Why We Use Alternators in Automobile Electrical System.

Alternators in automobile electrical systems are used as a generator to help supplement the electricity. In this article, I will discuss the full details of alternators used in automobile vehicles. 

Alternators in Automobile

Alternators in Automobile

Alternators are also known as the AC Generator for the engine. An alternator is an electrical generator that converts mechanical energy into electrical energy. This system plays a vital role in charging the car’s battery. It also supplies the current to the car’s electrical system. The alternator takes drive from the engine cranking.

The alternator works by utilizing the engine’s mechanical power to rotate a magnetic field within the alternator. The alternator uses the diodes to generate the alternating current into direct current. The movement of magnets, induces an electrical current in the stator windings, causing the electrical energy that is then used to charge the battery and supply power to the car’s electrical systems.

Also read- How to charge a 12-volt car battery at home?

Below the working principle of the alternator is discussed.

Working Principle of Alternator in Automobile

In a DC generator, the conductors are rotated in a stationary magnetic field and current flows in the same direction. But in an AC generator, the magnetic field is rotated and the conductors remain stationary. The current flows first in one direction and then in another alternately.


Working Principle of Alternator in Automobile

As shown in Fig, a rotating bar magnet furnishes the moving field which cuts the U-shaped conductor. As at(a), when the north pole passes the upper leg of the conductor, the current flows in one direction. As at(b) when the south pole passes the upper portion of the conductor, the direction of the magnetic lines of force is reversed, and the current flows in the reverse direction in the conductor. Thus, the magnet is revolving continuously, the direction of line force is also changing continuously, and the current alternates in direction alternating current flows. The strength of the current depends upon the following factors-

  1. Strength of the magnetic field.
  2. Speed of the magnetic field with which it revolves.
  3. No. of conductors. 
Instead of a simple bar magnet, two or more pole pieces, having field windings, are assembled on a shaft. When the current flows in the windings, a strong magnetic field is created and the pointed ends of the pole pieces become alternately north and south poles. The two ends of the conductors are connected to the two slip rings fixed on the shaft. The brushes make continuous sliding contact with the slip rings, through which the current is taken out to an external circuit for transmission and distribution. 
The alternator-type generator differed from the commutator-type generator in the voltage and current control method and in design. It uses silicon diodes to change the alternating current to the direct current for the vehicle’s electric system. Also, it does not require any cutout to prevent the battery from discharging through it, because the diode rectifiers allow the current to flow in one direction only.

Components of Alternator in Automobile

Components of Alternator in Automobile
An alternator in an automobile engine consists of several key components that work together. These components together generate electrical power. Here are the main parts of an alternator:

1. Rotor

The rotor is a central shaft that rotates within the stator. The rotor consists of coil windings and permanent magnets. The rotation of the rotor generates a magnetic field that interacts with the stator’s windings. This rotation generates electrical power with an electromagnetic field. 

2. Stator

The stator is a stationary component that covers the rotor. It contains multiple sets of coil windings. The stator windings are connected to the vehicle’s electrical system and output terminals. This is a type of step-up inverter. When the rotor’s magnetic field rotates within the stator, it induces an alternating current (AC) in the stator windings.

3. Diodes

Diodes are the fundamental component used in the electrical system. These are semiconductor devices that allow current to flow in one direction only. In an alternator, diodes are used to rectify the AC generated in the stator windings into direct current (DC). The direction of the electric flow and the rectification of the current are done by the diodes.

4. Voltage Regulator

The voltage regulator is responsible for the electrical voltage output from the alternator. It monitors the vehicle’s electrical system voltage and adjusts the field current supplied to the rotor windings. The voltage regulator ensures the production of a stable voltage for charging the battery.

5. Rectifier

The rectifier is called the rectifier bridge. The rectifier bridge consists of multiple diodes arranged in a specific configuration. It converts the AC output from the stator windings into DC, allowing the generated electrical power This helps to charge the battery. 

6. Brushes and Slip Rings

In traditional brushed alternators, brushes are used to maintain electrical contact with the slip rings. The slip rings allow current to flow into the rotor windings, creating the magnetic field necessary for power generation. However, modern alternators often use brushless technology to eliminate the need for brushes and slip rings.

7. Cooling System

Alternators generate heat during operation, especially at higher output levels. If there were no cooling system then the magnetic field could be clogged. Many alternators have built-in cooling systems, such as cooling fans or fins, to dissipate the heat and prevent overheating.

8. Pulley and Belt

The pulley is connected to the rotor shaft and is driven by a belt connected to the engine’s crankshaft. In an alternator, as the engine runs, the rotation of the crankshaft drives the alternator’s pulley, causing the rotor to spin within the stator and generate electricity.
These are the components that convert the mechanical energy to electrical energy which is useable to the vehicle’s electrical system.

Charging Circuit of Alternator

Charging Circuit of Alternator
This Fig shows the charging circuit of the alternator. When the ignition switch is turned on, the rotor receives current from the battery through the voltage regulator. This current produces the magnetic field of the rotor. As the rotor is turned by the pully, the current is induced in the stator windings. This alternating current is changed into a direct current by rectifiers. The voltage depends upon the rotor speed. A voltage regulator limits the generator voltage to a correct value. 


After the DC generator, the AC generator is introduced to the automobile system. This AC generator is called the Alternator. The alternator is responsible for charging the lead-acid battery of the vehicle. 
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