Wiper breaker. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices
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The continuous operation of the windshield wiper of a car with slight precipitation causes excessive driver fatigue and leads to useless wear of the brushes. A simple device will help make the wiper work periodically.
When the device is turned off (switch contacts S1 are open), the wiper operates, as usual, in one of two modes - slow motion of the brushes, or accelerated. When the device is turned on, the wiper blades perform one cycle of movement every 5 s; in this case, the windshield wiper switch located on the vehicle's instrument panel must be set to the Stop position.
The device is connected in parallel with the contacts of the wiper limit switch. When the wiper is switched to intermittent (cyclic) mode, the contacts of switch S1 are closed. Capacitor C2 charges quickly (through the motor), and capacitor C1 charges slowly (through resistor R2). After a few seconds, the voltage across the capacitor reaches approximately 1,8 V. This will open the transistor V2, followed by the trinistor V1. Since the open trinistor is connected in parallel to the open contacts of the limit switch, the rotor of the electric motor begins to rotate, setting the wiper blades in motion. The speed of the brushes corresponds to the accelerated mode of operation.
After several revolutions of the motor rotor, the contacts of the limit switch are closed, the capacitors are quickly discharged (C1 - through the diode V3), and the transistor V2 and the trinistor V1 are closed. At the end of the brush movement cycle (double stroke), the limit switch contacts open, the brushes stop, and the capacitors C1 and C2 are charged again - a new cycle of the device begins. Capacitor C2 protects the contacts of the limit switch from burning.
If the car is equipped with a two-speed brush movement device, such a breaker cannot be installed, but another one should be used.
When the contacts of switch S1 are closed, the normal wiper circuit is restored.
Replacing one resistor in the charging circuit of capacitor C1 with two, of which one is variable (R2), allows you to adjust the pause time between strokes of the brushes, depending on weather conditions. With the resistor values indicated on the diagram, this time can be changed within 3 ... 10 s.
Wiper motors draw a lot of current when starting up. Therefore, the load circuit of the trinistor V1 should be mounted with wires of a sufficiently large cross section, connecting them directly to the terminals of the trinistor, and not to the printed tracks of the board. Switch S1 must be rated for a current of at least 6 A.
See other articles Section Automobile. Electronic devices.
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