Monitor for equal voltage at the terminals of two 12V batteries.

Circuit presentation

Most 24V back-up power systems, such as fireplaces, etc., use two 12V batteries. The charging system of the voltage source monitors and maintains the nominal sum of the voltages of the two batteries. If one of the batteries fails, discharging more than the other, reaching its maximum operating cycle, the system does not detect the event, unless the amount is much too small. In this case, the battery in good condition may be damaged before the deadline life specified by the manufacturer. Using the proposed monitor circuit, mounted in the system, it is possible to detect in time if one of the batteries has a different voltage from the other one. This is in fact a circuit that monitors whether the voltages at the terminals of the two batteries are equal or not, by detecting the voltage difference.

Bill of materials available in the download section, and the schematic as well.