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chemical reaction occurs and almost all the overcharge energy results in
heat generation. If the environment is such that the heat produced can be
dissipated, no thermal runaway problem occurs. If the rate of heat
generated exceeds the dissipated rate, the battery temperature rises and
more current is required to maintain the float voltage. The additional
current results in more heat generation, which raises the battery
temperature further, and the cycle is repeated. Thermal runaway and
destruction of the battery result. Elevated ambient temperature (above 72°F)
or cell and/or charger malfunction will aggravate this condition.
Ventilation and temperature control is critical for VRLA cells, and the
battery should reach thermal equilibrium at no more than 5°F above
heat generation. If the environment is such that the heat produced can be
dissipated, no thermal runaway problem occurs. If the rate of heat
generated exceeds the dissipated rate, the battery temperature rises and
more current is required to maintain the float voltage. The additional
current results in more heat generation, which raises the battery
temperature further, and the cycle is repeated. Thermal runaway and
destruction of the battery result. Elevated ambient temperature (above 72°F)
or cell and/or charger malfunction will aggravate this condition.
Ventilation and temperature control is critical for VRLA cells, and the
battery should reach thermal equilibrium at no more than 5°F above
ambient for the hottest cell.
As cells approach full charge, battery voltage rises to approach the charger
output voltage, and charging current decreases. The battery is fully charged
output voltage, and charging current decreases. The battery is fully charged
when the charging current has not changed more than 10 percent for more
than 3 hours. If the charging voltage has been set higher than float voltage
to reduce the charging time, reduce the charging voltage to normal float
than 3 hours. If the charging voltage has been set higher than float voltage
to reduce the charging time, reduce the charging voltage to normal float
value after the charging current has stabilized.
Caution:
Never exceed the
maximum charging voltage recommended by the manufacturer.
5.3 EQUALIZING CHARGE
5.3 EQUALIZING CHARGE
Equalizing charge is not normally performed on VRLA cells. An equalizing
charge may be necessary if a low float voltage is indicated or if a fast
recharge is needed. The battery manufacturer should be consulted before
proceeding if an equalizing charge is needed. The exact voltages and charge
times indicated by the manufacturer must be followed carefully.
charge may be necessary if a low float voltage is indicated or if a fast
recharge is needed. The battery manufacturer should be consulted before
proceeding if an equalizing charge is needed. The exact voltages and charge
times indicated by the manufacturer must be followed carefully.
5.4 CHARGER
5.4 CHARGER
A VRLA cell charger must have at least two capabilities: (1) extra electrical
filtering to protect the cells from AC ripple, which may lead to thermal run-
away, and (2) temperature compensation to prevent thermal run-away. Do
not try to charge these cells with a charger designed for a
filtering to protect the cells from AC ripple, which may lead to thermal run-
away, and (2) temperature compensation to prevent thermal run-away. Do
not try to charge these cells with a charger designed for a
flooded
lead-acid
cells.
5.5 BATTERY MAINTENANCE
5.5 BATTERY MAINTENANCE
The regimen described below is strongly recommended to maximize
performance and life expectancy. See manufacturer's data and IEEE 1188-
performance and life expectancy. See manufacturer's data and IEEE 1188-
1996--Recommended Practice for Maintenance, Testing, and Replacement of Valve-Regulated
Lead-Acid (VRLA) Batteries for Stationary Application for further information.
5.6 VISUAL INSPECTIONS
5.6 VISUAL INSPECTIONS
Visual inspections are made to assess the general condition of the battery,
mounting rack and battery room, and safety equipment.
mounting rack and battery room, and safety equipment.