the universal adoption of litharge PbO, for this purpose, applied as a putty-like mass, made by mixing the litharge with dilute sulphuric acid. An initial charge, or "formation," converts the litharge into metallic sponge lead, giving the plate a characteristic light slate color. Plante Negative.-There are still a few Plante negatives used, in this country only, such a one being shown in Fig. 10, but their weight and cost are against them, and they are to-day almost a thing of the past. Positive Plates.- The positive plate offers a more complicated problem, chiefly because lead peroxide, under the conditions which exist in a storage battery, does not possess much sustained mechanical strength, but gradually becomes soft, and in time is loosened from the plate, falls to the bottom of the cell and thenceforward plays no useful part in the life of the battery. To maintain the capacity over an extended period of charges and discharges three distinct methods are employed. Plante Negative Plate for Train Pasted Positive.-In the pasted type of plate, when new, only a part of the lead peroxide is available for entering into the chemical reactions of the cell, as the acid penetrates only partially into the interior of the mass. As the surface wears away the action penetrates farther in, and thus the inner part of the mass acts as a reserve and maintains the capacity for a number of cycles, roughly stated at 300 to 500. By making the plate very thin, say of the order of one-eighth inch, the reserve of active material is cut down to a minimum, hence giving a plate of maximum capacity per unit of weight, but of relatively shorter life. Positive plates of the pasted type are universally employed where lightness, or maximum capacity for given weight, is the primary consideration, and the correct balance between thick, heavy plates of long life and thin, light ones of shorter life, to meet special conditions, is a continual problem to the designer. The general trend of modern practice, however, is toward much thinner plates than were thought practicable a few years ago, a thickness of three-thirty-seconds inch being quite common. The Exide type of pasted plate, Fig. 11, which has become standard in the United States, and largely so in Europe, is very similar to the negative plate, except as to its active material. The grid, Fig. 12, is, however, more substantial FIG. 11. E.S.B.CO. 257 Exide Positive Plate Vehicle ent manufacturers as positive active material, the usual material is red lead, PbO, mixed to a putty-like mass with weak sulphuric acid, or ammonium sulphate solution. The initial charge, or formation, converts this into lead peroxide, a material which when dry has about the consistency of plaster of Paris and a very characteristic dark chocolate brown color. Plante Positive.- The Plante plate is also subject to the continual, slow washing away of its lead peroxide, but the original layer is more durable than the peroxide made from red lead, so it lasts a considerable time in spite of its A 176 A FIG. 13. Cross-Section Tudor Positive Plate. Section at AA Not to scale. two or three times as long as in the case of the pasted plates. For effecting this extended life, however, there is required a large reserve of pure lead; so that in actual practice the Plante plates weigh from two to three times as much as pasted plates of equal capacity. Figs. 13 and 14 show a Plante type of plate known in this country as the "Tudor," used largely in Europe, and consisting of an integral one-piece casting; while Fig. 10, though actually a negative, may be used as illustrating the Gould type, made from rolled sheet lead, by a spinning process. In this country and in England a modified Plante plate, known as the "Manchester," has largely superseded all of the above, chiefly on account of its superior mechanical construction. The Plante plate is made of pure lead, because this metal is attacked by the electrolytic action at about the right rate to replace the loss of lead peroxide; but pure lead is very soft, hence these plates are much subject to buckling and breaking. The Manchester plate (Fig. 15) differs in that a rigid grid, or frame, of anti FIG. 15. E.S.B.C.260 FIG. 14. Tudor Positive Plate for Train mony-lead alloy furnishes mechanical strength, while small, pure lead, spirally wound "buttons" (Fig. 16) inserted in holes of the grid (Fig. 17) furnish the active material which FIG. 17. Section of Manchester Plate. Approx. 