lead oxides, is applied to the grids in paste form, then
allowed to dry and harden like cement. Part of a grid is
shown in figure 12-2 with a cross section showing the
active material in place. The plates are then put through
an electrochemical process that converts the hardened
active material of the positive plates into brown lead
peroxide, and that of the negative plates into gray,
spongy, metallic lead. This process is known as forming
b. Groups. After the plates have been formed,
they are built into positive and negative groups. The
plates of each group are permanently joined by melting a
portion of the lug on each plate to form a solid weld with
a connecting post strap. The heat necessary for this
process, termed lead burning, is produced by a gas
flame or an electric arc. The connecting post strap to
which the plate lugs are burned contains a cylindrical
terminal that forms the outside connection for the cell.
The negative group of plates has one more plate than
Figure 12-3. Cell Group Construction.
the positive group to provide a negative plate on both
sides of all positive plates. These groups are shown in
against the positive plate) is grooved so the gas that
forms during charging will rise to the surface more
readily. These grooves also provide room for any
c. Separators. To prevent the plates from touching
material that flakes from the plates to drop to the
and causing a short circuit, sheets of insulating material
sediment space below.
(microporous rubber, fibrous glass, or plastic-
impregnated material), called separators, are inserted
d. Elements. The assembly of a positive and
between the plates. These separators (fig. 12-4) are thin
negative group, together with the separators, is called an
and porous so the electrolyte will flow easily between the
element (fig. 12-4). Because storage battery plates are
plates. One side of the separator (that is placed
more or less of standard size, the number of plates in an
element is, roughly, a measure of the battery capacity.
The distance between the plates of an assembled
Figure 12-2. Plate Construction.