alternator causes

Alternator Not charging – Causes and Fixes

In Engine by Magnus Sellén11 Comments

alternator causes

Many people assume that the car’s battery is the only thing that powers all electrical components in the car.

But, this is not true.

The alternator plays a vital role in supplying power to the car’s AC, recharging the battery and ignition. When your alternator is faulty, the battery power is drained fast and you will find yourself with a stalled car. But how do you diagnose a faulty alternator?

Reasons why your alternator is not charging

There are several different reasons why your car may not charge properly. Here are the most common reasons.

1. Worn out or damaged alternator

The most common reason why your car is not charging is actually because of a worn out or damaged alternator. You can carefully tap it with a hammer while the car engine is running while checking it with a multimeter to see if the voltage is changing. Sometimes there is an electrical problem in the alternator and even if the voltage does not change, it might be damaged.

2. Broken belt

A closer observation of the radiator will reveal a system of pulleys or belts that work to convert mechanical energy into electrical energy. The alternator will stop working the moment your belt wears out and breaks or the pulley becomes damaged. These items are easy to replace.

3. Faulty fuse

Fuses blow up due to a power surge or they wear out. When this happens, current will stop flowing to the alternator. The solution is to check your car’s manual for the particular fuse that controls the alternator and replace it.

4. Computer error

Cars are increasingly coming with modern electronics. In this regard, the engine control unit (ECU) controls most of the car’s electrical components. When there are problems with the ECU, then your alternator will stop charging.

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4. Wiring issues

Power is supplied to the alternator through a set of wires. With time, these wires can become loose and cause the alternator to stop charging.

5. Damaged battery

The alternator and the car’s battery work hand in hand. A good battery should give you service for the next five years before its lifespan ends. If your battery is dead, then it will not give power to the car’s alternator. The alternator normally lasts longer than the battery.

Diagnosing a faulty alternator

There are some easy steps you can go through to check the function of your alternator.

  1. Tap the alternator carefully with a hammer while the engine is runnin; if the charging goes back to normal, the coals inside it are worn out.
  2. Check the large power cable to the alternator and the fuse, usually a large 40-60 amp fuse located near the battery.
  3. Check the ground cable between the engine and the body.
  4. Check the serpentine belt and make sure the alternator is spinning with the engine.
  5. Check the small power supply wire and the charging light wire. You can measure it with a multimeter but you might need a wiring diagram and some car electronic skills to do this correctly.

How the alternator works

alternatorThe main function of the alternator is to power the car’s battery. When your AC, headlights, and stereo are on, a lot of power is needed. The battery cannot supply all this power on its own, hence the need for the alternator. The alternator converts mechanical energy into electricity.

The alternator is connected to a set of belts which when loose can cause it not to function as required. To differentiate an alternator problem from the battery, you will need to use a voltmeter to check for voltage. First, turn off the engine and check the battery voltage.

A fully charged battery should have a reading of 12.65 volts. Next, turn on the engine and recheck the voltage. You should have a reading of 13.5 to 14.5 volts. This is an indication that the alternator is charging the battery just fine.

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Symptoms of a bad alternator

Battery problems

The car’s battery is incapable of charging all the car’s electrical components. This process is continuous whenever your engine is running. When the battery charge is not restored, you will first experience problems starting the car. Secondly, you will notice the flickering lights.

The battery is usually the first culprit when you have problems with electrical current in the car. If you need to use jumper cables in the morning but the car continues running just fine after starting then the problem is the battery rather than the alternator.

Battery light

If the alternator is not charging the battery, you will have a red “ALT” or “charge” sign on your dashboard. This means that your battery is no longer being supplemented for power by the alternator. You will need to recheck the wiring because the light could also be faulty. Most motorists will also experience dimming lights whenever the battery is not being fully recharged.

Slow engine cranks

When you have a faulty alternator, the car’s engine will crank slowly and at times even refuse to crank. You will also need to inspect the ignition system before concluding it is the alternator at fault. The failure to crank may also be accompanied by a buzzing or squealing noise under the hood. This can be a result of a loose or worn-out serpentine belt.

Noisy alternator

If your alternator makes a lot of noise, then it could be that you are experiencing problems with the belt or pulley. Also, the belt could be misaligned with the pulley. You can fix this by replacing the belt then properly aligning the belt to the pulley. If the noise persists, then your alternator has outlived its purpose and it is time to replace it.

Noise from the alternator could be caused by a faulty rotor shaft, rectifiers, bearings, slip rings, stator winding or brushes. You will need to carefully inspect each of these components and replace them. One sure way of confirming that the noise is coming specifically from the alternator is to use a vacuum hose. After starting the engine, connect one end of the vacuum hose to the alternator with the other on your ear. You will hear noisy bearings and other sounds.

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Charge indicator comes on while driving

This could be due to some faulty alternator wiring. You will need to inspect the belts and the wiring that surrounds the alternator. A bad circuit can also cause the above.

Alternator voltage leak

Diodes within the alternator are critical for converting the current from the alternator into direct current. The diodes wear out with time and you may start experiencing dimming lights. You can use an AC voltmeter to check for leakages. Faulty diodes can easily be replaced, but you will need to dismantle the alternator.


It is impossible to drive the car with a faulty alternator. While it is the work of the battery to power the electrical components in the car, it cannot do this alone. Loose serpentine belts, worn out bearings and faulty diodes can all contribute to your alternator not functioning as it should.

You will need to carefully inspect each component of the alternator and check for wear. Your mechanic can help you dismantle the unit, replace worn out parts and fix it again. A good working alternator should be noise free. If you start hearing noises from the engine then it means you need to tighten the belts.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

11 thoughts on “ Alternator Not charging – Causes and Fixes ”

  1. Good day magnus your explanation on the alternator has been so helpful and I quite appreciate the in-depth knowledge on this singular topic. Well done.

  2. 1999. 6 magnum dodge Dakota. New battery . New alternator. But alternator want charge. Why??

  3. Hey magnus
    I’m using 24volts on my machine, I connected two 12volts batteries , which is 24 volts. My alternator charging does not exceed 25. 7 volts,, what could be the problem??

  4. For My KIA SEDONA , i installed a new battery and a new alternator after giving me problems 2,3 times. But it still keep not charging.

    1. The rectifier converts the AC electricity being produced by the alternator into DC so it can be stored in the battery. The battery’s DC power is what runs everything in your car, even your alternator.

  5. Didnt use bmw for a while and battery wouldn’t hold charge so replaced with new battery started first time then ran flat and wouldn’t start no lights etc….recharged battery and started first time again…could this be the alternator.?…thankyou Karen.

  6. My 87 Chey truck. My alternator charges when disconnected from battery. When I reconnect the battery the alternator stops charging and starts whining. One of the alternator wires reads as ground.

  7. Hi

    I have a 1989 Honda Prelude which I have just put in a brand new alternator and brand new battery.
    This after the battery light did not light up when ignition key was switched on.
    I can start car but as soon as I disconnect battery +ve terminal, the engine shuts down: a sign that alternator is not supplying power.

    where should I look next to fix the problem?

  8. I had my battery tested and it was fine they told me that it was my alternator in my 2001 Lincoln Town Car Signature Series as soon as I shut it off it doesn’t even click when I try to start it again I just now came into possession of it 3 days ago and then this has been my only issue with it I haven’t even been able to drive it since I got it so as far as I know that is the only issue I have I was told that you cannot drive with a bad alternator so what else could it be

  9. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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