Method and system for charging multi-cell lithium-based battery packs

Abstract

A method and system for charging multi-cell lithium-based batteries. In some aspects, a battery charger includes a housing, at least one terminal to electrically connect to a battery pack supported by the housing, and a controller operable to provide a charging current to the battery pack through the at least one terminal. The battery pack includes a plurality of lithium-based battery cells, with each battery cell of the plurality of battery cells having an individual state of charge. The controller is operable to control the charging current being supplied to the battery pack at least in part based on the individual state of charge of at least one battery cell.

What is claimed is: 
     
         1 . A battery charger, comprising:
 a housing;   at least two terminals including a power terminal and a sense terminal to electrically connect to a power tool battery pack supported by the housing, the power tool battery pack including a plurality of lithium-based battery cells, each battery cell of the plurality of battery cells having an individual state of charge; and   a controller operable to
 supply a charging current to the power tool battery pack through the power terminal, 
 receive an individual state of charge of at least one of the plurality of battery cells over the sense terminal, 
 control the charging current being supplied to the power tool battery pack based at least in part on a comparison of the individual state of charge of the at least one of the plurality of battery cells to at least one state of charge threshold value, wherein the at least one state of charge threshold value includes an average cell voltage of the plurality of battery cells, 
 control the charging current being supplied to the power tool battery pack by controlling the battery charger to supply the charging current in a plurality of pulses, the plurality of pulses each having a first period of time during which the charging current is being supplied to the power tool battery pack at a predefined amplitude, and a second period of time during which the supply of charging current is suspended, and 
 control the charging current being supplied to the power tool battery pack by modifying the first period of time based on the comparison and controlling the second period of time to be constant. 
   
     
     
         2 . The battery charger of  claim 1 , wherein the controller is operable to modify the first period of time by shortening the first period of time. 
     
     
         3 . The battery charger of  claim 1 , wherein the controller is operable to receive the individual state of charge of each battery cell of the plurality of battery cells over the sense terminal. 
     
     
         4 . The battery charger of  claim 1 , wherein the controller includes a first charging module and a second charging module, the first charging module operable to provide a first charging current to the power tool battery pack and the second charging module operable to provide a second charging current to the power tool battery pack. 
     
     
         5 . The battery charger of  claim 4 , wherein the first charging current and the second charging current differ in one of average current amplitude and duty-cycle. 
     
     
         6 . The battery charger of  claim 5 , wherein the first charging module includes a fast charge module. 
     
     
         7 . The battery charger of  claim 6 , wherein the fast charge module is operable to provide a fast charge current to the power tool battery pack. 
     
     
         8 . A method of operating a battery charger, the battery charger including a housing, a controller, at least two terminals including a power terminal and a sense terminal to electrically connect to a power tool battery pack supported by the housing, the power tool battery pack including a plurality of lithium-based battery cells, each battery cell of the plurality of battery cells having an individual state of charge, the method comprising:
 supplying a charging current to the power tool battery pack through the power terminal; receiving, by the controller, an individual state of charge of at least one of the plurality of battery cells over the sense terminal;   controlling, by the controller, the charging current being supplied to the power tool battery pack based at least in part on a comparison of the individual state of charge of the at least one of the plurality of battery cells to at least one state of charge threshold value, wherein the at least one state of charge threshold value includes an average cell voltage of the plurality of battery cells;   controlling, by the controller, the charging current being supplied to the power tool battery pack by controlling the battery charger to supply the charging current in a plurality of pulses, the plurality of pulses each having a first period of time during which the charging current is being supplied to the power tool battery pack at a predefined amplitude, and a second period of time during which the supply of charging current is suspended, and   controlling, by the controller, the charging current being supplied to the power tool battery pack by modifying the first period of time based on the comparison and controlling the second period of time to be constant.   
     
     
         9 . The method of  claim 8 , further comprising modifying, by the controller, the first period of time by shortening the first period of time. 
     
     
         10 . The method of  claim 8 , further comprising receiving, by the controller, the individual state of charge of each battery cell of the plurality of battery cells over the sense terminal. 
     
     
         11 . The method of  claim 8 , further comprising:
 implementing, by the controller, a first charging module operable to provide a first charging current to the power tool battery pack; and   implementing, by the controller, a second charging module operable to provide a second charging current to the power tool battery pack.   
     
     
         12 . The method of  claim 11 , wherein the first charging current and the second charging current differ in one of average current amplitude and duty-cycle. 
     
     
         13 . The method of  claim 12 , wherein the first charging module includes a fast charge module. 
     
     
         14 . The method of  claim 13 , wherein the fast charge module is operable to provide a fast charge current to the power tool battery pack.