Page 140 - Battery Reference Book

516 Silver batteries
.-I energy density of practical batteries is in the
range 24-73Whkg as cells and 18-44Whikg as
E
9
9 200 Sizlc batteries. The practical volumetric energy density is
2 150 36-171 Wh/dm3 as cells and 24-122Wh/dm3 as
batteries.
The low internal resistance of silver-cadmium bat-
N ickel-cadmium teries permits heavy drains and wide variations in
Lead-acid load at virtually constant voltage. Leakproof, spill-
UI Nickel-iron proof packaging with high impact strength helps ensure
dependable operation under severe environmental and
0 2 4 6 8 10 mechanical stress conditions. The extremely low in-
Discharge time (h)
ternal resistance of silver-zinc batteries permits dis-
Figure 5.2 Comparison of energy density at various discharge charges at rates as high as 30 times the ampere hour
rates: Silcad silver-cadmium batteries (Courtesy of Union capacity rating, and its flat voltage characteristic allows
Carbide) the highest operational efficiency and dependability.
Cells have been built with capacity ranging from
Although the theoretical energy density of the 0.1 Ah to 20 000 Ah. The use of silver in silver-zinc
silver-cadmium battery is 310 Wh/kg, the actual and silver-cadmium cells obviously increases initial

Table 5.3 Characteristics of Yardney HR and LR Silvercell silver-zinc batteries

Chemical reaction Ag + Zn(0H)z = Ago + Zn + H20
discharged charged
Energy output 20- 120 W hikg; as much as 220 W hlkg for certain types
Open-circuit voltage 1.86 f 0.04V (70-100% charged)
1.60 f 0.04V (30-70% charged)
Nominal voltage under load 1 SO V
Plateau voltage regulations &2% at a fixed load and temperature limits within f 5°C
Recommended discharge 1.oov
cut-off voltage
Recommended charge cut-off 2.05 V
voltage
Cycle life (before output drops HR cells: 5-20 cycles (1 h rate)
to SO% of nominal capacity- 10-15 cycles (30min rate)
depends on model and 5- 10 cycles (time-limited dncharge)
conditions of use) 1 cycle (6min rate or higher, full-capacity discharge)
LR cells: SO-100 cycles
Dry storage life Up to 5 years
Operating (wet) life HR cells: 6-12 months
LR cells: 1-2 years
Gassing on discharge or stand Very slight
Operational temperature +7 to -23°C down to -50°C with heaters; optimum cell performances at 51-10°C
range
Storage temperature range Wet, 37 to -48°C; dry, 73 to -65°C
Operating attitude In any position, although for optimum service upright is recommended
Internal resistance Very low, varies with cell model, temperature and rate of discharge
Resistance to mechanical stress Excellent; Silvercell batteries have met the stringent requirements of Spec.
MIL-E-5272A and are currently used in missiles, rockets, torpedoes, etc.; they are
extremely rugged, leakproof and spillproof, and can be packaged to meet the most
severe requirements
Charging time Can be fully recharged in 10-20 h, depending on requirements and type of cell
Charge completion Indicated by sharp rise in cell voltage at 2.0 Vkell during charge
Charge retention Up to 85% of nominal capacity after 3 months charged stand at room temperature

These data apply mainly to individual cells; when the cells are assembled to form batteries, performance will be determined by specific application
and packaging requirements. HR = high-rate batteries; LR = low-rate batteries