Smart battery with maintenance and testing functions, communications, and display

• US 6,198,253 B1
• Filed: 12/23/1999
• Issued: 03/06/2001
• Est. Priority Date: 01/26/1998
• Status: Expired due to Term

• Current Assignee: Physio-Control Incorporated (Stryker Corporation)
• Original Assignee: Medtronic Physio-Control Manufacturing Corp. (Medtronic Plc)
• Inventors: Nordness, Rockland W., Firman, Stephen L., Choi, Peter Y., Gustavson, Douglas M., Kurle, Wayne D., Johnson, Stephen B.
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/471,695
• Time in Patent Office: 439 Days
• Field of Search: 320/127, 320/132, 320/134, 320/136, 320/149, 320/FOR.142, 320/FOR.147, 320/DIG.18, 320/DIG.21
• US Class Current: 320/132
• CPC Class Codes: A61N 1/3975 Power supply A61N1/378 takes precedence
• CPC Class Codes: H01M 10/4257 Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A smart battery that self-monitors and maintains information about itself that includes its state of charge, its need for maintenance, and for conditions that indicate that it has reached the end of its useful life and should be discarded. The information maintained by the battery is then either displayed on an on-board display or is communicated to another device on a communication bus. The state of charge quantifies the smart battery'"'"'s ability to reliably deliver charge to a host device and is dynamically adjusted over the lifetime of the smart battery. The state of charge may not exceed a full charge capacity value maintained by the smart battery and initially set to an estimated value. This full charge capacity value is dynamically adjusted throughout the life of the smart battery using information accumulated and maintained by the smart battery that indicates the smart battery'"'"'s actual performance during use and by using messages received from a battery maintenance and testing system. The smart battery also accumulates and maintains information that indicates that the smart battery requires maintenance. A battery maintenance and testing system can read this need for maintenance from the smart battery and take the steps necessary to automatically maintain the smart battery. Conditions that indicate that the battery is defective or has exceeded its useful life are also maintained by the smart battery and communicated through the on-board display or to another devices over a communication bus. The battery is specially configured for easy assembly.

Claims

1. A method for self monitoring a rechargeable battery'"'"'s ability to reliably deliver charge to a host device, the method comprising:

dynamically calculating a state of charge (SOC) that quantifies the ability of the rechargeable battery to deliver charge to a host device as charge is drawn from and supplied to the battery;

charging the rechargeable battery until an end of charge message is received, the end of charge message indicating that the rechargeable battery has stopped accepting charge; and

adjusting the SOC to a full charge capacity value if the SOC exceeds the full charge capacity value when the end of charge message is received by the rechargeable battery.

2. The method of claim 1, further comprising:

discharging the rechargeable battery until an end of discharge message is received, the end of discharge message indicating that the rechargeable battery has reached a nominal low battery threshold;

adjusting the full charge capacity by adding the SOC to the full charge capacity if the SOC is less than or equal to zero when the end of discharge message is received by the rechargeable battery; and

resetting the SOC to a minimum charge value after dynamically adjusting the full charge capacity.

3. The method of claim 2, further comprising not dynamically adjusting the full charge capacity by adding the SOC to the full charge capacity when the end of discharge message is received if any of the following conditions is not met during a discharge cycle:

(i) the rechargeable battery was discharged from a fully charged state;

(ii) the rechargeable battery was not partially charged;

(iii) an accumulated self-discharge value does not exceed a predefined percentage of an estimated initial full charge capacity; and

(iv) the rechargeable battery temperature did not exceed a predefined temperature limit.

4. The method of claim 2, further comprising:

setting a discard flag when the end of discharge message is received and the SOC is positive and exceeds a predefined error margin.

5. The method of claim 4, further comprising adjusting the SOC with an efficiency coefficient.

6. The method of claim 5, further comprising adjusting the efficiency coefficient as the SOC changes.

7. The method of claim 6, further comprising adjusting the SOC with a self discharge rate.

8. The method of claim 7, further comprising adjusting the self discharge rate to reflect for the time since the rechargeable battery was last charged.

9. The method of claim 1, wherein the SOC is dynamically calculated by a monitoring circuit using a discharging SOC equation.

