Car Keeps Killing and Burning Alternator: How It Goes Bad?

A car repeatedly burning out its alternator is often due to underlying electrical issues like battery problems, excessive accessory loads, short circuits, loose belts, bad grounds, contaminated components or a mechanically failing alternator. Proper diagnosis requires checking battery health, electrical connections, wiring, and components like the voltage regulator and rectifier. Ensuring good grounding, addressing leaks near the alternator, installing proper belt tension and limiting added loads can help prevent failure.

Having car trouble again? An alternator that continually fails can leave you stranded and facing expensive mechanical bills. This alternator burning has some simple fixes to try before spending money. In this guide, we’ll walk through possible culprits like loose connections and failing diodes behind the repeatedly burning alternator to get your ride back on the road.

Also Read: New alternator new battery still not charging

For smooth operation of the alternator, the voltage across battery terminals should be between 13.5 and 14.2 while the engine is running at idle and the lights are off.

If the voltage across the battery is less than 13.5V wih lights on, it means the battery will be undercharged. If the voltage across the battery is greater than 14.2V, it means the alternator is overcharging the battery. Either case will kill or burn out the alternator.

To promptly discuss the causes of a persistently burning car alternator, I will directly present them in the next section. However, I strongly advise visiting the subsequent section of this guide before that, which provides an explanation of the alternator. This is crucial to comprehend the underlying physics involved, such as the excitation of the alternator’s field coil to generate electricity and the various components including the diode rectifier, voltage regulator, stator, and rotor.

Some Key Insights for You
  • A car repeatedly burning out its alternator often indicates underlying electrical problems like bad battery, loose connections, overloads, leaks, bad grounds, or worn components.
  • Proper diagnosis requires methodically checking battery health, electrical connections, wiring, loads, grounds, tension pulleys, fluid leaks near the alternator and components like the voltage regulator and rectifier diodes.
  • Fixing leaks, cleaning connections, replacing damaged wires, adding grounds, adjusting accessories, and tensioning belts can help prevent alternator failure.
  • Understanding excitation principles and role of components like the rotor, stator, regulator and rectifier helps troubleshoot root causes of failure.

What You Will Learn:

My Personal Experience Car Keeping On Burning Alternator

My cousin drives an older model Toyota Camry. It started having trouble starting up and the battery light came on. I helped him troubleshoot by testing the alternator with a multimeter. It was only outputting 11 volts, way too low.

We replaced the alternator but that didn’t fix it. Turns out the battery cable connection was corroded. Cleaning the connection and securing it tightly solved the problem. Proper diagnosis and checking all system components is key to finding the root cause.

Causes of Car Keeps Killing or Burning Alternator

Here are the causes of car burning the alternator:

1. Weak Battery Overloading the Alternator

The battery in your vehicle serves as a crucial component that functions as a capacitor, effectively regulating the amperage produced by the alternator.

Similar to how the voltage regulator keeps an eye on the alternator’s voltage output, the battery is responsible for managing the current output from the alternator.

When the battery is weak, it is not strong enough to hold back the current from the alternator trying to recharge the battery.

When a healthy battery becomes fully charged, it resists the current from the alternator, due to which amperage output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5.

What Are The Consequences of a Weak Battery?

When a car’s battery is weak, it cannot hold a sufficient charge, which means it cannot provide the necessary backup power.

As a result, the alternator has to work harder to compensate for the battery’s deficiency and continuously supply a large current to the battery. The increased workload puts a strain on the alternator, causing it to overheat and, in some cases, burn out. 

Once the alternator starts working overtime to compensate for the weak battery, it becomes vulnerable to excessive heat and stress. Over time, this can lead to the alternator’s internal components wearing out faster than normal.

The strain on the alternator may also cause the voltage regulator to fail, resulting in erratic electrical output, which can further damage the alternator itself and other electrical components of the car. 

To put it in a simple way, you can consider an alternator as a water pump and a battery as a water tank. If the water tank has a leakage and drains water faster, the pump has to work hard to refill it. This is what a weak battery does with the alternator.

How to tell if a vehicle battery is weak?

