It is possible to connect the cells of a battery in such a way that total voltage of the group or battery is equal to the sum of the voltages of the individual cells. A battery connected in this manner is said to be connected in series. While the voltage of a battery is increased, by series connection, the number of amperes is the same as that given by a single cell, the same current flowing through the set.
(82) Series and Multiple Connections.
Fig. 86 shows the cells connected in series, the carbon terminal of one cell being connected to the zinc terminal of the second. The carbon of the second cell is connected to the zinc of the third, and so on throughout the series, the two remaining terminals of the battery being connected with the ignition circuit. The number of watts or power developed by the group is equal to the sum of the outputs of the separate cells. If the voltage of each cell shown in diagram is 1.5 volts, the total voltage of the group of five cells will be 1.5 × 5 = 7.5 volts, and if the current of a single cell is 15 amperes, the current output of the group will be 15 amperes, or the same as that of a single cell. Almost all ignition apparatus now on the market requires six volts for its operation, so with cells having a voltage of 1.5 volts such apparatus would call for four cells in series, as 6 ÷ 1.5 = 4.
Fig. 86. Five Cells in Series.
Owing to the increase of internal resistance caused by series connections it is usual to add one more cell than is theoretically required, making a group of five cells to supply the six volts required. A large number of cells will give a hotter spark than a smaller, but the excessive current causes the contact points of the igniter or vibrator to burn off rapidly and also hastens the destruction of the cells themselves.
Batteries connected in such a way that the total amperes of the group is increased without increased voltage are said to be connected in multiple or parallel. When batteries are connected in multiple, the total current in amperes is equal to the sum of the amperes delivered by the separate cells; and, while the current in amperes is increased by multiple connection, the voltage of the group remains equal to that of a single cell.
If each cell connected in multiple has an electromotive force of 1.5 volts, and can deliver 15 amperes, the total current delivered by this system of connection will be 15 × 5 = 75 amperes with five cells, and the electromotive force will be 1.5 volts as in the case of the single cell. By connecting batteries in multiple, the resistance is reduced, allowing a maximum flow of current. The demand on the individual cells is reduced by multiple connection, as each cell only furnishes a small part of the total current. The greater the number of cells, the less will be the current required per cell, with a given total current. As the life of a battery depends entirely upon the rate at which it is discharged, it is necessary, for economical reasons, to keep the current per cell as small as possible, therefore the multiple system would prove of value as it reduces the load to the smallest possible limit. Enough cells should be placed in multiple to reduce the current to less than a quarter of an ampere per cell. The cells shown will not have sufficient voltage to operate ordinary ignition apparatus requiring a potential of six volts, hence the multiple system must be modified in order to have an increased voltage, and at the same time secure the advantages of multiple connections.
(83) Multiple-Series Connections.
A compromise is affected by the multiple series system of connections in which are combined the advantages of both the series and multiple systems of connection.