Page 126 - Battery Reference Book

4/10 Nickel batteries

fact differ very little in construction from the heavy- 4.1.6 Comparison of characteristics of
duty nickel-cadmium type. Capacities are up to 23 Ah lead-acid and nickel-cadmium sealed
at 1.22V. This battery weights 1.390kg, its dimen- batteries
sions being 51 x 91 x 125 mm. Permissible operating
temperatures are the same as for the button type. For many everyday battery applications, the choice is
These cells comprise an assembly of two groups of still between the lead-acid and the nickel-cadmium
rectangular thin sintered plates and the separator in systems, rather than the more recently developed sys-
rectangular nickel-plated steel cases. Current take-off tems. Each of these two main types of sealed bat-
is through terminal studs. They have medium-pressure tery has its own advantages and the choice between
(4 x lo5 N/m2) self-reclosing safety valves. SAFT, for nickel-cadmium and lead-acid batteries depends very
example, supply three sizes of rectangular cell (VD much on the particular application and on the perfor-
series). There are three sizes of cell with capaci- mance characteristics required.
ties below 10 Ah: V04G (3.8 Ah), VO4US (4.4A h) The characteristics of the two types of battery are
and VO9 (9.9Ah) (Table 4.7). There are also high- compared in Table 4.8. Although this information will
reliability sealed VO cells for space applications (VOS be of assistance to the designer in helping to select
cells). VO cells and batteries may be continuously whether a lead-acid or a nickel-cadmium battery
discharged at currents up to 5C5A. They can supply is most appropriate to the application in mind, it is
short-duration peaks of up to 10C5 A. strongly recommended that a final decision should not
Sealed rectangular cells with mass electrodes (Varta be made until the problem has been discussed with the
D23 type) are suitable for continuous discharge up suppliers of both types of battery. The lead-acid bat-
to 10 times the nominal discharge current. They teries referred to in Table 4.8 are the Dryfit type sup-
are fitted with a safety vent which prevents exces- plied by Accummulator-enfabrik Sonnenschein (West
sive internal pressure damaging the cell case in fault Germany), although no doubt in many respects the
conditions. comparisons will hold good for sealed lead-acid bat-
Rectangular cells with sintered electrodes, SD series teries produced by other suppliers.
(Varta CD type), are suitable for applications in which Figure 4.6 plots the energy density (Whkg) as
a high rate of discharge, or operations at extremes a function of the 20h capacity for Dryfit batter-
of temperature, or permanent trickle is required. The ies and nickel-cadmium batteries supplied by Varta
cells are constructed from cut sintered positive and and SAFT. It can be seen that the rectangular mass
negative plates, separated by a highly porous separ- and sintered plate nickel-cadmium batteries exhibit
ator which absorbs all the free electrolyte within the lower energy densities than Dryfit batteries and cylin-
cell. A safety vent is incorporated within each cell to drical sintered plate nickel-cadmium batteries. The
enable gas which may build up under fault conditions increase in capacity which occurs in Dryfit batteries
to be released. All cells in this range have the cases after several charging cycles together with the as-
connected to the positive electrode. All cases are not sociated increase in energy density has not been taken
insulated but intercell separators and nickel-plated con- into consideration in the data presented in Figure 4.6.
nective links are available. The CD series is available Also not considered is the increase in weight when five
made up in metal boxes. nickel-cadmium cells are connected in a supplemen-
A range of rectangular cells available from SAFT is tary housing to form a 6V battery. The usual cylin-
listed in Table 4.7. drical sinter cell batteries, the large button cells and

Table 4.7 Sealed rectangular cells available from SAf7
Serial No. Rated Maximum dimensions Maximum Maximum discharge
capacity (mm) weight rates (A)
(g)
mA h, Height Width Depth Continuous Pulse
~ ~~ ~~ ~ ~ ~~
vo 4c 3.8 14 64 19 180 20 38
4us 4.4 14 64 19 220 22 44
9 9.9 107 98 19 400 50 100
vos 4 4 78.5 53 20.5 230 20 -
7 7 112.5 53 20.5 360 35 -
10 10 91 76.2 28.9 500 40 -
23 23 165 76.2 28.9 1060 60 -
26 26 186 76.2 28.9 1200 80 -