12-V On-Board Electrical System, Basic Function - GF54.10-P-1014A

Model all (CAR) 

Model all (4xWD) 

Overview 

This document contains the following information:

• General 
• Function 
  • 12 V On-Board Electrical System 
  • Secondary 12 V On-Board Electrical System (Vehicles For Conditionally Automated Parking Or Driving) 
  • Shutoff Of 12 V On-Board Electrical System (Vehicles With Battery Main Switch) 

General 

The 12 V on-board electrical system normally includes all components for voltage generation, voltage regulation and energy storage. The 12 V on-board electrical system supplies the electrical consumers of different systems, such as the interior lighting, exterior lighting or engine management, with electrical energy.

Depending on the equipment installed, the 12 V on-board electrical system may be supplemented by a secondary 12 V on-board electrical system.

Function 

• 12 V On-Board Electrical System 

On vehicles with a 12 V alternator, the necessary electrical energy is generated when the combustion engine is running. This is stored in the 12 V on-board electrical system battery. Vehicles with 48 V technology, hybrid vehicles and electric vehicles do not have a 12 V alternator. On these vehicles, the necessary electrical energy for the 12 V on-board electrical system is provided via a DC/DC converter by the 48 V battery or by the high-voltage battery.

• Secondary 12 V On-Board Electrical System (Vehicles For Conditionally Automated Parking Or Driving) 

The 12 V on-board electrical system is supplemented by a secondary 12 V on-board electrical system, which is supplied from the 12 V on-board electrical system in normal operation through a DC/DC converter. Electrical energy is stored in the secondary 12 V on-board electrical system battery.

To ensure safe operation of the service brake and steering when performing conditionally automated parking or conditionally automated driving, the system components needed for this must be performed redundantly. In the event of a fault or failure of the regular on-board electrical system, the secondary 12 V on-board electrical system takes over supply of these system components for a defined period of time.

This means that the vehicle can be brought to a safe condition, for example braked and parked, either automatically or by means of driver intervention.

Hybrid vehicles and electric vehicles for the Chinese market also have a small buffer battery that ensures the emergency supply for the telematics services communication module.

• Shutoff Of 12 V On-Board Electrical System (Vehicles With Battery Main Switch) 

Using the battery main switch, the user can disconnect the 12 V onboard electrical system battery from the 12 V on-board electrical system. In this way, the on-board electrical system battery can be preserved during extended idle time.

The on-board electrical system battery is disconnected via a contactor.

This is not opened while the engine timing is performing run-on cooling. This ensures that electrical energy is still available to ensure that the engine is sufficiently cooled.

To prevent a build-up of heat, the on-board electrical system battery must not be cut off when the stationary heater is active.

Example illustration 

Courtesy of MERCEDES-BENZ USA