Battery state of charge indicator

Claim 1

A device (1) for indicating changes in the state of charge of a rechargeable battery (2) comprising a current sensor (6) to sense current flow into and out of the battery (2) and to provide an output indicative of both the magnitude and direction of the current flow, timing means (11) to provide a timing signal, a computer (10) programmed to compute from the output of the current sensor (6) and the timing means (11), a signal representative of the charge dissipated from or accumulated in the battery (2) over a period of time, and data storage means (12) to store an indication of the state of charge of the battery (2), the computer (10) being programmed to use the signal representative of the charge dissipated from, or accumulated in, the battery (2) over the period of time to update the stored data on the state of charge of the battery (2) to provide an indication of the current state of charge of the battery (2), characterised by a voltage sensor (7) for sensing the potential difference subsisting across the terminals of the battery (2), in that the computer (10) is programmed to monitor an output signal of the voltage sensor (7) and, when the monitored voltage reaches a predetermined maximum or minimum value, to reset the data storage means (12) to indicate that the battery (2) is fully charged or fully discharged, respectively, and in that the computer (10) is programmed to compare the state of charge indication immediately before it is reset with the state of charge indicated by the voltage sensor (7) when the indication is reset, either when the battery (2) is fully discharged or when the battery (2) is fully charged, and to use the results of this comparison to vary automatically stored information concerning particular parameters of the battery (2) such as the conversion efficiency to tailor these parameters to the condition of the particular battery (2) connected to the device (1).

Claim 2

A device (1) for indicating changes in the state of charge of a rechargeable battery (2) comprising a current sensor (6) to sense current flow into and out of the battery (2) and to provide an output indicative of both the magnitude and direction of the current flow, timing means (11) to provide a timing signal, a computer (10) programmed to compute from the output of the current sensor (6) and the timing means (11), a signal representative of the charge dissipated from or accumulated in the battery (2) over a period of time, and data storage means (12) to store an indication of the state of charge of the battery (2), the computer (10) being programmed to use the signal representative of the charge dissipated from, or accumulated in, the battery (2) over the period of time to update the stored data on the state of charge of the battery (2) to provide an indication of the current state of charge of the battery (2), characterised by a voltage sensor (7) for sensing the potential difference subsisting across the terminals of the battery (2), in that the computer (10) is programmed to monitor an output signal of the voltage sensor (7) and, when the monitored voltage reaches a predetermined maximum or minimum value, to reset the data storage means (12) to indicate that the battery (2) is fully charged or fully discharged, respectively, and in that the computer (10) is programmed to compare the state of charge indication immediately before it is reset with the state of charge indicated by the voltage sensor (7) when the indication is reset, either when the battery (2) is fully discharged or when the battery (2) is fully charged, and to use the results of this comparison to vary automatically stored information concerning particular parameters of the battery (2) such as the conversion efficiency to tailor these parameters to the condition of the particular battery (2) connected to the device (1).

Claim 4

A device according to any one of the preceding claims, characterised by the computer (10) being programmed to take account of the conversion efficiency of the battery (2) by applying a correction factor to both the monitored charge accumulated in the battery (2) and the monitored charge dissipated from the battery (2).