Charging System | Components , Function , Working Principle

Charging System | Components , Function , Working Principle , Diagnosis Tips 

Vehicle is equipped with many electrical devices to drive safely and comfortably. The vehicle requires electricity not only while driving but also while it stops.

Therefore, the vehicle has a battery for a power supply and a charging system to generate electricity by the engine running. The charging system supplies electricity to all the electrical devices and charges the battery.

The Charging system is an important part of the electrical system. It provides electrical current for the lights, the radio, the heater, the engines electrical systems, and other electrical accessories. It also maintains the batteries in a charged state, recharging them as necessary.

The charging system has three main components: the alternator, the voltage regulator, and the batteries.

The alternator generates electrical power to run accessories and to recharge the batteries. It is normally driven by a belt located off the crankshaft. Mechanical energy from the crankshaft is converted by the alternator into electrical energy for the batteries and accessories.
The voltage regulator acts as an electrical traffic cop to control alternator output. It senses when the batteries need recharging, or when the vehicles electrical needs increase, and adjusts the alternators output accordingly.

The batteries are a reservoir of chemical electrical power. Their primary purpose is to crank the engine. They also supply power to vehicle accessories when the electrical load is too great for the alternator alone.

Three-phase alternating current

(1) When a magnet rotates within a coil, a voltage will be created between both ends of the coil. This will give rise to an alternating current.
(2) The relation between the current generated in the coil and the position of the magnet is as shown in the figure. The largest amount of current is generated when the N and S poles of the magnet are closest to the coil. However, the current flows in opposite direction with each half turn of the magnet. Current that forms a sine wave in this manner is called “single phase alternating current”.

charging system of automotive
charging system of automotive


In general, the components of the charging system are composed of alternators and regulators. However, the charging system needs to add some additional components so that the electricity generated can be supplied to the battery and to all electrical loads safely and precisely. The component, consisting of;

1. Battery

The function of the battery is as a storage of electrical energy. Like a warehouse, the battery will store all the electrical energy generated by the alternator and then this stored electricity is removed when necessary.

2. Fuse and Fusible links

Fuse and fusible links have different functions even though have the same shape. Fusible link can be called as main fuse which is placed near the battery positive terminal. The function of this fuse is to protect the entire electrical system of the car from excessive currents. Generally the fusible link has a capacity of up to more than 60 Ampere.

While the function of the fuse is as a safety of a series of specific electrical wiring, in conventional charging system there are two fuse with same capacity (its about 10-15 Ampere). A fuse is used as a voltage regulator fuse and another fuse is used to secure the CHG and Voltage relay.

3. CHG Lights

CHG lamp or commonly also called “charging warning light” is an indicator light to indicate the presence failure of charging system. When the ignition key ON then this light will light up normally, as well as when the engine life of this lamp should turn on, if it is dead then it could mean the charging system failure.

4. Ignition key

The ignition key works as a switch. The charging system will be activated automatically when the engine is running, but to generate a magnetic field on the rotor coil must be done by a switch.

Ignition switch is used as a switch to connect anddisconnect power (positive battery curents) from battery to rotor coil. When the ignition key is ON, then the electricity from the battery to the coil rotor will be connected. However, when the ignition key is turned OFF then the power supply will be cut off. So it is not possible the altenator generates electricity when the ignition key is OFF even the engine crankshaft is rotate.

5. Regulator

The function of the regulator is to regulate the voltage generated by the altenator. Why should it be there? because the voltage generated by the altenator depends the engine’s RPM. This means that if the engine RPM is low, the altenator voltage is also low, but if the engine RPM is high then the altenator voltage is also high.

The regulator will be used to keep the voltage generated by the altenator not exceeding 14 volts even if the engine run in high RPM. This voltage setting aims to protect the electrical components of the vehicle to prevents over-voltage.

There are two types of regulators, namely type or conventional type and type of IC. The point type/conventional uses two coils to adjust the altenator’s output voltage. While the IC Regulator uses an IC circuit (Integrated Circuit) to regulate the output voltage.

6. Altenator

The function of the altenator is to convert a partial engine’s rotating energy into electricity. The altenator input comes from the engine pulley connected through a V belt, the rotation of the rotor will cause the intersection of the magnetic force line with the stator coil so that the electrons flow on the stator coil.

The electricity in the stator coil is not directly connected to the battery, but it must pass through the diode bridge to rectify the current. This is done because the current in the stator coil is AC (Alternate Curent).

