How the alternator works, alternator types and troubleshooting

At Steves Auto Clinic, leader in die field of automotive repairs and servicing, we see to it that our care for you and your vehicle go beyond the confines of our workshops. That is why we want to inform you about your vehicle’s alternator and the problems it may pose, problems that is fairly common, to say the least.

You might not know or realize it at this stage, but the alternator, in its capacity as a charging system on your vehicle, plays an essential role in everything electrical. The logical conclusion to be made is that when the electrical charging system malfunctions, then it can cause major electrical and other problems. At Steves Auto Clinic we believe that it pays to know more about vehicle components. Buckle up while we tell you more about the alternator, how it works, the different types in use and of course, the most important of all, how to identify signs and symptoms of a failing alternator.

Let us start at what an alternator is, and for this purpose, we will turn ourselves to how Wikipedia describes it. According to Wikipedia, an alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. The term alternator (and maybe you made that connotation) comes from its capacity to generate alternating current. Yes, it generates, that is why the alternator has been (and sometimes is still being) called a generator.

This is the basic definition of what an alternator is, but how does it work?

How the alternator works

Many people – due to a lack of knowledge – have a misconception of the working of the alternator, added that they even know of the existence of this vehicle component. Do not despair; we are here to rectify this. It is as Goeres (2017) say, people may think that the BATTERY powers the electrics in your vehicle, but no, that is not the case. The battery provides electricity needed for the starter motor to start your vehicle. When your vehicle is running, the alternator generates energy to feed the electrical system and charge the battery. How does it do that? Well, what happens is that mechanical energy (generated by the engine) is sent to the alternator via the engine drive belt (the serpentine belt). Inside the alternator, this mechanical energy is converted to electricity (alternating current – AC). The latter works as follows. The stationary part of the alternator is called the stator (from there the word stator); within the stator is a rotor that rotates (maybe that is why it is called a rotor…). This rotation is made possible due to an interaction between windings and magnetic fields within the stator. By way of electromagnetism – due to this stator-rotor relationship – alternating current (AC) is formed.

Let your mind go and think back to when you were younger and most likely had (or knew someone who had) one of those bicycle lights. The alternator works on the same principle as the little component that generated electricity (by way of the turning wheel) for the flashlight.

Do you now have a better understanding of the working of an alternator? The alternator is surely an important part of your vehicle’s functioning. So, it is as Taylor (2018) say; the alternator may be a small component, but it plays one of the most critical roles in the operation of your vehicle. If you don’t believe us, simply turn the ignition to the on position without starting your vehicle and switch on as many electrical appliances and components in your vehicle on and see how long the battery is going to last. It will die, in a very short period of time. We do not advise you to do this; it should rather be a mental than a physical exercise, but you can trust us on this, the battery will not last.

Now that you have a better idea of the purpose and working of the alternator, let us look at the types of alternators. Having knowledge about the types may also be conducive to a better appreciation of the purpose of the alternator.

Types of alternators

According to the Redarc website, there are two main types of alternators commonly used in today’s vehicles: the traditional Fixed Voltage Alternator and the modern Smart Alternator.

Fixed Voltage Alternators are becoming less common on new vehicles; this is because of reduced fuel consumption targets and more stringent emission standards. Let us explain why. The Engine Control Unit (ECU) externally controls the output voltage of smart alternators (to be discussed next). This is not the case regarding fixed voltage alternators. An internal voltage regulator controls the output voltage of a fixed voltage alternator. How does this affect fuel consumption? When an alternator produce a charge, the electromagnetic field generated between the stator and the rotor (as discussed earlier) produces a mechanical load on the engine via the alternator drive belt. Whenever the requirement for voltage increase, the engine must work harder to turn the alternator. This work consumes more fuel, so there you have it. Traditional alternators maintain their voltage and this means that there is always a significant load on the engine from the alternator, which is not very fuel-efficient. This is not the case when it comes to Smart Alternators.

