What is Car Alternator?- 7 Signs of a Bad Alternator

You may think your battery is powering all things electrical in your car, be it your windshield wipers, headlights, or radio. In reality, it’s the car alternator that produces the majority of your vehicle’s electricity your battery is mainly just used to start your vehicle and provide power when the engine isn’t running.

The alternator is a critical component of a car’s charging system, so it’s helpful to understand how it operates in case you have to deal with your car not starting.

What is an alternator?

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.

Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually, the term refers to small rotating machines driven by automotive and other internal combustion engines.

An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators.

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Large 50 or 60 Hz three-phase alternators in power plants generate most of the world’s electric power, which is distributed by electric power grids.

What Does an Alternator Do in Your Car?

While the battery is essential for starting your car when it’s off, the alternator keeps your car alive when the engine is running.

The alternator powers most car’s electronic components while you’re driving around or idling, including your headlights, electric steering, power windows, windshield wipers, heated seats, dashboard instruments, and radio.

The alternator supplies all of them with direct current (DC) power. Your alternator is also responsible for charging your car battery while driving.

The alternator works by turning mechanical energy into electrical energy. When your engine is on, it powers a drive belt that rests on a pulley attached to the alternator.

The pulley turns the alternator’s rotor shaft, which spins a set of magnets around a coil. These spinning magnets generate alternating current (AC) around the coil, which is then channeled to the alternator’s rectifier. The rectifier converts that AC power into DC power, which activates your car’s electrical systems.

Alternators typically last the lifetime of your vehicle, but that doesn’t always happen. General wear and tear, heat damage, overuse, exposure to water, faulty parts, or frayed wires can put your alternator out of commission before your car heads to the scrap yard.

Components of an alternator

The components of an alternator are geared toward providing the right type and right amount of power to the vehicle. Your car’s charging system contains many parts, but these are the main components and their functions:

 alternator in Car
  • Regulator: The voltage regulator is a part that controls the amount of power supply from the alternator to the battery. It controls the charging process as it’s designed with various functions and work depending on their applications.
  • Rectifier: The rectifier is used to convert alternating current (DC) produce to direct current (DC) during the charging process.
  • Rotor: The rotor is a part that spins inside the alternator and rotates the pulley and drives belt system along. It acts as a spinning electromagnet.
  • Slip Rings: The slip rings are a means of obtaining direct current and offering power to the rotor.
  • Slip Ring End Bearing: Alternator bearings are designed to support the rotation of the rotor shaft.
  • Stator: A stator is an iron ring that contains several coils of wire wound around it. the part of the stator serves as the body of the alternator, creating an electrical current when a magnetic field is made.
  • Drive End Bearing: The drive end bearings also help to support the rotation of the rotor shaft.
  • Pulley: The pulley is a part connected to the rotor shaft and the drive belt system. Though the rotation is obtained from the engine transferred by the drive belt to the pulley. The rotation causes the charging process.

How do Alternators work?

You may think that the battery powers the electrics in your car, but that’s not the case. The battery provides the electricity needed for the starter motor to start the car.

When the car is running, the alternator generates energy to feed the electrical system and charge the battery. The alternator used to be called a generator, and it works in a similar way. In this case, a car’s internal combustion engine spins pulleys under the bonnet, which turns the pulley on the alternator and creates energy.

An alternator works together with the battery to supply power for the electrical components of the vehicle. The output of an alternator is direct current (DC). When the alternator pulley is rotated, alternating current (AC) passes through a magnetic field and an electrical current is generated. This is then converted to DC via the rectifier.

Advancements in technology have meant that alternators have changed vastly in the last 50 years. Originally, alternators were only used to generate a current that was controlled by an external regulator.

The introduction of a built-in regulator, in the 1990s, used the warning light to excite the alternator and start the charging process. Many modern vehicles adopted a load request type charging system with the introduction of smart charge systems and CANBUS systems which are now widely being used.

These systems are controlled by the vehicle Engine Control Unit (ECU). As the vehicle demands more load the ECU sends a signal to the alternator requesting it to start charging. The alternator has to cope with varying electrical loads and adjust its charge rate accordingly.

These days it is easy for these types of alternators to be misdiagnosed faulty if a charging fault is experienced on the vehicle but more often than not, no fault is found with the alternator.

How does the alternator charge the battery?

Before the battery can use the power coming from the alternator, it needs to be converted to a format that the battery can use. That’s because electricity can flow in different currents or directions. Car batteries operate on one-way direct current (DC) electricity, while alternators output alternating current (AC) electricity, which occasionally flows in reverse.

So prior to going to the voltage regulator, a power intended for the battery goes through a diode rectifier to turn into DC. After the conversion, the battery can use the power to recharge.

Wiring an alternator diagram

7 Signs of a Bad Alternator

1. Dim or Overly Bright Lights

When an alternator begins to fail, it provides inconsistent voltage to your electronic accessories. Generally, that takes the form of under-or over-performing equipment, such as headlights that are either too dim or extremely bright. You may also experience flickering lights or lights that erratically go from bright to dim and vice-versa.

2. Dead Battery

Sometimes a dead battery is just a dead battery it’s reached the end of its life after a few years of use or maybe you accidentally left the headlights on all night. Other times, however, a dead battery could be a sign that your alternator is malfunctioning.

A bad alternator won’t sufficiently charge the battery while the engine is running, causing the charge to deplete faster than usual. One way to test whether the issue is the battery- or alternator-related is to jumpstart the car.

If you jumpstart your car and it stays running, your battery may need replacing soon. However, if you jumpstart the car and it dies again shortly after, it might mean your alternator isn’t getting enough power to the battery.

3. Slow or Malfunctioning Accessories

An alternator that isn’t supplying enough power to your car’s electronics often results in slow or non-working accessories. If you notice your windows taking longer than usual to roll up or down, or if your seat warmers feel “off”, or even if your speedometer and other instruments start going haywire, you may have an alternator problem.

Many modern vehicles also have a priority list of equipment programmed into the car that tells the onboard computer were to cut power first if the alternator isn’t supplying enough electricity.

That way, if you’re driving with a failing alternator, you’ll lose power to your radio (or other nonessential accessories) before losing power to your headlights.

4. Trouble Starting or Frequent Stalling

As previously mentioned, trouble starting your engine might mean that your alternator is failing to charge the battery. This means that when you turn the key in the ignition, all you’ll hear is a clicking sound instead of the purr of your engine.

On the other hand, if your car is frequently stalling out while driving, it may be a sign that the spark plugs aren’t getting enough power from the alternator to keep the engine running.

5. Growling or Whining Noises

Cars make a ton of odd sounds some are harmless while others can indicate serious mechanical problems. If you ever hear growling or whining noises coming from under the hood, you could have alternator problems, which should be checked out by a professional ASAP.

This growling or whining sound happens when the belt that turns the alternator’s pulley becomes misaligned or rubs against the side of the pulley. You may also hear this sound if the bearings that spin the rotor shaft are going bad.

6. Smell of Burning Rubber or Wires

A foul odor of burning rubber or wires could indicate that parts of your alternator are starting to wear out. Because the alternator’s drive belt is under constant tension and friction and because it’s close to the hot engine it may wear out over time and emit an unpleasant burning rubber smell.

Similarly, if your alternator is being overworked or if it has frayed or damaged wires, you may smell a burning odor comparable to an electrical fire.

An overworked alternator tries to push too much electricity through its wires, causing them to heat up unsafely. Damaged wires also create resistance to the flow of electricity, causing the wires to heat up and emit a foul odor.

7. Battery Warning Light on Dash

When the battery warning light pops up on the dashboard, it’s commonly mistaken to be a battery-specific issue. However, the battery warning light indicates that there could be a problem within the wider electrical system of your car, including the alternator.

Alternators are designed to work at a specific voltage, typically between 13-14.5 volts. If your alternator is failing, its voltage may drop below capacity, causing the battery warning light to appear on your dash. Similarly, the battery light will also appear if the alternator is exceeding its voltage limit, depending on how much stress it is under.

Depending on the electrical load from your car’s accessories (headlights, wipers, radio, etc.), you may see the battery warning light flicker on and off as the alternator fluctuates in and out of its intended voltage capacity. While this may seem like a minor annoyance, it’s better to bring your car in for an alternator inspection rather than wind up stuck on the side of the road.

How to Test an Alternator?

Don’t test an alternator by disconnecting the negative battery cable. Use a voltmeter instead to conduct a simple, safe test.

How to Test an Alternator with A Voltmeter?

If you have a newer battery but your car won’t start, you may have a bad alternator. If you’re tempted to test an alternator by disconnecting the negative battery cable, don’t do it. A good alternator may indeed keep the engine running without the negative cable, but this was never a good test.

In the pre-computer days, you could pull it off without damaging anything. Today, you risk frying every electrical device in your vehicle. The second you disconnect the battery; the voltage regulator pegs the alternator to put out maximum power.

With no battery in the circuit to act as a buffer, the alternator can put out up to 150 volts, depending on engine rpm. When the smoke clears, that “simple test” could end up costing you several thousand dollars for new electronics.

Step 1: Conduct a Voltmeter Test

  • Get a cheap voltmeter.
  • With the engine off, battery voltage should be between 12.5 and 12.8 volts. If it’s below that, charge the battery with a battery charger before you conduct the test again.
  • Then start the engine and check for increased voltage readings. If you see higher readings, chances are the alternator is good. (More sophisticated testing equipment is needed to detect an open or shorted alternator diode.)

Step 2: If Your Alternator Passes

If you connect the meter leads to the battery terminals and the meter shows that it’s in the 13.8 to 15.3-volt ranges (engine running, lights, and accessories off), that means the alternator is working as it should be.

If the alternator is functioning correctly, it’s likely that your dead battery was caused by a computer module that isn’t shutting down when you turn off the car. If your alternator passes the voltmeter test, get your vehicle into a shop and pay a professional mechanic to find and correct the misbehaving module.

How To Test an Alternator with A Multimeter?

The following steps address how to test an alternator with a multimeter:

  1. Get a multimeter.
  2. Set your multimeter to DCV (DC Volts) above 15.
  3. Make sure your alternator’s positive and negative terminals are clean.
  4. Put the multimeter’s black cable to the negative terminal and the red cable to the positive terminal.
  5. Look for an ideal alternator reading of around 12.6.
  6. Start the car, and look for a reading of between 14.2 and 14.7.
  7. A reading of over 14.7 means the battery is being overcharged, while a reading under 14.2 means the alternator is undercharging the battery.
  8. Turn the lights, radio, fog lights, fan, and other electronics on, making sure the voltage reading doesn’t go below 13.
  9. When you shut off the car, make sure the reading is above 12.6.
  10. If any of these readings are off, you likely have an issue with your alternator and may want to visit an auto repair shop.

How To Replace an Alternator?

Following are the step of Replace an Alternator

  1. Disconnect the Battery.
  2. Disconnect the Wires.
  3. Remove the Belt From the Pulley.
  4. Remove Bolts.
  5. Halfway There.
  6. Examine the Replacement.
  7. Reverse the Removal Steps.

Step 1: Disconnect the Battery

First and most importantly: disconnect the battery. There may be several wires or just one wire on your alternator, but rest assured that one of them is hot.

If you don’t disconnect the battery, you’re very likely to end up grounding a live wire during the process. This causes cause all manner of bad things to occur not the least of which is giving you quite a shock.

Step 2: Disconnect the Wires

Now that the battery is out of the way disconnect the wire or wires from the back of the alternator. This is usually a very simple process but if you’re unsure as to where they go, label them as you take them loose.

Step 3: Remove the Belt From the Pulley

Every project has a tough spot, and this is the tough spot for alternator replacement: remove the belt from the pulley. Somewhere in your vehicle, there is a tensioner pulley. You’ll need to move it enough to slip the belt off the pulley. Our ’95 GMC has a standard spring-loaded GM tensioner that required us to pull it back with a wrench.

On some vehicles, you’ll find screw-type or rod-end type tensioners that apply tension by turning a bolt through threads to increase/decrease the length of a rod. In this case, just turn the bolt/rod-end with a wrench or socket until it releases enough tension to allow you to remove the belt.

In our case, we grabbed a Craftsman 17mm Cross Force wrench and pushed hard. Normally that would be a pretty painful experience, but the Cross Force was designed for just such a situation.

There’s a 90-degree twist in the middle of the Cross Force wrenches, so you end up pushing on a flat surface. The result: we could push harder without discomfort. So we just laid into it and the belt came free.

Step 4: Remove Bolts

Once the belt is off just remove whatever bolts connect the alternator to the bracket and you’re good to go. Our model required the removal of three bolts: one at the front and two at the rear.

Step 5: Halfway There

With the old alternator in your hand, you’re halfway home. You’ll likely find getting the new one back in goes much faster since you already know what size the bolt heads are and where everything is.

Step 6: Examine the Replacement

Examine the replacement unit before reassembly and make sure it will work for your application. Our replacement was a junkyard find so it is great to deal dirtier however it has the advantage of actually working a significant improvement over our previous busted unit.

Step 7: Reverse the Removal Steps

To complete the project just reverse the removal steps paying careful attention to belt routing and tensioning. Hell, even if you bought the set of Cross Force wrenches for the job you’d still be hundreds ahead of the cost of what a shop would charge and you get some new tools out of it. We can think of far worse outcomes.