  • If your car does not start at all or makes a clicking sound when you turn the key, it is likely that your battery is dead or very weak.
  • If your car starts fine but dies after running for a while, especially when you turn on more accessories, it is likely that your alternator is failing or not charging your battery enough.
  • If your car’s interior lights dim or flicker when you rev up or idle down your engine, it is likely that your alternator is not producing enough power or has a loose connection.
  • If your car’s dashboard shows a red battery warning light or a check engine light, it is likely that there is a problem with your electrical system, either with your battery or your alternator.
  • If you have access to a voltmeter or a multimeter, you can measure the voltage of your battery and your alternator to check their condition. A fully charged battery should have around 12.6 volts when the engine is off, and around 14 volts when the engine is running. An alternator should produce between 13 and 14.5 volts across the battery when the engine is running. If these values are lower than normal, you may have a bad battery or a bad alternator.
  • Look for any signs of corrosion or damage on the battery terminals. Corrosion appears as a white, powdery substance on the terminals. If you notice extensive corrosion or loose connections, it could be affecting the battery’s performance.

2. Corroded or Damaged Battery Cables Hindering Proper Power Transfer to Electrical System

damaged battery cables
Damaged battery cables

The battery cable serves as the conduit for electrical power flowing between the battery and the various components in the car’s electrical system. It carries the current necessary to power the starter, lights, ignition system, and other electrical accessories.

When a battery cable is faulty, it can create resistance in the electrical circuit. Resistance hampers the flow of electrical current, causing the alternator to work harder to compensate for the voltage drop. This increased workload puts a strain on the alternator, leading to its eventual failure.

A bad battery cable can also result in voltage fluctuations. Fluctuating voltage levels can cause the alternator to work erratically, overcharging or undercharging the battery.

Overcharging can cause the alternator to overheat while undercharging can lead to a drained battery. Both scenarios can ultimately lead to alternator failure.

Why does it happen?

Here are the following ways in which battery cables can burn out or kill the alternator:

  1. Loose Connections: Another potential problem is loose connections. If the battery cable connections are not tight, it can lead to an intermittent flow of electricity. This can cause fluctuations in voltage, putting unnecessary stress on the alternator and eventually causing it to fail.
  2. Frayed or Damaged Wires: Sometimes, the battery cable itself can become damaged. Wires may become frayed or insulation may wear off, exposing the wires. This can result in short circuits or even electrical arcing, which can damage the alternator and other electrical components.
  3. Overloading: If your car’s electrical system is drawing more power than the alternator can handle due to faulty battery cables, it can overload the alternator. This can cause it to work beyond its capacity and eventually fail.

How to test a bad battery cable or connection?

You can conduct a voltage drop test to inspect a bad battery cable or its connection. o Voltage drop test measures the voltage lost across a connection when current flows through it. It helps detect any resistance or corrosion in the electrical path.

Here’s how to perform a voltage drop test:

  1. To begin, you’ll need a digital multimeter set to measure DC volts.
  2. Start by checking the open circuit voltage of your battery. Connect the multimeter to the battery terminals, and you should get a reading close to the battery’s rated voltage. For instance, a fully charged 12-volt battery should read around 12.6 to 12.8 volts.
  3. Now, measure the voltage at the battery connector itself. Place one probe on the battery terminal and the other on the connector’s contact point. The reading should ideally match the open circuit voltage you obtained earlier. If there’s a significant difference, it indicates a volt drop across the connector and shows that either the battery cable or its connection is bad.

Note: Don’t forget to also check the cable that goes form the B+ terminal on the alternator to the positive terminal of the battery.

3. Faulty Ground Connections Resulting in Voltage Irregularities and Alternator Failure

Every electrical circuit is a complete loop, starting from the battery, passing through the device or sensor, and then returning to the battery through the ground.

Ground connections provide a stable reference point for the electrical system, enabling the smooth operation of various components, including the alternator. A good ground connection ensures that electrical charges are properly channeled, preventing any disruptions or excessive strain on the alternator.

In automotive systems, we often utilize the vehicle’s metal structure as a conductor, running a ground wire between the battery’s negative terminal and the vehicle chassis, effectively making the entire vehicle a return loop.

In a vehicle, usually, engine block, chassis, frame, firewall and transmission casing are grounded. The exact locations of all ground connections and ground bolts depend on the make and model of your vehicle. You have to check the owner’s manual.

