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Although alternators aren’t the most extraordinarily expensive parts in the world, they aren’t the cheapest. Without a functioning alternator, your car will eventually be unable even to start – never mind run – and so getting a new one is less of an advisory and more of a necessity.
We have put this article together to help you prepare for what might happen if it turns out that your car needs a new alternator.
Read through our advice, and feel free to leave a comment below!
A Quick Introduction to Electromagnetic Induction
Alternators function through the use of electromagnet induction. Although it might sound like a complicated principle, if you aren’t used to it, the basics that you should know are relatively simple.
All you need to know is this: when a coil of inductive wire is rotated within a stationary magnetic field, it produces an electrical charge in that coil. Alternatively, you could also keep the coil still and rotate the magnetic field around it – this is how alternators work.
The current induced into the coil is always an alternating current, usually shortened to AC. This means that it flows in both directions. It’s constantly oscillating between one direction and the other within the wire.
Keep this information in mind as we look at how alternators work.
What is an Alternator?
The alternator in your car is about the size of a mid-size football. The auxiliary drive belt drives it – the belt you can see when you open the hood, sitting on the front of the engine. It’s a dynamo, used for the production of current to charge the battery as it’s discharged.
The alternator produces AC (alternating current), hence the name “alternator.” You’ll find one in almost every light passenger vehicle or truck.
There are four main components to an alternator: the rotor, the stator, the armature coil, and the regulator.
The rotor sits inside the armature coil. It usually looks a little like a thick gear and produces a magnetic field. It does through electromagnetism – wrapping wires around an iron core and then sending a DC (direct current) charge through them. This DC charge either comes from an external source or a small generator directly attached to the alternator. If this is the case, the alternator produces DC to help power itself, and thus this type is called a “self-excited” alternator.
Attached to the end of the rotor shaft is a pulley. This pulley forms a part of the auxiliary drive belt system assembly. When you turn the engine on, the crankshaft begins to turn, causing the auxiliary drive belt to begin moving. As the drive belt moves, it turns the rotor pulley (along with all the other pulleys in the system, such as the AC compressor or the hydraulic power steering pump).
When the pulley attached to the rotor spins, the rotor spins. Remember how it sits within the armature coil. This spinning moves the magnetic field through the stationary coil windings, inducing an alternating electrical current in the coil.
In reality, it’s slightly more complex than this – you’ll find one end of the armature coil to be star connected to produce three-phase electricity, but that’s another story for another time.
Your car’s battery and equipment work due to DC power. It’s passed through a diode to convert the alternating current into direct current. This is a bit like a one-way street. Only the current traveling in one direction gets through, and the AC is converted to DC.
Finally, a regulator is used on top of all this to keep the supply of voltage relatively constant. It does this by “regulating” the output voltage going to the battery, and increasing or decreasing the current going to the rotor poles accordingly. If the output voltage (called terminal voltage) is too high, the current going to the rotor needs to decrease.
Why You Might Need a New One
It isn’t the simplest of parts. Yet it’s vital for your car’s functionality. In fact, when your car is running, the alternator is probably doing almost all of the work. The main job of the battery is to get your car started and work the locks and the lights.
As we’ve just seen, there are a few different parts in your alternator, any one of which has the potential to go wrong. Over time, like all parts, you should expect the efficiency of the alternator to decrease. It’s certainly true that some last much longer than others, due to the build quality, but over time, you will need to replace them.
Testing Whether You Need a New One
The first major sign that your alternator is on the way out will be dimming lights and failing electrical equipment. You’ll also eventually reach the point where your car either stalls very quickly for no apparent reason or doesn’t start at all. You may also hear some strange noises.
You can test your alternator using a multimeter when the car engine is switched on. Set it to the 20 V setting. Place the positive probe (the red one) on the positive terminal of the battery, and set the negative (black) probe on an earth point. Any piece of exposed metal bodywork within the engine bay will do. Don’t ground the alternator itself, though.
This reading should be between 13.5 V and 15 V. If it’s any higher or lower than these readings, you’ll need to get a new one.
How Much Should I Expect to Pay for a New Alternator?
You should expect a new alternator cost to start at $150 and go all the way up to $600, for the best brands and the rarest cars. You could ask your local garage to quote you for three different parts, if necessary. Ask them to give you a quote on a budget option, mid-range option, and high-quality option. You can decide as to which to go for, depending on what these prices come back as.
We would rarely recommend going for a budget option. Doing this is almost certain to result in needing to pay out more money in the future, meaning you’ll actually spend more than if you get a higher-quality part in the first place.
On top of the cost of the part, you’ll also need to pay labor rates, if you want the garage to fit your new part for you. Expect to pay between $45 per hour and $200 per hour, depending on the garage’s reputation and areas of expertise. We would suggest that a reasonable price for this job is between $60 and $100 per hour, but, again, it’s all dependent on your area, state laws, and other considerations.
Getting a professional to fix it also covers you in terms of their warranty. If you make a bad mistake while changing the alternator (which is unlikely, but certainly not impossible), you’ll fry your car’s electrical system. In most cars, unless you’re literally in love with your car, that means a write-off.
If a garage has done the work for you, a mistake like this is much less likely. However, in the very unlikely situation that a mistake does get made, the garage’s insurance should cover you in terms of getting the car fixed or getting a new car.
Should I Get a New One or Just Fix My Old One?
In terms of the cost of parts, it should be much cheaper to fix your alternator than to get a new one. However, practically, this is rarely the case.
Unless you know your way around the alternator and are confident about working safely with your car’s electrical system, you’ll probably want to take your car to an auto shop. This is what most people would do. The garage may let you know that your alternator is faulty and advise you on how to get this fixed. They’ll almost always recommend a new alternator altogether.
The reason for this is very simple: it’s an easier job for them, and it’s almost certain to be cheaper for you.
To repair an alternator, the mechanic needs to take the whole thing apart, visually inspecting and electrically testing every part until he finds the specific problem. At this point, the individual part that needs replacing will need to be ordered (or fabricated) and then installed. Once that’s been done, the alternator will need to be rebuilt and tested to make sure everything is working before being reinstalled in your car.
In this situation, your main cost will be labor charges. Let’s take an average labor rate of approximately $80 per hour. If it takes the mechanic 4 or 5 hours to fix your alternator (a reasonable assumption), you can expect to pay $320, plus the cost of the additional parts and tax to get the job done. Of course, it might be more, and it might be less.
You would probably expect to pay about the same amount when installing a new one – but the risk is considerably less. Changing an old alternator for a new one is generally a relatively simple job for someone who knows what they’re doing, and you should expect to pay about an hour or two’s worth of labor. The garage will be able to quote you for the parts plus the labor before completing the task, so you’ll know exactly how much you’ll pay.
This is completely different from the situation where you want your alternator to be fixed. Diagnosis alone could take many hours, never mind fixing it.
If you’re considering fixing your alternator yourself and you’re an experienced mechanic who knows what they’re doing, diagnosing and fixing it yourself could save you a lot of money compared to taking it to a garage. However, for most people, replacing it with a new part is by far the less risky route to take.
Your alternator should be high on your list of priorities. Getting it fixed will be expensive, but it’s necessary.