Exide Technologies Section 92.80 - Manual (Page 20)

20
It is best for users to establish their own baseline values for their
battery as specifically configured. Do not rely on reference values.
If users wish to enhance normal maintenance and record-keep-
ing with ohmic measurements, GNB recommends the trending
of this data over time. Use a first set of readings taken 6 months
after initial charge and installation as the baseline data.
Because cell positioning within the string (connector configura-
tion to a particular cell) can affect the reading, always compare
each cell at baseline to itself in the new data. Standalone ohmic
data is not sufficient to justify warranty cell replacement.
Responsible ohmic device manufacturers acknowledge that there
is no direct relationship between percent ohmic change from
baseline and battery capacity. A change from baseline of 25% or
less is in the normal noise or variability range. Changes between
25% and 50% may call for additional scrutiny of the system. An
IEEE compliant discharge test is usually warranted on systems
exhibiting more than a 50% change from baseline. Consult an
GNB representative for specific questions about ohmic data.
SECTION 14: EQUALIZING CHARGE
14.0 General
Under normal operating conditions an equalizing charge
is not required. An equalizing charge is a special charge
given a battery when non-uniformity in voltage has devel-
oped between cells. It is given to restore all cells to a fully
charged condition. Use 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 float voltage due
to improper adjustment of the charger or a panel voltmeter
which reads an incorrect (higher) output voltage. Also, vari-
ations in cell temperatures greater than 5°F (2.78°C) in the
series string at a given time, due to environmental condi-
tions or module arrangement, can cause low cells.
14.1 Equalizing Frequency
An equalizing charge should be given when any of the following
conditions exist:
A. The float voltage of any cell is less than 2.18 VPC.
B. A recharge of the battery is required in a minimum time peri-
od following an emergency discharge.
C. Individual cell(s) float is more than +/- 0.05 volts from aver-
age.
D. Accurate periodic records (See Section 15) of individual cell
voltages show an increase in spread since the previous semi-
annual readings.
An annual equalize charge is recommended to help ensure uni-
form cell performance.
14.2 Equalizing Charge Method
Constant voltage charging is the method for giving an equalizing
charge. Determine the maximum voltage that may be applied to
the system equipment. This voltage, divided by the number of
cells connected in series, will establish the maxi-mum volts per
cell that may be used to perform the equalizing charge in the
shortest period of time (not to exceed 2.35 VPC applicable at
77°F, 25°C). Refer to Table E for voltages and recommended time
periods.
NOTE: Charge volts listed in Table E are for 77°F. For other temper-
atures a compensation factor of .003 V/°F (.0055 V/°C) per cell is rec-
ommended. The minimum voltage is 2.20 VPC. The maximum volt-
age is 2.35 VPC. Temperature correction does not apply outside of
this range.
V corrected = V25°C - ((T actual-25°C) x (.0055 V/°C)) or V correct-
ed = V77°F - ((T actual-77°F) x (.003 V/°F))
See Appendix A for standard values.
A. Set constant voltage charger to maximum setting without exceed-
ing 2.35 VPC.
Example: For a target charge of 2.35 VPC on a 24-cell system, you
would set the charger voltage to 56.4 volts.
B. Record time and current at regular intervals – every hour as a min-
imum.
C. Continue charging the battery until there is no further drop in
charge current over 3 consecutive hours.
D. When the current has stabilized, proceed to step 2.
A. Continue the charge for the time listed in Table E depending on the
charger voltage setting. The time is IN ADDITION to the time spent
charging in Step 1.
Example, charge for 12 hours if the charger voltage is set to
2.35 VPC.
TABLE E
EQUALIZE CHARGE (77°F)
CELL VOLTS TIME (HOURS)
2.30 24
2.33 18
2.35 12
B. Record cell voltages hourly during the last 3 hours of the charge
time. If, after the charge time has completed, but the lowest cell volt-
age has continued to rise, you may extend the charge, monitoring
cell voltages hourly, until the lowest cell voltage ceases to rise.
C. Proceed to Step 3.
The Equalize charge is now complete. Charger voltage can now be
reduced to float voltage setting per Section 13.2. For a target float
charge of 2.25 VPC on a 24-cell system, you would set the charger
voltage to 54 volts.
STEP 3
STEP 2
STEP 1