The alternator in vehicles is grounded through its mounting to the engine block. So, you might not find a ground cable for the alternator.

In the below video, you can see all possible ground connections in a vehicle:

How bad grounds affect the alternator?

bad ground connection in vehicle due to damaged bolt
bad ground connection in vehicle due to damaged bolt

When there is a bad ground connection, the alternator may not receive the proper amount of current it needs to function. This can result in various issues that ultimately lead to alternator failure. Here are some ways bad ground connections can impact the alternator:

  1. Voltage Drop: A bad ground connection can cause a voltage drop, meaning that the alternator will not receive the required voltage to produce electricity. This can lead to a weak or failing alternator, as it struggles to meet the electrical demands of the vehicle.
  2. Excessive Heat: When a ground connection is weak or intermittent, it can cause the alternator to work harder to compensate for the lack of current. This increased workload can generate excessive heat, which may damage the alternator’s internal components over time.
  3. Erratic Charging: A bad ground connection can cause the alternator to provide inconsistent charging to the battery. This can result in an undercharged or overcharged battery, leading to battery failure or premature alternator wear.

How to spot the bad ground that is killing the alternator?

Firstly, the bad ground might show a burning sign on the ground bolt. Furthermore, you can also see signs of corrosion and rust around the ground bolt area.

bad ground strap connection

Furthermore, vehicles also have a ground strap that bridges the gap between various parts of the vehicle’s chassis, ensuring a continuous ground connection. You should inspect ground straps for wear, tear, or disconnection. If any signs of damage are present, the ground straps should be replaced

To test bad ground, you can also perform a voltage drop test. Here are the steps:

  1. First, you need to spot the ground point of the alternator i.e. the bolt of the alternator mounting which is grounded to the engine.
  2. Ensure the grounding point’s surface is clean and free of paint or corrosion to get an accurate reading.
  3. With the engine off, place the negative side of the multimeter on the bare metal of the grounding point and the positive side on the positive terminal of the battery.
  4. Take the reading and compare it to the battery voltage with the engine off. If the reading matches the resting voltage, the grounding point is likely fine. If there’s a drop of 0.4 volts or more, it may indicate a potential ground fault in that area.
  5. Repeat the same process with the engine running. The voltage reading with the engine on should be higher, around 13.7 to 14.7 volts, due to the alternator’s charging. This additional test can reveal ground faults that might not be evident when the engine is off. Compare the readings with the engine running to the battery voltage and note any significant drops, as these could indicate ground fault issues.

How to fix?

Corrosion and debris can accumulate on the contact surfaces of ground bolts and ground straps, impeding the flow of electrical current. Use a wire brush or sandpaper to clean these surfaces, ensuring optimal conductivity.

When reassembling the electrical components, make sure to tighten the ground bolts securely. Loose connections can lead to increased resistance and subsequent alternator failures. 

After cleaning and tightening the connections, apply a thin layer of dielectric grease to the metal surfaces. This will help protect against future corrosion and improve conductivity.

However, if a ground bolt is damaged or has burning marks, it should be replaced.

In some cases, adding additional grounding points can help distribute the electrical load more evenly. This can be achieved by installing an extra ground strap.

4. Fluid Contamination of Alternator Windings Compromising Insulation and Short-Circuiting Components

alternator contamination signs

Contamination in alternators refers to the accumulation of foreign substances on both internal and external components.

When external fluids infiltrate the alternator, they can lead to a range of problems, resulting in the car repeatedly burning and killing the alternator.

Firstly, the fluids can cause corrosion and rusting of the alternator’s internal parts, leading to increased resistance and reduced efficiency. This can strain the alternator, causing it to work harder and eventually fail.

Moreover, the presence of external fluids can create electrical shorts, where the conductive properties of the fluids interfere with the intended flow of electricity within the alternator.

This can cause irregular voltage output and fluctuations, leading to malfunctions in the electrical system of the car. As a result, the alternator may not be able to provide the necessary power, leading to repeated failures and a dead battery.

