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Alternator Overcharging: Signs and Sources

Alternator Overcharging: Signs and Sources

Your vehicle’s alternator has a few jobs. It helps to keep the battery fully charged and supplies additional electricity for operating other accessories (when needed). 

It isn’t uncommon for your alternator to be weak and unable to supply adequate current. However, it’s also possible that the alternator is producing excess current.

Some signs your alternator is overcharging include high voltmeter readings, low battery electrolyte, burnt bulbs, battery heating, swollen battery, or seeping battery.

Serious damage can occur, so it’s best to get the issue fixed immediately.

Learn more about the signs your alternator’s battery is overcharging here.

Signs Your Alternator is Overcharging

You will notice a few signs that your vehicle’s alternator is overcharging. Some of the most common signs this is happening include:

High Gauge Reading

If your alternator is overcharging, it will cause your vehicle’s voltmeter (found on the dash) to show a high reading related to the voltage. This may or may not vary based on engine speed.

Normally, the reading should be high when you start up and then fall back into the normal range.

If the alternator is overcharging, the meter will stay in the high reading position after the initial startup.

Low Battery Electrolyte

Are the battery electrolyte levels low?

If so, it’s a sign the alternator is overcharging the batter. It’s caused by the heat that’s generated from overcharging that cause the electrolyte to evaporate.

When the electrolyte is depleted, the battery won’t be able to hold an electric charge as, well. This results in even more heat and even more electrolyte loss.

Burnt Bulbs

When your alternator is overcharging, it can cause your taillights and headlights to blow out prematurely, one at a time or at the same time.

Additionally, symptoms of an alternator that is overcharging include ongoing blown fuses, interior lights that blow out, and lights that get extremely bright when you increase the speed of your engine.

Battery Heating

Overcharging of your battery by a malfunctioning or defective alternator can cause the battery to reach a state where it is overcharged. If this happens, the plates inside the battery will shed the material and lose their ability to hold on to electricity.

When this happens, the battery will resist additional charging, and the extra electrical charge will continue to build up, being released as heat.

This makes the whole battery feel hot or warm when you touch it after your engine has been running.

Swollen Battery

Batteries that are overcharged by a bad alternator can cause excessive amounts of hydrogen gas. For batteries that aren’t properly vented or fully sealed, the buildup of gas can cause the battery’s top or size to start swelling outward. This may warp the casing around the battery.

Seeping Battery

Leakage or seeping occurs when the alternator overcharges your battery, and hydrogen gas builds up inside the battery.

This will force the electrolyte out of the battery through the vent or even around the vent caps. In more serious cases, the housing may become cracked and start to leak.

What Causes Alternator Overcharging?

There are a few issues that may cause an alternator to overcharge.

Battery Related Issues  

For example, if you jump-start your vehicle improperly, it may send a surge through the battery that destroys one or several cells or that shorts it out.

The surge can disrupt the wiring inside your alternator, which can cause it to overcharge.

Also, improper placement of your battery in your vehicle can result in overcharging. This is often seen in newer vehicles that have alternators that require a signal from the electronic control unit.

Output and Size of the Alternator

Replacement alternators have voltage output and design specifications. This means you must find the right one for your vehicle. It’s important to note this since some re-manufactured alternators come with higher output designs and ratings.

If you don’t install the right alternator or if the pulley has undersized dimensions, the charging supply is more than the demand, which causes the overcharging.

Important Tip: Never install racing or performance alternators on stock passenger vehicles.

External Regulator

This part is typically found on the fender well or engine firewall, provides the current for the internal rotor field coil. This coils is located inside the alternator. It controls how much electricity the alternator requires to work at varying speeds.

The three electromagnetic contact switches inside the alternator housing open and close; if one gets stuck, it can cause overcharging issues.

Internal Regulator

Internal Regulator

This part is used as a replacement for the older regulators mounted externally. It mounts inside the case and has a more compact design.

If a contact switch is stuck, it creates an overcharge rate that’s usually 15 volts or more. Older fender-mounted regulators and newer alternators with the regulator inside will show the same overcharging issues.

Temperature Compensated and Computer Controlled Alternators

Computer-controlled regulating devices are found in newer alternators. One design is a “temperature-compensated” computer sensor.

The sensor will dictate the total amount of voltage the alternator puts out based on the temperature.

Hot batteries require less voltage and cold batteries require more. Defective sensors can send the wrong signal and cause the alternator to overcharge.

How to Fix Alternator Overcharging

There is information out there that will help you create a temporary bypass solution to an overcharging alternator. However, this isn’t recommended.

It’s important to address the problem properly. The only way you can fix an overcharging alternator is by taking it off to have it repaired or by installing a new one.

To fix the voltage regulator, you need to open the alternator and have knowledge of various electrical systems – this isn’t a job for most DIY mechanics.

The difficulty of this job depends on where your vehicle’s alternator is located.

Final Remarks on Alternator Overcharging

If you have noticed the symptoms of an overcharging alternator in your vehicle, you shouldn’t ignore it.

You need to try to repair the problem yourself or enlist the help of professionals.

Doing this will fix this and sure additional damage does not occur.

Zach Reed

Hi, I'm the founder of! Having owned a wide variety of vehicles in my life, I was astounded at how hard it can be to find answers to common automotive questions. Rather than sit idly, I decided to create this website to help others!