TM 11-6140-203-14-1
FUNCTIONING OF NICKEL-CADMIUM BATTERIES
Section I. GENERAL
2-1. Purpose and Use
a metal carrier. The welding together of the individual
grains of nickel powder onto the carrier, results in a
Vented nickel-cadmium (Ni-Cad) batteries derive their
highly porous structure known as a plaque. Positive
name from the composition of their plates; nickel
(nickel) electrodes are formed by soaking the plaque in
oxide on the positive and metallic cadmium on the
nickel salts and then subjecting the salt-impregnated
negative. They are "vented" in that gases generated
plaque to electric current. Negative (cadmium) elec-
during the charging process can be expelled from the
trodes are formed by the same processes except that
cells in a controlled manner. They are used to provide a
cadmium salts are used. Plates are formed by cutting
source of direct current (dc) power in both aircraft and
the plaque to size and welding a nickel tab to a corner
nonaircraft applications. The following characteristics
for connection purposes.
provide major advantages over other storage batteries.
(2) Electrolyte. The electrolyte is normally, by
a. Vented nickel-cadmium batteries will maintain a
weight, a 30 percent solution of potassium hydroxide
relatively steady voltage when being discharged at
(KOH) in distilled water. It provides a path for con-
high currents.
ducting the current that flows between the positive
b. Vented nickel-cadmium batteries can be charged
and negative plates. The electrolyte does not take part
and discharged at a high rate current without causing
in the chemical react on in nickel-cadmium batteries,
permanent damage to the battery.
but acts as an ion carrier. The specific gravity of the
c. Vented nickel-cadmium batteries can stand idle
electrolyte, which is approximately 1.300, remains the
in any state of charge (fully charged, partly charged or
same whether the battery is charged or discharged.
discharged) without any damage.
Therefore, specific gravity measurements cannot be
d. Vented nickel-cadmium batteries can withstand
used to determine state-of-charge as is the case with
extremely cold temperatures without damage.
lead-acid batteries.
e. Vented nickel-cadmium batteries can withstand
(3) Separator. The separator is a continuous thin
high levels of vibration and shock without failure.
porous multiluminate of nylon and either cellophane
f. Vented nickel-cadmium batteries are composed of
or plastic, that keeps the positive and negative plates
individually replaceable cells.
from coming into contact with each other and causing
g. Vented nickel-cadmium batteries have a long
a short. The layer of cellophane or plastic, also has the
service life under severe conditions of use.
added function of preventing oxygen generated on
2-2. Construction
overcharge from coming into contact with the nega-
tive electrode and lowering the end-of-charge voltage.
a. Batteries. The term "battery" is generally used to
Before 1979 (except for BB-433A/A, which is prior to
describe a unit consisting of one or more cells. Cells are
1978) all aircraft and nonaircraft batteries contained
the basic building blocks of a battery. A battery can be
cellophane separators. After 1979 (1978 for the
a single cell which has terminals and is insulated and is
BB-433A/A) most aircraft nicad batteries used plastic
ready for use; but usually a battery is a series combina-
film separators such as "Permion" or "Celgard:" These
tion of individual cells assembled in a case containing a
plastic film separators have greater resistance to de-
connector and proper insulation. Each cell has a nomi-
gradation and longer life than cellophane, greatly
nal voltage of 1.20 volts; however, the actual operating
reducing the possibility of "thermal runaway."
voltage of a cell will range from 1.2 to 1.3 volts. A
nominal 6-volt battery will contain 5 cells connected in
(4) Cell assembly. The cell is assembled into its
series and a nominal 24-volt battery will contain 19 or
final form by welding the tabs of the negative plates to
20 cells.
one terminal post and the tabs of the positive plates to
b. Principal Parts and Materials. The principal
a second terminal post. Once assembled, it is inserted
parts and materials used in the vented cells of the
into a plastic case (nylon for aircraft batteries and ny-
nickel-cadmium battery are shown in figure 2-1 and
lon on Acrylonitrile-Butadine-Styrene (ABS) for non-
are described in paragraphs (1) through (5) below.
aircraft batteries) and fitted with a cover and vent
(1) Plates (electrodes). The sintered plates of nick-
assembly that permits the terminal posts to project
el-cadmium cells are made by a process in which carbo-
through the top of the case. After the cover is sealed to
nized nickel powder is sintered at high temperature to
the case, electrolyte is added.
