The 10volt DC source represents a Gel Cell Battery while the 13.8volt source represents a regulated power supply. As the 10volt source raises in voltage, current flow through the 1.3ohm resistor is reduced. Eventually the 10volt source will equal the 13.8volt source and the current will be arounds at times so make sure it is at least a 25 watt resistor. Diodes should be large enough to handle any load you use. The load is taken from the middle of the two diodes.