10. The method of claim 9, wherein the discharging SOC equation is:

${\mathrm{SOC}}_1={\mathrm{SOC}}_0-\left\{K_T·<br><br>E_D·<br><br>\left(\frac{I_{\mathrm{D1}}+I_{\mathrm{D0}}+I_{\mathrm{B1}}+I_{\mathrm{B0}}}{2}\right)·<br><br>\left(\frac{t_1-t_0}{3600·<br><br>C_{\mathrm{nom}}}\right)\right\}$

the variable in the discharging SOC equation being defined as;

SOC₁ is a present value of the calculated SOC in percent;

SOC₂ is a prior value of the calculated SOC in percent;

K_T is a temperature coefficient of discharge current and has no units;

I_D1 is a present charge current into the rechargeable battery in amperes;

I_D0 is a prior charge current into the rechargeable battery in amperes;

I_B1 is a present bias current for the monitoring circuit in the rechargeable battery in amperes;

I_B0 is a prior bias current for the monitoring circuit in the rechargeable battery in amperes;

t₁ is a present time of the measurements in seconds;

t₀ is a prior time of the measurements in seconds;

E_D is the efficiency of discharge in percent;

2 is an averaging factor;

3600 is a constant conversion factor accounting for time in seconds and capacity in amp hours;

C_nom is a battery manufacturer'"'"'s capacity rating in AH; and

SD_T is an amount of capacity lost due to self discharge in percent.

11. The method of claim 9, wherein the charging SOC equation is:

${\mathrm{SOC}}_1={\mathrm{SOC}}_0+\left[\frac{E_C·<br><br>\left(I_{\mathrm{C1}}+I_{\mathrm{C0}}-I_{\mathrm{B1}}-I_{\mathrm{B0}}\right)·<br><br>\left(t_1-t_0\right)}{7200·<br><br>C_{\mathrm{nom}}}\right]<br><br>{<br><br><br><br>}_{{\mathrm{SOC}}_0<<br><br>\mathrm{FCC}}$

the variables in the discharging SOC equation being defined as;

SOC₁ is a present value of the calculated SOC in percent;

SOC₀ is a prior value of the calculated SOC in percent;

E_C is a efficiency of charge acceptance in percent;

I_C1 is a present charge current into the rechargeable battery in amperes;

I_C0 is a prior charge current into the battery in amperes;

I_B1 is a present bias current for the monitoring circuit in the rechargeable battery in amperes;

I_B0 is a prior bias current for the monitoring circuit in the rechargeable battery in amperes;

t₁ is a present time of the measurements in seconds;

t₀ is a prior time of the measurements in seconds;

7200 is a constant conversion factor accounting for averaging;

C_nom is a battery manufacturer s capacity rating in amp hours; and

FCC is the full charge capacity.

12. The method of claim 1, further comprising maintaining a log of critical errors in the non-volatile memory, each critical error indicating that the rechargeable battery may not be reliable and should be discarded.

13. The method of claim 12, wherein a critical error is logged if the number of cycles that the rechargeable battery has been through exceeds a predefined maximum number of cycles.

14. The method of claim 12, wherein a critical error is logged if an interval of the time that the rechargeable battery has been in use exceeds a predefined maximum lifetime.

15. The method of claim 12, wherein a critical error is logged if the contents of a non-volatile memory of the rechargeable battery have become corrupted.

16. The method of claim 12, wherein a critical error is logged if the rechargeable battery receives a notification from another device that the rechargeable battery should be discarded.

17. The method of claim 12, wherein a critical error is logged if the full charge capacity is less than a predefined full charge capacity minimum value.

18. The method of claim 12, wherein an indication that the rechargeable battery may not be reliable and should be discarded is displayed if a critical error has been recorded in the log of critical errors.

19. The method of claim 12, wherein a critical error is communicated by the rechargeable battery to a host device via a communication interface.

20. The method of claim 12, further comprising displaying the ability of the rechargeable battery to reliably deliver charge to a host device by displaying an indication of the SOC of the rechargeable battery.

21. The method of claim 1, further comprising maintaining at least one non-critical critical error flag in a non-volatile memory of the rechargeable battery, each non-critical error flag indicating that the rechargeable battery requires maintenance.

