Patent ID: 8390145

Claim:
A battery isolator unit for controlling a switching means having a first contact for electrical connection to a terminal of a first battery, a second contact for electrical connection to a corresponding terminal of a second battery, and an actuating input for biasing a switch element of the switching means to a closed position to connect the first contact to the second contact, the battery isolator unit including: a sensing circuit for periodically determining a first and second value attributable to terminal voltage values of the first battery and the second battery respectively; and a switch controller responsive to detecting a predetermined condition of the first battery and/or the second battery to provide to the actuating input a control signal having a characteristic for biasing the switch element to the closed position; wherein the switch controller periodically determines a difference between the first and second values when the switch element is in the closed position to obtain a sequence of difference values, and controls the characteristic of the control signal according to a comparison of a present difference value with a previous difference value to modify the bias of the switch element; wherein the switch controller includes a processing unit for determining the first and second values by sensing N values over a time period T, the N values comprising N/2 voltage values attributable to the terminal voltage of the first battery and N/2 voltage values attributable to the terminal voltage of the second battery, and processing those values to determine the first value and the second value; wherein the processing unit determines the first value as a statistical value derived from at least some of the N/2 sensed values attributable to the terminal voltage of the first battery and determines the second value as a statistical value derived from at least some of the N/2 sensed values attributable to the terminal voltage of the second battery; and wherein the processing unit determines the first value as the statistical mean or average value of voltage values attributable to the terminal voltage of the first battery acquired over the time period T, and the second value as the statistical mean or average value of voltage values attributable to the terminal voltage of the second battery acquired over the same time period T.