Demonstrate construction of various electrical accessories

Demonstrate construction of various electrical accessories e.g. horn, wiper & flashers etc.

HORN

Horn is a sound creating device. Electrical horns are used in all the automobile vehicles. When the horn is operated it creates loud vibrating sound indicating that vehicle is coming so that the passengers or the other slow moving vehicles may clear off the path to pass it. Horn is also used as a calling well to call the persons when the vehicle is ready to start. Lights, breaks and horns are the devices that prevent accident. Light flashes the road, horn makes the road clear and breaks stop the vehicle, all the three devices make the driv ing safe from accident.

Fig. shows diagram of the horn circuit. It consists of a armature, a diaphragm, a winding and a pair of contact points connected in series. When the horn button is pushed, it connects the horn winding to the battery. The current passing through the winding produces the magnetic field which pulls the armature down, creating a loud click. The armature is attached to a diaphragm.

The movement of the diaphragm opens the contact points, due to which the circuit is broken. The cycle is repeated rapidly. The rapid movement of the diaphragm produces a distinctive noise. The tone pitch of the horn depends upon the size and shape of the diaphragm and also upon the path through which the sound must travel.

A relay is also used in some systems to avoid carrying heavy current required by the horn through the steering column and back. The relay closes its contacts to connect the horn to the battery. This way, the voltage drop in the wiring from battery to horn is eliminated and higher voltage is available for operating the horn with better performance.

The horn relay serves a second purpose also in some cars. It gives a warning that the ignition key has been left in the ignition switch when the car door is opened. When the ignition key is in the ignition switch, a special set of contacts are closed. Now if the car is opened, the door switch will complete the circuit through the buzzer (upper) contacts and winding of the relay to the battery. The current flowing through the winding produces a magnetic field which pulls the armature down. This opens the contacts and the winding loses its magnetism so that the spring closes the contact again. The cycle is rapidly repeated so that the relay emits a buzzing sound to warn the driver that he has forgotten the ignition key in the ignition switch. This prevents the car from being stolen by thefts.

WINDSHIELD WIPER

A Windscreen wiper or Windshield wiper is a device used to remove rain, snow, ice and debris from a windscreen or windshield. Almost all motor vehicles, including cars, trucks, train locomotives, watercraft with a cabin and some aircraft, are equipped with such wipers, which are usually a legal requirement.

A wiper generally consists of a metal arm, pivoting at one end and with a long rubber blade attached to the other. The arm is powered by a motor, often an electric motor, although pneumatic power is also used in some vehicles. The blade is swung back and forth over the glass, pushing water or other precipitation from its surface. The speed is normally adjustable, with several continuous speeds and often one or more "intermittent" settings. Most automobiles use two synchronized radial type arms, while many commercial vehicles use one or more pantograph arms.

On some vehicles, a windshield washer system is also used. This system sprays water or an antifreeze window washer fluid at the windshield using several nozzles. The windshield washer system helps to remove dirt or dust from the windshield when it is used in concert with the wiper blades. When antifreeze windshield washer fluid is used, it can help the wipers to remove snow or ice. For winter conditions, some vehicles have additional heaters aimed at the windows or embedded heating wire in the glass. These defroster systems help to keep snow and ice from building up on the windshield. In rare cases, miniature wipers are installed on headlights.

WINDSCREEN WASHER

Most windscreen wipers operate together with a windscreen (or windshield) washer; a pump that supplies a mixture of water, alcohol, and detergent (a blend called windshield washer fluid) from a tank to the windscreen. The fluid is dispensed through small nozzles mounted on the hood. Conventional nozzles are usually used, but some designs use a fluidic oscillator to disperse the fluid more effectively.

In warmer climates, water may also work, but it can freeze in colder climates, damaging the pump. Although automobile antifreeze is chemically similar to windscreen wiper fluid, it should not be used because it can damage paint. The earliest documented idea for having a windshield wiper unit hooked up to a windshield washer fluid reservoir was in 1931, Richland Auto Parts Co, Mansfield, Ohio. Uruguayan racecar driver and mechanic Héctor Suppici Sedes developed a windscreen washer in the late 1930s.

FLASHER UNIT

There are two basic types of flasher unit. One is operated by a piece of wire or a bimetallic strip which expands and contracts as it is heated by the current; the other is a relay operated by a transistorised circuit. The first type is easy to locate if it is working at all because of the clicking sound it makes. To check whether it is faulty, use a circuit tester or test lamp in the way described below. The transistorised type does not make a clicking sound, and cannot be checked with a circuit tester. It can be damaged by a short circuit. The only way to determine if a transistorised type is faulty is by eliminating all the other components in the circuit.