Page 409 - Battery Reference Book

36/6 Carbon-zinc primary batteries
is most dramatic. At these drain rates they out-perform movie camera applications runs from 250 to 500mA.
ordinary carbon-zinc cells by as much as 1O:l. Cameras with cell-operated flash require up to 750 mA.
Electronic shutters require up to 90mA.
While most applications in cameras have sufficient
36.2.5 Calculators drain rates to justify alkaline (or mercury or
Some pocket calculators on the market today still silver) cells, there are other reasons why most
employ LED (light emitting diode) display. This is camera mandacturers design their photographic
the same basic circuitry or chip used in the new LED equipment almost exclusively around this system.
watches. A considerable amount of energy is required Their superiority in resisting extreme temperature
to power these displays when they are in use, and a variations is perhaps the most important of these, since
relatively high drain rate results. The drain rate of the cameras are obviously used extensively out-doors in
LED calculator runs from 30 to 80 mA. all kinds of weather. The shelf life advantage is also
Some of the newer calculators employ the LCD important, as cameras are often left for long intervals
(liquid crystal display), which does not light up; between use.
therefore, the drain rates are dramatically lower than In flash applications, the sharp demands in drain rate
with LEDs. Drain rates on LCD-type calculators can over very short time periods can only be handled by
run as low as 0.05 mA (50 p A). The drain rates in these premium cells, as carbon-zinc cells simply could not
new LCD-type calculators are so low that any type of respond to them.
cell would last for a considerable period of time. In
fact, it is likely that shelf life may be a factor of equal 36.2.7 Hearing-aids and watches
importance to service life in these applications. Since
smallness in size is the key with portable calculators, Unlike most conventional battery applications, hearing-
the smaller cells are generally involved. This will lead aids and watches require miniature specialized mercury
to the use of alkaline-type button cells or other new or silver oxide cells to provide the continuous power
shapes. In addition, the new low-drain lithium cells supply necessary. While the button cells used in
are becoming a serious contender here because of their hearing-aids and watches are similar in appearance,
extremely long shelf life. they differ in internal construction as they are designed
However, since the majority of calculators on the to satisfy various power requirements at different drain
market or in use today employ LED display, they rates and they are therefore not interchangeable.
present ideal applications for alkaline cells. Consumers LCD and quartz analogue watches (watches with
are discovering this advantage very quickly as over a conventional face) have drain rates as low as
40% of the cells used in calculators are alkaline. The 0.0025 mA (2.5 PA). Generally speaking, drain rates
advantage of alkaline cells over carbon-zinc cells in for hearing-aids are moderate, ranging from 0.15 mA to
these types of calculators runs as high as 6:l. a high of 5 mA. In hearing-aids, as well as in LCD and
quartz analogue watches, the drains are continuous.
36.2.6 Cameras However, LED watches require drains up to 40mA
during the pulse. Thus, the requirements needed to
In cameras, cells perform a wide variety of functions, power the displays in these watches are about eight
including discharging flash units, motor powering, times greater than in hearing-aids and 16000 times
shutter control and film ejection. Obviously, the drain greater than in LCD and quartz analogue watches. For
rate for these different functions varies significantly. this reason, a wide variety of mercury and silver oxide
The higher drain rates again apply to those applications cells meets the growing demands of the various types
involving motors or lights (flash). The drain rate in of hearing-aids and watches.