Cell balancing battery pack and method of balancing the cells of a battery

• US 7,598,706 B2
• Filed: 01/26/2007
• Issued: 10/06/2009
• Est. Priority Date: 01/26/2007
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lindquist, Paul Daniel, Koski, Roy Donald
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): Fantu; Yalkew
• Application Number:
  US11/627,562
• Publication Number:
  US 20080180061A1
• Time in Patent Office: 984 Days
• Field of Search: 320/117, 320/116, 320/122, 320/128
• US Class Current: 320/117
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0024 Parallel/serial switching of connection of batteries to charge or load circuit
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery with a battery balancing assembly that regulates the discharge of battery cell charge and a method of evenly discharging battery cells, the battery comprising a plurality of cells. The balancing assembly includes switches disposed between the cells such that the switches may configure the cells in a normal configuration and a balance configuration, wherein in the normal configuration the plurality of cells may be connected to an electronic device and wherein in the balance configuration the plurality of cells are connected to a balancing circuit. The balancing circuit serving to balance the charge in the plurality of cells prior to the recharging of the cell.

Claims

1. A method of evenly discharging a plurality of electrical cells configured to provide electrical power as a battery, the method comprising:

connecting the plurality of electrical cells to a balancing circuit, the balancing circuit comprising a programmable load, the programmable load drawing a current;

operating the programmable load to draw a constant current;

monitoring the voltage across each of the plurality of electrical cells;

upon the monitored voltage across one of the electrical cells falling below a predetermined threshold, operating the programmable load to draw a minimum recommended discharge voltage from the plurality of electrical cells;

increasing the resistance of the programmable load with respect to a change in the current to maintain the minimum recommended discharge voltage across each cell;

monitoring the current drawn from the plurality of electrical cells; and

discharging the cells until the current drawn from cells is tapered below a predetermined threshold current.

2. The method of claim 1 wherein discharging the cells forces a balance in the voltage, state of charge, and remaining capacity at the point of chemical discharge for the cells.

3. The method of claim 1, further comprising:

monitoring the level of charge in each of the plurality of electrical cells; and

upon sensing that the charge of one of the plurality of electrical cells is below a predetermined threshold, discharging the plurality of electrical cells.

17. The method of claim 1, further comprising recharging the plurality of electrical cells after the cells are discharged.

18. The method of claim 1, further comprising connecting the plurality of electrical cells in parallel to each other and to the balancing circuit.

19. The method of claim 18, wherein the plurality of electrical cells of the battery are connected in series during operative use of the battery and before discharging, the connections between the electrical cells must be switched from series to parallel connections.

20. The method of claim 3, further comprising:

monitoring the level of charge across the battery; and

upon sensing that the charge across the battery is below a predetermined minimum battery charge, discharging the plurality of electrical cells.

4. A rechargeable battery for providing charge to an electronic device, comprising:

a first cell storing an electric charge in an amount between a charged capacity and a depleted capacity;

a second cell connected in parallel to the first cell, the second cell storing an electric charge in an amount between a charged capacity and a depleted capacity;

a variable resistance discharge load connected in parallel to the first cell and the second cell, the variable resistance discharge load drawing a constant current from the first and second cells until the first cell reaches a predetermined minimum cell voltage, upon when the resistance of the discharge load varies to constantly draw the predetermined minimum cell voltage from the cells until the current drawn from the cells reaches a predetermined minimum current.

5. The rechargeable battery of claim 4 further comprising a plurality of switches connected between the first cell, second cell, discharge load and the electronic device, wherein the switches are operated in a first configuration to provide charge from the first cell and the second cell to the electronic device and to disconnect the first cell and the second cell from the discharge load and the plurality of switches are operated in a second configuration to connect the first cell and the second cell to the discharge load, while disconnecting the first cell and the second cell from the electronic device.

6. The rechargeable battery of claim 5, further comprising:

a first voltage monitor monitoring the voltage across the first cell; and

a second voltage monitor monitoring the voltage across the second cell.

7. The rechargeable battery of claim 6, further comprising a controller connected to the first voltage monitor, the second voltage monitor, and the plurality of switches, the controller operating the switches in the first configuration to provide electrical charge to the electronic device, and wherein when a voltage from the first or second voltage monitor falls below a predetermined threshold, the controller operates the switches in the second configuration to connect the first and second cells to the discharge load.

8. The rechargeable battery of claim 7 wherein when the controller is operating the plurality of switches in the first configuration the controller further monitors the total voltage of the first cell and the second cell, the controller operating the plurality of switches in the second configuration if the total voltage falls below a predetermined minimum total voltage threshold.

9. The rechargeable battery of claim 5 further comprising a controller that controls the plurality of switches between the first configuration and the second configuration.

10. The rechargeable battery of claim 4, wherein the variable resistance discharge load is a constant-current, constant-voltage discharge load.

11. The rechargeable battery of claim 4, wherein the first cell and the second cell are lithium ion cells.

12. The rechargeable battery of claim 4, wherein the electronic device is a medical device.

13. An assembly for regulating the discharge of a plurality of cells within a battery, the plurality of cells having unbalanced cell charges, the assembly comprising:

a balancing circuit, comprising a programmable discharge load and selectively connected to the battery, the balancing circuit, when connected to the battery, balances the charges in the plurality of cells by first operating the programmable discharge load to draw a constant current out of the battery and then operating the programmable discharge load to draw a constant voltage from the battery until the plurality of cells are evenly discharged; and

a plurality of switches between the plurality of cells and the balancing circuit, each of the switches being positionable in a closed state whereby electrical current is allowed to pass and an open state whereby no electrical current is allowed to pass, the plurality of switches having a normal configuration wherein the plurality of switches connect the plurality of cells in series and a balance configuration wherein the plurality of switches connect the plurality of cells in parallel to the balancing circuitry.

14. The assembly of claim 13, further comprising a controller connected to the plurality of switches, the controller operating the switches in the normal configuration to provide electrical charge to an electronic device connected to the plurality of switches, and wherein when a voltage across one of the plurality of cells falls below a predetermined threshold, the controller operates the switches in the balance configuration to connect the plurality of cells to the discharge load.

15. The assembly of claim 14, wherein when the controller is operating the plurality of switches in the first configuration the controller further monitors the total voltage of the battery, the controller operating the plurality of switches in the second configuration if the total voltage of the battery falls below a predetermined threshold.

16. The assembly of claim 13, wherein the controller is further connected to the balancing circuit and when the controller operates the switches in the balance configuration, the controller operates the balancing circuit to first draw a constant current out of the battery while monitoring the voltage across each of the plurality of cells, and when one of the monitored cell voltages falls below a predetermined threshold, the controller operates the balancing circuit to draw a constant voltage at the predetermined voltage from the battery, until the plurality of cells are evenly discharged.