8
Lead-calcium types may be floated at any of the voltage val-
ues (Table B) shown for a particular nominal specific gravity.
Float in the lower voltage range for the given specific gravity
where system equipment high voltage limits exist. Where
equipment high voltage limits do not prevent it, floating at
the high end of the range may make equalization unneces-
sary altogether. However, floating toward the high end of
range in environments warmer than 77°F (25°C) will result
in reduced battery life.
9.3 Voltmeter Calibration
Panel and portable voltmeters used to indicate battery float
voltages should be accurate at the operating voltage value.
The same holds true for portable meters used to read
individual cell voltages. These meters should be checked
against a standard every six months and calibrated when
necessary.
When the cell voltage reaches 2.33, the charge rate should
be reduced to the normal finish charge rate. The finish
charge rate is defined as amperes equal in numerical value
to 5% of the cell’s 8-hour capacity in ampere hours. For
example, if the cell has an 8-hour capacity of 1000 AH, its
finish rate is 50 amperes. The charge should be stopped
when the specific gravity is ten (.010) points below the nor-
mal fully charged value.
The battery is now available for the next discharge require-
ment. The battery should be given an equalizing charge
monthly by continuing the regular charge until there is no
increase in specific gravity of the pilot cell for three hours.
when using the finish charge rate.
9.4 Recharge
All batteries should be recharged as soon as possible fol-
lowing a discharge (within 8 hours). With constant voltage
chargers, this will be accomplished automatically. However,
to recharge in the shortest period of time, raise the charger
output voltage to the highest value which the connected sys-
tem will permit. Do not exceed those voltage values listed
in Table D or Table E on page 9.
SECTION 10
10.0 Equalizing Charge
An equalizing charge is a special charge given a battery
when non-uniformity in voltage or specific gravity has devel-
oped between cells. It is given to restore all cells to a fully
charged condition using a charging voltage higher than the
normal float voltage and for a specified number of hours, as
determined by the voltage used.
Non-uniformity of cells may result from low floating voltage
due to improper adjustment of the charger or a panel volt-
meter which reads incorrect (higher) output voltage. Also,
variations in cell temperatures greater than 5°F (2.78°C) in
the series string at a given time, due to environmental con-
ditions or rack arrangement, can cause low cells.
10.1 Equalizing Frequency
A Equalize when the temperature corrected specific
gravity of the pilot cell (or any cell for the quarterly
reading) is more than 10 points below its full charge
value. (See Section 11.2)
B Equalize when the float voltage of the pilot cell (or any
cell for the quarterly reading) is below 2.13 volts (nom-
inal 1.215 sp. gr.), 2.18 volts (nominal 1.250 sp. gr.) or
more than .05 volts below the average for the battery.
D.
Equalize to complete a recharge of the battery in a min-
imum length of time following an emergency discharge.
E. If accurate quarterly records are maintained (See
Section 14.0) and the individual cell voltages and
teperature corrected specific gravities show no increase
instead from the previous quarterly readings, equalizing
may be deferred. (See Section 11.2)
10.2 Equalizing Charge Method
Constant voltage charging is the preferred method for giving
an equalizing charge. Determine the maximum voltage that
may be applied to system equipment. This voltage, divided
by the number of cells connected in series, will establish the
maximum voltage per cell that may be used to perform the
equalizing charge in the shortest period of time.
Refer to Table C for equalizing voltages and durations.
The recommended time periods below are considered min-
imum. Raise the voltage to the maximum value permitted
by the system equipment. When charging current has
tapered and stabilized (no further reduction for three hours),
charge for the hours shown in the appropriate table and for
the battery temperature, at the time of stabilization, until the
lowest cell voltage ceases to rise. Monitoring of cell voltag-
es should be started during the latter 10% of the applicable
time period to determine the lowest cell in battery.
EQUALIZING CHARGE
Recommended Voltages and Time Periods
TABLE C
Lead-Calcium Types
Cell Volts
Time-Hrs.
1.215
sp. gr.
Time-Hrs.
1.250
sp. gr.
2.24
222
—
2.27
166
—
2.30
105
—
2.33
74
166
2.36
50
118
2.39
34
80
2.42
—
54
2.45
—
36
2.48
—
—
NOTE:
Time periods listed in Tables D are for cell tem-
peratures from 70°F (21°C) to 90°F (32°C). For tempera-
tures 55°F (13°C) to 69°F (20.5°C) double the number of
