What Causes An Alternator To Go Bad, What Causes An Alternator To Go Bad [8 Causes], KevweAuto

What Causes An Alternator To Go Bad [8 Causes]

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The alternator powers all of your vehicle’s electronics and keeps the battery charged. Without it, the engine won’t run long.

Unfortunately alternators eventually wear out and need replacement. Understanding the common causes of alternator failure can help you maximize the lifespan of this critical component.

How Alternators Work

What Causes An Alternator To Go Bad, What Causes An Alternator To Go Bad [8 Causes], KevweAuto

First, a quick alternator overview. The alternator converts mechanical rotation from the engine into electrical current to power the vehicle when running.

Key components include:

  • Belt driven pulley
  • Rotating magnets called the rotor
  • Stationary coiled wires called the stator
  • Voltage regulator
  • Rectifier diodes
  • Front and rear bearings
  • Internal cooling fan

As the pulley spins the rotor, the magnetic fields generate AC current in the stator windings. This is converted to DC and regulated to 14 volts to charge the battery and run electronics.

Wearing Out Over Time

What Causes An Alternator To Go Bad, What Causes An Alternator To Go Bad [8 Causes], KevweAuto

Even under normal operating conditions, alternators will eventually fail just due to age and accumulated run time. The typical alternator lifespan averages around 5-7 years or 60-100k miles.

Bearings get worn, brushes deteriorate, internal windings break down, and components like diodes or regulators randomly fail over time. No alternator lasts forever.

But other factors can accelerate alternator demise and cut its useful life short. Here are some common causes of premature alternator failure:

1. Bad Bearings

The front and rear alternator bearings enable the rotor to spin freely. Bad bearings cause:

  • Excessive grinding or squealing noises
  • Rotor dragging and poor charging
  • Eventual seizing as bearings overheat

Age, lack of lubrication, contamination or improper installation can ruin bearings.

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2. Failed Diodes

Diodes convert AC current from the stator to DC for battery charging and electronics. Just one failed diode can cause:

  • Reduced charging output
  • Battery draining rather than charging
  • Erratic operation
  • Burnout of remaining good diodes

Heat, electrical spikes, and age take a toll on diodes.

3. Worn Brushes

Carbon brushes contact the spinning rotor. As they wear, brushes cause:

  • Diminished alternator output
  • Intermittent charging failures
  • Sparking and arcing damage
  • Rotor grooving

Frequent high load cycles wear brushes faster.

4. Voltage Regulator Issues

The regulator controls charging voltage to avoid battery overcharge. When it fails, you may get:

  • No charging or undercharging
  • Severe overcharging – boiling battery
  • Flickering lights and electronics
  • Eventual alternator burnout

Regulators often fail due to age, heat, voltage spikes or manufacturing defects.

5. Damaged Windings

The stator windings generate current when exposed to the rotor’s magnetic field. Damaged windings produce:

  • Reduced charging output
  • Higher resistance leading to excessive heat
  • Short circuits blowing fuses

Vibration, heat cycling, moisture and manufacturing flaws harm stator windings over time.

6. Contamination

Dirt, moisture and debris entering the alternator can cause:

  • Bearing wear
  • Shorting and arcing
  • Corrosion of windings and slip rings
  • Internal circuit failures

Proper sealing is critical to prevent contaminant penetration.

7. Overcharging Issues

Persistently overcharging the battery leads to:

  • Overheated diodes and windings
  • Boiled away battery fluid
  • Premature battery failure
  • Eventual alternator component breakdown

Faulty regulators, loose connections and undersized alternators contribute to chronic overcharging.

8. Extreme Operating Conditions

Alternators are designed for typical driving conditions. But extreme situations accelerate wear:

  • Towing heavy loads over long distances
  • Off-roading environments producing severe vibration
  • Exposure to water crossings or pressure washing
  • Extended hot weather operation
  • Aftermarket high output stereo/lighting upgrades

Using the vehicle outside of normal parameters stresses the alternator.

While some causes of failure cannot be prevented, proactive maintenance and avoiding damage can maximize your alternator’s service life. But once signs of reduced charging appear, prompt professional diagnosis and replacement restores reliable electrical operation.

