Valve regulated lead-acid cells

Portable valve-regulated lead-acid cells can operate in any orientation without acid leakage and find use in many different applications, such as in electronic cash registers, alarm systems, emergency lighting unit equipment, telephone boxes, switching stations, minicomputers and terminals, electronically controlled petrol pumps, cordless television sets and portable instruments and tools. 

Fig. 1.4. Conceptual view of internal oxygen cycle in a valve-regulated lead-acid cell (Nelson, 1999) [11].

In this chapter, we will focus our attention mostly on VRLAB with AGM separator. In the 1970s, McClelland and Devitt invented the first valve-regulated lead—acid cell with electrolyte immobilized in microporous glass mat with gas channels in the AGM and a safety valve mounted on the cell lid, and thus forced the COC to proceed within the active block [13]. Figure 14.7 presents a schematic diagram of the transport of oxygen, H ions and water between the two... 

Schematic representation of the internal COC in a valve-regulated lead—acid cell [14],...

Fig. 5.2 Cutaway of valve-regulated lead-acid cell (EnerSys Energy Products, Inc., approval obtained)...

Vents in use on valve-regulated lead-acid cells with immobilized electrolyte instead of normal venting plugs have to be designed in a way such that the user cannot open or remove them. 

Today valve-regulated lead-acid cells and batteries are delivered to the customers in filled and charged state, and in most cases they have the filling date on it. That is the birthday of the battery, since with the filling of the acid all chemical and electrochemical reactions have started. 

Bernardi, D. M., Ying, R. Y, and Watson, P. (2004). Study of charge kinetics in valve-regulated lead-acid cells. Journal of the Electrochemical Society 151, A85-A100. 

Different types of lead-acid batteries have been developed as energy sources for many power applications, like traction and backup or standby power systems. The flooded lead-acid batteries have an excess or flooded electrolyte and they were the largest used at the beginning of the last century for many applications. Valve-regulated lead-acid (VRLA) batteries were developed as an alternative to the flooded lead-acid batteries, in order to maintain levels of distilled water and prevent drying of cells, which means safe operation for battery packs in electric... 

Besides improvement of the utilisation of active materials (lead and lead dioxide), another crucial issue that has been in the focus of battery researchers and design engineers for many years now is the immobilisation of battery electrolyte via its absorption in the glass mat separator or by converting it into gel state. Thus, the valve-regulated lead—acid (VRLA) battery was invented which requires minimum or no maintenance and has found wide application. In the VRLAB construction, die active block in the SLI cell is higher and occupies the upper electrolyte reservoir space, thus increasing the capacity of the cell within the same volume. 

Bullock KR, Vincent CA (1997) Secondary lead-acid cells. In Vincent CA, Scrosati B (eds) Modem batteries, 2nd edn. University of Chicago Press, Chicago Rand DAJ, Moseley PT, Garche J, Parker CD (2004) Valve-regulated lead-acid batteries. Elsevier, Amsterdam... 

Table 5.3 Economic results from US army testing of valve-regulated lead acid (VRLA) battery set and PEM fuel cell unit... 

Standards for Portable Maintenance-Free, Valve-Regulated Lead-Acid (VRLA) Cells... 

Valves allow only the escape of gas and are required in valve-regulated lead-acid batteries for the escape of hydrogen, but are also used in most other sealed batteries to prevent damage of the cell in the case of a too high internal pressure when the battery is abused, e.g. overcharged at a too high current rate or reversed. 

Figure 4.11 shows a three-cell monobloc valve-regulated lead-acid battery and a comparison of other lead-acid battery types with an outlook on possible future design. 

Already today valve-regulated lead-acid batteries are in widespread use in many applications, and this trend will increase in the future since the reduction of maintenance is a signihcant advantage. This battery system requires high quality of all parameters that influence the performance and other characteristics. Valve-regulated lead-acid batteries that are installed in cabinets require sufficient air circulation to achieve equal temperature for all cells or monoblocs. Monitoring or control systems may be used. 

Since the 1970s also maintenance-free valve-regulated lead-acid batteries have been in widespread use in the field of stationary applications. Sometimes they are called recombination cells or "sealed lead-acid cells". Their correct designation, however, is in accordance to DIN 40 729 valve-regulated lead-acid batteries ( VRLA batteries). 

Thus, in valve-regulated lead-acid batteries electrolyte- and gas-tight pole bushings are a must, and vented batteries allow the use of copper inserts and screws for cell and battery connectors and thus install the battery as usual in electro technics. 

EUROBAT. Guide to the Specification of Valve Regulated Lead Acid Stationary Cells and Batteries. EURO BAT, CH 3001 Bern. 

STANDARDS FOR PORTABLE MAINTENANCE-FREE, VALVE-REGULATED LEAD-ACID (VRLA) CELLS... 

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