Alternator Overcharging and How to Fix It

As important as the car battery is to start up the car engine, the alternator is a critical electrical component that produces an electrical current to charge the battery and helps keep the vehicle running.

At times, the alternator may malfunction and lead to issues like undercharging, but also overcharging. This article will cover the causes, symptoms, and solutions for alternator overcharging.

What causes the alternator to overcharge?

An overcharging alternator is typically caused by a defective or malfunctioning voltage regulator or transistor. Also, the presence of excessive corrosion can contribute. It can result in the battery swelling up or losing electrolytes. In rare cases, an incorrect alternator replacement or faulty battery can also cause overcharging.

What are the symptoms of an overcharging alternator?

  • Flickering lights: excessively bright or flickering lights (that can eventually blow) could be a sign of overcharging an overcharging alternator
  • Battery dashboard warning light: this could indicate that the alternator is not providing the optimal voltage range required to charge your car battery. Keep an eye out for the check engine light too, as this can also illuminate indicating there is an issue with the alternator or battery.If you have a multimeter handy and you’re confident in checking it yourself, you can check the voltage of the battery – if it’s reading anything above 14.7-15 V with the engine running, then it’s possible the alternator is overcharging.
  • Reduced lifespan of bulbs: variable or high voltage can significantly reduce the overall lifespan of headlights or taillights.
  • Blown fuse and relay: if there is excess voltage due to an overcharging alternator then a fuse will blow in the circuit it is protecting.
  • Bulging battery: if overcharging happens over an extended period of time, the battery can bulge or swell due to the electrolyte boiling and generating gas, leading to some level of battery expansion. In some cases, it may also cause some leakage on the surface of the battery.

Can a bad ground cause an alternator to overcharge?

It is disputable, but it is possible that a bad ground can cause an alternator to overcharge. An alternator with a bad ground has the potential to produce a higher voltage output because resistance increases. This could then cause the alternator to overheat and overcharge the battery.

Is 14.7 volts too high for an alternator?

The normal voltage range for a properly functioning alternator is generally considered between 13.5 and 14.5 volts as long as there is no additional or major load on it. A voltage of 14.7 volts is slightly above the expected range, but it does not always mean it’s a cause for concern.

However, if the voltage reading is above 15V then there could be an overcharging issue. If in doubt, it’s always best to ask for a mechanic’s advice as issues with the alternator or battery can lead to further damage to electrical components.

How to fix an overcharging alternator?

An overcharging alternator is likely caused by a malfunctioning voltage regulator. Repairing the voltage regulator requires technical knowledge of electrical systems and involves opening the alternator, making it a task most suitable to a professional and trained mechanic.

In such cases, it is advisable to seek the advice and service of a mechanic. More often than not, the alternator cannot be repaired and will need to be replaced entirely. It’s also a lot more cost-effective to replace it rather than attempt to repair it.

You can get an upfront price for an alternator replacement simply by entering your car registration number and postcode on our Alternator Replacement page.

Can I drive with an overcharging alternator?

Although you don’t need to come to an immediate halt when you notice signs of an overcharging alternator, we do not recommend continuing to drive the car for long periods of time. Driving with a faulty and overcharging alternator increases the risk of failure of the electrical components of the car such as light bulbs and also damages the battery permanently. It’s best to get it checked and fixed as soon as possible to avoid damage to other parts of the vehicle.