US Patent 10116149 Automatic control system for a rechargeable battery system

An automatic battery control system automatically switches from charge to discharge modes with a single relay, thereby preventing the need to manually reset a relay switch due to an over or under voltage situation. An automatic battery control circuit is coupled with a battery management system and a relay contactor is opened and closed by a signal from the battery management system. The battery management system monitors a state of charge of the battery unit as well as current flow to and from a battery unit. A parallel resistor is configured across the input and output sides of the single relay contactor and the voltage drop across the resistor indicates a connection to either a charging power source or a load. The connection is communicated to the battery management system by an optocoupler and if the battery unit has an acceptable state of charge, the relay contactor is closed.