BOTTOM BASED BALANCING IN LITHIUM ION SYSTEM

• US 20090096419A1
• Filed: 10/14/2008
• Published: 04/16/2009
• Est. Priority Date: 10/15/2007
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Matson, Lyle, White, Daniel J., Cruise, Nathan
• Granted Patent: US 9,136,716 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 2010/4271 Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H01M 2200/00 Safety devices for primary or secondary batteries
• CPC Class Codes: H01M 2220/30 Batteries in portable systems, e.g. mobile phone, laptop
• CPC Class Codes: H01M 50/543 Terminals
• CPC Class Codes: H01M 50/574 Devices or arrangements for the interruption of current
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0045 concerning the insertion or the connection of the batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A method comprises discharging each of a plurality of cells of a battery pack, stopping the discharging of a selected cell of the plurality of cells when the selected cell reaches a predetermined capacity, and charging the plurality of cells after the discharging has stopped for all of the plurality of cells.

Claims

1. A method comprising:

discharging each of a plurality of cells of a battery pack;

stopping the discharging of a selected cell of the plurality of cells when the selected cell reaches a predetermined capacity; and

charging the plurality of cells after the discharging has stopped for all of the plurality of cells.

2. The method of claim 1 further comprising:

measuring a voltage of each of the plurality of cells; and

determining that the selected cell has reached the predetermined capacity when the measured voltage of the selected cell is less than a threshold voltage.

3. The method of claim 1 wherein the charging is performed uniformly and simultaneously across the plurality of cells.

4. The method of claim 1 further comprising stopping charging the plurality of cells when any one of the plurality of cells reaches a predetermined maximum capacity.

5. The method of claim 4 further comprising:

measuring a voltage of each of the plurality of cells; and

determining that the one of the plurality of cells has reached the predetermined maximum capacity when the measured voltage of the one of the plurality of cells is greater than a threshold voltage.

6. The method of claim 1 further comprising:

selectively applying a first load to a first cell of the plurality of cells;

applying a second load to the first cell after applying the first load to the first cell; and

stopping discharging the first cell after applying the second load to the first cell.

7. The method of claim 6 further comprising:

measuring a voltage of each of the plurality of cells;

applying the second load to the first cell after the measured voltage corresponding to the first cell is less than a first threshold voltage; and

stopping discharging the first cell after the measured voltage corresponding to the first cell is less than a second threshold voltage.

8. The method of claim 7 wherein the first and second threshold voltages are approximately equal.

9. The method of claim 6 wherein the second load draws less current than the first load.

10. A battery charger comprising:

a discharging device that discharges each of a plurality of cells of a battery pack;

a charging device that charges the plurality of cells; and

a control module that selectively instructs the discharging device to discharge the plurality of cells, that selectively instructs the discharging device to stop discharging a selected cell of the plurality of cells when the selected cell reaches a predetermined capacity, and that selectively instructs the charging device to begin charging the plurality of cells after discharging is stopped for all the plurality of cells.

11. The battery charger of claim 10 further comprising a measurement device that measures a voltage of each of the plurality of cells, wherein the control module determines that the selected cell has reached the predetermined capacity when the measured voltage of the selected cell is less than a threshold voltage.

12. The battery charger of claim 10 wherein the charging device charges the plurality of cells simultaneously.

13. The battery charger of claim 10 wherein the control module instructs the charging device to stop charging the plurality of cells when any one of the plurality of cells reaches a predetermined maximum capacity.

14. The battery charger of claim 13 further comprising a measurement device that measures a voltage of each of the plurality of cells, wherein the control module determines that the one of the plurality of cells has reached the predetermined maximum capacity when the measured voltage of the one of the plurality of cells is greater than a threshold voltage.

15. The battery charger of claim 10 wherein the discharging device includes first loads that are selectively applied to the plurality of cells and second loads that are selectively applied to the plurality of cells, wherein the discharging device applies one of the second loads to a first cell of the plurality of cells after applying one of the first loads to the first cell, and wherein the discharging device stops discharging the first cell after applying the one of the second loads to the first cell.

16. The battery charger of claim 15 further comprising a measurement device that measures a voltage of each of the plurality of cells, wherein the discharging device applies the one of the second loads to the first cell after the measured voltage corresponding to the first cell is less than a first threshold voltage, and wherein the discharging device stops discharging the first cell after the measured voltage corresponding to the first cell is less than a second threshold voltage.

17. The battery charger of claim 16 wherein the first and second threshold voltages are approximately equal.

18. The battery charger of claim 15 wherein the second loads draw less current than the first loads.

19. A battery system comprising:

the battery charger of claim 10; and

a battery having N cells and an external electrical contact for each of the N cells.

20. A power tool system comprising:

the battery system of claim 19; and

a power tool that receives the battery.

21. A battery system comprising:

a battery comprising;

N cells arranged in series and each having a positive terminal and a negative terminal; and

N+1 external electrical contacts corresponding to the positive terminals of each of the N cells and the negative terminal of one of the N cells, respectively; and

a battery charger comprising;

a plurality of terminals that electrically connect to the N+1 external electrical contacts of the battery;

a capacity determination device that determines a capacity for each of the N cells; and

N discharge devices that are selectively applied to each of the N cells respectively via the plurality of terminals.

22. The battery system of claim 21 wherein the battery further comprises a charging protection device that stops conducting when a current through the charging protection device exceeds a first threshold, wherein the charging protection device is connected between one of the N+1 external electrical contacts and one of the positive terminal and the negative terminal of one of the N cells.

23. The battery system of claim 22 wherein the battery further comprises:

an additional external electrical contact for connection to a tool; and

a short-circuit protection device that stops conducting when a current through the short-circuit protection device exceeds a second threshold, wherein the short-circuit protection device is connected between the additional external electrical contact and the one of the positive terminal and the negative terminal of the one of the N cells.

24. The battery system of claim 23 wherein the first threshold is greater than the second threshold.

25. The battery system of claim 21 wherein the battery further comprises a temperature measurement device that measures a temperature of the battery.

26. The battery system of claim 21 wherein the N discharge devices each selectively apply a first load at a first time and a second load at a second time.

27. The battery system of claim 21 wherein the capacity determination device comprises:

a measurement device; and

a multiplexer that selectively connects two of the plurality of terminals to the measurement device.

28. The battery system of claim 27 wherein the measurement device comprises:

a voltage measurement device; and

an analog-to-digital converter that converts a voltage measured by the voltage measurement device to a digital value.

29. The battery system of claim 27 wherein the battery charger further comprises a balancing capacitor that is selectively connected to an output of the multiplexer.