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.
Thus far we have limited our selves 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 In the one case the separator is a veneer about one-sixteenth inch thick, with split wood dowels slipped over it to give the necessary space between plates; in the other it is made of a thicker piece, grooved, and in either instance treated by a special chemical process. The dis tinctive feature of the wood separator is that it is not perforated, with the result that short circuits are practically eliminated, while its electrical resistance is nevertheless almost neg ligible.
General Assembly.— So much variety ex ists in the details of assembly employed by dif ferent manufacturers and for different purposes 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 port able 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 acid— are 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 station ary installations.
Electrolyte.— The electrolyte in lead bat teries is dilute sulphuric acid of the highest available purity and of strength varying ac that it will be possible to mention only a few of the controlling factors and to give a few illustrations of complete cells (Figs. 24, 25 and 28).
In all present-day designs, positive and nega tive plates are placed alternately side by side, all of like polarity being firmly united into "groups" by means of ((lugs° which project from the upper corners. Fig. 23 shows a posi cording to conditions. Where space and weight are of.utmost importance, stronger acid, about 1280 specific gravity, is employed, but where these items are non-essential a greater bulk of weaker acid, say 1,200 specific gravity, answer-, better, in that it causes less loss from local action. especially on the nesrative plates.
tive and a negative group as used in the small auto starting battery of Fig. 26; and these trations also show the general manner in which the plates are united, by a lead welding procec, to the connecting straps which form the termi nals of the cell.
The corrosive action of the acid electrolyte makes this lead welding necessary, and in most instances it is applied, not only in fastening the plates to the cell terminals, but also in fasten ing adjacent cell terminals together, so that of electro deposited lead. In Fig. 27 is shown a connector as used, not only for auto starting batteries, but for most other portable and semi 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 station ary ones.
The plates are usually either supported upon ridges projecting upward from the bottom of the jar (Fig. 24) or are suspended from the j 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 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 bat tery determine the size of cells to be employed, and the voltage requirements the number of 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.