Identifying contamination in an alternator can be crucial to preventing major issues. Some common findings of a contaminated alternator include:

  • Insufficient or no output: Contamination can disrupt the flow of electricity, leading to a decrease in power output or complete failure.
  • Unusual noises: Heavy contamination can cause mechanical friction and lead to abnormal sounds.
  • Rough ball bearing: Contaminants can interfere with the lubrication of the ball bearing, resulting in rough operation.
  • Thermally discolored windings: Overheating due to poor heat dissipation can cause discoloration in the copper windings and cables.
  • Worn carbon brushes and slip rings: Contaminants can accelerate wear on these components, impacting their lifespan.
  • External contamination: A visibly dirty or encrusted alternator on the outside indicates contamination.

You should especially check the power steering fluid as the alternator lies closer to it. One person found that the steering fluid of his vehicle was continuously leaking which was burning out its alternator.

Why does alternate contaminate and how contaminated alternators are impacted?

Here is how alternators are contaminated and they are affected:

  • Dust and environmental contaminants: Dust and debris from the environment can accumulate on the alternator, hindering its performance.
  • Liquid ingress: Leakage of oils, fuel, coolant, power steering fluid, or bearing grease can lead to increased adhesion of dust and contaminants, exacerbating the problem.
  • Reduced heat dissipation: Contamination obstructs the cooling airflow around the alternator, causing thermal overload and damage to its components.
  • Ball bearing thermal overload: Contaminants can reduce the bearing’s load-bearing capacity, leading to potential damage to the ball tracks.

How to fix?

Check if any coolant is continuously leaking from the engine, especially engine oil and coolant. If yes, then you have to fix the leak first before replacing the alternator.

5. Misaligned or Loose Alternator Pulley Assembly Errors Increasing Mechanical Resistance

alternator shaft threads and distance washer
alternator shaft threads and distance washer

One possible reason for your car’s alternator repeatedly failing is assembly errors related to the alternator pulley.

Some findings suggest that the thread of the shaft may become damaged or torn off, leading to issues with the alternator’s performance. This can occur when the belt pulley nut is tightened with excessive torque or using an impact wrench in an uncontrolled manner.

Visible wear of the shaft near the ball bearing and grinding marks on the stator can be observed when the nut of the alternator pulley is loose.

This can result in the alternator providing no output, noise, battery charge indicator lights illuminating, loose belt pulley, and wear on the thread and rotor.

How to fix?

When you install an alternator pulley over a shaft, never use a hammer to push the pulley as it will damage the shaft threads. Always slide the pulley by hand. Ensure that the shaft is fastened properly with the prescribed torque for the belt pulley nut using the impact wrench.

Moreover, if you don’t install a distance washer while installing the pulley over the shaft, the alternator bearing will not fasten tightly to the shaft.

This will increase play between the alternator shaft and the bearing on which the alternator is supported and rotating. This will cause the rotor to rub against the stator. The laminations of the stator will damage and cause a short circuit which will burn out the rotor. 

Note: Alternators designed for a particular engine require the correct pulley to be installed. These pulleys may possess multiple grooves or a solitary V-type design.

6. Defective Silicon Diode Rectifiers Hindering Proper Voltage Regulation in Alternator

Older vehicles have separate rectifiers (more on rectifiers in later section). If the rectifier is defective and you are just replacing the alternator, your car will keep burning out the alternator.

When rectifier diodes become defective, several issues can arise that can cause the car to kill the alternator repeatedly. Let’s examine some of the common effects of faulty diodes:

  1. Increased Voltage Ripple: Defective rectifier diodes can lead to an increase in voltage ripple, which refers to the fluctuation in the output voltage of the alternator. This fluctuation can be detrimental to the sensitive electronic components in the car, causing them to malfunction or fail prematurely. Additionally, the increased voltage ripple can place additional stress on the alternator, leading to its premature failure.
  2. Overcharging the Battery: Another consequence of defective rectifier diodes is overcharging the battery. When the diodes fail, they may allow excessive current to flow into the battery, causing it to become overcharged. This can lead to accelerated battery wear, electrolyte loss, and even battery failure. Moreover, an overcharged battery can put additional strain on the alternator, potentially leading to its failure as well.
  3. Insufficient Charging: On the flip side, defective rectifier diodes can also result in insufficient charging of the battery. When the diodes fail to convert the AC into DC effectively, the battery may not receive the required amount of charge to operate optimally. This can lead to a weakened battery, reduced electrical system performance, and ultimately, a vehicle that struggles to start or keep running.