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Warning Signs of Failing Alternator

Catching alternator problems early provides the best chance for affordable repair or replacement. Watch for these common warning signs:

1. Illuminated Battery or Charging Warning Light

The most obvious indicator is a battery or alternator warning light on the dash. This alerts the driver that low voltage is detected.

2. Dim Headlights at Night

As the alternator loses generating capacity, headlights and other accessories may become noticeably dimmer, especially at idle.

3. Battery Not Holding a Charge

An alternator not fully charging allows the battery to gradually run down. This may become apparent when longer and more frequent jump starts are needed.

4. Electrical Gremlins

Unpredictable electrical issues like flickering lights, contested warning lights, and electronics glitches point to inconsistent charging voltage.

5. Ghining Noise from Under Hood

While some alternator whine is normal, excessive or increasing noise can indicate a bearing going bad.

Watch for these symptoms to avoid being left stranded when the alternator finally dies. Diagnose and remedy charging system issues promptly.

Professional Alternator Testing

Home charging system testing is limited. For definitive alternator diagnosis, most do-it-yourselfers rely on their local shop. Professional technicians use:

  • Sophisticated scan tools to check data and trouble codes
  • Precision digital multimeters to test voltage, resistance and amperage
  • Specialty test equipment applying load to measure output
  • Infrared cameras and thermometers to spot overheating parts
  • Noise detectors to identify bearing wear sounds

This professional-grade diagnostic approach quickly zeros in on root cause failure. DIY troubleshooting only goes so far.

Alternator Replacement Considerations

Once the alternator is confirmed faulty, replacement restores normal charging. But keep in mind:

  • Replacing only the alternator may provide a temporary fix if system damage exists. Thorough diagnosis is needed to identify underlying issues.
  • Late model alternators often require reprogramming by the dealership after installation.
  • Upgraded high-output alternators help support additional electronics and accessories.
  • Only use new replacement units from reputable suppliers, not salvaged parts.
  • Confirm proper belt tension after installing the replacement alternator.
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Getting professional alternator troubleshooting and replacement promptly prevents getting stranded and guards against related failures. With care and maintenance, most original alternators provide many years and miles of reliable service. But once showing signs of failure, replacement before total failure is key.

Preventing Premature Alternator Failure

You have limited control over manufacturing defects causing premature alternator failure. But here are some proactive maintenance tips to help maximize alternator lifespan:

  • Keep your battery properly maintained to avoid taxing the charging system.
  • Have alternator output tested annually to establish a performance baseline.
  • Inspect pulley, bearings and belt for wear signs during routine maintenance.
  • Address charging system warning lights and symptoms immediately, don’t ignore them.
  • Consider upgrading your alternator to a high-output model if adding electrical accessories.
  • Avoid frequent high-amp draw situations like winching or snow plowing.
  • Install an alternator isolator to protect from voltage spikes.
  • Keep the alternator clean and dry to prevent corrosion issues.
  • Confirm the belt tensioner keeps tension steady as belts stretch.

Your driving habits and maintenance practices have a definite impact on getting the most service life out of your alternator. But once problems develop, swift diagnosis and replacement is key to restoring reliable operation. By better understanding common failure causes, maximizing longevity, and watching for telltale symptoms, alternator problems can be caught early.


While designed to provide years of service, even the best alternators eventually wear out. Bearing wear, diode failure, aged brushes and wound stator windings take a toll over time and miles. But extreme operating conditions, chronic overcharging, contaminated housing and manufacturing flaws can accelerate demise. Watch for warning lights, odd electrical issues, bearing noise and dimming headlights. Professional load testing and diagnostic equipment can definitively pinpoint root causes. Replace defective alternators promptly to avoid getting stranded with a dead battery. With diligent preventive maintenance and early diagnosis of problems, your alternator can deliver reliable service throughout your vehicle’s lifespan.

Ejenakevwe Samuel

I'm Ejenakevwe Samuel, and my blog is all about sharing the love for cars. Through my blog, I pour my heart into educating fellow car enthusiasts in everything they need to know about their beloved rides. Whether it's driving tips, maintenance tricks, or the latest trends, I aim to empower others to make informed decisions and take care of their vehicles like a pro.

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