System and method for battery cell balancing

1. A system for balanced charging of multiple series-connected battery cells, the system comprising:

resistors being selectably electrically coupled in parallel with respective battery cells, among the multiple series-connected battery cells, through activation and deactivation of respective switches; and

a control unit configured to determine a battery cell having a lowest voltage among the multiple series-connected battery cells, resulting in a determined lowest battery cell, and configured to activate and deactivate each of the respective switches as a function of a respective difference in voltage between the lowest voltage of the determined lowest battery cell and a respective voltage of each respective battery cell to provide balanced charging of the multiple series-connected battery cells during a charging process, the control unit further configured to activate or deactivate the respective switches by setting a number of balancing bits all at once based on each respective difference in voltage between the lowest voltage of the determined lowest battery cell and each respective voltage of each respective battery cell, the control unit still further configured to activate a respective switch of the respective switches in an event the respective difference in voltage between the lowest voltage of the determined lowest battery cell and the respective voltage of the respective battery cell exceeds a threshold value, wherein the threshold value is a larger threshold value at a beginning of the charging process and a smaller threshold value as cell voltages increase.

2. A system as in claim 1 wherein the control unit is configured to adjust the threshold value based on trends of voltage differences over time.

3. A system as in claim 1 wherein the control unit is configured to adjust the threshold value based on the voltage of the determined lowest battery cell.

4. A system as in claim 1 wherein the control unit is configured to determine the lowest battery cell and update the activation states of the switches according to a time interval.

5. A system as in claim 4 wherein the control unit is further configured to adjust the time interval dynamically based on trends of voltage differences over time.

6. A system as in claim 1 wherein the control unit is configured to disable charging of the battery cells in an event one of the battery cells reaches a first maximum voltage limit or in an event a total voltage of all the battery cells reaches a second maximum voltage limit.

7. A system as in claim 1 further including a temperature sensor coupled to the control unit and configured to disable charging of the battery cells in an event the temperature of at least one of the battery cells or the ambient temperature around the battery cells exceeds a temperature limit.

8. A system as in claim 1 wherein the control unit is configured to disable charging of the battery cells during active use of the battery cells.

9. A system as in claim 1 wherein the control unit is active during a portion of charging of the battery cells.

10. A system as in claim 1 wherein the control unit includes an analog-to-digital converter, processor, and addressing logic.

11. A method of balanced charging of multiple series-connected battery cells, the method comprising:

selectively electrically coupling resistors in parallel with respective battery cells, among the multiple series-connected battery cells, using respective switches;

determining a battery cell having a lowest voltage among the multiple series-connected battery cells, resulting in a determined lowest battery cell;

determining a respective difference in voltage between the lowest voltage of the determined lowest battery cell and a respective voltage of each respective battery cell; and

activating and deactivating the respective switches as a function of each respective difference in voltage to provide balanced charging of the multiple series-connected battery cells during a charging process, wherein activating and deactivating the respective switches includes:

activating or deactivating each of the respective switches by setting a number of balancing bits all at once based on each respective difference in voltage between the lowest voltage of the determined lowest battery cell and each respective voltage of each respective battery cell; and

activating a respective switch of the respective switches in an event the respective difference in voltage between the lowest voltage of the determined lowest battery cell and the respective voltage of the respective battery cell exceeds a threshold value, wherein the threshold value is a larger threshold value at a beginning of the charging process and a smaller threshold value as cell voltages increase.

12. A method as in claim 11 further including adjusting the threshold value based on trends of voltage differences over time.

13. A method as in claim 11 further including adjusting the threshold value based on the voltage of the determined lowest battery cell.

14. A method as in claim 11 wherein determining the lowest battery cell, determining the respective differences in voltage, and activating and deactivating the switches occur according to a time interval.

15. A method as in claim 14 further including dynamically adjusting the time interval based on trends of voltage differences over time.

16. A method as in claim 11 further including disabling charging of the battery cells in an event one of the battery cells reaches a first maximum voltage limit or in an event a total voltage of all the battery cells reaches a second maximum voltage limit.

17. A method as in claim 11 further including:

measuring a temperature of at least one of the battery cells or the ambient temperature around the battery cells; and

disabling charging of the battery cells in an event the temperature of at least one of the battery cells or the ambient temperature around the battery cells exceeds a temperature limit.

18. A method as in claim 11 further including disabling charging of the battery cells during active use of the battery cells.

19. A system for balanced charging of multiple series-connected battery cells, the system comprising:

means for selectably electrically coupling resistors in parallel to respective battery cells;

means for determining a battery cell having a lowest voltage among the multiple series-connected battery cells, resulting in a determined lowest battery cell;

means for determining respective voltage differences between the lowest voltage of the determined lowest battery cell and each respective voltage of each respective battery cell; and

means for adjusting currents applied to the battery cells all at once during charging as a function of the respective voltage differences determined and a threshold value to provide balanced charging of the multiple series-connected battery cells, wherein the threshold value is a larger threshold value at a beginning of the charging process and a smaller threshold value as cell voltages increase.

20. A system as in claim 1 wherein the number of balancing bits are set all at once in a register to turn on or off respective balancing circuits reducing impact from a surge reading due to sudden changes in current.