Page 95 - Battery Reference Book

Primary batteries a13
Despite these initial difficulties, commercially avail- 1.7
able D and N cells were available in the UK in the
early 1970s. The ECL D-size cell outperformed D-size 1.6
nickel-cadmium cells under most conditions, except - 1.5
at sub-zero tl-mperatures, in a military ‘manpack‘ >
radio application. The cost of this zinc-air cell was m 1.4
about 25% of that of an equivalent nickel-cadmium 5 1.3
e
cell and proved to be more economical. However, >
the nickel-cadmium cell had the advantage of being 1.2
rechargeable. (Primary zinc-air batteries were used 1.1
extensively during the Vietnam War.) The N-size cell
has been used successfully for the small pocket paging 1 .o 0 20 40 60 80 100
equipment market. The demise of zinc-air D and N Percentage of service life
cells rests on economic factors rather than on technical
grounds. The picture for zinc-air button cells is quite Figure 2.5 Heavy duty effect. SP11 and HPII (R14) alkaline
different; Gould have manufactured them in the USA manganese dioxide batteries. Beneficial effect of using a high-
power battery (HPI 1) on service life; high current drain (10 a,
for several years for applications such as hearing-aids, 2 h/day discharge)
watches, etc., and Gould and Berec have both been
marketing them in the UK since 1980.
LeclanchC and alkaline manganese batteries retain
1.6
the great majority of the primary battery market for 1.6
portable-in-use applications. They are widely available 1.5
1.5
in a variety of equivalent cylindrical sizes.
The LeclanchC system has the property of ‘recov- 1.4
1.4
>
ering’ during rest periods in the discharge regimen. > 1.3
;
;
1.3
This property and the low cost resulting from high- a
a
= 1.2
volume automated manufacture make the EeclanchC = 1.2
ideal for the intermittent usage pattern found in most 8 8 1.1
1.1
consumer appliances. Figure 2.4 shows the effect of
.o
increased current drain on the service life of the SP2 1 .o
1
(R20 size) battery. The discharge period is 5 Wday to 0.9
0.9
an end-voltage of 0.9 V.
0.8
For higher current &rains, for example in motorized 0.8
60
80
40
20
100
equipment, a high-power (HP) battery should be used. 0 0 20 40 60 80 100
HP batteries contain electrolyte or chemically prepared Percentage of service life
manganese dioxides, which have enhanced discharge Figure 2.6 Low discharge effect. SP11 and HP1 1 (R14) alkaline
properties. Figure 2.5 compares SP11 and HPl 1 (R14 manganese dioxide batteries. Effect of using a high-power battery
size) types on a 10 Q, 2Wday discharge - the advan- (HPI 1) on service life; high current drain (300 R,2 h/day discharge)
tage of using the high-power type is obvious. For
low-rate discharges, the additional cost of the HP ver-
100 sion is not warranted; Figure 2.4 compares the same
cells on a 300 Q, 2 Wday discharge.
The storage properties of modern LeclanchC batter-
ao ies are much better than those of early dry batteries
because of technological improvements. For example,
average discharge levels of SPll and HPll batter-
ies, on radio and tape recorded discharge respectively,
after 2 years’ storage at 20”C, are over 95% of those
obtained for similar batteries discharged within a few
weeks of production.
Transistor applications require multiples of the unit
cell voltage; the layer stack (‘power pack’) format
provides a convenient battery in a smaller volume
than the equivalent combination of round cells. Only
one unit needs to be replaced, and connection is
by simple non-reversible press studs ensuring correct
Percentage of service life polarity. Selection of the most economical layer stack
Figure 2.4 SP2 (R20) Leclanche cells. Effect of increased current battery should be made in conjunction with the battery
drawn on service life manufactuer. Specification of a battery which is too