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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
need to be increased to 2.33 volts per cell if the
battery charger output must also be considered
ambient temperature is 55 degrees F (13 degrees C);
Ripple voltage limits are specified by some battery
and may need to be decreased to 2.18 volts per cell if
manufacturers on their cell data sheets. Excess
the ambient temperature is 95 degrees F (35 de-
ripple may reduce the expected life of the battery,
grees C). Consult manufacturers' catalogs for spe-
particularly when the battery has a low internal
cific values for their cells. Ripple content of the
Section V-NICKEL-CADMIUM CELL BATTERIES
14-16. Description of nickel-cadmium batter-
normal routine maintenance. If readings are taken,
ies.
the temperature correction for the electrolyte is the
same as for lead-acid batteries. The electrolyte in a
The nickel-cadmium technology results in more ex-
nickel-cadmium cell with a specific gravity of 1.190
pensive batteries but these batteries are resistant
will start to freeze (slush) at approximately minus
to mechanical and electrical abuse; will operate well
10 degrees F (minus 23 degrees C). Occasionally,
over a wide temperature range; and can tolerate
grayish-white deposits of potassium carbonate may
frequent shallow or deep discharging.
be seen on the cell tops. These deposits form be-
a. Construction. Nickel-cadmium (NiCad) batter-
cause the electrolye entrained in the escaping gas
ies may be flooded cell type; valve-regulated cell
reacts with the carbon dioxide in the air. Although
type, or sealed cells.
not corrosive, this deposit is a conductor when damp
(1) Flooded cells. These units utilize plates
and needs to be removed from the battery.
made of nickel-oxide for the positive electrode and
a. Parameters. The maintenance procedures for
cadmium for the negative electrode. The electrolyte
flooded lead-acid cell batteries, discussed previ-
is an alkaline solution of potassium hydroxide
ously, also apply to nickel-cadmium cell batteries if
which does not take part in the cell reaction. Accord-
the parameters are changed to those appropriate for
ingly, its specific gravity does not change during
alkaline cells. Float voltages for nickel-cadmium
charge or discharge, and the electrolyte retains its
cells are significantly different from those for lead-
ability to transfer ions irrespective of the charge
acid cells. For the same battery terminal voltage,
level. The majority of cells used in station battery
the number of cells will be greater, because a lead-
applications are of the vented type. During dis-
acid battery is a nominal 2-volts per cell while a
charge, vented-type cells can produce hydrogen gas
nickel-cadmium battery is a nominal 1.2-volts per
and oxygen gas in a potentially explosive mixture
cell. Degradation of nickel-cadmium batteries or ex-
which must be adequately exhausted. Since the gas
cessive capacity loss is indicated when the battery
is free from corrosive vapors, a dedicated battery
capacity has dropped more than 1.5 percent of rated
room is not required, although it is still recom-
capacity per year from its previous performance test
mended.
capacity. Thereafter, annual performance tests must
(2) Value-regulated cells. These are similar in
be provided in accordance with ANSI/IEEE 1106
construction to the vented types, except that their
requirements.
design allows evolved gases to combine and thereby
b. Temperature. Nickel-cadmium batteries are
reduces water losses.
less affected by temperature than lead-acid batter-
(3) Sealed cells. B ecause of their limited capac-
ies. They can sustain high temperatures more eas-
ity, sealed cells without valve-regulation are nor-
ily, because the chemistry in the active materials is
mally used only for backup of electronic devices.
relatively stable. For example, at 90 degrees F (32
degrees C) the normal life of a nickel-cadmium cell
14-17. Requirements for nickel-cadmium bat-
is reduced by about 20 percent, compared with a
teries.
reduction of about 50 percent for a lead-acid cell.
With a normal electrolyte, the battery will operate
In general, all of the procedures and tests described
at temperatures as low as minus 30 to 40 degrees C.
for flooded lead-acid cell batteries are valid for
With a higher specific gravity electrolyte, it will
nickel-cadmium batteries, except for specific grav-
operate at even lower temperatures. The available
ity. The nickel-cadmium electrolyte is a solution of
capacity is reduced at low temperatures, but at mi-
potassium hydroxide in water with a specific grav-
nus 40 degrees C a nickel cadmium battery can still
ity between 1.180 and 1.200, depending upon the
deliver 60 percent or more of its rated capacity.
manufacturer. The electrolyte does not enter into
c . Memory effect. Nickel-cadmium cells charged
the reaction of the nickel-cadmium cell. Therefore
specific gravity is not an indication of state-of-
at very low rates are subject to a condition known as
charge and specific-gravity readings are not part of
a "memory effect." Repeated shallow cycling, to ap-
14-12
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