Patent ID: 8521459

Claim:
A capacitor's remaining lifetime diagnosing device for diagnosing the remaining lifetime of an electric accumulator comprising an electric double layer capacitor, which is provided in an electric power compensating device, the capacitor's remaining lifetime diagnosing device comprising: temperature measuring means adapted to measure the temperature of the electric accumulator, voltage measuring means adapted to measure the DC voltage of the electric accumulator, current measuring means adapted to measure DC current outputted by the electric accumulator; capacitance computing means adapted to compute the capacitance of the electric accumulator, which is obtained when the electric accumulator is in a discharging state, based on the measured voltage measured by the voltage measuring means and the measured current measured by the current measuring means, when the electric accumulator is in the discharging state; internal resistance computing means adapted to compute the internal resistance of the electric accumulator, which is obtained when the electric accumulator is in the discharging state, based on the measured voltage measured by the voltage measuring means and the measured current measured by the current measuring means, when the electric accumulator is in the discharging state; discharge time period computing means adapted to compute a discharge time period for which the electric accumulator can discharge while outputting a rated electric power, when the electric accumulator is in the discharging state, based on the capacitance obtained by the capacitance computing means and the internal resistance obtained by the internal resistance computing means; and remaining lifetime computing means adapted to compute a remaining lifetime indicating how much time is left from a time point at which the electric accumulator is put into the discharging state to a time point at which the discharge time period of the electric accumulator becomes less than a rated compensation time period required as a time period for which the electric power compensating device has to output the rated electric power, based on the discharge time period obtained by the discharge time period computing means, the measured temperature obtained by the temperature measuring means, and a prestored remaining lifetime characteristic.