Voltage Sources in Series

A voltage source is an energy source that provides a constant voltage to a load. Two or more of these sources in series will equal the algebraic sum of all the sources connected in series. The significance of pointing out the algebraic sum is to indicate that the polarity of the sources must be considered when adding up the sources. The polarity will be indicated by a plus or minus sign depending on the source’s position in the circuit.

In Figure 78 all of the sources are in the same direction in terms of their polarity. All of the voltages have the same sign when added up. In the case of Figure 78, three cells of a value of 1.5 volts are in series with the polarity in the same direction. The addition is simple enough:

However, in Figure 79, one of the three sources has been turned around, and the polarity opposes the other two sources. Again the addition is simple: