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 in Car?
The alternator is a generator whose purpose is to distribute electricity to the car and recharge the battery. Outside of some hybrid models, all vehicles with a standard internal combustion engine will have an alternator.
About the size of a coconut, the alternator is generally mounted to the front of the engine and has a belt running around it.
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:
Rotor and stator
The rotor and stator are the electricity-producing components of an alternator. The rotor, a cylindrical piece surrounded in magnets, spins inside of the stator, which holds a fixed set of conductive copper wiring. The movement of the magnets over the wiring is what ultimately creates electricity.
The voltage regulator oversees the power the alternator makes. It monitors the level of voltage that is output to the battery and delivers power to the rest of the vehicle.
The diode rectifier converts the voltage from the alternator into a form that can be used by the battery to recharge.
Alternators give off a lot of heat and need to be cooled to operate efficiently. While they’re built with vents and aluminum casing to better release heat, they’re also equipped with rotating fans for added cooling. New alternator models have internal cooling fans, whereas older versions tend to have external fan blades.
How do Alternators work?
An automotive charging system is made up of three major components: the battery, the voltage regulator, and an alternator. The alternator works with the battery to generate power for the electrical components of a vehicle, like the interior and exterior lights, and the instrument panel. An alternator gets its name from the term alternating current (AC).
Alternators are typically found near the front of the engine and are driven by the crankshaft, which converts the pistons’ up-and-down movement into circular movement. Some early model vehicles used a separate drive belt from the crankshaft pulley to the alternator pulley, but most cars today have a serpentine belt, or one belt that drives all components that rely on crankshaft power.
Most alternators are mounted using brackets that bolt to a specific point on the engine. One of the brackets is usually a fixed point, while the other is adjustable to tighten the drive belt.
Alternators produce AC power through electromagnetism formed through the stator and rotor relationship that we’ll touch on later in the article. The electricity is channeled into the battery, providing voltage to run the various electrical systems. Before we learn more about the mechanics of the alternator and how it generates electricity, let’s look at the various parts of an alternator in the next section.
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 to Watch Out For
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 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 where 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.
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 Replace an Alternator?
Following are the step of Replace an Alternator
- Disconnect the Battery.
- Disconnect the Wires.
- Remove the Belt From the Pulley.
- Remove Bolts.
- Halfway There.
- Examine the Replacement.
- 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 on 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 half way 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 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.