Smart Alternators (also known as variable voltage alternators or computer-controlled alternators) allow the vehicle to control the output voltage from the alternator based on vehicle operating conditions. It does this in order to reduce electrical load and in turn, mechanical load on the engine by the alternator. Where the control of the output voltage in the fixed alternator happened internally, the smart alternators have their output voltage controlled externally via the Engine Control Unit (ECU). How does this affect fuel consumption? Being ECU-controlled, the voltage output can be varied so that the voltage can be brought below the standard voltage during periods when no charging is required. In this way engine load is reduced, which in turn means better fuel consumption.

You may ask yourself how will you be able to identify between the two, well, smart alternators require battery-sensing technology (for the ECU) in order to determine load coming from the battery. Simply inspect your vehicle’s battery terminals, you may find a sensor on the (usually negative) battery terminal. This will tell you that you have a smart alternator in your vehicle. If there is no sensor, then you most likely have the old traditional alternator.

So you should understand by now that the working of an alternator is more extensive than you may have initially thought. You may also now understand better that a failing alternator simply will not be able to keep up with all of the things you ask your vehicle to do during a typical drive. Let us therefore come to the final part of our alternator discussion, and that is the troubleshooting part.

Alternator Troubleshooting

From dash lights flashing briefly, headlights dimming, not to mention odd smells and growling sounds – these may all hint to possible alternator problems.

The Diesel Electric and Pep Boys websites, as well as Popely (2016), collectively points out some possible alternator warning signs of which you should take note. One thing we should not forget is the simple fact that an alternator not only provides power to the vehicle’s electrical system, computer, and electrical accessories, it also keeps the battery charged. Precisely because of this, it is of utmost importance to ensure that your alternator functions properly. How will you know if it starts to malfunction? If you take note of the following signs, then you will be a step ahead, so when any of these manifest themselves, address them immediately.

Dim lights

If you notice dimming headlights and/or dashboard lights or pulsating headlights at night (dim & bright), then warning lights should go on in your head. This indicates potential alternator failure and it can cause other electronic accessories (power windows, seats etc.) to operate slower than usual.

Warning light

Most modern vehicles have a dashboard warning light that alerts you when the alternator is giving issues. Baxter & Threewitt add to this by reminding us that if the alternator’s output goes below or above a pre-set limit, then the dash light will come on. Once the output is within range, the light will go out. In the early stages of alternator problems the light can seem to flicker for just a second and then go off again; it may even light up only when accessories are activated.

Weak or dead battery

An alternator can only recharge your vehicle’s battery to the point that it has a decent amount of life left in it and is able to accept a charge. If the battery is weak or dead, the alternator cannot bring it back to life. To see whether the issue is the alternator or the battery, simply charge the battery and restart the vehicle. If the battery is weak, the vehicle will continue to run but the lights will become dim after a short time, indicating a problem with the charging system. If the vehicle has difficulty starting after the battery is fully charged, the problem is likely with the alternator. Adding to this, Baxter & Threewitt points to the fact that when an alternator begins to fail or fails outright, the vehicle’s battery have to take up the slack. Even the best battery will eventually run down, leaving you stranded, and you surely do not want this, do you?

Odd sounds

Many different parts spin inside your vehicle’s alternator to produce electrical current. If one of these parts worn out or break, this could cause a grinding or whining noise. Worn out bearings (usually due to an over tightened belt wearing down the unit) or a loose pulley is known to cause this noise. If the bushings that the alternator is mounted on have gone bad, a noise will also be produced.

Weird smells

An alternator works in conjunction with a system of belts. If a belt is not turning freely, the excess friction could cause the belt to heat up which produces a burning rubber smell. If you detect a smell similar to that of an electrical fire, this could indicate that the belt is slipping on the alternator pulley, causing poor alternator output. Tightening the belt could fix this. An overheated alternator that push too much power through the rotor and stator may also cause this smell.

