As an Amazon Associate I earn from qualifying purchases.

Can a Bad Alternator Cause High Voltage?


At times, your car battery suddenly overheats, and you can’t decide which part is causing the problem. So one of the questions that cross your mind is, Can a bad alternator cause high voltage?

The simple answer is Yes. There are many reasons why your car could be experiencing high voltage. A bad or faulty alternator is one of them.

What You Should Know About an Alternator and How It Works

 The Alternator is one of the two major electricity suppliers to a car. The other part that produces a substantial amount of the car’s electricity is the battery. But, contrary to what most people think, the Alternator puts in most work. All vehicles with an internal combustion engine possess an alternator, except for hybrids.


The Alternator is a self-generation powerhouse of an automobile. Its central purpose is to charge the battery, which keeps all the car’s electrical components up and running. The Alternator is responsible for powering the battery whether you’re driving or idling around. It also supplies direct current to the car’s radio, headlights, windshield wipers, heated seats, and other components powered by electricity.

Typically, an alternator requires little or no maintenance to stay in optimum condition. As a result, it can last up to 15 years in a car without any repair. Therefore, It is challenging to detect if an alternator is faulty because the vehicle may still be up and running. The reason for this is the battery can still power the car, albeit for a short period.

However, it would soon become noticeable once the Alternator does not sufficiently charge the battery. In this case, the engine stalls or starts to crank. When an alternator overcharges, it releases excess voltage to the battery, which boils its electrolyte. Once your car alternator becomes faulty, it can fry your vehicle’s electrical system.

The task of an alternator is to convert mechanical energy into electrical and distribute it. When an alternator is defective, it does not distribute power correctly and transmit to suitable components.

Symptoms of a Bad Alternator

Frequently, the symptoms of a problematic alternator are mistaken for a bad battery or dysfunction of other parts resulting in similar symptoms. Even if your car is experiencing any of these issues above, the Alternator might not be the problem. Before replacing a car part, you should precisely diagnose which part is acting up.

The following are tell-tale signs that indicate your Alternator might be faulty:

  • Your car engine is unresponsive or struggles to start.
  • The battery dashboard light or check engine warning light refuses to turn off after the engine starts.
  • Dimmed or overly bright interior light bulbs.
  • Turning signals blink at an incorrect pace.
  • A grinding or whining noise emanating from the Alternator under the hood.
  • Worst case scenario, the high voltage overheats the battery and ends up with a defective battery.

While it is pretty rare to overcharge your Alternator since the voltage output is regulated, it is not entirely impossible. A good alternator’s standard voltage is between 13.9 and 14.8 volts. Once your voltage is reading 15 volts and above, you need to get your car checked as this signals alternator troubles.

Causes of High Voltage in an Alternator

Different kinds of issues can arise from a high voltage. A high voltage does not do any good to a gadget, including a car. Imagine you overcharged your phone. In the long run, you begin to notice the consequences of overcharging. The same thing applies to your vehicle. The voltage of an alternator can be too high, which can damage the battery and, consequently, the car.

A common cause of high voltage is an alternator is a defective voltage regulator. The voltage regulator exists to preserve the car’s electrical circuits by regulating the charging voltage the Alternator emits. The regulator maintains a voltage of 13.5 to 14.5 volts. This range is sufficient to charge all the electrical circuits in the car safely.

The regulator has a warning system that maintains this fixed voltage output. However, when the regulator develops a fault, the whole system goes haywire.

How to Check if Your Alternator Is Overcharged

If your car is acting up and you suspect it has to do with the Alternator, you can determine if overcharging is the issue with a simple voltage test. This test procedure entails checking the battery voltage while the engine is off and while it is running. Get out a Voltmeter or a digital multimeter and follow these simple steps to conduct this test.

Turn off your engine and ensure that you set the voltmeter to DC volts. Place the voltmeter’s red lead on the battery’s positive terminal and the black lead on the negative terminal. The test is to ascertain how much voltage the Alternator is emitting.  

The next test is reading the voltage while the engine is on. Connect your voltmeter across the battery and rev the engine. Since the Alternator supplies additional power while the engine is running, The battery voltage should increase. To diagnose if your Alternator is overcharged, pay attention to the voltage reading. Ideally, it should not go beyond 14.8 volts. You might have a bad alternator on your hands if it does not.

Solution: How to Fix a Bad Alternator

Overcharging your Alternator is a difficult feat to achieve since it is more common to undercharge. When you overcharge your Alternator, the most reliable way to fix the problem is to replace it with a new one or refurbish the faulty one.


There are several DIY temporary solutions to fixing a bad alternator, but they are not advisable. Agreeably, replacing an alternator can be expensive and could cost you a whopping sum from Amazon or other local parts stores. However, the good news is that the expense will save you the stress of dealing with a faulty alternator.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top