Method and system for battery protection

Abstract

An electrical combination. The combination comprises a hand held power tool, a battery pack and a controller. The battery pack includes a battery pack housing connectable to and supportable by the hand held power tool, a plurality of battery cells supported by the battery pack housing, each of the plurality of battery cells having a lithium-based chemistry, being individually tapped and having an individual state of charge. A communication path is provided by a battery pack sense terminal and a power tool sense terminal. The controller is operable to monitor a state of charge of a number of battery cells less than the plurality of battery cells and to generate a signal based on the monitored state of charge of the number of battery cells less than the plurality of battery cells, the signal being operable to control the operation of the hand held power tool.

What is claimed is: 
     
         1 . A method of operating an electrical combination, the electrical combination including a battery pack configured to supply power to a cordless power tool having a motor, the method comprising:
 monitoring, with a controller, a respective battery cell state of charge of a plurality of battery cells included in the battery pack, the plurality of battery cells operable to supply a battery pack discharge current to the motor of the cordless power tool, each of the battery cells being individually tapped, the battery pack including:
 a terminal configured to provide a communication path between the battery pack and the cordless power tool, and 
 a battery pack housing connectable to and supportable by the cordless power tool; 
   controlling, with the controller and by communicating a signal via the terminal, a switch to be in a conducting state to enable the supply of discharge current from the battery pack to the motor, the controller being electrically connected to the switch; and   modifying operation of the battery pack, with the controller, by causing the switch to move from the conducting state to a non-conducting state to interrupt the supply of discharge current from the battery pack to the motor when the monitored respective battery cell state of charge of one of the battery cells reaches a predetermined threshold.   
     
     
         2 . The method as set forth in  claim 1 , wherein modifying operation of the battery pack includes varying the discharge current being supplied to the motor of the cordless power tool over a time period. 
     
     
         3 . The method as set forth in  claim 1 , wherein modifying operation of the battery pack includes decreasing the discharge current being supplied to the motor of the cordless power tool over a time period. 
     
     
         4 . The method as set forth in  claim 1 , wherein modifying operation of the battery pack includes interrupting the discharge current being supplied to the motor of the cordless power tool such that substantially no discharge current is supplied to the motor of the cordless power tool for a time period. 
     
     
         5 . The method as set forth in  claim 1 , further comprising:
 further modifying operation of the battery pack, with the controller, when the monitored respective battery cell state of charge of one of the battery cells reaches a second predetermined threshold, the second predetermined threshold being different than the predetermined threshold.   
     
     
         6 . The method as set forth in  claim 5 , wherein the second predetermined threshold is greater than the predetermined threshold. 
     
     
         7 . The method as set forth in  claim 5 , wherein further modifying operation of the battery pack includes causing the switch to change from the non-conducting state to the conducting state to conduct the discharge current when the monitored respective battery cell state of charge of one of the battery cells reaches the second predetermined threshold. 
     
     
         8 . The method as set forth in  claim 5 , wherein each of the battery cells has a battery cell chemistry that is Lithium-based. 
     
     
         9 . The method as set forth in  claim 1 , wherein the controller is located within the battery pack housing. 
     
     
         10 . The method as set forth in  claim 1 , wherein the switch is located within the battery pack housing. 
     
     
         11 . A battery pack comprising:
 a battery pack housing connectable to and supportable by a hand held power tool;   a plurality of battery cells supported by the battery pack housing, each of the plurality of battery cells being individually tapped and having an individual state of charge, the plurality of battery cells including:
 a cylindrical first battery cell within the battery pack housing and defining a first axis, and 
 a cylindrical second battery cell within the battery pack housing and defining a second axis, 
 wherein the first battery cell and the second battery cell are arranged with the first axis substantially perpendicular to the second axis; and 
   a plurality of battery pack terminals to electrically connect to a plurality of power tool terminals; and   a controller operable to monitor a state of charge of a number of battery cells less than the plurality of battery cells and to generate a signal based on the monitored state of charge of the number of battery cells less than the plurality of battery cells, the signal being operable to control operation of the hand held power tool.   
     
     
         12 . The battery pack of  claim 11 , further comprising a switch operable to control operation of the hand held power tool, the signal being operable to control the switch to control operation of the hand held power tool. 
     
     
         13 . The battery pack of  claim 11 , wherein the state of charge of a number of battery cells less than the plurality of battery cells includes an individual state of charge of one of the plurality of battery cells. 
     
     
         14 . The battery pack of  claim 13 , wherein the controller is operable to monitor the individual state of charge of each of the plurality of battery cells. 
     
     
         15 . The battery pack of  claim 14 , wherein the controller is operable to communicate the signal based on the individual state of charge of each of the plurality of battery cells. 
     
     
         16 . An electrical combination comprising:
 a hand held power tool including:
 a power tool housing, 
 a motor supported by the power tool housing, and 
 a plurality of power tool terminals electrically connected to the motor; 
   a battery pack including:
 a battery pack housing connectable to and supportable by the hand held power tool, 
 a plurality of battery cells supported by the battery pack housing, each of the plurality of battery cells being individually tapped and having an individual state of charge, the plurality of battery cells including:
 a cylindrical first battery cell within the battery pack housing and defining a first axis, and 
 a cylindrical second battery cell within the battery pack housing and defining a second axis, 
 wherein the first battery cell and the second battery cell are arranged with the first axis substantially perpendicular to the second axis, and 
 
 a plurality of battery pack terminals to electrically connect to the plurality of power tool terminals; and 
   a controller operable to monitor a state of charge of a number of battery cells less than the plurality of battery cells and to generate a signal based on the monitored state of charge of the number of battery cells less than the plurality of battery cells, the signal being operable to control operation of the hand held power tool.   
     
     
         17 . The electrical combination of  claim 16 , further comprising a switch operable to control operation of the hand held power tool, the signal being operable to control the switch to control operation of the hand held power tool. 
     
     
         18 . The electrical combination of  claim 17 , wherein the controller is supported in the battery pack housing. 
     
     
         19 . The electrical combination of  claim 18 , wherein the switch is supported in the battery pack housing. 
     
     
         20 . The electrical combination of  claim 16 , wherein the controller is supported in the power tool housing.