Page 310 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

3
Electrical systems 293

Phase
connection
Warning light To battery
connection positive
WL W +
Field diodes Positive diodes

Extra diodes
to increase output
Brushes
Slip rings
Negative diodes
Field windings

Stator (star wound)
Regulator

Figure 3.77 Modern alternator circuit

voltage induced in the stator reduces until it falls below the rated voltage of the
zener diode. The zener becomes non-conductive and allows the current to return
once again to the rotor windings. This cycle occurs very quickly in the regulator
to maintain a constant voltage output.
A typical circuit for a modern alternator is shown in Fig. 3.77 . The extra diodes
from the centre of the stator help to improve the overall effi ciency.

3.3 Lighting and indicators

3.3.1 Lighting systems

Vehicle lighting systems are very important, particularly where road safety is
concerned. If headlights were suddenly to fail at night and at high speed, the Safety fi rst
result could be serious. Remember that lights are to see with and to be seen by. Lights are to see with AND to be
Lights are arranged on a vehicle to meet legal requirements and to look good. seen by.
Headlights, sidelights and indicators are often combined on the front ( Fig. 3.78 ).
Taillights, stoplights, reverse lights and indicators are often combined at the rear
( Fig. 3.79 ).
The number, shape and size of bulbs used on vehicles are increasing all the time.
A common selection is shown in Fig. 3.80 . Most bulbs used for vehicle lighting
are generally either conventional tungsten fi lament bulbs or tungsten halogen.
In the conventional bulb, the tungsten fi lament is heated to incandescence by an
electric current. The temperature reaches about 2300°C. Tungsten, or an alloy
of tungsten, is ideal for use as fi laments for electric light bulbs. The fi lament is
normally wound into a ‘spiralled spiral’ to allow a suitable length of thin wire in a
small space, and to provide some mechanical strength.
Almost all vehicles now use tungsten halogen bulbs for the headlights ( Fig. 3.81 ).
The bulb will not blacken and, therefore, has a long life. In normal gas bulbs,
about 10% of the fi lament metal evaporates. This is deposited on the bulb wall.
Design features of the tungsten halogen bulb prevent this deposition. The gas in