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9.4
Equalizing Charge
Under NORMAL conditions an equalizing charge is NOT required. An equalizing charge is a
special charge given to a battery when nonuniformity in voltage has developed between cells. It
is given to restore all cells to a fully charged condition.
Nonuniformity of cells may result from:
•
low float voltage due to improper adjustment of the charger.
•
a panel voltmeter that reads high, resulting in a low charger output voltage.
•
selection of too low a float voltage.
•
variations in cell temperatures in the series at a given time, due to environmental
conditions or module arrangement. The maximum cell-to-cell temperature difference is
5˚F (3˚C). If cell temperature is the problem, review the location instructions in Section
5.0 to ensure proper location of the battery system.
9.4.1
Equalizing Charge Method
Constant voltage charging is the method for giving an equalizing charge.
Determine the equalizing voltage based on the maximum voltage allowed by the system
equipment connected to the DC bus.
The charge table shown in Table 9.3 lists the minimum hours of equalizing charge to be given
after the charging current has stabilized (no further current reduction for 24 hrs).
Alloy
Sp. Gr.
V.P.C.
2.24
2.27
2.30
2.33
2.36
2.39
2.42
2.45
2.48
Table 9.3 applies for cell temperatures between 60
o
temperatures 40
to 59
o
o
39
F (4
C) or below, use four times the number of hours.
NOTE: The voltage of a warm cell will be lower than the average. Its voltage can be
corrected for temperature by adding 0.003V for each degree Fahrenheit (0.005 V/
that the cell temperature is above the average temperature of the other cells.
www.enersys.com
TABLE 9.3 – MINIMUM HOURS OF CHARGE
AFTER CURRENT STABILIZATION
Antimony
1.215
1.250
100
160
70
110
50
78
35
55
25
28
o
o
o
F (5
to 15
C), use twice the number of hours. For cell temperatures
Publication No. US-FL-IOM-002 January 2007 Page
Calcium
1.215
1.250
1.300
100
70
110
50
80
125
35
55
90
25
40
60
28
45
30
o
o
o
to 90
F (16
o
to 32
C). For cell
o
C)
33
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