Many people assume that the car battery is the only thing that powers all of the car’s electrical components.
But this is not true. The alternator plays a vital role in supplying the car with alternating current, recharging the battery, and starting the car.
When your alternator fails, the battery drains quickly and you end up with a broken car. But what can cause the alternator to deteriorate and stop charging the battery?
The most common reason an alternator will not charge the battery is due to worn carbon brushes or a damaged alternator. It can also be caused by a blown fuse or poor wiring. If your serpentine belt has broken, the alternator will of course not charge either.
Now that you know the most common reasons, you probably want to know them in detail as well. Here is a list of the 5 most common reasons why your alternator is not charging the battery.
Causes of discharged alternator
1. Worn carbon brushes or damaged alternator
The most common reason your car won’t charge its battery is actually a worn or damaged alternator.
You can carefully tap it with a hammer while the car engine is running while you check it with a multimeter on the car battery to see if the voltage changes.
If the voltage changes and returns to normal when tapped with a hammer while the car is running, the Carbon brushes They are worn and must be replaced in the alternator, or in the alternator assembly.
Sometimes there is an electrical problem with the alternator, and even if the voltage does not change, it can be damaged.
Another common cause is poor diode board or a Tension regulator. You may need knowledge about alternators to replace them in most cases.
It was more common to replace parts inside the alternator such as carbon brushes, diode plate or voltage regulator in older cars. Alternators these days are quite cheap, and most of the time it is better to replace the entire alternator.
If you have already replaced it with a new alternator, but it still does not charge the battery, you should continue reading on this list.
2. Broken serpentine belt
A closer look at the alternator will reveal a system of pulleys and belts that convert mechanical energy into electrical energy.
The serpentine belt powers the alternator, and if it fails, the alternator will stop working as the belt wears and breaks, or the pulley becomes damaged.
It can also occur if the serpentine belt is not properly tensioned. Most cars have automatic tensioners, but these can fail, so it’s best to double check them.
Some older cars have manual tensioners, in which case you may need to adjust the serpentine belt.
The serpentine belt and pulleys are usually fairly easy and inexpensive to replace.
3. Defective fuse
There is often a huge fuse connected to the large alternator power wire. This is usually an 80 amp or larger fuse and is most commonly found in your car’s fuse box in the engine compartment.
Fuses blown due to overvoltage or wear. When this happens, the current stops flowing from the alternator. The solution is to consult your car’s manual to find the particular fuse that controls the alternator and replace it.
On some cars, you can also find another small fuse for the alternator control, usually a 15A to 20A fuse.
4. Wiring or connector problems
An alternator usually has 3 or 4 wires to work properly. You will find one large main cable with two or three small ones.
All of these cables are important to the operation of the alternator and if any of them break, you may lose charging function.
Check the connectors on the large power cable between the alternator and the car battery to make sure there is no corrosion. You can usually find the cable getting hot if there is a bad connection somewhere.
Check or measure these wires with a multimeter. Remember that your measurement is not always correct because you have to carry half-broken or poorly connected test leads.
Typically, you should have 12 volts on one of these wires, and the other goes to the battery light on the dash. If you have a third, it often goes to the engine control unit. To measure this correctly, you need a wiring diagram for your specific car model.
5. Damaged car battery
The alternator and car battery work hand in hand. A really bad car battery may not support alternator charging, which will cause the alternator to not charge at all.
In theory, a car can only run on charging from the alternator, but this can cause severe voltage spikes and other strange symptoms, meaning that a faulty battery can cause the alternator to stop working and also charge.
6. Engine control module error
Cars are increasingly equipped with modern electronics. In this sense, the engine control unit (ECU) controls most of the car’s electrical components.
Modern cars also control the alternator. In rare cases, there may be a problem with the engine control module not controlling the alternator charging.
Check the trouble codes with an OBD2 scanner to determine if something is another damaged part that is preventing it from charging.
In rare cases, there may be a faulty engine control unit. But always check all other possible causes first.
Diagnose an alternator that is not charging
There are some simple steps you can follow to check the operation of your alternator.
- Carefully tap the alternator with a hammer while the engine is running; If the load returns to normal, the internal carbon brushes are worn and need to be replaced.
- Check the large alternator power wire and fuse, usually a large 40-60 amp fuse near the battery.
- Check the ground cable between the engine and the body.
- Check the serpentine belt and make sure the alternator is turning with the engine.
- Check the small power cable and charging light cable. You can measure it with a multimeter, but you may need a wiring diagram and some automotive electronics skills to get it right.
- You can measure the diode assembly and voltage regulator to make sure they are not damaged. You can replace them with some alternators, but it often costs the same to buy a new alternator these days. It’s up to you to decide what you think is worth it.