In addition to the above, a bad diode in the rectifier of the diode can also drain the battery when the engine is off, which will cause additional strain on the alternator.

How a bad rectifier diode causes current leakage from the battery?

A bad diode causes current leakage from the battery because it does not block the reverse current flow from the alternator to the battery when the engine is off. Normally, a diode allows current to flow in only one direction, from the alternator to the battery.

However, if the diode is defective, it can create a path for the current to flow back to the alternator, which can drain the battery and damage the alternator. This is also known as a parasitic draw or a battery drain.

In a properly functioning diode, there is a barrier created between the P-type and N-type semiconductor materials within the diode. This barrier prevents current from flowing in the reverse direction, effectively blocking it.

When a diode becomes defective, the barrier breaks down and the diode becomes “shorted” or loses its ability to block the reverse current.

How to test a bad rectifier of the alternator?

To test a rectifier of the alternator, you have to basically check whether a diode is allowing current in the reverse direction i.e. from B terminal on the alternator back to the alternator casing. If it is, it means the rectifier is bad.

For better understanding, I found the following youtube video of testing an alternator rectifier really helpful.

7. Bad Electrical Connection Of B+ Terminal Of Alternator Causing Erratic Voltage and Overheating

B terminal on alternator can have a loose nut and damage alternator
B terminal on alternator can have a loose nut and damage alternator

The ‘B’ terminal is the biggest terminal on the alternator that is directly linked to the battery to transfer the current and charge it.

A loose nut at connection B+ can cause burning marks and melting on washers, nuts, and terminal studs. Insufficient charging of the vehicle battery and discoloration/burning of terminal stud B+ may also occur.

Incorrectly tightened or loose nuts can result in contact resistances, increased component temperatures, and electric arcs. Ultimately, this will cause repeated burning of the alternator.

8. Damaged Voltage Regulator unable to Control Alternator Output as Per System Demand 

Like a rectifier, a voltage regulator (discussed in the later section) can also be separate or built-in, depending on the make and model of your vehicle. 

Usually, the voltage regulator has the following three terminals:

  • S terminal: This terminal is connected to the B+ terminal on the alternator to sense the battery voltage
  • IG terminal: This terminal is connected to the ignition switch to get an initial DC current from the battery to excite the field coil of the rotor
  • L terminal: This is optional and for the battery lamp on the dashboard

A faulty voltage regulator can cause your alternator to fail in two ways: 

  1. By undercharging the battery: If the voltage regulator does not send enough voltage to the battery, the alternator will have to work harder to keep up with the electrical demand of the car. This can cause the alternator to overheat and wear out faster.
  2. By overcharging the battery: If the voltage regulator sends too much voltage to the battery, the alternator will also overheat and may produce sparks or smoke. This can damage the internal components of the alternator and cause it to stop working.

You can watch the following video to test the voltage regulator of the alternator:

9. Worn Out or Tight Serpentine Belt Increasing Mechanical Resistance and Overworking Alternator

A serpentine belt is a long, rubber belt that runs around several pulleys in your engine. It transfers power from the crankshaft to the alternator, power steering pump, air conditioning compressor, water pump, and other accessories. A serpentine belt is also known as a drive belt or an accessory belt.

The serpentine belt is kept under tension by a spring-loaded device called a belt tensioner. The tensioner ensures that the belt does not slip or squeak on the pulleys. However, sometimes the tensioner can fail or be adjusted incorrectly, causing the belt to be too tight or too loose.

If the serpentine belt is too tight, it can put excessive stress on the alternator pulley and the alternator bearings. This can cause the alternator to overheat, wear out faster, and eventually fail.

In what ways a serpentine belt can be too tight?

A serpentine belt can be too tight in the following ways:

  • Incorrect belt size or type: Using the wrong belt length can also result in a serpentine belt being too tight. If a belt that is too short is installed, it will be stretched tightly across the pulleys, causing excessive tension. 
  • Improper belt installation: Each vehicle has a specific routing diagram of the serpentine belt. If you have replaced the serpentine belt before and have not followed the routing diagram, it will also cause over-tightening of the serpentine belt, due to which it will exert excessive strain on the alternator.

How to spot the cause?

First, you should check whether the serpentine belt installed on your vehicle has the recommended size or not.

