Page:Popular Science Monthly Volume 92.djvu/327

 Electrical Devices and How They Work

Secondary Cells; Storage Batteries— II

��Accumulators are cells of battery that will receive a charge of electricity and keep it stored until it is released through mains for power and liglit

By Peter J. M. Clute, B. E.

��I

��N the primary cell, electric current is produced by the decomposition of the electrolytic solution and the consump-

��In other words,

Projecting ormfor connecting plates

���Positive lead grid of a storage cell

��tion of a zinc electrode the varying natural potentials of two sub- stances, such as zinc and copper or zinc and carbon, constitute the original impulse to a succession of reactions whereby chemical energy is transformed into continuous elec- trical energy. On the other hand, in the secondary, or storage, battery, electric cur- rent is generated by a somewhat similar chemical reaction, originated, however, by chemical changes, produced by an electric current passed through the cell at the start of operations. This operation is termed the charging of the cell.

Such cells are called secondary cells be- cause their action is dependent upon the effects of the energy impressed upon them by a primary electrical source. They are designated as storage batteries because, apparently, a quantity of electrical energy is stored in them in the form of current, to be delivered, also in the form of current, when the battery is connected as a source of electricity.

Storage cells of all descriptions are charged from D. C. service mains, or from special charging generators. The current may be regulated to the required rating by suitable resistance, usually through special switchboards, designed to meet the requirements of charging. If the only available current supply is alternating, it can be transformed into direct current by means of a rectifier, or a

��motor-generator set. The secondary cell is capable of being recharged after ex- haustion by passing an electric current through it in a direction opposite to that of the current on discharge. This dif- ference constitutes the principal ad- vantage of the storage battery over the primary cell.

The typical storage cell is the lead-lead couple in an acid electrolyte. There are, however, other varieties of such cells, all of them more or less experimental in character. These may be designated as lead-copper, lead-zinc, alkaline-zincate, etc., all using corrosive electrolytes. In addition to these, and in a class by itself, is the Edison nickel-iron cell, using an alkaline and non-corrosive electrolyte.

The commercial storage cell consists of an even number of positive plates and an odd number of negative plates, immersed in a dilute electrolyte (generally sulfuric acid) contained in a jar or box of non- conducting material. The plates are ar- ranged alternately positive and negative, and are cast with

��Negative plote

���Positive Plate

��Positive plates of per- forated steel tubes

��a projecting arm as shown in Fig. 1, so that all posi- tives may be con- nected by a single stud, and all nega- tives similarly united — each such unit of several plates being one element of the cell. The positive ter- minal at which the charging cur- rent enters the cell, passing to all positive plates, and at which the

��current leaves the cell on discharge, is called the anode. Similarly, the negative

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