When the load voltage does not exceed the electromotive force of a voltage source and the load current exceeds the rated current of the voltage source, the parallel voltage source shall be used.
The parallel connection condition of voltage sources is that: the electromotive force of each voltage source must be equal, and their internal resistance must also be equal, otherwise a large circulating current will form in the voltage source and burn the voltage source. After m voltage sources with equal electromotive force and equal internal resistance are filed, their total electromotive force is:
E=E1=E2 ··· Em, the total internal resistance is: γ o= γ o1÷m