Cell Monitoring And Balancing

Abstract

A method for monitoring the voltage of each of a plurality of cells of a battery pack is provided. The method may include monitoring a voltage potential for each of a plurality of cells in a battery pack utilizing a single channel of battery control unit within the battery pack. If, during discharge of the battery, e.g., the battery is being used to power a hand tool, the voltage potential of any cell is determined by the battery control unit to be below a predetermined minimum voltage, the battery control unit discontinues a current flow from battery pack to the tool.

1 . A method for monitoring the voltage of each of a plurality of cells of a battery pack, said method comprising:
 sequentially sensing a node voltage at each of a plurality of nodes of a monitoring and balancing circuit, each node connecting one of the cells to a respective one of a plurality of monitoring and balancing (M&B) sub-circuits of the monitoring and balancing circuit;   receiving the node voltage from each of the M&B sub-circuits at a measurement node common to each of the M&B sub-circuits, where the common measurement node is coupled via a single analog to digital converter (ADC) to a single input channel of a battery control unit and a resistor is coupled between the measurement node and ground;   monitoring a voltage potential for each of the plurality of cells in a battery pack utilizing the a single channel of a battery control unit within the battery pack by receiving the node voltage signals from each of the M&B sub-circuits during a discharge mode, at a first sample rate, via a single discharge mode ADC coupled to a common measurement node, the discharge mode ADC interposed between the battery control unit and each of the M&B sub-circuits; and   receiving the node voltage signals from each of the M&B sub-circuits during a charge mode, at a second sample rate that is slower than the first sample rate, via a single charge mode analog to digital converter (ADC) coupled to a common measurement node, the charge mode ADC interposed between the battery control unit and each of the M&B sub-circuits;   discontinuing current flow from battery pack when the voltage potential of any cell is determined by the battery control unit to be below a predetermined minimum voltage during discharge of the battery pack; and   
       reducing the voltage potential stored in any one or more of the cells when a voltage differential between the respective one or more cells and any other one of the cells having a lesser voltage potential is determined by the battery control unit to exceed a predetermined maximum differential during charging of the battery pack. 
     
     
         2 . The method of  claim 1 , wherein reducing the voltage potential stored in any one or more of the cells comprises applying a shunt current to the one or more cells having the voltage differential with one of the cells having a lesser voltage potential that exceeds the maximum differential. 
     
     
         3 . The method of  claim 1 , wherein reducing the voltage potential stored in any one or more of the cells comprises substantially simultaneously reducing the voltage potential in two or more cells. 
     
     
         4 . The method of  claim 1 , wherein monitoring the voltage potential for each of the plurality of cells comprises varying a sample rate at which the voltage potentials of the cells are measured, based on a predetermined parameter of the cells during discharge of the battery pack. 
     
     
         5 . The method of  claim 4 , wherein the predetermined parameter comprises one of measured cell voltages, current draw on the battery pack and temperature of the cells. 
     
     
         6 . The method of  claim 4 , wherein varying the sample rate comprises determining which of an active discharge mode, a standby discharge mode and a hibernation discharge mode the battery pack is in. 
     
     
         7 . The method of  claim 6 , wherein varying the sample rate comprises:
 sampling the cell voltages at a constant sample rate when the battery pack is in the active discharge mode;   sampling the cell voltages at a varying rate, based on the predetermined parameter of the cells during discharge of the battery pack, when the battery pack is in the standby mode; and   ceasing to sample the cell voltages when the battery pack is in the hibernation mode.   
     
     
         8 . The method of  claim 7 , wherein sampling the cell voltages at a varying rate comprises increasing the rate at which the cell voltages are sampled as the measured cell voltages decrease in value. 
     
     
         9 . The method of  claim 7 , wherein sampling the cell voltages at a varying rate comprises:
 measuring the cell voltage potentials and determining an average voltage potential of the cells;   executing a variable sample rate algorithm, using the average voltage potential as a variable of the algorithm, to determine a delay time before the cell voltages are measured again; and   subsequently measuring the cell voltages to determine a subsequent average voltage potential after the delay time has expired.   
     
     
         10 . The method of  claim 9 , wherein executing the variable sample rate algorithm comprises at least one of:
 accessing one or more look-up tables to determine the delay time based on the average voltage potential;   applying one or more conditional predetermined thresholds to determine the delay time based on the average voltage potential; and   implementing a mathematical equation to determine the delay time based on the average voltage potential.   
     
     
         11 . The method of  claim 6 , wherein varying the sample rate further comprises:
 sampling the cell voltages a constant first sample rate when the battery pack is determined to be in the active discharge mode;   sampling the cell voltages a constant second sample rate when the battery pack is determined to be in the standby discharge mode, the second sample rate being slower than the first sample rate; and   ceasing to sample the cell voltages when the battery pack is in the hibernation mode.   
     
     
         12 . The method of  claim 1  further comprising reducing the voltage potential stored in any one or more of the cells when the voltage potential of the respective one or more cells is determined by the battery control unit to be above a predetermined maximum voltage during charging of the battery pack. 
     
     
         13 . The method of  claim 12 , wherein reducing the voltage potential comprises applying a shunt current to the respective one or more cells to discharge a desired amount of voltage from the respective one or more cells. 
     
     
         14 . The method of  claim 13 , wherein reducing the voltage potential further comprises substantially simultaneously discharging the desired amount of voltage from the respective one or more cells. 
     
     
         15 . The method of  claim 1 , wherein monitoring the voltage potential for each of the plurality of cells further comprises calculating the voltage potential for each cell by sequentially subtracting from the node voltage of each respective cell from the node voltage of the previously sensed cell. 
     
     
         16 . The method of  claim 1  further comprises coupling at least one resistor, capacitor or combination thereof to the common measurement node.