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Windscreen Wash-Wipe Circuit Schematic Circuit Diagram

Decoupling of Windscreen Wash Pump and Wiper Function in Cars

In numerous automobiles, the windscreen wash pump operates independently of the windscreen wipe function. This circuit, however, activates the wiper motor for a set duration each time the pump is activated. Pressing the pump switch initiates the wiper motor, and the wipers persist in operation for a brief period even after releasing the switch.

Windscreen wash-wipe circuit Schematic diagram

Diode Anode and Pump Motor Connection in Wiper Control Circuit

The anode of diode D1 typically connects to the ground through the wash pump motor. Upon activating the pump, capacitor C1 undergoes rapid charging, alongside D and R1. This prompts the activation of T1, T2, and T3, subsequently energizing relay Re1. The relay stays charged as long as both the pump motor and wipers are operational. Releasing the pump switch halts the washing process, yet wiping persists for a duration dictated by R2-C2. Diode D1 ensures that C2 remains uncharged via the pump motor, while diodes D2 and D3 safeguard the circuit from the back electromotive force generated by the relay coil.

Simple Installation in Cars with Three Key Connection Points

The installation of this circuit in a car is straightforward, involving only three connection points aside from the supply voltage. However, it is crucial to note that the circuit is designed to function with a pump motor featuring a fixed ground contact, and its positive contact is linked to the wash switch.

Relay Specifications and Connection Details

The relay integrated into the board possesses the capability to switch between 10 and 20 A. Its contacts are linked across the wiper switch via terminals ‘A’ and ’13’ using heavy-duty wiring. Connections to the board utilize spade terminals and mating sockets commonly found in car electrical systems. The spade terminals are securely screwed and soldered onto the board to minimize contact resistance. Two compatible relay options are the Omron Type G2L-113P-4S-SV, which fits on the PCB, and the Bosch Type 0 332 016 101, which does not.

Windscreen wash-wipe circuit Schematic diagram

Windscreen wash-wipe circuit Schematic diagram

Parts list

  • Ri = 220 Ω
  • R2 = 120 kΩ
  • R3 = 100 kΩ
  • R4 = 3.3 kΩ
  • R5 = 10 kΩ
  • C1 = 100 nF
  • C2 = 19 μF, 63 V
  • C3 = 10 nF
  • C4 = 100 μF, 25 V
  • D1, D2, D3 = 1N4148
  • T1 = BC550C
  • T2 = BC560C
  • T3 = BD140
  • Re1 = 12 V relay for PCB mounting.
  • Z>90 Ω,contact rating >10 A

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