7. Charging Wires

The function of charging wires are to connect every component of the charging system, there are at least two types of wires: standard wire and B + wire. The standard wire has a small diameter like the car’s electrical wiring in general, the function of this wire is connecting each terminal on the entire charging system.

While the B + wire has a larger diameter than the standard wire and almost matches the stater wire. The function of this wire is to connect the terminal B altenator with Battery.


Flow of electricity in charging system

Electricity in each position of the ignition switch.

Ignition switch ACC or LOCK

Ignition switch ON (when engine is not running)

When the ignition switch is in the ON position, current flows from the battery to the alternator. The reason for this is as follows. The alternator generally used for the vehicle generates electricity by rotating the magnet. The magnet is not the permanent magnet but the electromagnet that generates magnetic force by flowing electricity inside. Therefore, it is necessary to supply electricity to the alternator before starting the engine to prepare for generating electricity.

Ignition switch ON (when engine is running)


The alternator plays a major role in the charging system. Alternator has three functions of generating electricity, rectifying current and regulating voltage.

(1) Generation

Transmitting the engine revolution to the pulley via the v-ribbed belt turns the electromagnetized rotor, generating alternating current in the stator coil.

(2) Rectification

Since the electricity generated in the stator coil is alternating current, this cannot be used for the DC electric devices installed on the vehicle. To use the alternating current, the rectifier is used to rectify the alternating current into direct current.

(3) Regulation of voltage

IC regulator regulates the generated voltage to make the voltage constant even when the alternator speed or the amount of current flowing into the electric devices change.


The following general information has been assembled as a guide for charging system diagnosis. Refer to the appropriate Original Equipment Manufacturer’s service manual for specific information pertaining to charging system diagnostic procedures and safety precautions for your vehicle.


If an alternator test bench is available, follow the procedures found in the bench tester’s instruction manual to conduct an alternator performance test. This test will determine if the alternator output is within its performance specification, preventing unnecessary alternator replacement.
If the alternator output is within specification during bench testing, resolve problems in the remainder of the vehicle’s charging circuit and other electrical circuits that may affect charging circuit performance. Refer to the appropriate vehicle manufacturer’s service manual for the procedures and circuit schematics necessary to identify and correct additional charging circuit problems.
If the test bench results show the alternator’s output performance to be out of specification, replace the alternator. Follow the vehicle manufacturer’s recommended procedures to inspect the remainder of the charging circuit and other electrical circuits that may affect charging circuit performance.


1. What is the condition of the battery?
• A visual inspection and a performance test of the battery must always be performed before inspecting the charging system. The battery must be fully charged (12.6 volts) and the battery cables, terminals and case in good, clean condition. This includes the frame and body grounds as well (refer to Battery Visual Inspection and Performance Testing).

2. Are any fuses open?

• Check the fuses in all the fuse box(es). An open fuse indicates circuit problem(s) that may have an effect on the charging circuit. Check the owner’s manual or the manufacturer’s service manual for the location of each fuse box.

3. Is the fusible link(s) open?

• There may be several fusible links controlling battery voltage to the vehicle’s electrical circuits. If a fusible link is open, supply voltage will be completely lost to all electrical systems or to the electric circuit(s) that the open fusible link controls. Check the owner’s manual or the manufacturer’s service manual for the location of each fusible link.

4. Is the alternator’s drive belt tension within specification?

Too loose – If the drive belt is too loose, it will slip around the pulley causing the alternator to charge irregularly or not at all.
Too tight – If the drive belt is too tight, internal bearing damage will cause premature alternator failure.

5. Is the alternator’s drive belt in good condition and the proper size?

Worn or too narrow – If the alternator’s drive belt is worn or too narrow, it will slip around the pulley, causing the alternator to charge irregularly or not at all.
New drive belt – The life of a new alternator drive belt is approximately 10 minutes. It is important to check and adjust the belt’s tension to the “used” specification after the initial 10 minutes of operation.

6. Has the vehicle been modified or additional equipment installed after it left the factory?

Accessories – Non-factory accessories such as phones, computer outlets, televisions, refrigerators, stereo equipment or lights, among others, can overburden alternator performance and cause premature failure.
• Improper accessory installation – Improper accessory installation procedures can cause charging problems. Some of these problems may include poor ground points, loose connections or improper wiring.

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Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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