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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
tion of the load current plus the charging current.
c. Float voltages. Float voltages are directly re-
The charging current will decrease and eventually
lated to cell type and plate alloy, as well as to the
stabilize when the battery is fully charged. If the
specific gravity of the cell. The higher the specific
---
connected load is variable, the battery voltage needs
gravity, the higher the minimum float voltage must
to be monitored. If the voltage across the pilot cell is
be. This ensures that sufficient charging current is
stable for 6 consecutive hours, the battery is 100
available to overcome the increased local action. Too
percent charged. A constant current level for 3 con-
high a float voltage will result in overcharging and
secutive hours indicates a charge of 95 to 98 per-
reduce battery life. A slightly higher float voltage is
cent.
sometimes selected for maintenance purposes to re-
duce or even eliminate the need for periodic equal-
a. Initial charge. Initial charge for placing a new
izing charges required because of nonuniform cell
battery in service is covered in section VIII.
voltages.
b. Recharge. Following a discharge, all batteries
should be recharged as soon as possible. To do this
14-12. Equalizing battery charge.
as quickly as possible, the battery charger output
voltage is raised to the highest value that the con-
An equalizing charge is an extended charge to a
nected system will permit.
measured end point on a storage battery cell to
ensure complete restoration of the active materials
14-11. Normal floating battery charge.
in plates of the cell. Equalizing charges are provided
after a battery discharge or for periodic mainte-
The floating (trickle) charge method is commonly
nance. Equalizing voltages are selected by the bat-
used for returning the full charge on station batter-
tery chargers equalizing timer, as covered in section
ies permanently connected to battery chargers. The
VII. Equalizing charges may need to be given a
floating charge rate is the sum of the low current
monthly check.
(trickle rate) required to counteract internal battery
a. After discharge equalizing. An equalizing
losses, plus the average current requirements for
charge is required after any battery discharge. Al-
the rest of the circuit. The required floating current
though it is called an equalizing charge, it is basi-
is provided automatically, when the proper voltage
cally a recharge, at about a 10 percent higher volt-
is supplied to the battery.
age, than the float voltage to restore the discharged
a. Float action. The float-voltage point should
battery to a fully charged state within a reasonable
just overcome the battery's trickle rate and cause
length of time.
the least amount of corrosion and gassing. Ambient
b. Periodic equalizing. Lead-acid battery indi-
temperature differences will affect the charging
vidual cell voltages will begin to drift apart, even if
ability of the selected float-voltage level. The recom-
the battery is not discharged. A manually set charg-
mended float voltages range from 2.25 to 2.28 volts
ing rate will be necessary to "equalize" the voltage
per cell. Select any volts-per-cell value within this
irregularities. Nonuniformity of cells can result
range that is equal to the average volts per cell'in a
from a low float voltage due to improper adjustment
series string. The excess energy of too high a float
of the battery charger, a panel voltmeter that is
voltage results in loss of water, cell gassing, acceler-
reading an incorrect output voltage, or variations in
ated corrosion, and shorter cell life. To eliminate
cell temperatures greater than 5 degrees F (2.75
such actions, on daily or frequent discharges, the
degrees C).
charge is stopped slightly short of a fully-charged
condition. However, permissible cell manufacturing
(1) Provision. Equalizing voltages should be
tolerances and ambient temperature influences will
given if the float voltage of the pilot cell is less than
cause individual cell-charge variations.
2.20 volts per cell or more than 0.04 volts per cell
below the average of the battery. Equalizing voltage
b. Recharge requirements on loss of ac input. Pro-
is required if the individual pilot cell voltages show
viding the precise amount of charge on each and
an increase in spread since the previous readings,
every cell for each and every recharge (caused by
or if the periodic check of all cell voltages reveals a
loss of ac input to the battery charger) is impractical
difference of 0.04 volts between any cell and the
for a continuously-floating battery operation. An
average cell voltage.
overlong interval would be required to restore full
charge on a deeply discharged battery if the battery
(2) Action. An equalizing charge is made at a
charger remained at the low float voltage rate. To
rate not higher than the normal charging rate of the
shorten the recharge period, a higher voltage charg-
battery. It is continued until all the cells gas freely
ing rate is usually provided, either automatically or
and any low cells are fully charged. Low cells are
manually, This recharge is known as an equalizing
usually found in the warmest section of the battery.
charge.
They normally have the lowest voltage while on
14-10
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