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than a lead-plate battery of equal capacity, and costs about two and one-half times as much, but it is said to retain its full capacity for three or four years. The lead-plate type will deliver about 10 watt-hours per pound weight; an Edison battery will give nearly. 14 watt-hours per pound.
The usual number of lead-plate cells provided to charge from a 110-volt circuit is forty-two or forty-four, having 11, 13 or 15 high-capacity plates per cell, while sixty-cell Edison batteries are
supplied to meet the same conditions. The battery weight of the average electric vehicle is about 35 per cent. of the total unloaded weight. In order to insure a rate of discharge that will not injure the batteries, electric vehicles are usually geared for moderate speeds, seldom more than 18 to 20 miles per hour for pleasure or passenger-carrying cars on pneumatic tires. Heavy trucks seldom run faster than 6 miles; medium-capacity commercial vehicles may run 10 or 12 miles per hour. A number of electric vehicle-makers have adopted a 24-cell battery, using motors wound for about 48 volts.
The motors used are almost always of the series-wound type, because they provide more power for starting. The usual pleasurecar size is a motor of 2 k.w. rating, or about 234 horsepower. Vehicle motors have an overload capacity of 200 to 300 per cent., though, of course, this is practical for only relatively short periods of operation. The speeds are controlled by different combinations of the motor field windings.
In some electric vehicles the various car speeds were obtained by parallel and series parallel combinations of the battery cells. From four to six forward speeds are generally provided, a simple reversing arrangement making it possible to have the same number of reverse speeds if necessary, though this is not always done. Another scheme of control is to have the motor field windings or coils so wired that they may be put in series or in parallel groups. A resistance is used in securing the first speed with the field coils in series. The second speed is obtained by cutting out the resistance and leaving the fields in series. Third speed is obtained by shunting the resistance across the fields, which are still in series. The fourth speed is obtained by leaving the field coils in parallel connection and with resistance out, the fifth speed by shunting the resistance in with the parallel connected fields. The parallel connection gives greater speed, the series field connection more pulling power.
Electric motors for electric trucks usually have about one kilowatt capacity per ton load added, the minimum being 2 k.w. on a one-ton truck; thus a two-ton truck will need a 3 k.w. motor, a four-ton truck 4 k.w., and 5 k.w. for a five-ton vehicle. The usual
range on good roads is about 40 miles for a truck and 75 to 100 miles for pleasure cars on one battery charge. Vehicle batteries are generally carried in hard rubber jars and are nearly always of the sealed type on account of the liability of splashing the electrolyte when the car is operated over ordinary highways. The cells are grouped in trays for easy handling, and all connections and couplings, terminals and battery straps are of unusually rugged design.
The present tendency in lead-battery design seems to be toward the use of more thin plates, as fifteen are furnished as a standard equipment more often than a smaller number. Such an equipment will give 180 ampere-hours, and in some types may develop fully 200 ampere-hours. The reasons for the increasing adoption of the thin-plate lead battery are, first, an augmenting demand for more speed and greater range of action per charge, and secondly, a realization on the battery-maker's part that the life of a thin plate is equal to that of the heavier ones if the installation is properly made. One standard jar size now being produced will work with from 11 to 15 plates. The high-ribbed type of jar is used, having at least three inches below the bottom of the plates for sediment space, this reducing the amount of washing and necessary cleaning out of the cells. The jars are assembled side to side in trays, with the plate surfaces set at right angles to the direction of car movement. One row of cells is mourted in each tray, these being set lengthwise in the battery compartment. This arrangement is said to reduce jar breakage.
Isolated Lighting Plants.- Many makers of storage batteries have developed types for use in residence and factory lighting where central station power is not available. The advantages of electricity for the supply of light, heat and power have led to a demand for the satisfactory and economical operation of isolated plants. The marvelous development of the internal combustion gas, gasoline or kerosene engine and the improvements in the various forms of lamps have created an active interest in the application of the storage battery to isolated plants of moderate size, it now being recognized where uninterrupted twenty-four-hour service is desired a storage battery is an absolute necessity. Usu