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