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Electrical Equipment Yesterday and To-day T HE change in design and
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the increase in efficiency of lowvoltage lighting and starting . equipment that has taken place during the past ten years or more is interesting and often not fully appreciated, owing to its having pome about gradually. Throughout this period it can be said that there has not been any startling development or departure from the orthodox in, the design of low-voltage .equipment, although, of course, a number of ingenious devices has been produced.
When comparisons are made, however, the enormous increase in efficiency is, in itself, worthy of note. .As an . example, if a dynamo, as fitted to a double-deck vehicle with its full complement of lamps, be considered, we should find it has an output of 12, 24 or 30 volts, with a Maximum wattage, according to the voltage, somewhere in the region of 1,600, the approximate diameter of the instrument being from 8 ins. to 10 ins. Six and 12-volt machines of former years, with a maximum wattage in the region of 700, were of similar size. This change shows a corresponding rise in the wattage-weight-ratio of from approximately 7 watts to 18 watts per lb.
A number of factors is responsible for this alteration. To meet the demand for a wider range of electrically operated components an almost endless variety of accessories is available. Higher average speeds of vehicles and • the importance of strict time-schedule working have created a= dtmand for better and more powerful driving lamps. Increased engine power with high starting torques necessitate heavy duty starters, resulting in additional battery • loads. • Co-operation of chassis and engine manufacturers, as well as that of bodybuilders, has gone hand-in-hand with this increase in electrical equipment, such co-operation being essential to the accessible accommodation of the numerous components. No longer is such equipment considered in the light of extras to be fitted where space permits, but it has now become part of the vehicle itself, and, after all, on the modern oil or petrol-engined vehicle it is almost as important as the engine itself.
The perfection of te compensated-voltage control system has played an important part in making possible the high performance of the modern dynamo, so necessary to the maintenance of the large-capacity batteries as normally fitted. With few exceptions, the change-over from third-brush control instruments is now almost complete. With the compensated-voltage control system, the output of the dynamo is entirely independent of the speed at which it is driven; that is, after the speed has passed the minimum at which the full output can be prodaced.
• The regulator,_ or nerve centre of the system, maintains the voltage of the dynamo,aly..ays slightly in excess of the battery voltage, so as to ensure a charging current into the battery. Furthermore, if the battery becomes discharged, the output of the dynamo is automatically increased, whilst it .becomes less as the battery becomes charged. When the battery is fully charged it is sub
. jected to only a trickle charge, thus eliminating any danger from overcharging.
With this ideal arrangement of control it is possible light the lamps direct from the dynamo without fear of burning them out, because, as distinct from the thirdbrush type of dynamo, the compensated-voltage control ntachine does not depend on the resistance of the battery to control the maximum voltage. This serves to illustrate the principle of the system, but it is not a practical proposition to fit a dynamo without a battery, for reasons that will be obvious. .
Starter motors show a corresponding advance in performance. Formerly, it has been the practice to pass the main starter current through a heavy duty make-and-break switch mounted 'n the cab and operated either by hand or foot. With modem engines. however, heavy starting torques requiring anything from 800 to 1,000 amps. are by no means unusual.
This, of course, renders the old system obsolete, owing to the excessive voltage drop that occurs in the cable between the starter and swath, together with the difficulty of designing a reasonably priced switch which is sufficiently robust to carry this enormous load. Through . necessity, therefore, the switch is now mounted, either on or near the starter motor, and con
-trolled by push-rods or by a solenoid.
The starting of oil and heavy petrol engines not only causes a heavy drain on the battery, but subjects the engaging pinion and spring on the Orthodox type of "crash" drive to excessive loads. To overcome this, starters are now available on which the complete armature moves forward slowly and slides the pinion into mesh with the teeth on the engine flywheel, so that it is when the pinion is engaged only that the full starting torque is applied to the starter armature. to Head Lamps of Pleasing Design.
Both interior and exterior lighting on passenger vehicles have not been left behind in the general advance. The one-time large and heavy head lamps, with their dazzling uncontrolled beams, have been superseded by lamps of comparative light construction, but robust and of pleasing shape. The careful design of reflectors, glasses and bulbs has produced a powerful, controlled beam, whilst additional safety from dazzle has been achieved through the introduction of various methods of dipping and switching, usually by means of movable reflectors or double-filament bulbs.
The introduction of the heavy ribbed and fluted glasses, as well as the "stepped " or split reflectort giving a low, wide-angle beam, have, together with other systems,
produced an added factor of safety. "
A comparative newcomer is the lamp specially designed for use during fog, or as an auxiliary driving light. It is usually fitted well forward of the vehicle in a low position, the beam being directed towards the near side of the road, and, if well designed, the beam of light projected-is devoid of upward or backward glare.
Yet another addition to safety is the stoplight, so well known to the_ modem motorist, but possibly even more important when applied to passenger-service vehicles.
' Improvements in Interior Lighting.
Interior lighting on the modem passenger-carrying vehicle has been carefully thought out, and has resulted in an even distribution of light without •waste or discomfort to the passengers. The actual design of the fittings varies considerably with the type of vehicle, although, generally speaking, it tends to be• simple, easily accessible for bulb replacement, and pleasing to the eye.
It is interesting to note that, whilst the lamp load on such vehicles has increased, it has not gone up in the same proportion as with other items. of • electrical equipment, and, as the actual lighting quality has iniproved, it tends
to emphasize the high efficiency of modern interior-lighting equipment.
• As to the control of interior, lighting, the general tendency is to fit a separate svvitchbox with appropriate fuses in preference to a single box controlling all lighting accessories. Single switches and fuses, mounted either on busbars or panels, also prove popular, owing to the fact that they are " flexible " and make it possible for any number of control points to be built up as desired.
Cables, .too, are now hidden behind panels or carried in unobtrusive conduit, terminating generally at one central point to facilitate circuit checking and the tracing of faults. This feature has helped in the producing of plain,but serviceable, interior panelling, .a.nd in general body construction.
Deep down inthe chassis and below
the feet of the passengers there reposes probably the most neglected of all the items of electrical• equipment—the
battery. Be. it •of the acid or alkaline type, it is expected to meet the demands of all loads placed upon it withoat giving trouble and with little attention. Despite being• subjected to vibration and duty of a nature scarcely .dreamt of a few years-ago, the modern battery easily stands up to its task during years of service. This has been • made possible in the acid battery by careful construction of the .plates and by methods of assembly in shock-resisting con taineii, whilst the all-metal .construction of the alkaline. type naturally lends itself to such hard conditions of service.
A factor that is not generally appreciated is the consideration now given to the safety of passengers. The careful .manner in which the various circuits are protected with fuses reduces to a minimum the risk of fire through shorting. The design of terminals and connections is such that movement and the possibility, of short-circuits is prevented. Main battery cut-off switches are often used, so that, in a case of emergency, or when work is to be carried out on any part of the wiring, the copplete-system can be isolated from the battery by the operation of a single switch.
In addition to the equipment already mentioned, there are many accessories, such as windscreen wipers, direction indicators, interior heaters, radio sets, etc., that have been developed and perfected quietly, but effectively, during the past few years to add to the comfort and safety of passenger vehicles.