Next, you should check the condition of the tensioner pulley. If it has any play in it or the tensioner pulley spring is damaged, you should replace it.

Moreover, make sure that the nut of the tensioner pulley is not overly tightened. You should follow the torque specs of nut tightening of the tensioner pulley. 

Next, check the tension of the serpentine belt after installation and with the engine off. There are two rules of thumb:

At the midway between two pulleys, you should be able to twist the serpentine belt 90 degrees by hand. At a point midway between the two farthest pulleys, the belt should not depress more than 1/4 of an inch when you pinch the point between your index finger and thumb.

10. Recycled or Inferior Alternators with Substandard Components Causing Premature Failure

Car owners may also consider aftermarket alternators as a cheaper alternative to brand new ones. 

Refurbished or aftermarket alternators may not always meet the same quality standards as new OEM (Original Equipment Manufacturer) alternators.

They are often disassembled, and only the faulty components like brushes, diodes, or bearings are replaced before being resold. This means that there is a chance that other components may still be worn or damaged, leading to premature failure.

Furthermore, in an effort to cut costs, these alternators may be assembled using inferior-quality materials and components. This can lead to issues such as poor voltage regulation, inadequate cooling, and increased wear and tear on critical parts.

Over time, these substandard components can cause the alternator to malfunction and fail, leaving the car without a functioning electrical system.

Similar to refurbished alternators, aftermarket alternators may have compatibility issues. They may not perfectly match the electrical requirements of the car, leading to compatibility problems and potential damage to the alternator and other electrical components.

The alternator has a certain amperage rating. If it doesn’t match with OEM, it will keep on failing.

11. Overuse of Power Hungry accessories Overloading the Alternator Capacity

One common cause of overloading the electrical system is the addition of aftermarket accessories, such as high-powered sound systems, additional lights, or power-hungry gadgets.

These accessories draw additional power from the alternator, exceeding its capacity and causing it to work harder than it was designed for. 

Furthermore, as a car ages, its electrical components may deteriorate or become worn out. The wiring may fray, connectors may become loose, or insulation may break down.

These issues can increase electrical resistance in the system, making it harder for the alternator to deliver power efficiently. Consequently, the alternator may become strained and fail prematurely. 

When adding aftermarket accessories or audio systems, it is crucial to ensure that they are installed properly. This includes using appropriate wiring, fuses, and relays to handle the increased electrical load.

When you upgrade the stereo system of your vehicle, make sure that it has a proper ground connection.

Moreover, if you upgrade the stereo of your car, you might need an alternator with a higher amperage rating. Otherwise, your car will keep killing the alternator.

To ensure your audio equipment receives sufficient power for optimal performance, you need to calculate the available wattage based on your alternator’s capacity.

Let’s take an example: Suppose your car has a 65 amp alternator, and it is charging at 14.4 volts. The available wattage can be calculated as follows:

Available Watts = Alternator Amperage (65 amps) × Charging Voltage (14.4 volts) Available Watts = 936 watts

For standard vehicle components to operate correctly, they require approximately 30 to 50 percent of the available wattage. Let’s take the middle 40 percent for our calculation:

Power for Audio Equipment = Available Watts (936 watts) × (100% – 40%) Power for Audio Equipment = 561 watts

However, keep in mind that this calculation assumes 100 percent amplifier efficiency, which is unrealistic. Most amplifiers operate at around 80 percent efficiency. So, when choosing an amplifier, consider its efficiency rating and adjust the available wattage accordingly.

Suppose you opt for an amplifier with 80 percent efficiency. In that case, the actual power it will produce can be calculated as follows:

Amplifier Power = Power for Audio Equipment (561 watts) × Amplifier Efficiency (80%) Amplifier Power = 448 watts

As you go beyond the available power limits, your system starts drawing power from the battery reserve. This not only decreases amplifier efficiency but also puts a strain on both the alternator and the amplifiers, leading to increased heat and potential system failures.

Principle Of Excitation In Car Alternator

The production of a magnetic field by the rotor in an alternator can be a somewhat intricate process.

As the alternator’s main objective is to generate electricity, it may be puzzling to comprehend how the rotor manages to create a magnetic field. Well, the rotor of the alternator needs to be initially excited to produce a magnetic field.

