b. Battery chargers supplied for use in the field are the constant
potential type. A charger usually consists of a DC generator powered by a gasoline
engine. They are made with 7-1/2-and 15-volt outputs or with a 15-and a 28-volt
output.
(1) When using the battery charger to charge one 12-volt battery,
connect its 15-volt output or load terminals to the battery terminals. Connections
must be positive to positive and negative to negative. If more than one battery is
to be charged from the 15-volt output they must be connected in parallel. If you
connect the batteries in series their voltage will be higher than the charging
voltage and the charger could not force current through the batteries. Care must
be taken when charging batteries in parallel. The current demand on the charger
may be excessive if the batteries are extremely weak.
(2) To charge 12-volt batteries from the 28-volt output of a charger,
connect two batteries in series, then connect them to the 28-volt terminals. To
charge more than two batteries they must be connected in series-parallel. The
batteries in each series group should be in about the same condition.
(3) When a battery is first placed on a constant potential charging
system its voltage is much lower than the charging voltage, so a high current will
flow. As the battery is charged its voltage increases, but the charging voltage
remains constant. This causes the current to decrease as the battery is charged
and in the end will taper off to a very slow rate. Less attention is required near
the end, but care must be taken to prevent overheating the battery at first. The
constant potential battery chargers are generally equipped with a variable resistor
so the operator has some control over the charging rate.
16. CHARGING PROCEDURES.
a. Batteries should only be charged in the open air or a well ventilated
room due to the gases they expel. Before attempting to charge a battery give it a
thorough cleaning and inspection. Don't waste your time on batteries that are
cracked or damaged in any way that will make them unserviceable. Place good
batteries on a board or wooden rack; never place them on top of each other or on
the ground or a concrete floor.
b. Check and record the specific gravity of each cell of all the batteries
to be charged. Add water to bring the electrolyte to the proper level. Arrange
and connect the batteries for charging. All batteries connected in one series
group should have about the same specific gravity readings. Make sure all the vent
plugs are secure and the vents not plugged, then begin the charge.
c. Watch closely for overheating or excessive gassing for the first few
minutes of charge. If either occurs, reduce the charging rate. For best results
the battery electrolyte should not exceed 1100 F. The battery should gas very
little when it is first placed on charge, but steady gassing later on when the
battery nears full charge is normal.
d. Check the specific gravity of the battery often while it is being
charged. Just how often will depend on the rate of charge. Check the gravity
hourly when the batteries near full charge. You may reduce the time between checks
if the charge rate is decreased. Add water to replace any lost during the charge.
A battery is fully charged when three successive hydrometer readings show no
further rise in specific gravity.
OS 010, 3-P30
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