7.3: Voltage Source Circuits
Multiple power sources can be connected in series or parallel in order to meet the different voltage or current output requirements for various applications:
- Power sources are connected in series to increase the voltage output.
- Power sources are connected in parallel to increase the current capacity
Series Sources
Voltage sources are sometimes connected in series to produce a higher voltage value. This is common in devices such as flashlights and portable transistor radios, in which 1.5 V battery cells are used.
To obtain a higher voltage output from series-connected sources, you must observe correct polarity. In Figure \(\PageIndex{1}\), a net voltage of 6 V is obtained if the individual 1.5 V cells are acting in the same direction. This is called series aiding .
For the voltages to accumulate, the negative terminal of one source connects in series with the positive terminal of the next source, and so on.
When voltage sources are connected in series opposing, the net voltage value is derived by subtraction. This is illustrated in Figure \(\PageIndex{2}\).
- Three of the cells are connected series aiding to produce 4.5 V.
- One cell is connected with opposite polarity of 1.5 V.
- The net voltage is 4.5 V – 1.5 V = 3 V.
- Overall polarity acts in the direction of the largest cell.
Parallel sources
Voltage sources are connected in parallel whenever it is necessary to deliver a current output greater than the current output that a single source of supply can provide, without increasing voltage across a load.
An advantage of parallel-connected power sources is that one source can be removed for maintenance or repairs while reduced power to the load is maintained. This is common in RVs that have dual batteries. For parallel batteries, current capacity is equal to that of one battery multiplied by the number of parallel batteries. If a 6 V battery has a maximum current output of 1 amp, and if it is necessary to supply a load requiring 2 amps, then you can connect a second 6 V battery in parallel with the first, as shown in Figure \(\PageIndex{3}\).
Whenever batteries or other power sources such as transformers or generators are to be connected in parallel, it is very important that the power sources have the following:
-
The same terminal voltages
A lower voltage source connected to a higher one acts as a load itself, rather than helping share the real load current with the other sources of supply.
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Properly connected polarity.
Like terminals of the power sources must be connected together; that is, positive-to-positive and negative-to-negative.