- Battery Cells Definition: A battery is defined as a device where chemical reactions produce electrical potential, and multiple cells connected together form a battery.
- Series Connection: In a battery in series, cells are connected end-to-end, increasing the total voltage.
- Parallel Connection: In parallel batteries, all positive terminals are connected together, and all negative terminals are connected together, keeping the voltage the same but increasing the total current.
- Mixed Grouping: Series-parallel batteries combine both series and parallel connections to achieve desired voltage and current.
- Internal Resistance: Internal resistance in a battery reduces the terminal voltage when the battery is supplying current.
Battery Cells
A battery is defined as an electrical element where chemical reactions produce electrical potential. Each electrochemical reaction has a limit to the electric potential difference it can generate between two electrodes.
Battery cells are where electrochemical reactions occur to produce a limited electric potential difference. To achieve the desired voltage, multiple cells are connected in series. Thus, a battery is a combination of several cells. For example, Nickel-cadmium cells produce about 1.2 V each, while lead acid battery cells produce about 2 V each. Therefore, a 12-volt battery typically has six cells connected in series.
EMF of Battery
The electric potential difference measured between a battery’s terminals when no load is connected is called the electromotive force (EMF) or no-load voltage. This is the voltage generated when no current is flowing through the battery.
Terminal Voltage of Battery
Terminal voltage of battery is the potential difference across its terminals when the current is being drawn from it. Actually when load is connected with the battery, there will be load current flowing through it. As a battery is an electrical equipment, it must have some electrical resistance inside it. Because of this internal resistance of battery , there will be some voltage drops across it. So, if any one measures the terminal voltage of the load i.e. terminal voltage of battery when load is connected, he or she will get the voltage which is less than emf of the battery by internal voltage drop of the battery.
If E is the emf or no-load voltage of the battery and V is the terminal voltage of load voltage of the battery, then E – V = internal voltage drop of the battery.
As per Ohm’s law, this internal voltage drop is nothing but the product of electrical resistance offered by the battery and the current flows through it.
Internal Resistance of Battery
The entire resistance encountered by a current as if it flows through a battery from the negative terminal to the positive terminal is known as internal resistance of battery.
Series Parallel Batteries
Battery cells can be connected in series, in parallel and as well as a mixture of both the series and parallel.
Series Batteries
In a series battery, the positive terminal of one cell is connected to the negative terminal of the next cell. The overall EMF is the sum of all individual cell voltages, but the total discharge current remains the same as that of a single cell.
If E is the overall emf of the battery combined by n number cells and E1, E2, E3, …………… En are the emfs of individual cells.
Similarly, if r1, r2, r3, …………… rn are the internal resistances of individual cells, then the internal resistance of the battery will be equal to the sum of the internal resistance of the individual cells i.e.
Parallel Batteries
When positive terminals of all cells are connected together and similarly negative terminals of these cells are connected together in a battery, then the cells are said to be connected in parallel. These combinations are also referred as parallel batteries. If emf of each cell is identical, then the emf of the battery combined by n numbers of cells connected in parallel, is equal to the emf of each cell. The resultant internal resistance of the combination is,
The current delivered by the battery is sum of currents delivered by individual cells.
Mixed Grouping of Batteries or Series Parallel Batteries
As we said earlier, the cells in a battery can also be connected in mixture of both series and parallel. These combinations are some time referred as series parallel battery . A load can require both voltage and current more than that of an individual battery cell. For achieving the required load voltage, the desired numbers of battery cells can be combined in series and for achieving the required load current, desired numbers of these series combinations are connected in parallel. Let m, numbers of series, each containing n numbers of identical cells, are connected in parallel.
Again assume emf of each cell is E and internal resistance of each cell is r. As n numbers of cells are connected in each series, the emf of each series as well as the battery will be nE. The equivalent resistance of the series is nr. As, m number of series connected in parallel equivalent internal resistance of that series and parallel battery is nr/m.
