Figure 17.
Batteries.
b. If the lamp is left connected to the battery, current flow continues and
the electrolyte will get weaker and weaker until it is almost all water. At the
same time, the negative and positive plates will be gradually turning into lead
sulphate. Finally, the battery reaches a point where it will no longer supply
enough voltage to cause the current flow and the lamp will stop glowing. The
battery is then said to be discharged.
c. The chemical reaction in the battery can be reversed and a discharged
battery returned to a charged state. This is done by supplying direct current from
an external power source, such as a DC generator, and running it through the
battery opposite the direction it travels when the battery is discharging. This
causes the atoms from the acid to return to the electrolyte making the electrolyte
stronger. As the acid atoms leave the battery plates they change back to their
original nature--spongy lead and lead peroxide (fig 19).
d. As a battery is charged some of the water in the electrolyte is broken
down and passed off in the form of gas. If charging is continued after the battery
is fully charged, the amount of gas given off is increased and the battery
overheats. This is called overcharging and can damage the battery. The gas given
off by a battery during the charging process is explosive and can be easily ignited
by a spark.
e. Repeated charging and discharging slowly wear out the battery. It
causes the lead peroxide to fall off the positive plates into the sediment space in
the bottom of the container. It is possible for the sediment to build up high
enough to cause a short circuit between the negative and positive plates, but
normally the cell will be worn out before the sediment reaches the short circuit
stage.
OS 010, 3-P23
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