IEEE 1189:2007 pdf free download

IEEE 1189:2007 pdf free download.IEEE Guide for Selection of Valve-Regulated Lead-Acid (VRLA)Batteries for Stationary Applications.
4.4 Immobilized electrolyte technology
4.4.1 Gelled electrolyte cells
Gelled electrolyte cells (see 3.2 ) are designed such that voids develop in the gel. These voids serve as passages through which oxygen transport to the negative plates is enhanced.
4.4.2 Absorbed electrolyte cells
Absorbed electrolyte cells (see 3.1 are designed with an absorbent separator. known as an Absorbed Glass Mat (AGM). that is approximately 95% filled with liquid electrolyte. The remaining voids provide t’or optimized oxygen transport from positive to negative plates.
4.5 Hydrogen evolution
It is possible to design VRLA cells in which, under normal float conditions, the oxygen recombination will operate at virtually 100% efficiency. However, even under normal float conditions, some water will be lost by electrolysis. There are also reactions that occur at the positive plates whose only possible corresponding reaction at the negative plate is the formation of hydrogen gas. The most familiar of these reactions is corrosion of the lead in the positive grid to lead dioxide, which results in hydrogen evolution at the negative plates. These reactions cannot be prevented. (See Annex A for more details.)
4.6 Pressure-regulation valve
The internal cell pressure caused by the evolved gases is regulated by a valve that allows these gases to escape periodically. This is the origin of the term valve-regulated. VRLA valves operate over a relatively narrow range, typically within the limits of 3.5 kPa to 350 kPa (0.5 psig to 50 psig). depending upon design, allowing the escape of un-recombined gascs and preventing the backflow of air into the cell. Under normal conditions, the valve opens just long enough to release pressure then reseals. (See 5.9.)
4.7 Catalysts
The oxygen recoinbination cycle within the valve-regulated lead-acid cell is typically 95% to 99% efficient. Some battery manufacturers may use a catalytic device within the cell to augment the recombination process and to address the effects of negative self-discharge (see 5.3.3). See also 6.2 for charging considerations.
5. Comparisons of vented (flooded) and valve-regulated technologies
5.1 Reactions
Both technologies undergo the same chemical and elcctrochcmical reactions. The rates of some of these reactions are different (see 4.3).