Page 28 www.enersys.com Publication No. US-RE-IOM-002 January 2012
9.4 Equalizing Charge
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:
• repeated deep discharge or idleness in a discharged state.
• failure to fully recharge the battery on a regular basis (partial state of charge
operation).
• 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
MPPT Charge controllers use constant voltage charging as the method for giving an equalizing
charge.
Use the voltage setting given in section 9.1 for correct equalize charge setting.
Equalize charge should be done every 6 months for a minimum of 1 hour, maximum of 3 hours.
If possible, add water during the last 30 minutes of equalize charge. This helps ensure good
mixing of the electrolyte when the water is added. Water tends to float on top of the electrolyte
for awhile, but the gassing action of equalize charge will mix the water into the electrolyte.
Alternatively, if an outside charging source is available, the batteries may be constant current
equalized at 4.5%, in amps, of the battery’s nominal amp hour rating (C
20
).
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