Page 369 - Battery Reference Book

31/18 Secondary batteries

0°C
\
\ 25 "C
\ z 2 4 6 8 10 12 14 16 18 20 22 24
p 20 Storage time (months)
- I I I I (a) DK, DKZ and round mass plate types
0
4 - 0 50 100 150 200 250 300 350 c
.m
4 Storage time (days)
Figure 31.47 Capacity retained as a function of storage time at -20 OC
various temperatures: General Electric D cell (Charge, 2.45V at u 40 kko Oc
23°C for 16h; discharge, 0.25A at 23°C to 1.4v) (Courtesy of c. 5 60 R6O'C
General Electric)
5 80
100 r
Storage time (months)
:\ -
(b) RS and SD sintered plate types
, : t i . -20 OC
I
8
50
60
-
40 - 60
30, ' ' ' I ' I ' ' ' ' ' ' I I-'
1 2 3 4 5 6 80 600~
Storage time (months) ?
a
2 4 6 8 10 12 14 16 18 20 22 24
Storage time (months)
(c) D rectangular mass plate types
3L Figure 31.49 Self-discharge charge retention characteristics of
Varta sealed nickel-cadmium batteries (Courtesy of Varta)
2
temperature, they should not immediately be charged,
-20 -10 0 10 20 30 40 50 but should first be fully discharged and then charged
(bl Temperature ("C) once at half the no&d rate,-that is, 28h at the
20 h rate.
Figure 31.48 Nife Jungner NlGA sealed nickel-cadmium cells:
(a) self-discharge at 25°C (stored and charged at 25°C);
(b) multiplication factor for calculating self-discharge at other tem- 31.14 Float life characteristics
peratures between -20 and +50"C (Courtesy of Nife Jungner)
Batteries used in standby applications such as emer-
gency power and lighting, where the demand for
short-circuits because the short-circuit current is very them to supply power is spasmodic, would often be
high. When storing for more than 6 months a storage returned to full charge by the float charging regimen
temperature less than 15°C is recommended by the in which the battery is kept on continuous charge.
manufacturers. As in the case of lead-acid batteries, Under these conditions the battery is usually charged
self-discharge performance varies appreciably from by the constant potential method at a potential suf-
one manufacturer to another and this point should ficient to maintain it at full charge. In addition to
be carefully investigated before a battery selection making up any power loss due to use of the bat-
is made. tery this also compensates for any long-term self-
Button cells These cells have a moderate self- discharge processes that occur when the battery is not
discharge characteristic at normal temperatures, as under load.
shown in Figure 31.49. For applications requiring In the case of lead-acid batteries the float constant
good charge retention, mass plate electrodes are potential is maintained continually at 2.28-2.30 Vkell.
preferred. When button cells have been stored for a The limiting current is between 1 and 20% of the rated
long period (over 6 months), regardless of storage capacity.