Aircraft Batteries
Types of Batteries:
Aircraft batteries are usually identified by the material
used for the plates. The two most common types of battery used are lead-acid
and NiCd batteries.
Lead-Acid Batteries:
Dry Charged Cell Lead-Acid Batteries
Dry charged cell lead-acid batteries, also known as flooded
or wet batteries, are assembled with electrodes (plates) that have been fully
charged and dried. The electrolyte is added to the battery when it is placed in
service, and battery life begins when the electrolyte is added. An aircraft
storage battery consists of 6 or 12 lead-acid cells connected in series. The
open-circuit voltage of the 6 cell battery is approximately 12 volts, and the
open-circuit voltage of the 12-cell battery is approximately 24 volts. Open
circuit voltage is the voltage of the battery when it is not connected to a
load. When flooded (vented) batteries are on charge, the oxygen generated at
the positive plates escapes from the cell. Concurrently, at the negative
plates, hydrogen is generated from water and escapes from the cell. The overall
result is the gassing of the cells and water loss. Therefore, flooded cells
require periodic water replenishment.
NiCd Batteries:
A NiCd battery consists of a metallic box, usually stainless
steel, plastic-coated steel, painted steel, or titanium-containing a number of
individual cells. These cells are connected in series to obtain
12 volts or 24 volts. The cells are connected by highly conductive nickel-copper links. Inside the battery box, the cells are held in place by partitions,
liners, spacers, and a cover assembly. The battery has a ventilation system to
allow the escape of the gases produced during an overcharge condition and
provide cooling during normal operation.
NiCd cells installed in an aircraft battery are typical of
the vented cell type. The vented cells have a vent or low-pressure release
valve that releases any generated oxygen and hydrogen gases when overcharged or
discharged rapidly. This also means the battery is not normally damaged by
excessive rates of overcharge, discharge, or even negative charge. The cells
are rechargeable and deliver a voltage of 1.2 volts during discharge.
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