Patent ID: 7659692
Filing Date: 2010-02-09
Classification: H02J

Abstract:
1. A rechargeable battery pack for a power tool, said battery pack comprising: a battery stack composed of a plurality of series connected secondary cells; a pair of power output terminals connected across said battery stack to supply a current from said battery stack for operating said power tool; a signal connector configured to include a charge control terminal, a discharge control terminal, and a signal ground terminal connected to a circuit ground, a charge detector configured to monitor a cell voltage appearing across each of said secondary cells and to provide a high charge-control signal when all of the cell voltages are lower than a first threshold (V a discharge detector configured to monitor said cell voltage across each of said secondary cells and to provide a discharge stop signal when any one of said cell voltages becomes lower than a second threshold (V a charge terminal configured to be separated from one of said power output terminals and connected to said battery stack for flowing said charge current from said charger to said secondary cells not through said one of said power output terminals; an interrupter inserted in a charge current path between said charge terminal and said battery stack; and an over-charge detector configured to monitor said cell voltage across each of said secondary cells and to actuate said interrupter to open said charge current path when any one of said cell voltages becomes higher than a third threshold (V wherein said interrupter is a non-resettable element, and wherein said discharge detector comprises a voltage monitor and a power controller, said voltage monitor comprising a plurality of comparators and a plurality of constant voltage elements each providing a constant voltage which defines said second threshold (V