IEEE 1184-2006 pdf download IEEE Guide for Batteries for Uninterruptible Power Supply Systems
4.3 Vented lead-acid (VLA) batteries
4.3.1 General
VLA cells are constructed with the liquid electrolyte completely covering (flooding) the closely spacedplates. The electrolyte maintains uniform contact with the plates. Depending on plate thickness (amongother factors) cells of this design can provide a very high, short-duration current due to their low internalresistance.(See Annex C.)
4.3.2 Voltage
The fully-charged lead-acid cell has an open circuit voltage of approximately 2.10 V, which varies as afunction of cell-specific gravity and temperature. Open circuit voltage increases with specific gravity anddecreases with temperature, and typically ranges from 2.06 V/cell to 2.10 V/cell. The float voltages rangefrom 2.15 V/cell to 2.30 V/cell, depending on individual cell design, temperature, and manufacturerrecommendations.
4.3.3 Construction
Lead-acid batteries are described by their plate construction and the alloying elements (if any) that are usedto strengthen the plate structure. Several designs have been created to improve performance characteristics.including cycling and life expectancy. Each design, however, places its own constraints on cell operation.See C.2 for plate construction.)
4.4 Valve-regulated lead-acid (VRLA) batteries
4.4.1 General
VRLA cells are sealed with the exception of a valve that opens as required to relieve excessive internalpressure. These cells provide a means for recombination of gases to limit water consumption. This isaccomplished by allowing oxygen evolved from the positive plate to pass across to the negative, where the recombination reaction occurs. The valve regulates the internal pressure to optimize recombinationefficiency; hence, the term “valve regulated.
VRLA cells are more sensitive to elevated operating temperatures and abusive conditions. In extreme casesthis can lead to thermal runaway (see 5.4.2; Annex C for construction).
4.4.2 Voltage
The fully-charged VRLA cell has an open circuit voltage of approximately 2.15 V, which varies as afunction of cell-specific gravity and temperature. Open circuit voltage increases with specific gravity anddecreases with temperature, and may range from 2.06 V/cel to 2.17 V/cell. The float voltage ranges from220 V/cell to 2.35 V/cell. depending on individual cell design, temperature, and manufacturerrecommendations.
4.4.3 Electrolyte immobilization
One of the requirements for effective recombination is that the electrolyte be immobilized. There are twomeans by which this can be accomplished, known as absorbed electrolyte and gelled electrolyte.
4.4.3.1 Absorbed electrolyte systems
VRLA cells of this design are constructed with a controlled volume of liquid electrolyte contained in ahighly absorbent blotter-like separator, positioned between closely spaced plates. This non-woven separatordistributes the electrolyte uniformly and maintains it in contact with the plate active material. whilepermitting the passage of oxygen evolved during charging. Cells with absorbed electrolyte technology haveinherently low internal resistance and can be designed to provide a very high-rate, short-duration current.Cells with absorbed electrolyte are also known as “absorbed glass mat”(AGM) types.
4.4.3.2 Gelled electrolyte systems
VRLA cells of this design are similar to vented designs, except that the electrolyte has been gelled toimmobilize it They can provide a high-rate. short-duration current, but because of the higher internalresistance they are not as effective as the absorbed electrolyte design. However, the higher thermaconductivity in gelled designs makes them better suited for elevated temperature applications thanequivalent absorbed electrolyte cells. A gelled electrolyte cell is typically heavier and larger than anabsorbed electrolyte cell for a given capacity.
IEEE 1184-2006 pdf download
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