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Rev.12/31/97
5. CONDENSED INSTRUCTIONS
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VALVE REGULATED LEAD-ACID BATTERIES (GEL CELLS)
5.1 GENERAL
5.1 GENERAL
Valve regulated lead-acid batteries (VRLA) are usually manufactured in
multi-cell blocks, (called modules) rather than single cells. The cases are
often made of ABS plastic material and do not permit visual inspection of
plates or electrolyte levels. They are called starved electrolyte or absorbed
electrolyte cells and operate under a positive pressure. The hydrogen and
oxygen are not expelled but recombined. Cells are sealed and require no
water addition or specific gravity readings. These cells are typically lead
calcium pasted-plate type cells with the electrolyte retained in gel or
fiberglass mats.
multi-cell blocks, (called modules) rather than single cells. The cases are
often made of ABS plastic material and do not permit visual inspection of
plates or electrolyte levels. They are called starved electrolyte or absorbed
electrolyte cells and operate under a positive pressure. The hydrogen and
oxygen are not expelled but recombined. Cells are sealed and require no
water addition or specific gravity readings. These cells are typically lead
calcium pasted-plate type cells with the electrolyte retained in gel or
fiberglass mats.
These batteries are normally used for emergency lighting,
telecommunications, and other uninterrupted power supply (UPS) service.
telecommunications, and other uninterrupted power supply (UPS) service.
They are best applied where long slow discharges are needed. Heavy short
discharges required for breaker operations are not recommended for this
type battery. The life has been found to be only 18 months to 10 years in
actual service.
type battery. The life has been found to be only 18 months to 10 years in
actual service.
These cells are
not flooded
and do not effectively dissipate heat. This
characteristic can lead to thermal runaway if ambient and battery
temperatures are not carefully controlled (see 5.2 below). Cases have
occurred in which the battery has burst into flame. Maintaining the cells as
close as possible to 77 EF is
temperatures are not carefully controlled (see 5.2 below). Cases have
occurred in which the battery has burst into flame. Maintaining the cells as
close as possible to 77 EF is
imperative.
Ambient temperature should be
maintained as close as possible to 72 EF. Air circulation must be sufficient
to eliminate any ambient temperature differences. The maximum cell
temperature spread (hottest to coldest cell) should not exceed 5 EF, and the
temperature spread (hottest to coldest cell) should not exceed 5 EF, and the
hottest cell should not be more than 5EF above ambient. Colder
temperatures reduce capacity, and
higher temperatures greatly reduce service life.
About 50 percent of the service life will be lost for every 15 EF above 77EF.
Do not allow sunlight or other heat sources to raise the temperature of
individual cells.
individual cells.
These cells are not recommended for station service because of these
characteristics
characteristics.
VRLA modules/cells are typically shipped fully charged and do not require
initial charge.
initial charge.
5.2 FLOAT CHARGE
5.2 FLOAT CHARGE
VRLA cells are typically floated at 2.25 to 2.30 volts depending on the
manufacturer. Correct battery float voltage is critical for valve-regulated
cells. The float voltage must be within the manufacturer's recommended
limits compensated for temperature. See the manufacturer's literature for
temperature compensation of float voltages.
manufacturer. Correct battery float voltage is critical for valve-regulated
cells. The float voltage must be within the manufacturer's recommended
limits compensated for temperature. See the manufacturer's literature for
temperature compensation of float voltages.
When VRLA cells are operated on float at normal full charge, no net