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What is the Point of an Alternator and How Does it Work?

What is the Point of an Alternator and How Does it Work

With a car as big as it is, sometimes it is a wonder how it manages to stay running and powered considering the parts that are powering it under its hood are not really that huge. How is it even possible? If you think that the battery powers the whole car, it is not entirely false. But if it does it alone, the battery would be empty in no time. The battery gives electricity that is essential to the car’s overall operation. If the car has no electricity, the lights won’t light up, the wipers can’t be used, your air conditioning won’t work, and obviously, none of these things will matter since your car won’t even start. For these reasons, a car must always have power. It must have a rechargeable battery and a charging system that can help maintain the battery’s power level – that’s when a car alternator comes in.

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What is a car alternator?

The alternators are used in automobiles to charge the battery and supply power to the car’s electrical system when it’s running. The first alternators ever used were for by the WWII militaries that supply their high electric demands. In 1960, the alternators were made available for commercial use and the first vehicle to use it was the Chrysler Valiant.  The alternator is small and lightweight and can be seen fitted close to the car’s engine and mostly built using an aluminium outer housing since the lightweight metal does not magnetize. If you are familiar with how the wind turbines work and how it produces electricity, then you can picture the alternators working like that. But unlike the wind turbines that convert the energy of the wind to electricity by rotating its blades around a rotor, the alternator produces Alternating Current (AC) when the engine belt drives its rotor. It is similar to the electric current in our homes. The alternator produces electricity every time the engine is running.

Parts of the alternator

When you disassemble an alternator, you will find its components that include a rotor, stator, diode assembly, and the voltage regulator. 


The rotor or the rotating magnetic core is the moving part in an alternator. It consists of a coil of wire wrapped around an iron core. The rotor is basically an electromagnet that is fed with a small amount of electricity by the slip rings and brushes. Electromagnetism is achieved when electricity is produced by spinning magnets at incredibly fast speeds along a set of copper wires. The spinning is made possible since the rotor is mounted on a shaft with a bearing at either one end or both ends that is connected to the engine. When the engine starts, the engine belt will make the rotor spin. The engine is essential since the rotor only functions when there is an existing motion, and the engine does that. That is why the alternator can only do its work when the engine is running.  



The stator is the stationary part of an alternator. It does not turn. It houses a set of three wire coil windings that is fixed to the shell of the alternator. Each of the three coils generates its own AC voltage. As the rotor spins inside the stator windings, the rotor’s magnetic field moves through the stator windings, creating an electrical current in the windings. An alternating current is produced because of this rotation. It is called an alternating current because it periodically reverses direction. Now, the current that is generated by this process won’t do much to the car because cars use direct current or DC. It is the type of electricity that is produced by the battery, a current that flows in one constant direction. To correct this, that’s when the rectifier assembly does its job.

Rectifier Assembly

The conversion of AC to DC takes place in the Bridge Rectifier. The bridge rectifier is where the six diodes are mounted, one pair of diodes for each winding. The diode is an electronic component that makes the current flow in only one direction while blocking the current flow in the other end, therefore becoming a one-way valve that only allows current to pass in the same direction. It works like a switch as the rectifier converts the AC voltage to DC voltage. After the AC to DC conversion, the resulting voltage will then be ready to use in the battery. 

Voltage Regulator

The voltage regulator is the one that regulates and controls the charging voltage that the alternator creates, usually keeping it between 13.5 and 14.5 volts, just enough to keep all the electrical components of the car protected. This is important since it can cause problems when the voltage is either too high or too low. If it’s too low, the electrical components of the car will not work properly and when it’s too high, it can break the fuse and can cause other damage. For this reason, the voltage regulator also controls the amount of power it delivers to the battery. It is done to keep the battery from overcharging and burning out. In order to do its task, the regulator switches the rotor control circuit on and off, reducing its magnetic field, thus, reducing the voltage entering the stator. When the car battery is discharged or drained, current from the alternator is allowed to flow back into the battery again. 

Field Current Supply

There are two different sources that provide the field current supply, the battery and the alternator. The battery provides the field current supply when you get in the car and turn the key on. During this time, the engine is not yet running therefore the alternator is not producing electricity, yet. It is the battery that turns on the switch and the warning lamps. At the time that you turn the engine on, that is when the alternator comes to work and takes over as the source of current in the field current supply. 

