If you’ve heard the term “alternator” before, you probably know that it’s an essential part of your cars. But what exactly does an alternator do? Simply put, your alternator keeps your car battery charged so you can turn on your car and use electronic accessories like your headlights and radio.
If you are having alternator problems, you may find that your car will not start or stay on for more than a few minutes. Before that happens, however, you’ll likely encounter one or more of these signs of a bad alternator.
What Does an Alternator Do?
The alternator converts mechanical energy from the vehicle’s running engine into electrical energy that is used to power the vehicle’s electrical systems and charge the battery. It is so named because it creates AC (alternating current) power, which reverses direction periodically.
Alternating current has been used in vehicles since the 1960s since it is more efficient and produces more voltage than DC (direct current) power, which is unidirectional. Vehicle batteries and accessories use DC power so the alternator’s electricity is transformed to DC power as it leaves the alternator.
AC power is generated in a copper coil when a magnetic field rotates with respect to the coil. This process is known as electromagnetic induction.
How Does an Alternator Work?
In order to understand how the alternator does its job, it’s helpful to first know how it’s put together.
This coconut-sized part usually sits near the top of the engine and consists of an outer housing covering a stator and rotor. The housing is made of aluminum because it cannot be magnetized and dissipates heat well.
The rotor has roughly 10 to 20 magnetic poles sticking off of a center prime mover like petals of a flower growing off of a stem. These magnetic poles alternate North and South.
The rotor is powered by the turning crankshaft of a running engine via a belt (usually the serpentine belt in modern vehicles), which connects to the prime mover and turns the entire rotor (following the previous example, the flower spins). As the poles move in this way, magnetic flux is generated.
Brushes, which produce the magnetic field in each pole, are located near the poles and send them a direct current via slip rings around the prime mover. This power comes from an external power source or from small generators attached to self-excited alternators.
The stator assembly is made up of a system of copper coils. Most often vehicles use a three-phase assembly, where there are three sets of copper coils spaced 120 degrees out of phase of each other. This makes three times the electricity as one set would.
As the rotor spins, the magnetic flux generated creates alternating current in the copper wire.
At the other end of the alternator, a diode (also known as rectifier) converts the AC power into DC power which is the format that can actually be used by the vehicle and stored in the battery.
Older vehicles have a voltage regulator between the alternator and the battery to make sure the battery doesn’t get too little or too much electricity. This can harm the battery or other electrical components. In newer vehicles, the ECU does this job.
Since cooling is critical to the proper function of an alternator, there are vents on the front and back to dissipate heat and cooling fans that are also powered by the serpentine belt.
Several terminals on the back of the unit connect the alternator to the electrical system in order to turn it off and on and send data from sensors to the ECU.
How Do You Know if a Car Alternator is Bad?
It can be difficult to tell whether your car has a bad alternator or a bad battery. If you jumpstart your car but it dies immediately after, you most likely have a problem with your alternator. Some warning signs of a failing alternator include:
- Trouble starting your car
- Frequent stalling
- Whining or screeching noise after the vehicle starts
- Dim or overly bright lights
- The smell of burning rubber or wires
- Dead battery
- Battery dashboard warning light is on
If you have noticed any of the warning signs that your alternator is failing, let’s discuss in detali one by one.
7 Symptoms Of Bad Alternator
#1. Trouble Starting.
The alternator doesn’t provide the power to start the vehicle – that’s actually the job of the battery. It does, however, charge the battery as the vehicle is running. If the battery can’t be charged, the car won’t start.
This is a tricky situation as the problem could be with the alternator or the battery itself, or even a plethora of other issues (bad starter, spark plugs, etc).
#2. Frequent Stalling.
A bad alternator almost always results in a car that won’t start. But before things get that far, you may encounter a number of other issues. A faulty or dying alternator may only work intermittently. As a result, the alternator may not have what it takes to keep your battery fully charged—even with the engine running.
As a result, your car may stall at unusual times. The immediate cause of such a stall is often the fuel injectors, which require power to do their job. If a faulty alternator isn’t keeping your battery constantly charged, the injectors may not fire and your engine will stall.
#3. Whining or screeching noise after the vehicle starts.
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.
Related Posts: How Much Does It Cost To Replace An Alternator?
#4. Failing Electrical Systems
The electricity created by the alternator is also what powers the vehicle’s accessories such as air conditioner, power windows, power mirrors, stereo, heated seats, heated mirrors, headlights, entertainment, etc.
If you notice that any or all of these are not working well or at all, especially when the vehicle is at idle (since the RPM isn’t high enough to produce enough power if there are other issues), the alternator may be the cause.
You may also notice failing electrical gauges on your dashboard. Since those give you important information about safe driving conditions (i.e. speed) and the state of your vehicle (i.e. oil temperature) it’s imperative to stop driving as soon as possible and get the issue fixed.
#5. Smell Of Burning Rubber Or Wires.
A foul smell from b burning rubber or wiring could indicate that parts of your alternator are starting to wear out. Because the alternator drive belt is under constant tension and friction—and because it’s close to the hot engine—it can wear out over time and give off an unpleasant burnt rubber smell.
Similarly, if your alternator is overloaded or has frayed or damaged wires, you may smell a burning odor that is comparable to an electrical fire. An overloaded alternator tries to force too much current 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 give off a foul odor.
When you start noticing certain issues, it’s time for an alternator replacement. You can go to your local auto shop to get this work done. But you should be prepared for a hefty bill.
#6. 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.
Related Posts: How To Test an Alternator with A Multimeter?
#7. ALT Or Battery Warning Light Turns On.