2/3 size. The plate consists of a number of cylindrical pencils, one of which is shown in section in Fig. 19; a central-lead ant mony core furnishes support and conductivity for the surrounding mass of active material, itself again enveloped by the perforated hard rubber tubes (Fig. 18). The perforations in the tube consist of minute saw cuts of the order of one onehundredth inch wide; and so effective are these tubes as "retainers" that the plates which employ them have a life approximating 1,000 come the "separators." Considerations of space, weight and electrical resistance all demand that adjacent positive and negative plates be maintained as close together as possible, yet without touching anywhere. To fulfil these requirements spacers or separators of some sort are inserted between them. Here again countless schemes have been tested out, but to-day practically only two types have survived, and these often used in conjunction. The older of the two is the perforated rubber separator, shown in Fig. 20, as a flat sheet of perforated hard rubber, and often, when used alone, provided with a series of parallel ridges on one side, to afford sufficient acid FIG. 19. Vertical Section Ironclad Tube minimum, and, contrary to what might be expected, the protective rubber tube offers but very slightly increased resistance to the passage of the electric current. This type of plate, in conjunction with an exide negative of suitable thickness, is fast becoming standard in this country in all portable service where durability is a prime factor. Separators. Thus far we have limited ourselves to the question of the plates of the lead battery; but though they undoubtedly constitute the greater problem of storage battery design, yet the manner in which they are assembled is almost as important as the design of the plates themselves; and next in order of importance FIG. 22. Flat Wood Separator General Stationary In many cases the grooved separator and plain perforated rubber are used together, the flat of the wood against the negative plate, this making an excellent combination, used in most of the vehicle propulsion and many other portable batteries. The flat veneer with split dowels is used chiefly in large stationary batteries, where the grooving would constitute too great a wastage of wood. Containers.- The vessels which contain the complete element-plates, separators and acidare of three different kinds: hard-rubber jars, where lightness and ruggedness are required, that is, for all kinds of portable service; glass jars for stationary service in the smaller sizes; lead-lined wooden tanks for the larger stationary installations. Electrolyte.-The electrolyte in lead batteries is dilute sulphuric acid of the highest available purity and of strength varying ac Tige 1919 FIG. 24. FIG. 25. Manchester-Box Stationary Cell. tive and a negative group as used in the small auto starting battery of Fig. 26; and these illustrations also show the general manner in which Three-cell Auto Starting Battery. there is a solid metallic contact from cell to cell throughout the whole battery. Between the plates, and thus keeping them apart, lie the separators; the whole element so proportioned as to fill the container, tightly in portable batteries, somewhat loosely in stationary ones. The plates are usually either supported upon ridges projecting upward from the bottom of the jar (Fig. 24) or are suspended from the top of the jar (Fig. 25) or from the lid or in some equivalent manner. Tight covers for the containers have to be provided only for portable service; stationary cells are generally left open for ready inspection and access. General Principles of Complete Battery Assembly. Till now we have dealt with only the single cell, which forms the electrical unit of which a battery is built up. This unit has a current output dependent upon the number and size of plates which it contains, while its electro-motive force has a fixed value, roughly two volts, virtually independent of its size. Hence the current requirements of a given battery determine the size of cells to be employed, and the voltage requirements the number of FIG. 28. Large Stationary Cell. Stand-by portable types. Composed of lead, or alloy, it is made to fit over the tapered terminal posts (Fig. 23), to which it is permanently secured by means of a hydrogen flame, or its equivalent, which melts the lead of both post and connector till they flow together and become united In Fig. 25 there are no connectors proper, the pure lead straps to which the plates are attached having prolongations adapted to be bolted together from cell to cell. FIG. 27. Inter-cell Connector Auto Starting Service. Approx. 1/4 size. cells to be used in series. As the field of the storage battery is very broad, so the design varies greatly, including almost every conceivable combination from the small three-cell battery for auto starting (Fig. 26) to the large central station battery of 150 cells, as shown in Fig. 30. Inter-Cell Connectors.-For connecting the individual cells together electrically various forms of "connectors" and "bus bars" are in use, usually made of lead or lead-antimony alloy, occasionally of copper, protected by a coating FIG. 29. Large Exide Plate for Stand-by Service. Each plate 150 amp. 1 hour. 1/15 size. In the large stationary batteries the plates of adjacent cells are as nearly as possible welded directly together, each plate (Fig. 29) |