Visual cues (belts)

If you experience electrical problems, and the alternator seems fine, then the problem could be with one of the belts connected to the alternator. As Baxter & Threewitt suggest, have a look, a broken or loose belt is obvious. A quick visual check of the belt for cracking, excessive wear, and other age issues, you have preventative results. Keep in mind that the belt must have the proper tension to run the alternator correctly; too much tension is just as bad as not enough.

Broken or Loose Connections

Baxter & Threewitt also say that if everything with the alternator seems fine, then it might mean that the alternator is producing electricity but it’s either not going anywhere or it is not the right type. If there is any problem within the wires, cables or connections at either end of the alternator-battery, then it can reduce or prevent electricity flow. If this is the case, you may experience brighter lights (the alternator produces more energy to overcome the resistance in a bad wire or broken/loose connection). This is usually accompanied by the smell of hot wires. Another problem could be the alternator’s diode rectifier. Alternators produce alternating current, but vehicle accessories require direct current (DC) to operate. The rectifier changes the current from AC to DC. Without that critical component operating properly, the electricity produced by the alternator, will be useless.

Slow Accessories

Baxter & Threewitt points out that modern vehicle features are great right up until the moment they are not, and the complex computers and wiring systems that operate our power accessories lend more opportunity for something to go wrong. If you notice one electrical quirk, you will want to get that specific feature checked out. If you experience several issues at once, it is probable your alternator is malfunctioning. You might not even notice that your vehicle is running with reduced electricity until you make additional demands on the system, such as turning on an interior light or adjusting windows. Avoid using these in order to reduce the chances of alternator failure until you can get your vehicle checked out.

David Taylor (2018) adds to the points mentioned thus far by saying that if an alternator has no charge, then it can be down to a variety of issues, such as a loose or missing fan belt; a break in wiring; a blown fuse or blown rectifier diode. If there is only a low charge, then it might be because of a loose fan belt or poor wiring connections. If there is an overcharge, then it is probably caused by a poor battery condition or failed regulator or rotor

A final point of concern – always ensure that the battery is fully charged before replacing an alternator. The most common cause of alternator failure, says David Taylor (2018) is due to shoddy mechanics not doing their job correctly. According to him, mechanics do not properly ensue that the vehicle’s battery is fully charged after replacing an alternator. If the battery is not fully charged, the alternator will charge the flat battery and fail to handle the vehicle’s electricity demand. This is likely to result in an overloaded alternator. The rectifier will then blow and the unit will be rendered useless.

These then are the signs and symptoms to look out for when you drive your vehicle and when you maintain it. It is true that alternator repair is not too hard, but you will definitely need a serpentine belt diagram for your specific vehicle so that you can put the belt back on correctly. At Steves Auto Clinic, we have qualified mechanics and technicians who can assist you in this regard. If you suspect your vehicle to suffer from any alternator related issue, please do not procrastinate. Have the system checked for any signs of failure and let us fix that for you.

Happy driving.

Sources consulted during the writing of this article:
Baxter, E., Threewitt, C. (Undated). Top 10 signs of alternator problems. Online available at: Accessed on 26 July 2018.
Briggs, J. (Undated). How Alternators Work. Online available at: Accessed on 26 July 2018.
Diesel Electric. (Undated). Taking care of your alternator. Online available at: Accessed on 27 July 2018.
Goeres, E. 2017. What does a car’s alternator do? Online available at: Accessed on 27 July 2018.
My Auto Repair Advice. (Undated). Alternator problems and repair. Online available at: Accessed on 27 July 2018.
Pep Boys. (Undated). Six alternator warning signs. Online available at: Accessed on 27 July 2018.
Popely, R. 2016. Common alternator problems. Online available at: Accessed on 27 July 2018.
Redarc. (Undated). Alternator vs Fixed Alternator. Online available at: Accessed on 27 July 2018.
Taylor, D. 2018. Common signs and causes of alternator problems. Online available at: Accessed on 27 July 2018.
Wikipedia. 2018. Alternator. Online available at: Accessed on 27 July 2018.