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How Does the Car Battery Voltage Charging System Work?

10 April 2025
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It cannot be denied that a car is a tool filled with complex components inside, such as the charging system. This device functions to charge the battery voltage and electrical components when starting, and it turns out to have a complicated circuit. Here is an explanation of how the charging system works that you should know. 

1. When the Ignition Key is On but the Engine is Off 

The charging system starts when the vehicle key is in the on position, but you have not yet started the engine. At this moment, the engine will automatically activate the lights and provide magnetic power to the rotor coil. This activity is clearly visible, as the main lights or headlights will turn on.

This occurs because the voltage from the battery enters the fusible link and then to the ignition switch. This voltage flows from contact point O (Po) to Point 1 (P1), which then causes the lights to turn on. At that time, the voltage goes to Terminal IG, PL1, PL0, and to terminal F, rotor coil, plus terminal E of the alternator. This is where the magnetic power occurs. 

Read also: 30 Components of Car Carburetors and Their Functions

2. When the Engine is at Idle or Stationary

The operation of the charging system continues as you start the engine. In the initial ignition state, the lights will turn off and battery charging occurs. Generally, this happens because the ignition system transmits the engine's rotation to the alternator pulley. The charge warning light must be turned off to facilitate the voltage transfer. 

It can be said that this happens because the voltage switch directs to the charge warning lamp for a moment. Then it continues to the B terminal of the regulator and alternator. In this device, there is a diode that redirects the voltage in one direction only, causing the light to turn off. 

Battery charging also occurs due to the voltage from the stator coil. The stator generates 3-phase AC and DC voltage. This alternating voltage is also accompanied by 12-volt DC voltage, which is the way the charging system works for all electrical components in the car. 

Read also: Understanding the Working Principle of Electric Motors and Their Functions

3. Engine Running at Low RPM

At this stage, the magnetism and the voltage produced are not very high. However, this voltage is then redirected to the resistor which continues to the F terminal of the alternator and regulator. The magnetism in the rotor coil tends to be low with battery power less than 12 volts. 

4. Engine Running at High RPM 

It is different when the vehicle is moving and has a very high RPM. At this time, there will be no charging or charge. This is because the magnetic power produced by the regulator is very high and connects PL0 and PL2. Thus, the power from the battery will be redirected directly to the fusible link. 

Then, the operation of the stopped charging system will flow voltage to the ignition switch and fuse. From this path, power will be channeled to the IG terminal and continue to PL0 and PL2. However, after reaching PL2, the voltage actually directs to ground. This causes the rotor coil to have no voltage for charging. 

From this explanation, it can be concluded that charging operates under 4 different system conditions. When the vehicle key is installed, when the engine starts but is stationary, when it has low RPM, and at high RPM. These four conditions are part of a continuous system in the operation of the car. 

Read also: Five Types of Car Batteries You Must Know

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