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What does wet-cell
battery gassing mean? C.M., via e-mail
Gassing is
the process whereby hydrogen is given off at the negative plates and oxygen
is given off at the positive plates during battery charging. To explain
how this happens, let’s first look at what takes place when a load
is put on a typical 12-volt wet-cell battery.
As the battery discharges,
lead in the positive plates combines with sulfate in the sulfuric acid
electrolyte to form lead sulfate. Oxygen, also present in the active material
that makes up the positive plates, combines with the hydrogen in the electrolyte
to form water. A similar reaction happens on the negative plates (also
known as sponge lead plates), and as the amount of lead sulfate on the
plates increases, so does the water in the electrolyte. The combination
of decreased active material with weakened electrolyte results in a discharged
battery that can no longer produce sufficient enough current to power
the load.
During charging, as
illustrated in the accompanying diagram, the input voltage drives the
reaction in reverse. Lead sulfate in both plates splits into its original
components of lead and sulfate, and water is split into hydrogen and oxygen.
As the sulfate leaves the plates, it combines with the hydrogen to become
sulfuric acid. At the same time, the oxygen at the positive plates will
combine with the lead there and form lead dioxide. When most of the lead
sulfate is converted to lead at the negative plate, hydrogen bubbles form
and rise through the electrolyte. This gassing indicates the battery is
nearly fully charged. The voltage at which this occurs is called the gassing
voltage.
I have an older,
small auxiliary genset that will not hold a load. Before I call in a mechanic,
is there anything I can check? C. H., via e-mail
Begin by checking
both the fuel and air filters for clogs. If you recently changed the fuel
filter or if there are leaks, you may also have air in the fuel system.
Finally, check for a faulty governor or voltage regulator.
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