It’s never a good idea to ignore vehicle warning lights, even though some car owners do. Whether it’s a low oil indicator or a service engine soon light, it’s important to address these needs as soon as possible.
Many cars will show a light shape like a battery on the dashboard display or close to the speedometer. While this can sometimes indicate a battery problem, the car’s computer is telling you that the battery is not fully charged, which can also indicate alternator trouble.
Learn more about why the battery light may be on.
With some vehicles, the warning light for the alternator may be an ALT indicator. When the voltage begins to decrease, different accessories will be affected. For example, if you are using your windshield wipers and radio, power from the alternator may not be sufficient to get the headlights on too, as the alternator is already working too hard to power the other systems.
How To Diagnose A Failing Alternator?
If you have a “Check Engine” light on, connect a code reader to the diagnostic port. If you find code P0562, you most likely have a faulty alternator (note that codes can vary by vehicle make/model/year). Get it checked out before it fails altogether.
If you suspect a bad alternator but don’t have a warning light, open the hood and check the condition of the belt. If it looks glassy and slightly burned, that’s an indication it’s slipping. The belt is too loose so it slips on the pulleys instead of riding along them.
The metal-to-rubber friction heats the belt and wears it out quickly. Adjust the tensioner so the belt is just right (too tight can also damage an alternator’s bearings) or replace the serpentine belt as it is one of the cheapest auto parts you can buy. It should be a quick and easy fix.
If everything looks good under the hood, grab your multimeter and test your alternator to the norm. If any of the voltages are below the recommendation, this is a strong case for a new alternator. Also, if you check all of your wiring for corrosion or a loose connection, you may find that you need new alternator connectors, rectifier sets, or brush sets.
Alternator Replacement Cost
It’s usually a better idea to replace the alternator entirely if it is malfunctioning. While new ones can be spendy, they are usually a better choice than remanufactured or rebuilt options. Those probably won’t last as long as a new one since the mechanical parts have miles on them already.
If you can’t afford a new one, check for a remanufactured or rebuilt alternator at your local auto parts store. If a mechanic is doing the job, make certain that they are giving you a new alternator and not trying to cut costs by using a remanufactured or rebuilt one.
Some vehicles with greater electrical needs, such as ambulances or vehicles with large, power-hungry stereo systems, may need a high-output alternator which costs more.
The cost for the parts varies greatly depending on the type of vehicle but will usually fall in the range of $150 to $300. More expensive vehicles will usually require more expensive parts so an OEM alternator for a newer Mercedes or Audi can easily set you back close to $1,000.
Labor costs vary as well, since some alternators are easier to get to and thus take less time, but expect to pay between $200 and $600 for the labor.
All together, expect to pay somewhere in the range of $350 to $900 total for an alternator replacement. Having an independent mechanic do the work is going to be cheaper than a dealership in most cases.
Alternator Repair Cost
It’s not always easy or possible to get replacement parts for the alternator to try to repair it yourself. Some vehicles actually offer alternator repair kits, which cost from $20-$50 and can be purchased at a local auto parts store.
Check the service manual to see what is offered and what is possible for your specific alternator. You also may want to replace the belt at the same time, as that has a much shorter lifespan and can cause problems with the alternator later if not now.
In general, replacing the alternator is almost always the better option versus attempting a repair.
How Long Do Alternators Last?
As with everything mechanical, alternators have a lifespan that is determined by several conditions. Vehicle and engine type, conditions and amount of driving, and electrical load all affect the wear of the alternator.
Usually an alternator lasts for 80,000 to 120,000 miles, or 5 to 8 years, though the lifespan can be significantly more or less.
A belt that is too tight, fluids leaking onto the alternator, and having an old battery can all cause the alternator to give out early.
Can You Still Drive with a Bad Alternator?
Technically yes, if it’s not causing your vehicle to stall, but not for long. The alternator won’t be able to keep the battery charged, so each time you start the vehicle you’ll likely need to jump start it or have externally recharged the battery.
Neither of these are good for the battery and eventually it will stop holding a charge. So if you’re going through new batteries like candy thinking they are the problem, it would be wise to have the alternator checked out.
How to Load Test Your Alternator
To give you more information about the health of your alternator, testing it with a voltmeter (which is a function on a multimeter) is helpful.
With the engine of the vehicle off, a good and fully charged battery should measure 12.6 to 13.2 volts. With the RPM of the vehicle around 1k, the voltage should still be between 12 and 14 volts. Then start turning on the accessories in the power and rev the engine – the voltage should not drop below 12 or above 14 volts.
If any of your numbers are out of range, the alternator may be bad. If the voltage is too high, the voltage isn’t regulated which can be frying the battery. If the voltage is too low, the alternator can’t provide the battery with enough charge which isn’t good for the battery.
FAQs.
What happens when an alternator goes out?
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.
How do you know if your alternator pulley is bad?
A damaged or worn-out alternator pulley can produce many issues, including unusual noises, such as rattling, squeaking, or chirping.
How long will a battery last with a bad alternator?
If your alternator fails when you’re far from home, you can typically drive up to 200 miles on battery power alone. That’s assuming your battery is in good shape and fully charged. Of course, it’s best to get the alternator repaired or replaced as soon as you can.
Will a bad alternator throw a code?
If you have a “Check Engine” light on, connect a code reader to the diagnostic port. If you find code P0562, you very likely have a failing alternator (note that codes may vary by vehicle make/model/year). Get it checked out before it fails entirely.
How do I know if it’s my battery or alternator?
An effective method to determine whether it’s your battery or alternator that’s gone bad is to connect jumper cables from a running vehicle’s battery to yours. After a few moments, try starting your vehicle. Once it’s started, remove the jumper cables — if your engine stalls, your alternator has probably gone bad.