# Raspberry Pi_Eng_25.4.3 Series and Parallel of Power

### 25.4.3Series and Parallel of Power

There are three ways of connecting the power supply: series connection, parallel connection and series/parallel connection.

#### 25.4.3.1Series Connection

The way to connect a (+) pole of one cell to a (-) pole of another is series connection. At this time, the total electromotive force is the sum of the electromotive force of all the batteries.

This serial connection is used when the voltage needs to be increased. In reality, if you connect batteries together in a row, they are connected in series. That is, when three 1.5V batteries are connected in series, it becomes 4.5V, three times of 1.5V.

#### 25.4.3.2Parallel Connection

The way to connect same (+) pole of each battery together and connect same (-) pole of each battery together is referred to as parallel connection. The electromotive force at this time is the same as one electromotive force, but the lifetime of the battery is increased by the number of the batteries.

#### 25.4.3.3Series and Parallel Connection

This is how several batteries are connected in series and then in parallel. The total electromotive force is equal to the electromotive force of a series-connected cell, and the lifetime of the cell is proportional to the number of parallel connections. It is also referred to as a mixed connection, which takes advantage of series connectionl and parallel connection.

For example, when you have 4 pieces of 1.5V batteries and connect each 2 piece of 1.5V batteries in parallel and again them in series, the voltage is 3V and the usage time is as same as 2 pieces of batteries.

Another thing you should know about battery is internal resistance. When current is used in a battery, a voltage drop occurs due to the internal resistance. Therefore, the voltage measured at the terminal of a battery is as follows.

V = (electromotive force) - (current) x (internal resistance of the battery)

This voltage V is referred to as a terminal voltage of battery. The internal resistance of the battery is about 0.1Ω or less.