Isolation Is Not Gilligan’s Island.
Battery isolation simply means keeping the batteries in your RV separate to operate different things while being able to charge them from a single source. Sounds complicated but it is really a simple task that can be accomplished by a battery isolator or a series of relays or a combination.
The battery isolator used in most RV’s today is a simple device that uses the principle of the silicon rectifier diode. A diode is simply an electronic gadget that will let electricity flow in one direction but not in the other. It is like a one way valve in a hydraulic circuit. Way back in the time machine a guy names Walter Schottky, a drinking buddy of Al Einstein and equally as bright, discovered that when a direct voltage current was applied to one side of a wafer of silicon and a load (like a light bulb) attached to the other side, the light would like when the current was traveling in one direction but not the other. And so was born the silicon diode and the dawn of the electronic age.
From the diode came transistors and a raft of other electronic goodies that we all take for granted today. The battery isolator is simply put a device that uses several diodes to control the flow of electrical current.
The simple isolator that we use in RV’s is an arrangement of diodes that lets the center terminal be connected to the alternator of the engine and the engine or chassis battery connected to one side, and the house or coach battery pack connected to the other side. The diodes inside the isolator simply let current flow from the alternator center terminal to either or both of the outer terminals which are the house on one side and the chassis battery on the other but will not let the current flow back to the center or to the other battery. The one down fall of diodes is that they will produce heat ahen in heavy load so the box that contains this stuff has cooling fins and should be securely mounted to provide anoher escape route for heat.
The flow of current to each side is controlled by the internal resistance of each battery and that is the state of charge of each battery. The lowest charged battery will get more current than the higher state of charge battery.
Some systems also use a by pass system or auxiliary start to by pass the isolator for emergency use, like you have discharged the house batteries to the point that the generator will not start. You can then momentarily connect the chassis battery to get the generator fired up. We will look at that circuit next time.
Till then, keep on camping.