Cells and batteries
Cells are a voltage source that generate a difference of potential via a positive and negative electrode separated by an electrolytic solution. The electrolytes pull free electrons from one of the materials which creates a positive charge. The other material gains the free electrons creating a negative charge.
A battery is a combination of two or more cells.
Cells which cannot be recharged are called primary cells. Cells which can be recharged are called secondary cells.
Connecting batteries
Cells and batteries can be connected to each other in electrical ciruits to increase the overall voltage and current that is produced. There are three main connection types:
- series
- parallel
- series-parallel
The key thing to remember: cells configured in series increases the overall voltage available and cells configured in parallel increases the overall current available
The table below summarises the relative differences:
Series connections
With series connections we distinguish series aiding and series opposing configurations.
In the case of series aiding, cells are connected one in front of another with the positive terminal connecting to the negative terminal of the other in a line.
In this configuration the same current flows through all the cells; it is not cumulative. We represent this as follow> However the voltage is cumulative: it is the sum of the individual cell voltages, represented below as electrical field:
$$ E_{T} = E_{1} + E_{2} + E_{3} \\ $$
Thus series connections increase voltage but keep current constant.
Series battery connection:
Can be represented in a circuit diagram in one of the following two ways: as a series of cells or as a single battery:
In the case of series opposing, negative terminals are connected to each other and positive terminals are connected to each other in a series. This doesn’t have many applications.
Parallel connections
In parallel connections all positive terminals are connected to each other and all negative terminals are connected to each other.
This time the voltage is the same as each individual cell but the current is the sum of the individual cell currents. So the voltage is constant but the current is cumulative:
$$ E_{T} = E_{1} = E_{2} = E_{3} \\ $$
$$ I_{T} = I_{1} + I_{2} + I_{3} $$
Parallel battery connection:
Parallel battery circuit diagram:
Series-parrallel
If we want both a higher voltage and a higher current we can use series-parallel configurations. Connecting cells in series increases the voltage and connecting cells in parellel increases the current so doint both boosts the amount of both quantities.
