TM 10-6140-200-14
Section II. CHARGING
charged when nearly all of the active material has been
2-5. General
converted and when the specific gravity of the electrolyte
a. Economical and dependable performance from a stor-
and cell voltage have reached their maximum or constant
age battery depends, to a great extent, upon proper
values (corrected for temperature), as indicated by similar
readings over a two or three hour period.
charging. Faulty charging causes a decrease in battery
service life and dissatisfaction with its performance. The
b. Batteries used in motive power applications are cycled.
selection of suitable charging equipment and methods is
They are either being charged or discharged. In most such
as important as the application of the correct battery. An
electric truck installation is completely satisfactory only
circumstances batteries are charged after each shift of use.
when the truck, battery and charger operate as a
As a result they are cycled many times during their
smooth-functioning team. This text on chargers is for
lifetime. Incorrect charging for only a few cycles will do
general information and guidance only. Because of the
little harm, but if this should be repeated day after day,
complexities and many types of chargers available, it
the battery's service life will be seriously shortened.
would be virtually impossible to furnish complete operat-
ing characteristics for all types. Therefore, if specific data
2-7. Charging Rates
is required on a particular type of charger, contact the
nearest manufacturer's representative.
a. Proper charging means charging the battery sufficiently
without overcharging, overheating or excessive gassing. To
b. When preparing a battery to be charged, make certain
accomplish this the charge is usually started at high
that all points of contact between the charger and the
amperage which is known as the starting rate. Later
battery are clean to assure good conductivity. Also make
during the charge this rate of current flow is reduced to
certain that the positive terminal of the battery is
what is called the finishing rate. Manufacturers generally
connected to the positive terminal of the charger and,
suggest that this finishing rate should not exceed 5
correspondingly, negative of battery to negative of
amperes per 100 ampere-hours of rated battery capacity.
charger.
The starting rate may be as much as four to five times
higher.
NOTE
b. Lead-acid batteries should be charged for a sufficient
length of time and at a rate which will put back into the
Permanent damage to the battery or charger
battery the same number of ampere-hours removed on
may result if the battery is connected incor-
discharge plus an approximately 10% additional which is
rectly.
an acceptable, and in fact desirable, overcharge. The
specific amount of overcharge depends upon the tempera-
ture, age and history of the battery. In general it is more
2-6. Charging Principles
harmful to excessively overcharge an older battery, or one
which is operating at high temperature, than a new
a. Charging, as applied to a storage battery, is the
battery or one operating consistently at room tempera-
conversion of electrical energy into chemical energy
ture. Any charge rate is permissible which does not
within the cell or battery. This restores the active
produce excessive gassing or cell temperatures greater than
materials and is accomplished by maintaining a unidirec-
110 degrees F.
tional current to the battery in the opposite direction to
that during discharge. When a cell or battery is said to be
2-8. Control of Gassing
charged it is understood to mean fully charged. The type
of battery, service condition, time available for charging
a. Gassing is the evolution of gases from one or more of
and the variation in battery voltages will strongly in-
the electrodes during electrolysis. It is a natural phenome-
fluence which charging method is best for a particular
non which takes place when a battery on charge can no
situation. Normally lead-acid batteries are recharged in 8
longer accept all of the current being applied to it.
hours following a full discharge. However, they can be
Gassing is evidenced by bubbling of the electrolyte. The
recharged within other time periods when desirable. A
gases liberated are oxygen, evolved at the positive plates,
deeply discharged battery will absorb high current rates
and hydrogen, evolved at the negatives.
when the voltage is low. As the charge progresses, the
voltage steadily increases until it reaches gassing voltage
which is approximately 2.37 volts per cell at 77 degrees
b. The point at which significant gassing begins is deter-
F. It is at this point that the battery chargers normally
mined by voltage, but the amount of gas depends upon
reduce charging rates automatically when the battery
the portion of the charging current that is not being
reaches gassing voltage and taper to finishing rates which
absorbed by the battery. Normally, noticeable gassing will
are used to complete the charge. The battery is fully
begin when the voltage exceeds 2.30 volts per cell. At
2-3