“Exciting” the alternator means starting the process of producing electricity. It’s like waking up the alternator and saying, “Hey, it’s time to work and make some power for the car!”

An initial electric current flow (also called magnetizing current) is needed to excite the field coil of the rotor and produce a magnetic field when you turn on ignition switch.

If no electric current is provided to the field coil, it will not generate a magnetic field and induce a voltage in the stator. In order to shed light on this matter, I will delve into the intricacies and provide a comprehensive explanation.

The alternator gets “excited” when we send a little bit of electricity (from the car’s battery) in the form of DC current to this rotor. We can consider this rotor like a little magnet that spins around really fast.

As you turn on the ignition, initially, the DC current from the battery flows to the carbon brushes. When the rotor of the alternator rotates and slip rings pass by the carbon brushes, a small amount of DC current flows to the rotor. This energizes the rotor, due to which it produces a magnetic field.

Once the rotor of the alternator starts producing a magnetic field, the current to the field coil i.e. excitation is regulated by the voltage regulator.

Note: You might be thinking why car alternators don’t use permanent magnets as a rotating field coil of the rotor inside the magnetic field of the permanent magnet produces electric current as well, so, there won’t be a need to excite the field coil.

The answer is that alternators with permanent magnets are difficult to regulate as there will be a constant supply of the same current and voltage due to permanent magnets.

Understanding The Working Of Alternator

The alternator is an electromechanical component in vehicles that is responsible for charging the battery while the engine is running. The alternator is run via a serpentine belt which transfers power from the engine’s crankshaft to the alternator pulley.

As a result of mechanical energy from the engine, the magnetic coil inside the alternator rotates that generate electrical energy. This electrical energy is responsible for charging the battery.

An alternator consists of several crucial components, each playing a specific role in the generation and regulation of electrical power. The main components are as follows:

  1. Rotor Assembly
  2. Stator Assembly
  3. Rectifier or Diode Trio
  4. Voltage Regulator

Rotor Assembly

rotor assembly of alternator

The rotor, driven by a belt pulley system, contains an electromagnet known as field windings. The field windings are wound on an iron core. The field winding is surrounded by claw-type iron poles.

Each end of the rotor field winding is attached to slip rings. Stationary brushes are conductive carbon or copper parts that make direct contact with slip rings. These brushes are stationary because they do not rotate with the rotor but remain fixed inside the alternator.

Stator Assembly

The stator is where the induced voltage from the rotor is collected. The stator’s three coil windings are spaced evenly around the iron shaft, producing three AC voltages that are 120 degrees out of phase from each other. This is also called three-phase AC voltage.


rectifier of alternator

In the above image, the circles you see are diodes of the rectifier of the alternator. The AC voltage from the stator is converted into DC (direct current) voltage using a rectifier that consists of a series of 6 diodes. This ensures a stable and constant power supply to charge the battery. 

After the current is converted to DC by the rectifier, it flows to the positive terminal of the battery from the B terminal on the alternator.

Voltage Regulator

The voltage regulator monitors the battery’s voltage and adjusts the field current produced by the magnetic coil to control the alternator’s output and prevent overcharging and undercharging of the battery.

Let me explain to you in very simple terms how a voltage regulator monitors battery voltage.

The voltage induced in the stator of the alternator depends on the following factors:

  1. The speed with which the rotor of the alternator is rotating
  2. Current flowing through the field coil of the rotor

When the current flow through the field coil increases, the coil will produce a stronger magnetic field. As a result, a greater voltage will be induced in the stator of the alternator. 

Similarly, when the rotor rotates at a higher speed, it will induce a higher voltage.

As you know the alternator is directly connected to the engine via a serpentine belt. When you rev up the engine, the rotor of the alternator will rotate faster. This will also increase the output voltage of the stator of the alternator.

After the initial voltage supplied by the battery to excite the field coil, the alternator keeps on spinning and inducing voltage based on its residual magnetism

So, basically after the initial excitation of the battery, the alternator gets current for its field coil from itself via diode trio. Like a rectifier, a diode trio also connects to each stator voltage output. The diode trio converts it into DC voltage.

After that, the diode trio feds that DC voltage to the voltage regulator to energize the field coil of the rotor.

