Page 388 - Battery Reference Book

Nickel-cadmium secondary batteries
ickel--cadmium secondary 5. Switch tripping batteries in high-voltage distribu-
batteries tion systems are well suited for use with distribution
ring mains. They offer reliability of operation and
33.1.6 Open and semi-open smaller types provide the high current necessary to close the cir-
cuit breakers and switches associated with power
The wide applicability and range of sealed nickel- stations and substation networks.
cadmium batteries is a result of their remarkable 6. Small hand lamps for powerful light output.
performance characteristics, some features of which 7. Train lighting batteries are installed in containers
are: below the carriages and supply the coach lights
during steps at stations or in the case of a power
1. Total absence of maintenance. supply failure. Nickel-cadmium cells are also used
2. Very long operational life. for the uninterrupted emergency power supply to
3. Ability to accept permanent overcharge.
railway main stations and signalling systems.
4. Very favourable prolonged storage time character- 8. Marine applications require an unintenuptible
istics in stock, whatever the state of charge; bat- power supply to the emergency systems for radar,
teries producled by some manufacturers are better communications, steering and navigation, and for
in this respect than those produced by others. If the emergency lighting on board.
charge acceptance deteriorates markedly after a few 9. Air transport batteries provide the ground power
months' storage the capacity can be restored by supplies and also the support battery systems on
cycling. board aircraft. Also, at the airport, all the essential
5. Ability to be overcharged at high rates. lighting and communication relies on the batteries.
6. Rapid and ultra-rapid chargeability. In this method of working, the system will operate
7. Constancy of discharge voltage characteristics even in the standby mode, giving uninterrupted power
at very high discharge rate. supply on mains failure.
8. Mechanically robust and resistant to electrical dam-
age (overcharge reversal).
9. Operation over a wide temperature range: -40 to 33.1.2 Sealed nickel-cadmium batteries
+50"c. The application of sealed nickel-cadmium batteries
Some applications of vented large nickel-cadmium may be subdivided into four main categories, which
batteries axe discussed below. are discussed below: self-contained supply, emer-
gency supply, auxiliary supply, starting and highpower
Large nickel-cadmium batteries are made in a vari-
ety of designs to suit different types of application. supplies.
The major appli'cations are discussed below:
Self-contained supply
1. Central batteries for emergency, safety and auxil- Sealed nickel-cadmium batteries are mainly used
iary lighting are used for public meeting places in portable devices as the only source of energy.
(theatres, warehouses, sports halls, etc.) and fac- Examples of this type of application are: transceivers.
tories. They permit the safe evacuation of buildings razors, portable equipment and tools, remote radio
in the case of mains failure, by providing secondary and ultrasonic controls, flashguns, toys, portable spray
illumination. equipment, toothbrushes, hair curlers, hearing aids,
2. Nickel-cadmium batteries are used for special cine cameras, calculators, computers, model ships,
emergency power supplies, as required in medical etc., test and control instruments, survey equipment,
centres, intensive care units and operating theatres rangefinders, sonar, timers, digital counters, domes-
and similar applications where lighting interruption tic electricity and telephone meters, clocks, time and
can be a matter of life or death. security check clocks, ticket, money and petrol dis-
3. Engine starting batteries are used to start motor pensers, identity check machines, electronically con-
generator sets as required for standby power sys- trolled machine tools, lamps, tape recorders, television
tems. The batteries have to start the engines in bad dictation equipment, measuring and test instruments,
weather conditions where low temperatures may medical equipment, miners' lamps, transceivers, tele-
prevail. These engine starting batteries must be phones, incubators, heated clothing, underwater lamps,
highly reliable, have a high performance capabil- portable refrigerators, telephone answering machines,
ity and be free from the effects of high stress and metal detectors, invalid chairs, control instruments,
vibration, such as occurs in vehicles and the engine emergency lighting, security alarms, portable electron-
rooms of shilps. ics, portable tools, communications, computers, elec-
4. Back-up standby batteries provide power in the tronic back-up and, most recently, mobile telephones.
event of a mains failure, for example in the opera- In these types of application, sealed nickel-cadmium
tion of a crane to prevent the load being released. batteries are ideal sources of energy, meeting the
Another application is in computers and processing requirements of medium energy ai low rate and free-
systems. dom from a.c. supply loads. Thus, in the operation