Page 120 - Battery Reference Book

4/4 Nickel batteries

Table 4.2 Unibloc batteries: dependence of maintenance-free intervals on capacity and charging methods
Type Capacity at Maintenance intewal (years)
10 h rate (Ah)
Fully automatic operation without Close voltage application with 6-monthly boost of
boost (float voltage 1.47 Vkell) 1.65- 1.70 V/cell (float voltage 1.42 V/cell)
5LP7 7.5 8 14
5LP7 12.5 5 9
5LP12 15.0 4 7.5
5LP27 27.0 2.5 5

Simple snap-on or
bolt-on terminals

1 2 345 1015 30451 2 345 101520
Time (min) (h)
Figure 4.3 Discharge curves at 25°C: Chloride Alkad Unibloc
nickel-cadmium battery (Courtesy of Chloride Batteries)

and therefore originally used the same active mater-
ial and similar intercell components that had proved
their reliability in production and service. Because the
active material in the vented batteries was a pow-
dered mass, it was logical for the earlier ranges of
sealed batteries to use the same material. Since then
materials and production techniques have improved,
enabling sealed battery performance to be improved
by optimizing the active material. These changes in
active material, while not significantly improving the
Easy-to-clean surfaces provide performance at low discharge rates (10 or 5 h rate),
maximum protection against
corrosion and dirt have changed the voltage characteristics at the higher
Extra-generous electrolyte rates of discharge. An example of this improvement
reserve means negligible for a Varta 0.225 Ah cell (10 h rated, 22 mA discharge
maintenance current at 10 h rate) is shown in Figure 4.4 by compar-
ison of the characteristics in (a) original plate materials
Figure 4.2 Chloride Alkad Unibloc nickel-cadmium battery con-
struction (Courtesy of Chloride Batteries) and (b) improved plate materials. This improvement
in discharge performance has been achieved without
adversely affecting the cell’s good charge retention or
dependent on the float charge voltage, the capacity external dimensions.
of the battery and the frequency of boost-charging. Sealed nickel-cadmium cells are normally rated
Table 4.2 shows how the maintenance interval across at either the 5 or 10h rate, that is, the discharge
the Unibloc range of batteries is related to battery current that can be taken from a cell to discharge
capacity and charging method. it fully in 5 or 1Oh. Sintered cells are rated at the
The discharge performance of Unibloc batteries is 5 h rate (I5) and, occasionally, particularly with US
shown in Figure 4.3. manufacturers, at the 1 h rate (II), and mass plate cells
at the 10 h rate (Ilo). The nominal on-load voltage of a
nickel-cadmium cell is 1.2V and this voltage is said
4.1.2 Sealed nickel-cadmium batteries to be the average value for the total discharge period.
Characteristics of sealed nickekadmium batteries The cell’s fully charged open-circuit voltage, if taken
within 24 h of terminating a charge, can vary between
Sealed nickel-cadmium batteries were first developed 1.35 and 1.4V. The voltage characteristic is flat for
in the 1950s from vented nickel-cadmium batteries most of the discharge curve, even at comparatively