Alternator Not Charging The Battery: Here’s 4 Reasons Why

Is your car’s charging system behaving differently? Do you see your dashboard displaying the Charge warning and not lighting down after your start your engine? If so, there could be issues with your alternator or the charging system.

See, you need a working charging system to keep your car running after it starts. Most of the electricity runs out when starting the engine. And the engine needs the electricity generated by the alternator to keep it running.

But what if it fails to work or charges the battery? Before coming up with any conclusion, you need to find out why your alternator is charging.

4 Causes Of Alternator Not Charging

There are many reasons why the alternator won’t do its work.

1.     Worn out Alternator or Bad Battery

The alternator and the battery work hand-in-hand to run your car engine. If any one of these two is at fault, I’m afraid your charging system won’t work. There are many reasons your alternator can get faulty. You got to test your alternator with simple steps.

Set up a multimeter to monitor the voltage when doing the test. Tap the alternator lightly while running the engine and check if the voltage changes. If it does and the voltage returns to the normal level, the alternator has worn out carbon brushes, and it would be wiser to replace the entire alternator.

But even if the voltage did not change, it does not mean your alternator still has no problem. Sometimes, it’s in the diode plate or voltage regulator.

Your alternator should last up to seven years or after every 80,000 miles. On the other hand, your battery should serve up to five years. If the problem is in the battery, it will not take the generated electricity by the alternator.

Your car battery’s life could extend if you have a colder environment. But if you live in a hot location, expect your battery to last shorter.

2.     Broken Belt or Pulley

Your belt system and pulley work hand-in-hand to convert mechanical energy to electrical energy. If one of them has broken, your alternator will not charge.

The serpentine belt rotates continuously to generate power. It powers not only the alternator but other systems: the AC compressor, power steering pump, or even a water pump. They call this belt the drive belt because of its ability to generate power.

But because of the constant rotation, it may wear out, overstretch, and snap broken. If you have a broken drive belt, it will not generate energy to supply the alternator. But sometimes, the belt slips out, misaligns, or detaches from the pulleys. You can find out quickly if this is the case since it will produce squealing noises.

Like the drive belt, the pulley constantly rotates to distribute power to all other parts or components attached to the crankshaft. If the pulley malfunctions, it will disrupt the system, cause irregular noises and possibly damage the other components connected to the crankshaft.

Auto mechanic repairing drive belt in the engine.

You can easily spot the problem in the pulley if it doesn’t only affect the alternator but also the power steering pump. If you noticed constant engine vibration or noises, idling of the engine, dead alternator notice, and the power steering is also affected. The problem is in the pulley.

If the pulley and driver belt is faulty, your alternator will not charge.

3.     Wiring Issues

There are about three or four main wires connected to the alternator.

  • The exciter wire connects to the alternator’s L Terminal to keep it running.
  • The ignition wire turns the field coils and voltage regulator on.
  • And lastly, the positive and negative cables connect the battery and the alternator to transmit converted electrical energy.

If one of these wires is burnt or broken, the alternator will not charge. The alternator will not run if the problem is in the main wire. Additionally, the field coils or the voltage regulator will not do their job if there’s no running electricity to power it up.

The power cable between the alternator and the battery should have no corrosion. If there’s a faulty connection, the wire gets warm. Also, it is advisable to have a ready multimeter in your toolbox to test the wires. Find the cables that have a poor connection or are half-broken.

4.     Blown Fuse

A fuse is a safety mechanism for your car, and it protects other electrical components in it. The fuse may break if there is a sudden blow or excessive current. And this will cause the alternator not to charge.

Note that there are primary and secondary fuses on your charging system. The primary fuse is a high amperage fuse, most likely 80A, and connects to the battery terminal of the alternator. The secondary fuses have low amperage and connect to sensory and ignition terminals. They are most likely 15A to 20A.

Replacing the fuse in the fuse box of the car.

When you have a problem with one of these fuses, it will affect your charging system. Your car will have a dead battery, and your engine will not run if the primary fuse has blown up. Moreover, your lighting components, such as headlights and dash lights, will start blinking or dimming if the alternator fuse has blown.

Your dashboard shows charge system warnings on your dashboard if you have a blown-up fuse. It could also trigger more warnings as your charging system undercharges when you have a blown-up fuse.

Moreover, your electricity shortage due to a blown-up fuse may trigger electrical warnings on your other modems or computer-controlled devices attached to your computer.


If you find your alternator not charging, one of its components has malfunctioned. When testing the voltage, you want them to have a reading around 12V or 13V. You must find out the cause of the alternator not charging or undercharging.

Surprisingly, these problems in the alternator or battery rarely happen. These two components of the charging system have a long lifespan. If the problem is in the alternator components, it is best to replace it entirely than repair it as other components may get faulty sooner.

And when you replace your alternator, consider replacing your drive belt too. It is probably wearing out too. It is not so costly to replace it, anyway.

If you’re still having trouble finding the causes, you can always seek help from the experts.

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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