Battery gas gauge

• US 20050231206A1
• Filed: 06/28/2004
• Published: 10/20/2005
• Est. Priority Date: 04/16/2004
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Denning, Bruce S.
• Granted Patent: US 7,095,211 B2
• Time in Patent Office: Days
• US Class Current: 324/430
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm

Abstract

Full capacity determination in a battery gas gauge. Operations include measuring instantaneous open circuit voltage levels during an open circuit time interval for a specific battery cell and correlating such measurements to estimate values. Such estimated values may then be correlated to associated relative state of charge levels. Finally, a full capacity calculation can be made based on the associated relative state of charge levels. A plurality of full capacity determinations may also be made and compared to each other to assess the reliability of such determinations.

Claims

1. A method comprising:

opening a battery cell circuit during a first and second time interval, said battery cell circuit comprising a battery cell;

measuring a first instantaneous open circuit voltage level of said battery cell during said first time interval and a second instantaneous open circuit voltage level of said battery cell during said second time interval;

correlating said first instantaneous open circuit voltage level to a first estimated value and said second instantaneous open circuit voltage level to a second estimated value;

correlating said first estimated value to a first relative state of charge level of said battery cell and said second estimated value to a second relative state of charge level of said battery cell; and

calculating a first full capacity level of said battery cell in response to a difference between said first and second relative state of charge levels.

2. The method of claim 1, wherein said opening of said battery cell during said first and second time intervals comprises interrupting charging of said battery cell during a charging mode, and said method further comprises updating said first and second estimated values in response to a charging current level before said interrupting of said charging of said battery cell.

3. The method of claim 1, wherein said first time interval is associated with a first capacity level of said battery cell and said second time interval is associated with a second capacity level of said battery cell, and wherein said calculating operation comprises dividing a difference between said first and second capacity levels by said difference between said first and second relative state of charge levels to obtain said first full capacity level.

4. The method of claim 3, further comprising storing said first and second estimated values and said first and second relative state of charge levels, and updating said first and second estimated values and said first and second relative state of charge levels in response to additional openings of said battery cell circuit at additional time intervals associated with said first and second capacity levels.

5. The method of claim 1, further comprising:

opening said battery cell circuit during a third time interval;

measuring a third instantaneous open circuit voltage level of said battery cell during said third time interval;

correlating said third instantaneous open circuit voltage level to a third estimated value;

correlating said third estimated value to a third relative state of charge level of said battery cell; and

calculating a second full capacity level of said battery cell in response to a difference between said second and third relative state of charge levels.

6. The method of claim 5, further comprising calculating a third full capacity level of said battery cell in response to a difference between said first and third relative state of charge levels, and comparing said first, second, and third full capacity levels to assess a reliability of each of said first, second, and third full capacity levels.

7. The method of claim 1, wherein said first estimated value is representative of a first theoretical open circuit voltage level and wherein said second estimated value is representative of a second theoretical open circuit voltage level.

8. An electronic device comprising:

a storage medium having stored therein instructions that when executed by a machine result in the following;

opening a battery cell circuit during a first and second time interval, said battery cell circuit comprising a battery cell;

measuring a first instantaneous open circuit voltage level of said battery cell during said first time interval and a second instantaneous open circuit voltage level of said battery cell during said second time interval;

correlating said first instantaneous open circuit voltage level to a first estimated value and said second instantaneous open circuit voltage level to a second estimated value;

correlating said first estimated value to a first relative state of charge level of said battery cell and said second estimated value to a second relative state of charge level of said battery cell; and

calculating a first full capacity level of said battery cell in response to a difference between said first and second relative state of charge levels.

9. The electronic device of claim 8, wherein said opening of said battery cell during said first and second time intervals comprises interrupting charging of said battery cell during a charging mode, and wherein said instructions that when executed by said machine also result in updating said first and second estimated values in response to a charging current level before said interrupting of said charging of said battery cell.

