Page:Motors and motor-driving (1902).djvu/325

Rh of ebonite, which has proved itself to be a light acid-resisting material, and the most suitable for the purpose. The general arrangement of the plates and cells is very similar in all automobile batteries. The plates themselves, however, differ in the shape and construction of the grid, which sometimes resembles an open network, as in the Rosenthal and Oppermann batteries, and also in the composition of the paste and the methods of formation adopted.

As it will be recollected that each such cell, as shown in fig. 9, gives only a voltage of approximately 2·0, and as it is found that, owing to various reasons, the most satisfactory design of motors for electromobile purposes involves their being supplied with current at between fifty and one hundred volts— preferably nearer one hundred volts than fifty—a number of accumulator cells have to be arranged in series—that is to say, the positive terminal of one connected to the negative terminal of the next fifty cells thus connected giving approximately one hundred volts. Of course, according to the power of the motors they will take more or less current, which is measured, as already explained, in amperes, and the size of the cells supplied to a car is consequently so arranged that the normal rate of discharge of the battery that is, the amount of current measured in amperes it can give without inconvenience to itself shall be the same as the amount of amperes required by the motor or motors to develop their normal power.

It must be remembered that an accumulator or battery of accumulators can be so utilised that twice or three times the amount of current that it was designed to give may be taken out of it. This will not do much harm if it happens only rarely, and for short periods, but if it happens for long and often, it will shorten the accumulator's life. To get good results an accumulator should be treated with every possible care and consideration. An electric motor will also stand considerable overloading, but it is not so patient as the accumulator, for under most circumstances of at any rate prolonged overload, the motor will burn up before the