Central Locking Door System Overview
In automotive accessory shops, you can find kits that enable your car to have a central-locking door system at an affordable price. These kits typically include motors and a control unit, essential components for the system to operate. The example unit we present here showcases the functionality of such systems.
5-Wire and 2-Wire Motors
Central locking systems utilize two types of motors: 5-wire motors and 2-wire motors. The 5-wire version is suitable for doors equipped with a key-lock. It has two connections for the motor itself and three connections for sensors (‘open’ and ‘close’ contacts) determining whether the door should be unlocked or locked. For doors without a key lock, the sensors are unnecessary, and a simpler 2-wire motor suffices.
Motor Polarity Control
The direction in which the locking mechanism moves (up or down) is determined by the motor’s polarity. A circuit that can reverse the motor’s polarity effectively locks or unlocks the door. In the schematic, the motor winding is connected between points M1 and M2. When relay Re1 is activated, the motors rotate anti-clockwise, and by activating Re2, the motors rotate clockwise. The actual direction of rotation depends on the motor’s inherent polarity.
Connecting Sensors and Relays
Sensors play a crucial role and are linked to resistors R1 and R10. Precision is vital here. If relay Re1 is responsible for unlocking the door, it must be connected to the ‘open’ contact. Conversely, Re2 handles door locking, where R10 is linked to the ‘close’ contact. RC pairs R16/C3 and R15/C4 determine the relay activation duration, a crucial factor tailored to your door’s specific locking or unlocking time requirements.
Sensor Wire Configuration
The third sensor wire, serving as the common connection, is tied to +12 V. RC networks at Sopen and Sclose inputs ensure motor activation only during door locking or unlocking, enhancing control precision. Furthermore, there’s an option to integrate the unit with a car alarm system. Two alarm types, positive and negative control, can be accommodated for universal applicability. T3 and T4, along with diodes D3 and D8, manage rising and falling edges. RC time constants are employed to guarantee single activation of both relays, optimizing functionality. It’s imperative to install a motor unit in each door.
Relay Specifications and Wiring
The specific relay type isn’t overly critical, but certain properties are desirable: a 12 V coil with 400 Ω resistance; maximum switching current of 12 A (AC); and a maximum switching power of 1200 VA. Given the challenging electronic environment within a car, robust connections are paramount. Employ reliable automotive connectors, crimped onto wires using appropriate tools. Avoid soldering connections in wires, as they tend to weaken where the wire meets the soldered joint under vibrations. Secure the wires at regular intervals to minimize potential issues.