10. The electronic device of claim 8, wherein said first time interval is associated with a first capacity level of said battery cell and said second time interval is associated with a second capacity level of said battery cell, and wherein said calculating operation comprises dividing a difference between said first and second capacity levels by said difference between said first and second relative state of charge levels to obtain said first full capacity level.

11. The electronic device of claim 10, wherein said instructions that when executed by said machine also result in storing said first and second estimated values and said first and second relative state of charge levels, and updating said first and second estimated values and said first and second relative state of charge levels in response to additional openings of said battery cell circuit at additional time intervals associated with said first and second capacity levels.

12. The electronic device of claim 8, wherein said instructions that when executed by said machine also result in:

opening said battery cell circuit during a third time interval;

measuring a third instantaneous open circuit voltage level of said battery cell during said third time interval;

correlating said third instantaneous open circuit voltage level to a third estimated value;

correlating said third estimated value to a third relative state of charge level of said battery cell; and

calculating a second full capacity level of said battery cell in response to a difference between said second and third relative state of charge levels.

13. The electronic device of claim 12, wherein said instructions that when executed by said machine also result in calculating a third full capacity level of said battery cell in response to a difference between said first and third relative state of charge levels, and comparing said first, second, and third full capacity levels to assess a reliability of each of said first, second, and third full capacity levels.

14. The electronic device of claim of claim 8, wherein said first estimated value is representative of a first theoretical open circuit voltage level and wherein said second estimated value is representative of a second theoretical open circuit voltage level.

15. A battery gas gauge circuit comprising:

a switch network for coupling to a plurality of battery cells;

an analog to digital converter (ADC) coupled to said switch network, said ADC adapted to accept an analog signal from each of a plurality of battery cells via said switch network and convert each said analog signal to an associated digital signal; and

a processor capable of executing instructions stored in a storage medium to result in the following;

instructing said switch network to open a battery cell circuit comprising one of said plurality of battery cells during a first and second time interval;

instructing said switch network to couple terminals of said one of said plurality of battery cells to said ADC, said ADC adapted to provide said processor a first digital signal representative of a first instantaneous open circuit voltage level of said battery cell during said first time interval and a second digital signal representative of a second instantaneous open circuit voltage level of said battery cell during said second time interval;

correlating said first digital signal to a first estimated value and said second digital signal to a second estimated value;

correlating said first estimated value to a first relative state of charge level of said battery cell and said second estimated value to a second relative state of charge level of said battery cell; and

calculating a first full capacity level of said battery cell in response to a difference between said first and second relative state of charge levels.

16. The circuit of claim 15, wherein said first time interval is associated with a first capacity level of said battery cell and said second time interval is associated with a second capacity level of said battery cell, and Wherein said calculating operation comprises dividing a difference between said first and second capacity levels by said difference between said first and second relative state of charge levels to obtain said first full capacity level.

17. The circuit of claim 16, wherein said instructions that when executed by said machine also result in storing said first and second estimated values and said first and second relative state of charge levels, and updating said first and second estimated values and said first and second relative state of charge levels in response to additional openings of said battery cell circuit at additional time intervals associated with said first and second capacity levels.

18. The circuit of claim 15, wherein said wherein said instructions that when executed by said processor also result in:

opening said battery cell circuit during a third time interval;

measuring a third instantaneous open circuit voltage level of said battery cell during said third time interval;

correlating said third instantaneous open circuit voltage level to a third estimated value;

correlating said third estimated value to a third relative state of charge level of said battery cell; and

calculating a second full capacity level of said battery cell in response to a difference between said second and third relative state of charge levels.

19. The circuit of claim 18, wherein said instructions that when executed by said processor also result in calculating a third full capacity level of said battery cell in response to a difference between said first and third relative state of charge levels, and comparing said first, second, and third full capacity levels to assess a reliability of each of said first, second, and third full capacity levels.

20. The circuit of claim 15, wherein said first estimated value is representative of a first theoretical open circuit voltage level and wherein said second estimated value is representative of a second theoretical open circuit voltage level