This arrangement allows sufficient voltage to operate 6 volt apparatus and at the same time reduces the rate of discharge on the individual cells. The series-multiple battery shown in the diagram 88 consists of four groups of batteries connected in multiple, each group of which consists of five cells that are connected in series. The current and voltage in the various branches is shown in the diagram. The series-multiple system is adapted for use with multiple cylinder engines, as engines with more than one cylinder cause a severe drain on the ignition system. Arranging the series groups in parallel increases the life and efficiency of the cells. If an efficient coil is used, the drain of a single cylinder is not too great to be met with a single set of series cells. If possible the set should be provided with a duplicate, so that the load could be transferred from one set to the other at proper intervals by means of a double throw switch.
With a single set of batteries in series the working life of the cells will be approximately twenty hours under ordinary conditions. With four groups of four cells in series, the life of the cell will be approximately 160 hours, or eight times the life of the single set under similar conditions.
While the cost of the cells will be only four times that of the single set, it will be seen that the cost of battery upkeep is halved by reducing the demand on the cells.
Sometimes duplicate sets of series multiple connected batteries are used for heavy duty engines, the engine running on one set for a while and then on the other, allowing the first set to thoroughly recuperate before it is again thrown in service, by means of the double throw switch.
When batteries are multiple or series-multiple connected they should be of the same size and make and of the same voltage. If the cells are of different voltages useless local currents will circulate among the cross-connections, shortening the life of the battery and reducing the output.
Fig. 88. Cells in Multiple Series.
In connecting a dry cell use a good grade of rubber insulated wire, preferably wire with a stranded conductor, as it is less liable to break or loosen at the binding screw of the battery. Carefully remove the insulation from the end of the wire that is to be fastened under the binding screw of the battery. Scrape it until it is bright and perfectly free from dirt before fastening it in the battery terminal. Never allow a dirty or corroded connection or a loose wire to exist. An open battery circuit or loose connection will stop engine suddenly, or will prevent starting.
The battery connections should be screwed down tight with the pliers, care being taken that the screws are not broken by the tightening process. See that frayed ends of the wire do not project beyond the binding screw to which they are connected and make contact with other cells or metal objects. Be sure that no insulation gets between the contact braces of the binding screw.