(A) GENERAL DISCUSSION
38. Types of Batteries Used. -The storage batteries furnished with RCA Photophone equipment are of two types, the low gravity and the high gravity. The low gravity type is used to supply the necessary low voltage direct current for lighting the exciter lamps, Radiotrons, etc. The high gravity type is used when the battery is "floated" or connected permanently across a low voltage generator. The purpose of the "floated" battery is to filter out the "commutator ripple" of the low voltage generator which supplies the current for lighting the exciter lamps, Radiotrons, etc.
39. Description. Each battery is composed of three sections, or cells. Each
cell contains two groups of plates, positive and negative, immersed in a sulphuric
acid solution, called the electrolyte. The positive plates of a fully charged battery
are lead peroxide and are reddish brown in color. The negative plates are of spongy
lead and are grey in color. A porous non-conducting material is used to separate
the positive and negative plates. Figure 37 shows an Exide storage battery with
part of the side cut away to show plates, separators, and sediment space.
40. Chemical Action of Charging and Discharging the Battery.- When the battery is discharged, i.e., when current is drawn from it, two things occur. The acid acts on the negative plates to form lead sulphate and hydrogen, and on the positive
plates to form lead sulphate, water, and oxygen. Since sulphuric acid combines with the elements of the plates to form a deposit on the plates, the acid solution becomes weaker as the battery is discharged.
After a certain period of use, the chemical action taking place in the battery
will exhaust it, and the battery must be recharged. To do this, a direct current
from a generator or other source is passed through the battery in the direction
opposite to that in which the current flows when the battery is discharged, and
the chemical action is reversed. Lead sulphate and water combine to form lead,
sulphuric acid, and oxygen at the negative plates; and lead sulphate and water combine to form lead peroxide, hydrogen, and sulphuric acid at the positive plates.
Since sulphuric acid is formed, the acid solution becomes stronger as the battery is charged.
The hydrogen and oxygen formed are gases, which escape through the vent
caps of the battery. If these two gases are combined, by burning, they form water.
Therefore, water is "used up" both when the battery is charged and when it is
discharged, and needs to be replaced periodically to keep the acid solution above