Controlling Amperage.—But the metal plates may be made very large, or have a great surface in each cell. The greater the surface the greater the amperage, so that while each cell has only two volts, it may have a very small amperage, or it may have two, five, ten, or even more amperes flowing therefrom.
Dry Batteries.—Instead of using cells with liquid in them, as the electrolyte, a dry cell is made which acts efficiently. This is usually made in the form of a zinc cup, within which is centrally held a carbon rod, and the space around the rod is filled with ground carbon and dioxide of manganese, and moistened with sal ammoniac.
Cell Construction.—The zinc cell and the carbon have upwardly-projecting posts to which the wires are attached, and when thus made the top of the cup is closed with pitch, or some suitable preparation to prevent evaporation and to retain the substances within, and the whole is then inclosed in a jacket, usually of pasteboard.
Usually these cells give one and a half volts, and are very durable. This is, of course, a very low voltage, and it is necessary, for this reason, to use at least a half dozen, to operate the coil used in an ignition system.
Connecting Up Cells.—If we have a number of cells they can be connected with each other so as to get an additional voltage as well as greater amperage. This statement must be understood in a definite way. Supposing we have six cells, each with an output of 1-1/2 volts, and an ampere flow of 25 in each. Multiplying 25 by 9 makes 225 watts.
Fig. 84. Series Wiring.
We may connect up the six cells in such a way that we can get
First: 9 volts, and 25 amperes, equal to 225 watts, or,
Second: 1-1/2 volts and 150 amperes, equal to 225 watts, or,