Patent ID: 8269469

Claim:
An ultracapacitor charging method for charging a series connected string of ultracapacitor cells having a plurality of balancing circuits, said method comprising the steps of: a. specifying a voltage balance hysteresis as variable V_BAL_HYST; b. charging said string of ultracapacitor cells; c. turning all balancing circuits off; d. measuring the voltage of each ultracapacitor cell to determine the smallest measured cell voltage; e. storing said smallest measured cell voltage as variable V min in a digital controller; and f. for each ultracapacitor cell in the series connected string iteratively performing the following steps by said digital controller: i) measuring the voltage of the ultracapacitor cell to set Vcell; ii) computing the difference of Vcell and V min ; iii) comparing difference of Vcell and V min to V_BAL_HYST, wherein if the difference of Vcell and V min >V_BAL_HYST, then turning on the balancing circuit for the cell, draining current from the cell.