A car's engine keeps running only if there is regular supply of electricity for the spark. The battery is provided to supply this electricity, but it needs a regular source of charging. And, it is the alternators that produce this regular supply of current. An alternator is a type of generator that produces current, which is used for charging the battery.
Even though the output voltage of the battery is 12 volts, an alternator produces 14 volts of output so as to ensure 100% charging of the batteries. Current is produced in the alternator through the rotation of magnetic field. And, the alternating current (AC) produced by it is then converted into direct current (DC) through a diode bridge. You must already be knowing that the electrical accessories in a car can only be run on DC. And, another component, the voltage regulator would then direct this current to the battery to keep charging it. The battery keeps getting charged or keeps storing electricity even if the engine is running at minimal RPM.
The voltage regulators of yesteryears were external, large-sized black colored boxes that were placed under the hood. But, those found in today's car models are part of the alternators. Its purpose is to keep the car's battery protected from getting overcharged or to cut off the current when voltage crosses the limit of 14.5 volts. The current is reinstated once the battery starts getting discharged.
The alternator is basically an electromechanical device, having components that keep moving. This means that there is constant wear and tear and thus regular maintenance is a must. You can start finding signals of problems if the headlight doesn't get lighted to its potential or if the electrical accessories start working improperly. Check the light given on the dashboard that is labeled "ALT". If it is on, then it is an indication that the voltage output of the alternator is low.
There are a few more steps to confirm where the actual problem lies. Start the engine and leave it idle. Take a digital multi-meter and check the output voltage between the terminals. If the voltage is below 14 volts, there is some problem with one of the stages inside the alternator. If the voltage is not the problem, then put some additional load on the vehicle and check if the voltage drops. If it does, then it would be required to repair the alternator. It would also be ideal to check the battery's output voltage, as it may turn out to be dead.
Once it has been established that there is some problem with the alternators, you must check whether the electromagnet is working properly or not. If it is working correctly, then metal objects would be attracted to it. You must also check if there is any type of noise coming out of the alternator. If it is then it is a sign that the bearings have worn out. This would require the replacement of the bearings or the alternator on the whole. The problem may not be as acute if the rotor belt is slipping or if it has broken. And, the replacements can be easily purchased from online stores.
If you are unable to determine the problem because of any reason, it would be best to take the help of a professional, in this case a mechanic. An expert can better check the symptoms and tell you what precisely the problem is. It is important for every car owner to understand any type of car problem and its solution. It can be of great help in the future. It may be possible that the next time any problem comes, the mechanic may not be by your side.