs while driving, you need to take precautions. A car can only go so far without a functioning alternator. 

What if a car alternator fails? 

If the alternator fails while you are on the road, do these things: 

  • Turn off any of the electronics that you can. This includes the infotainment system, the air-conditioning, and the 12-volt outputs. 
  • Drive smoothly and try not to engage the brakes very often because modern car brakes need electric power to operate. 
  • Avoid heavy traffic. Stopping and moving puts strain on the electrical systems of the car. If you are in heavy traffic, pull to the side, and wait for the traffic to decrease. 
  • Head to the nearest service station and get the problem fixed.

If the signs are not severe and you just feel that your battery’s performance is progressively deteriorating, you can determine if it is the alternator or the battery that is faulty.

Let’s see how to test the car alternator to make sure it is the part that has the problem.

How to check the car alternator?

Although it is a professional’s job to check and determine if a car alternator is really bad, there are some tests that you can run yourself, just to confirm that the alternator is the problem. These include the following. 

Check if the alternator is spinning

To do that, you need to find out where the alternator is in the car.

  • Open the engine bay and look for a device with a pulley linked to the serpentine belt which has two wires attached to it.
  • Once you identify it, start the vehicle.
  • Make sure that the alternator pulley is rotating. 

CAUTION: Serpentine belts can be dangerous if your hair or clothing gets stuck in them. Make sure no loose clothing or hair can reach the engine bay when you are checking the alternator.

Sometimes the alternator might be spinning and still not producing enough current. This can be due to a loose serpentine belt. 

Check serpentine belt tension

The serpentine belt needs to be under the correct tension to provide traction to the alternator pulley. The amount of free play allowed in the serpentine belt varies from car to car but if you can push it easily with your hand, the belt does not have enough tension to correctly operate the alternator. 

If the serpentine belt is under the correct tension and the alternator pulley is spinning, you need to make sure it is putting out an electric current. Here’s how you can do that.

Check the voltage

One of the main indications that the alternator is working is the voltage it puts out. You will need a voltmeter or multimeter to check this. These things are pretty inexpensive; you can pick one up at an auto store for under $20.

  • Turn the engine off and open the engine bay. 
  • Make sure the multimeter is set to DC VOLTS. 
  • Connect the black wire to the negative terminal of the battery and the red one to the positive terminal.
  • The reading should be 12.56 volts. If it is under 12, the battery is either weak or not being properly charged by the alternator.
  • Turn the engine on and check the reading on the meter. If the reading is above 13 volts, the alternator is good, and the battery is causing the problem. 

If the alternator is putting out more than 13 volts and still the car has electrical issues, the battery is weak and needs to be serviced or replaced.

Frequently Asked Questions

What does a car alternator do?

A car alternator produces an electric current to charge the battery of the car. The battery then powers the onboard electronics.

Can you jump-start a car with a bad alternator?

Yes, you can jump-start a car with a bad alternator.

Can jump-starting the car damage the alternator?

No, jump-starting a car does not have any adverse effect on the alternator. However, if the alternator’s coil is damaged, it can affect the electric system of the car.

Can a car run with a bad alternator?

Yes, a car can run with a bad alternator, but once the battery charge ends it will no longer be able to move as the engine needs electric power to function the right way.

How long does a car alternator last?

The alternator of a car is not a consumable item and does not have a rated life. Alternator issues usually show up after a hundred thousand miles.

Do electric cars have alternators?

No, electric cars do not have alternators. These cars have DC to DC converters. These convert the high voltage from the car’s battery to 12 volts for using 12V equipment on the car.

How do you fix a car alternator?

Fixing a car alternator is a professional task and is done by trained, skilled, and certified professionals.

How long will my car battery last without an alternator?

That depends on the number of electrical devices that are using the battery power.

What causes the car alternator to fail?

Car alternators usually fail when the battery is bad. A worn-out battery can put more strain on the charging system than the alternator can handle, causing the alternator to fail.

How do you check if the battery or alternator is bad?

Check the voltage at the battery terminals with the engine running at 2,000 rpm. If the voltage is above 13.5 volts, the battery is bad. If it is under that, the alternator has a problem.

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