for the life of the battery (see also paragraph 1.2C--Equalizing Charge).
Prolonged undercharging also leads to large flaking on the interplate
Sulfate build-up caused by undercharging is the most common cause of buckling plates and
cracked grids. Sulfate takes up more room than the original material and strains the plates out
The pressure of expanding active material can break separators and
cause short circuits.
A badly sulfated cell should be treated as described in section 2.24. If
charged at too low a rate, the hardened sulfate is thrown out of plates and
settles in white ridges on the cell bottom. At higher rates, the gassing
distributes the sediment evenly without ridges. An over sulfated cell has
high internal resistance and requires extra voltage across the cell, which
also causes them to develop higher temperatures on charge. Buckled or
cracked plates cannot be repaired by removal of sulfate but may be used as
long as they retain satisfactory ampere-hour capacity. See section 3 for
2.11 OVER DISCHARGE
2.11 OVER DISCHARGE
The plates suffer greatly when over discharged.
Voltage per cell should not be
allowed to drop below 1.75 volts.
Specific gravity should not be allowed to
decrease below the limit given by the manufacturer, which is different for
various types and sizes of cells. As
normal discharge proceeds, active
materials are converted to normal lead sulfate, which requires only slightly
more space than active materials.
forms more lead sulfate in
the pores of the active material than they are able to hold. This process may
expand and bend or buckle plates or crack grids. In some instances,
sufficient pressure is created to crack or puncture separators.
The history of each cell is shown by the sedimentation because successive
layers are laid down in colored strata.
. These layers can be seen edgewise
against the inside of the case. Layers of fine, dark gray show periods of
excessive charging (current too high or charge too long). Lumpy gray layers
indicate times the battery was over discharged. These layers are generally
covered by a layer of white sulfate from the following charge. A considerable
amount of sediment and slivers will be found initially in Gould processed
plate batteries. This condition is a normal result of the forming process.
Some additional sediment and slivers will be dislodged in shipment and will
accumulate at the bottom of the case of these batteries during the first few
equalizing charges. With this exception, a perfectly charged battery should
have nothing but fine brown sediment, free from lumps and as scanty as
possible. If some experimenting is done with the charging program, slight
undercharging may result in a white sulfate layer. This layer indicates that
the charging should be slightly increased.