The voltage regulator can control the current to the field coil of the rotor of the alternator by turning it on and off, depending on the voltage level at any given time.

If the voltage in the battery falls under 13.5V, the regulator’s voltage sensor closes the circuit to the alternator. This delivers electrical current to the field winding to charge the alternator.

If the voltage level rises above 14.5V, the regulator will stop delivering the power supply to the field winding and prevent the alternator from charging.

Some Tips for Maintaining the Alternator

To ensure your alternator performs optimally and lasts longer, here are some maintenance tips:

  1. Regular Inspection: Make it a habit to inspect your alternator and its components during routine maintenance to catch any signs of wear or damage early.
  2. Keep it Cool: Ensure your car’s cooling system is functioning correctly to prevent the alternator from overheating, which can lead to premature failure.
  3. Battery Maintenance: A healthy battery prolongs the life of the alternator. Regularly check the battery’s terminals, clean them if necessary, and keep the battery well charged.
  4. Serpentine Belt Tension: The serpentine belt plays a crucial role in powering the alternator. Make sure it’s appropriately tensioned to avoid belt slippage and ensure efficient alternator operation.
  5. Keep Connections Clean: Ensure that all electrical connections are clean and secure to avoid voltage drop and related issues.
  6. Avoid Electrical Overload: Limit the use of high-power electrical accessories when the engine is off, as this can strain the alternator and lead to battery depletion.

Symptoms Of Repeated Failing Alternator

  • Battery voltage drops suddenly while driving.
  • Alternator emits a whining noise.
  • Car remains drivable for a short period before dying at idle.
  • Dashboard functions stop working when voltage drops to 9 volts.
  • Engine eventually dies out for good.

Final Thoughts On Car Burning The Alternator

An alternator repeatedly failing can be incredibly frustrating and costly. Properly diagnosing the root cause takes patience and diligence.

From battery issues to bad electrical connections to faulty components, many factors can contribute to alternator failure.

Meticulously testing each part of the system with a multimeter and inspecting for problems like corrosion provides invaluable insights. Ultimately, perseverance and methodical troubleshooting pays off.

Gaining a thorough understanding of how the alternator and electrical system function together is the best defense against repeating failures. With knowledge and persistence, you can get to the bottom of even the most elusive alternator issues.

Some First Hand Experiences Shared By Users In Different Communities

Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “car keeps killing alternator”.

User 1 says:

n my case with a Subaru Outback, the alternator was failing due to a leaky power steering fluid hose that dripped onto it. Replacing the hose and the alternator solved the problem.

User 2 says:

My Jeep Grand Cherokee had a similar issue. It was caused by a weak ground connection to the alternator. Improving the grounding fixed the alternator burnouts.

User 3 says:

Chevy Equinox owner here. Found out my alternator issue was due to a failing idler pulley. It wasn’t spinning freely, causing excess wear on the alternator. Replaced the pulley, and no more issues.

User 4 says:

On my Hyundai Santa Fe, the alternator kept dying. Turns out, the serpentine belt was too tight, putting extra strain on the alternator bearings. Loosening the belt fixed it.

Car Keeps Killing Alternator: FAQs

What are the signs that indicate my car’s alternator is failing?

Some common signs of a failing alternator include dimming or flickering lights, a dead battery, strange noises, and electrical failures.

How long does an alternator typically last?

The lifespan of an alternator can vary depending on various factors, including the make and model of the car, driving conditions, and maintenance. Generally, alternators can last anywhere between 80,000 to 150,000 miles or 7 to 15 years.

Why does my car keep killing the alternator?

There could be several possible reasons for your car repeatedly killing the alternator. Some common causes include a faulty voltage regulator, a short circuit in the electrical system, excessive electrical load, or a defective alternator itself.

How can I determine if my alternator is being killed by my car?

If your alternator keeps failing frequently, you may notice warning signs such as dimming headlights or interior lights, a dead battery, difficulty starting the engine, or the battery light illuminating on the dashboard. These symptoms indicate potential issues with the alternator.

Can a faulty battery cause the alternator to fail?

Yes, a faulty battery can potentially cause stress on the alternator and lead to its premature failure. If the battery is not functioning correctly, it may not hold a charge or may draw excessive current from the alternator, putting unnecessary strain on it.

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