Is your car battery continuously dying? It might be an alternator that isn’t charging properly.
But before you jump to conclusions and assume your alternator may be bad, let’s first look for reasons the alternator is not charging the car battery. This way, you may be able to recognize the charging system problems so you can fix them before your car doesn’t start at all.
7 Reasons Your Alternator Is Not Charging the Battery
A lot of people get mixed up when they start to have electrical problems with their vehicle. Misdiagnosing electrical problems as a bad battery instead of a bad alternator happens all the time.
To differentiate between the two, you must understand what causes an alternator to stop charging. Next, you can go ahead and inspect the vehicle to help determine if it is your alternator.
Below are some of the more common causes for the alternator not charging.
#1. Bad Alternator or Battery.
Let’s start with the most obvious. Both alternators and batteries have a finite lifespan. Car batteries usually last for 2 to 5 years, with lifespan determined by driving habits and climate. Batteries will usually outlast hot weather if all other variables are the same.
Modern alternators typically last between 80,000 and 120,000 miles, 5 to 8 years, and anything longer than that would be based purely on luck. You can regularly test the battery and alternators to help predict when they are nearing the end of their useful life.
#2. Broken Belt or Pulley.
The alternator relies on a belt and pulley system to help convert the mechanical power to electrical power.
Serpentine belts do stretch and break over time. Belt tensioners and other pulleys can become broken (i.e., from an accident) or may fail simply from wear and tear and functionality.
If the belt is broken or the pulley tensioners are not functioning appropriately, the alternator won’t provide a charge to the battery. You should do regular visual inspections to help catch potential issues early.
#3. Blown fuse.
Some vehicles have alternators that require the use of a fuse or fusible link to operate. Fuses can blow from power surges and/or age. Once the fuse blows, your alternator will not charge the battery.
Use the owner’s manual to help locate your alternator fuse and inspect it if you are experiencing a charging issue.
#4. Wiring Problems.
A vehicle’s electrical system is made up of various wiring components that supply power to the alternator. If a wire or connector becomes disconnected or damaged, we will lose the ability to generate or create power, and the alternator will not be able to charge the battery.
Finding and fixing issues with wiring can take professional diagnosis and repairs. However, unlike a parasitic battery drain, which can take place almost anywhere, a wiring issue in this situation will be localized and easier to locate.
#5. Worn or Damaged Alternator Bearings.
The alternator consists of many bearings that allow the internal components to rotate smoothly. With constant use as well as heat and vibration, the bearings can wear out or become damaged over time.
In the case of bearing wear or damage, the alternator rotor may not be able to spin freely as it should, resulting in increased friction. As a result, the alternator may fail to produce sufficient power to continuously charge the battery.
When the bearings are failing, the alternator may produce a grinding or whining sound that may be noticeable around the alternator area.
#6. Faulty Voltage Regulator.
The voltage regulator modulates the amount of electrical output from the alternator battery.
It helps maintain the correct voltage of the electrical system, which is typically between 13.5 to 14.5 volts. If the voltage regulator fails, it either allows the alternator to undercharge or overcharge the battery.
In an undercharging situation, the battery is unable to receive sufficient power, while in the reverse, an overcharging situation, will tend to damage the battery and other electrical components. Some vehicles have the voltage regulator built into the alternator, while others have a separate voltage regulator.
#7. Computer Error.
Most vehicles made today have a central computer system (ECU, ECM, or PCM) that controls all of the subsystems and components on the vehicle, including the alternator.
A computer error causes the alternator to malfunction, preventing it from being able to charge the battery properly. This may require diagnostic testing to identify and fix.
You do not want to misdiagnose because having to replace and reprogram a new control module is not typically an inexpensive repair.
How to Repair
The most frequent cause of a failed alternator to charge a battery is that one of them is going bad. Follow the steps below to first eliminate the battery and alternator, and then proceed onward.
#1. Begin with the Battery Test (check its voltage).
- Turn off the engine and connect a voltmeter to the battery terminals.
- A healthy and charged battery should read between 12.2 and 12.6 volts.
- If your test reads considerably lower, your battery may be your issue.
#2. Test the alternator output.
- Start the engine and let it idle.
- Measure the battery voltage again, and this time the voltage should read between 13.8 and 14.2 volts.
- Spin the engine up to about 2,000 RPMs.
- If at this new speed, the voltage drops off or does not increase, your alternator is not charging the battery properly.
#3. Visual Inspection.
- Inspect the alternator belt (look for wear and breakage, listen for unusual noises, and check to make sure it is tight enough)
- Inspect the alternator pulley (look for damage, unusual noises, movement, and misalignment)
- Inspect the wiring (look for loose or corroded connections)
#4. Locate and check the fuse.
Find the alternator fuse by consulting your vehicle’s manual (many manufacturers are now using computer systems, so the manual is necessary). Remember to replace the fuse if it is blown.
#5. Seek a Professional Diagnosis.
If you have completed the above tests and have not found the solution, or you do not feel comfortable trying to do these tests, you should have a mechanic evaluate the alternator.
A mechanic can perform more advanced diagnostic tests, check for any computer issues interfering with the charging system, and disassemble and inspect internal components of the alternator.
#6. Repair or replace.
Based upon the diagnosis:
- Minor repairs can often fix problems like loose wiring or a worn belt.
- If the problem is a serious internal problem with the alternator, or the alternator has simply failed, then usually you are better off replacing the bad alternator.
- In addition, if your vehicle is older, you might be able to make a diagnosis on the suitability of the repair or replacement option, depending also on the costs of any repairs that are not relatively inexpensive, as opposed to replacement costs.
Common Misconceptions About Alternators
Car owners typically hold a lot of misconceptions about alternators. Here are some of these common misconceptions:
Myth: Alternators charge the battery when the car is not running.
False. Alternators can carry out their functions only when the engine is running and will not charge the battery if the car is turned off.
Myth: Dead battery = Bad alternator.
This is false. A dead battery can be caused by a bad alternator, but a battery can fail due to leaving the lights on or any other malfunctioning system. In fact, the battery could just be bad.
Myth: Alternators last forever.
Nothing lasts forever. When it comes to alternators, they will last 5-8 years (80k-120k) depending on how the vehicle is driven, how old the alternator is, and the vehicle type.
Myth: Jump starting a car fully charges a battery.
Jump starts only supply just enough power to start the engine. The battery will begin to charge from the alternator but it can take time.
Myth: All alternators output the same capacity.
Alternators can be rated and can output from a couple of hundred watts to 1000 watts. In fact, some high-performance vehicles probably have higher output alternators just for the extra electrical accessories.
Myth: Noisy alternator is a bad one.
Noisy alternators can indicate problems. It is normal for alternators to make some noise. If it makes a great deal of noise and/or backfired noise, it’s worth a look; however, it is not exceptionally reasonable to assume it’s bad.
Myth: Alternators charge the battery only.
Actually, alternators only charge and supply power to all electrical systems when the engine is running granted it doesn’t exceed the rated output of the alternator. Not only the battery.