Page 124 - Battery Reference Book

4/8 Nickel batteries

Table 4.5 Sealed button cells (nominal discharge voltage 1.20V) available from SAFT
Serial No. Type Rated Maximum dimensions Maximum Maximum discharge
capacity (mm) weight rates (A)
(g)
(" mA h, Height Diameter Continuous Pulse
~ ~ ~ ~ ~~~
VBE 4 40 6 15.7 3.5 0.2 2.3
VB and VBE IO 100 5.3 23.0 7 I II
22 220 7.8 25.1 12 2.2 18.5
30 300 5.5 34.7 18 3 23
60 600 9.8 34.7 31 6 29

Cj (Table 4.5) at 20°C is defined as the capacity in 4.1.4 Nickel-cadmium cylindrical cells
ampere hours obtained at the 5h rate of discharge
(0.2C5 A) to an end-voltage of l.lOV/cell after a Nickel-cadmium cylindrical cells are designed for a
full charge at 0.1CsA for 14h. Rates of charge and wide range of applications requiring compact recharge-
discharge are expressed in multiples of the rated able batteries with high output capacity, heavy loads
capacity C5, thus 0.2CjA represents 20mA for a at steady voltages, the ability for rapid charge and
cell having a rated capacity C5 of 100 mA h. 5C5 A discharge, and exceptionally long life. Designed to
represents 500mA for the same cell. The range of be dimensionally similar to the principal cylindrical
button cells available from one leading manufacturer primary cells, of internationally standardized dimen-
is tabulated in Table 4.5. sions, these cells usually incorporate thin sintered plate
The life of button cells (SAFT, VB and VBE types, construction. Complete spirally wound plate assem-
Table 4.5) can extend over 10 years, but this is depen- blies are tightly fitted into a steel container to form
dent on operating conditions and is pricipally influ- cells. The container is closed by a cover having an
enced by the depth of discharge (discharged capa- automatic self-releasing safety valve for high pressures
cityhated capacity) in a cycling application and by the should excess gas pressure be caused by maltreatment.
number of ampere hours overcharged in a continuous Contact between the plates and the cover on the case is
charge application. The great reliability of button cells usually through a connection electrically welded to the
makes their life comparable with that of most electron- edges of the plates. This method of assembly improves
ics components. During cycling, approximately 500 battery performance on charge and discharge. A typical
cycles are obtained with 100% depth of discharge range of cylindrical cells available from one supplier
and 2000 cycles with 50% depth of discharge. After (SAFT) is listed in Table 4.6.
5 years' continuous charge at 0.05c5 mA, the failure Cylindrical cells are characterized by a nominal
rate for SAFT VB series button cells is not greater voltage of 1.2 V/cell and their remarkable power
than 5 per 1000. Under the same conditions their VBE (1.2 A Wcell) is, for example, capable of supplying
series button cells offer ten times better reliability; a a current of 100A at 0.6V for 0.3 s. Up to 170A
failure rate of 5 per 10000. peak discharge can be tolerated with a SAFT VR cell
Button cells with mass plate electrodes are pro- (Table 4.6) and the ultra-rapid charge time on a dis-
duced by Varta in two versions. DK type cells are charged battery can be as low as 60s when using
assembled using one positive and one negative elec- the appropriate charging equipment involving mon-
trode separated by porous insulating material. These itoring cell temperature, voltage or time of charge.
cells are suitable for operation at normal temperatures For uncontrolled rapid charge SAFT have developed
and discharge rates of up to 10 times the nominal dis- a special range of batteries. These batteries can be
charge current. DKZ cells have two positive and two discharged continuously at 20 times the normal rate
negative electrodes which lower the internal resistance and 40 times the normal rate for short periods. Apart
and therefore make the cell suitable for high rates of from ensuring the correct charging method, maintain-
discharge (20 times the nominal discharge rate) and ing end-voltages and temperature limits, no special
also for low-temperature operation. Button cells are care is needed. The rugged construction results in a
suitable for applications where low cost and good pack- battery that can withstand shocks and vibration. The
ing density are required. The charge retention of mass cylindrical cell is available in high reliability versions
plate button cells is superior to that of a11 other forms of (SAFT VRE type-Table 4.6) and versions for space
sealed nickel-cadmium cell. Many types of button cell applications.
can be made into stack batteries by connecting them Cylindrical cells when discharged at 1 V/cell at
end on end, in sleeves, thereby ensuring a minimum normal temperatures supply currents of the follow-
internal resistance. ing order: