Page 189 - Uninterruptible Power Supplies

Batteries
Batteries 187

The cell, irrespective of types, shown in Fig. 7.1 consists of the fol-
lowing components:

Positive plate
Separators
Negative plate
Electrolyte
Container
Vents
Intercell connectors

Types of Cell: Plante/Tubular/Pasted
Plate/VRLA
The design of the plates gives various qualities to the cell. The types
which interest us are Plante, pasted plate, tubular, and the valve reg-
ulated lead acid (VRLA) cell. Each of the aforesaid designs has certain
characteristics which may be suitable to the UPS design in question. It
should also be noted that further variations in design of the types men-
tioned above can be expected, for example, variations in plate structure
and thickness, specific gravity of the acid employed, and the alloy uti-
lized in the plate construction.
The actual thickness of the plates determines the availability and
length of the discharge; the surface area of the plates has a very sig-
nificant effect on the current output.
Since most UPS applications call for a short autonomy period, the
plate design is usually fairly thin. Acomparison of the qualities of Plante,
tubular, and VRLA cells is shown in Fig. 7.2. The figures are based on
equivalent A/Hr rated plates.
The Plante cell was used extensively in the early days of UPS devel-
opment, but its design and cost have relegated it to an unimportant
section of a growing market. Its advantages were a long life, the ability
to visually inspect the cell since the container was either of glass or
(SAN) plastic (see Fig. 7.3), and historically its competitiveness against
alternatives.
Drawbacks are the relative cost these days compared to newer cell
designs [plates (see Fig. 7.4) had to be virtually handmade], its size and
weight, and the need for a separate battery room with the incumbent
problems of protection against acid and gas evolution.
Pasted plate cells are easier to manufacture. The plate is as shown
in Fig. 7.5, the active material (in the form of a paste produced from
lead oxide and dilute sulphuric acid) being pressed into the grid. These

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