Charge Indicators

There are gauges and warning lights found on the dashboard of your car. It plays an important role as those lights specify an issue with your car that needs either an immediate action or checking. One of them is an alternator warning lamp.  When you turn the key on, current flows through the warning lamp and through parts like the resistors, transistors, and field coil, and then to ground that makes the warning lamps light up. And when you start the engine, the car proceeds to check if the alternator is outputting the correct voltage. If it is, the illuminated warning lamps will then be turned off after a few seconds. But if the alternator warning lamp is still turned on, it indicates that the car has detected a problem with the charging system. If it is still illuminating, it is best to conserve your car’s battery and only use the essential accessories like the headlights or the windshield wipers to refrain from excessively draining out your battery. Paying attention to your car’s warning lamps can save you a lot of trouble later.

Symptoms of a Bad Alternator

The alternator plays a critical role in the car’s charging system. Without it, your car won’t stay running for so long. It is true that the engine is the one that starts the car as it supplies the initial spark, but it is the alternator that takes over after that and keeps the car going – simultaneously charging the battery while the car is running and operating all the electrical components of the vehicle. With its very important duty, it is only right to care for it and be aware of the symptoms of a faulty alternator aside from the car’s illuminating warning lamp. The first thing you can notice is the reduced capacity for electrical use. Signs can include the dimming of your headlights or your dashboard lights, the power window takes a lot of time to operate, or the engine starts very slowly. Although these things only happen for a while as a partially charged battery can still supply enough power to operate the lights and windows, but it might not start again the next time. Another thing you can notice is when there is a loud grinding noise in your alternator. It is a sign of a bearing failure that prevents the rotor from spinning efficiently and eventually will seize. Make sure that when these things happen, when early signs of a faulty alternator starts to show up, do not take long drives or drive at high speeds because the battery will eventually run out of power and it will be difficult to stop it without the assistance of the engine. 

Diagnosing a Bad Alternator

The electrical components of the car are powered by the alternator and sometimes by the battery. Both of them supply power, so how can you be so sure that the faulty one is the alternator? There are some ways you can do it. 

One thing you can try is by doing a simple voltage test. This can be done if you can still start your car as this test requires checking of the battery voltage with the engine off and with the engine running. You will need a multimeter or a multitester to conduct this test. First thing to do is get the multimeter and turn its setting to 20 DC. Turn off your car, open its hood and connect the red wire to the positive terminal of the battery and the black wire of the multimeter to the negative terminal of the battery. Check the reading. Normally, it will give you an average of 12 volts. Next step is to turn on your car and check the reading again. This time, it should give you 14.2 to 14.7 volts. Then, turn on all the electronic components of the car and check the reading again. If the reading gives you a similar 14.2 to 14.7 volts, then your alternator is okay and good. But if the reading goes way below that voltage, it means that the alternator is not working properly. Turn off your car and disconnect the multimeter by removing the black wire first and then the red wire last. If your car won’t start and you can’t do a voltage test, you can jump start your car using a jumper cable. If it turns on, let it run for 15 seconds and remove the jumper cables. If the car turns off immediately after that, then your alternator is faulty. 

Faulty alternators can be caused by several things. One is when the serpentine belt is worn or loose. Bad belt is easy to replace and it doesn’t cost much. Some causes for a faulty alternator include worn out of the ball bearing, the connection terminals failing to connect properly, damaged and corroded wires, and a malfunctioning voltage regulator. 

When you already checked your alternator or maybe had a second opinion from the professionals and the verdict is to replace it, then you should. The alternators are mostly accessible and easy to replace. It is also less expensive compared to the other major components of the car. 

How to Make Your Alternator Last Longer

While alternators are usually trouble-free, it can just suddenly fail rather than gradual. If you notice the early signs like the examples written above, then act on it immediately. Cleaning your engine components and keeping them away from dirt and debris can help prolong your alternator’s life. Be cautious when driving and prevent water splashes from the road that can get inside the alternator and cause it to wear faster as it can cause a premature alternator failure. Make sure that your engine undershield is not damaged since it also keeps your alternator clean and dry. The alternator must always be protected from water. It is also helpful to replace the certain alternator components before they wear out as per the servicing schedule. It can help prolong its life. A healthy alternator means a healthy charging system. It keeps you and your car going. 

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