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 TM 5-684/NAVFAC MO-200/AFJlMAN 32-1082
trolyte should be changed. Follow the manufactur-
proximately the same depth of discharge, leads to
continual low-rate charging and results in a loss of
er's instruction when renewing the electrolyte. The
battery warranty may not permit renewal without
surface area in the negative active material, due to
the growth of large crystals. This increase in the
the manufacturer's permission.
e. Charging. Specific gravity or cell voltage read-
cell's resistance produces a grater voltage drop. The
result is a reduction in the effective reserve time of
ings generally cannot be used to determine the state
the system. The memory effect can be erased by
of charge of a nickel-cadmium battery. To ensure
providing a complete discharge followed by a full
that the battery is fully charged, it should be given
charge with constant current. This breaks up the
a booster charge once a month, after any heavy or
crystalline growth on the plates. The conditions of
intermittent discharges, or after the battery charger
station operation will rarely lead to this type of
has been out of service. Maintenance personnel
cycling, but users should be aware of the cause and
should maintain a record of the monthly booster
charges. The accuracy of the charger voltmeter
the cure.
should be checked against a recently calibrated volt-
d. Electrolyte level. Vented type units will need to
meter at least once a year. A summary of charging
have the electrolyte level checked, even though a
requirements for nickel-cadmium batteries is given
specific gravity reading may not be required.
in table 14-4.
(1) Electrolyte level. Caution must be taken
f. Precautions. In addition to the precautions
when handling the electrolyte. The electrolyte level
given for lead-acid cell batteries, prohibit the use of
in all cells should be checked monthly. The maxi-
acid-contaminated tools and equipment, such as hy-
mum level of the electrolyte is halfway between the
drometers and thermometers used for lead-acid cell
tops of the plates and the inside of the cell covers.
maintenance.
(Do not include vent heights.) The level can be
checked visually if the cell containers are transpar-
Table 144. Charging of nickel-cadmium batteries
ent. If not, the level may be determined by inserting
an electrolyte-level test tube (plastic or glass)
Charge
Requirements
through the vent until it rests on top of the plates.
Initial
Then place a finger tightly over the exposed end,
charge
1. The first charge of batteries that are delivered
and withdraw the tube for inspection. The electro-
discharged should be carried out at constant cur-
lyte must always be returned to the cell from which
rent.
2. When the battery charger's maximum voltage
it was withdrawn. When the electrolyte level is low,
setting is too low to supply constant current charg-
distilled water should be added to restore the elec-
ing, divide the battery system into two parts to be
trolyte to the proper level, but the cell should not be
charged individually.
overfilled. If the cells are overfilled, the electrolyte
3. Follow the manufacturer's instructions for set-
will be forced out of vents during charging and will
ting the charging rates.
Float
saturate trays. This causes electrolysis between the
1. Float charge voltage should be maintained at
charge
cells, corrosion of the cell containers, and trouble-
1.43 volts to 1.45 volts per cell to avoid gassing.
some grounds in the electrical circuit. Overfilling
2. Maintain constant voltage charging to prevent
the cells will also dilute the electrolyte to such an
the battery from discharging at a depressed voltage
extent that the battery's specific gravity will be re-
level.
3. To prevent excessive water consumption, avoid
duced and cell plates will be damaged.
charging the battery at higher values than recom-
(2) Electrolyte renewal. When electrolyte is
mended.
clear and colorless, it is in good condition. Electro-
Booster
lyte that has become contaminated with small
charge
1. The booster charge should be 1.65 volts per cell.
2. A fully discharged battery in good condition can
quantities of carbon dioxide from the air will form
be fully charged in 4 hours.
potassium carbonate and will appear cloudy. If the
3. If the float charge has maintained the battery in
solution becomes colored or cloudy, it is evident that
a fully charged condition during the month, the
the electrolyte is contaminated with impurities and
monthly booster charge will be minimal.
should be changed. It may also become necessary to
4. The booster charge should be continued until the
charging current has leveled off for two consecutive
change the electrolyte due to overcharging or over-
readings one-half hour apart.
flow, which cause the specific gravity to fall outside
5. When applying a booster charge, it is important
the manufacturer's specified range. If the specific
to watch the electrolyte temperature in the cells. If
gravity is low, continued operation will result in a
the temperature reaches 100 degrees F (43 degrees
rapid reduction in the life of the battery. Therefore,
C), the charging rate should be reduced at once.
when the specific gravity falls below 1.170, the elec-
14-13
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