<![CDATA[Off-grid photovoltaic (PV) systems are a viable solution for electrifying remote areas. However, the intermittent nature of solar energy necessitates the use of properly managed batteries to ensure a continuous power supply and preserve battery lifespan. While various battery control systems have been developed, most rely on relatively complex digital controls, making them less suitable for small-scale household applications. This study aims to develop an automatic switching system for charging and discharging between primary and standby batteries in a 12 V DC standalone PV (SAPV) system, utilizing state-based control logic. The proposed system employs two Valve-Regulated Lead-Acid (VRLA) batteries, two Low-Voltage Disconnects (LVDs), and three electromechanical relays (EMRs) to control charging and discharging operations based on battery voltage, which represents the State of Charge (SoC) and Depth of Discharge (DoD). The control system features four operating states and eight state transitions, prioritizing full charge-discharge cycles for the primary battery while utilizing the standby battery to maintain power supply continuity during the primary battery's charge. Test results demonstrate that the system successfully automates operational switching in accordance with the designed control strategy, thereby preserving the primary battery's full cycling and ensuring continuous power supply. The system is simple, cost-effective, and easy to implement using LVDs and EMRs. Observed transition voltages do not always align exactly with the set threshold values because of the dynamic characteristics of VRLA batteries.]]>
