Cells in parallel and series

4.2.3 Cells in parallel and series

Cells are connected in parallel and series to increase both the voltage and the current rating.  Below four cells are arranged in series to increase the effective to 6 volts and thereafter the series set are connected in parallel to increase effective current.  This increases current 3 times the single bank.

Activity

• How would modify the above arrangement and achieve 9.0 V?
• Draw the schematic symbol of the resultant diagram.

Parallel circuit diagram

4.4.2 Parallel circuit diagram

Parallel circuit diagram of cells

If a higher current is required than that which a single cell can supply, a number of cells are connected in parallel.  When connecting cells in parallel, all the positive terminals are interconnected and all the negative terminals are connected to each other. This has the effect of adding the surface areas of the cell electrodes. The larger surface area can allow more chemical action and, therefore, more electric energy.

Connecting the cells in parallel increases the current rating, but the voltage remains the same if the cells are identical.  If however, the cells have different Emfs then effective Emf of the connection is equivalent to the highest value of the arrangement as show in the parallel arrangement below.

Parallel circuit diagram of cells2

Cells connected in series

4.4.1 Cells connected in series

This is done to increase the effective voltage output of the battery.  The battery output is the arithmetic sum of each individual cell.

Cells connected in series

When four cells each of 1.5 volts are connected in series, the total voltage is (4 x 1.5 V) or 1.5 + 1.5 + 1.5 + 1.5 = 6V.

Circuit Diagram Symbols

4.4 Circuit Diagram Symbols

In a circuit diagram, the cells are represented by the symbols shown below. 

Electric cell symbol

Two cells in series symbol

Cells in series symbol

The long, thin stroke represents the positive electrode; while the short, thick stroke represents the negative electrode of the cell. These are conventional symbols and the polarity marks (+ or -) may be omitted.

Most electric cells source are 1.5 volts when new. This electric potential is too weak to deliver a large amount of electric energy. When this is needed, two or more cells are used. For example, a torch requires two size D cells to give enough light. But more powerful torches require three or four such units. Similarly, small radios require three size D cells, while the large ones require as many as twelve.

In principle, the term battery refers to more than one cell when used or connected together. Consequently, the two dry cells in a torch form a battery just as the six dry cells in the radio. The individual dry cell does not make a battery.

At times, manufacturers connect many cells and house them together to form powerful batteries. The 12-volt car battery consists of six lead-acid cells connected and housed in the same casing. In doing this the battery has enough power to start a car engine. Individual cells or batteries may be connected in various ways to achieve the required voltage and current supply.