The Alternator: Its Task in the Car and Signs of Failure

What is the alternator, and what does it do?

In automotive technology, the alternator is an important part that plays a vital role in ensuring the smooth functioning of a vehicle’s electrical system.

An alternator is a compact yet powerful generator that converts mechanical energy into electrical energy. An alternator comprises a rotor, stator, and diode assembly. As the engine runs, a belt connected to the engine’s crankshaft turns the rotor inside the alternator. This rotation induces a magnetic field in the stator windings, producing alternating current (AC). The diode assembly then converts the AC into direct current (DC), the current type required to power the vehicle’s electrical systems.

 While the starter motor draws current from the battery to start the engine, the alternator takes over once the engine runs. It replenishes the energy used to start the engine. It powers the vehicle’s electrical components, such as lights, air conditioning, and infotainment systems, while simultaneously recharging the battery for the next start.

How to know if your battery or alternator is faulty

If you get stuck on the side of the road and have problems starting the car or keeping it running, the battery or the alternator could be the culprit. Both the battery and the alternator provide energy, so why are they both necessary for the proper functioning of the vehicle? Although batteries and alternators have some overlapping tasks, they provide energy at different stages of vehicle operation.

 First, checking whether the battery is in good condition is necessary. Diagnosing a flat battery as opposed to a faulty alternator is relatively simple. Using the jumper cables to start the car, disconnect them as quickly as possible. If the car continues running smoothly, the battery is the problem, but it is necessary to have the battery and charging system tested immediately. If the vehicle shuts down, the alternator cannot charge the battery, so you have found the culprit.

Symptoms of a faulty battery

Unfortunately, standard car batteries typically last only three to five years. After that, their service life is limited. Things can drain a vehicle’s battery, but going without a charge for a long period or experiencing extremely hot or cold climates can shorten its lifespan. A discharged battery can leave you stranded, assuming you can start the car, so watch out for these low battery signs:

• Jolt when trying to start the engine;
• Slow start, with a sound similar to ‘rurr, rurr’, when trying to start the vehicle;
• Engine or battery warning light on;
• Swelling of the battery casing;
• Smell of sulphur or rotten eggs – if the battery emits this smell, it probably leaks: replace it as soon as possible!

A quick tip: if the battery has been tested and works well, but the engine struggles to turn, make sure that the battery cables and terminals are free of corrosion and dirt. If not, scrub them with a wire brush or sandpaper. If it doesn’t work, the problem could be the starter motor, so check for the signs of a faulty starter motor before replacing the battery!

Symptoms of a faulty alternator

Fortunately, alternators generally last longer than batteries, but exposure to water, excessive heat, excessive load and faulty components can cause them to fail prematurely. Like defective batteries, a faulty alternator is likely to leave you stranded.

Generally, the red battery warning light appears on the dashboard when the alternator malfunctions. As many mistakenly believe, this light does not necessarily indicate a battery malfunction. Instead, it can be indicative of a fault affecting the alternator itself. 

A malfunctioning alternator mainly leads to two types of problems:

Insufficient Charging: The alternator fails to supply adequate electricity to the car, resulting in inadequate charging of the battery. As a result, the battery has to compensate for this deficiency until it is completely depleted.

Overcharging: The alternator converts kinetic energy into electrical energy, which is then regulated and stabilised before being supplied to the system. This process can sometimes be disrupted, leading to excessively high voltage and intensity. Overcharging can damage various components of the car, many of them very expensive.

Once the alternator fails, all the vehicle’s electrical demands are placed on the battery, which cannot carry the load for a long time. Once the battery is depleted, the vehicle shuts down, leaving you stranded in potentially dangerous places such as the side of a motorway. Pay attention to the symptoms of a faulty alternator to prevent this from happening.

Signs of a faulty alternator

We strongly recommend that you take your car to a specialist workshop immediately if you encounter the following problems:

• Starting difficulties, i.e. the engine only starts after a few attempts;
• Illuminated battery warning light on the dashboard;
• Dashboard lights become dimmer;
• Low or abnormally high reading on the voltage indicator while driving (if fitted);
• Batteries repeatedly discharged;
• Vehicle battery overheats due to overcharging;
• Headlight illumination intensity varies with engine speed;
• Incandescent bulbs burn out at shorter intervals;
• Lights too weak, too bright or flickering;
• Underpowered or malfunctioning accessories (windows, radio, seat heating, etc.);
• Whining, screeching or growling noises under the bonnet;
• Caustic smell of burnt rubber.

Which components can cause the issues?

Before considering replacing the alternator, it’s essential to be aware of four potential ‘Achilles heels’ that can lead to various faults:

1. Outdated or defective vehicle battery
2. The alternator itself
3. The charge regulator
4. Cables and connectors
5. The V-belt
6. Belt tensioner or roller clutch

If the issue arises from a faulty alternator, the likely culprit is worn carbon brushes. This can be remedied by completely replacing the alternator.

Alternatively, the problem might lie with the charge regulator, which is responsible for controlling the electrical output from the alternator. In such cases, the component should be inspected and repaired at a specialised workshop.

Worn or damaged alternator sockets and cables that link the alternator to the battery can weaken or interrupt the power supply.

Furthermore, a loose or worn V-belt could also be the source of the problem. This would result in a weak power transfer between the alternator and the engine, preventing the alternator from effectively receiving mechanical energy from the engine.

What to do?

Alternators are designed to have a long service life; however, in the long run, they can wear and malfunction due to various factors. It is advisable to have them checked, even without noticeable symptoms. Often such symptoms only become apparent when the damage has become irreversible. The recommended interval for these checks is about every 100,000 miles to prevent the car from suddenly leaving you stranded. 

As you can imagine, replacing the alternator is not a simple operation that can be done anywhere and by anyone. Obviously, the first advice is always to go to a specialised mechanic who knows where to put his hands.

Has it been a long time since you had your alternator checked? Is your car starting to show symptoms that make you think it is malfunctioning?

Please make an appointment and entrust your car to our mechanics, who will be happy to advise you!