22. The method of claim 21, a cycles conditioning recommended flag is set if a count of cycles experienced by the rechargeable battery exceeds a cycles conditioning recommended interval.

23. The method of claim 21, a cycles conditioning required flag is set if a count of cycles experienced by the rechargeable battery exceeds a cycles conditioning required interval.

24. The method of claim 21, a time conditioning recommended flag is set if a time interval since the rechargeable battery was last conditioned exceeds a cycles conditioning recommended interval.

25. The method of claim 21, time conditioning required flag is set if a time interval since the rechargeable battery was last conditioned exceeds a time conditioning required interval.

26. The method of claim 21, an indication that the rechargeable battery requires maintenance is displayed if a non-critical error has occurred.

27. The method of claim 26, wherein the indication that the rechargeable battery requires maintenance is only displayed when the non-critical error is of a predefined type that indicates that maintenance is required.

28. The method of claim 27, wherein the predefined type is a cycles conditioning required flag that is set if a count of cycles experienced by the rechargeable battery exceeds a predefined cycles conditioning required interval.

29. The method of claim 27, wherein the predefined type includes a time conditioning required flag that is set if a time interval experienced by the rechargeable battery exceeds a predefined time conditioning required interval.

30. The method of claim 27, wherein the predefined type includes a temperature conditioning required flag that is set if a cumulative time over temperature interval experienced by the rechargeable battery exceeds a predefined temperature conditioning required interval.

31. The method of claim 26, wherein the non-critical error is communicated to a host device via a communication interface as a request for maintenance.

32. A smart battery apparatus, comprising:

a smart battery housing;

a user interface display area mounted upon the smart battery housing;

a monitoring circuit mounted upon a circuit board for monitoring a state of charge (SOC) of the smart battery and displaying the SOC on the user interface display area; and

a plurality of electrically conductive rods coupled to the circuit board in a manner that conducts an electrical signal through the electrically conductive rods to the monitoring circuit.

33. The apparatus of claim 32, wherein the monitoring circuit has a central processing unit that is programmed to adjust the SOC to a full charge capacity (FCC) when a host device communicates to the monitoring circuit that the host device has detected that the smart battery has stopped accepting charge.

34. The apparatus of claim 33, wherein the central processing unit is programmed to adjust the FCC if the SOC is less than or equal to zero when the host device communicates to the monitoring circuit that the host device has detected that the smart battery has been fully discharged.

35. The apparatus of claim 32, wherein the monitoring circuit has a central processing unit that monitors the smart battery'"'"'s need for maintenance.

36. The apparatus of claim 35, wherein the monitoring circuit is coupled to a non-volatile memory circuit and the central processing unit indicates that the battery requires maintenance by setting in the non-volatile memory a cycles conditioning required flag in if a count of cycles experienced by the rechargeable battery exceeds a predefined cycles conditioning required interval.

37. The apparatus of claim 35, wherein the monitoring circuit is coupled to a non-volatile memory circuit and the central processing unit indicates that the battery requires maintenance by setting in the non-volatile memory a time conditioning required flag that is set if a time interval experienced by the rechargeable battery exceeds a predefined time conditioning required interval.

38. The apparatus of claim 35 wherein the monitoring circuit is coupled to a non-volatile memory circuit and the central processing unit indicates that the battery requires maintenance by setting in the non-volatile memory a temperature conditioning required flag that is set if a cumulative time over temperature interval experienced by the rechargeable battery exceeds a predefined temperature conditioning required interval.

39. The apparatus of claim 35, wherein the central processing unit communicates the need for maintenance to a host device via a communication interface that is coupled to the central processing unit.

40. The apparatus of claim 35, wherein the central processing unit determines when the smart battery should be discarded by logging a critical error in a non-volatile memory that is coupled to the central processing unit.

41. The method of claim 40, wherein a critical error is logged by the central processing unit if a count maintained by the central processing unit of the number of cycles that the rechargeable battery has been through exceeds a predefined maximum number of cycles.

42. The method of claim 40, wherein a critical error is logged by the central processing unit if an interval maintained by the central processing unit of the time that the rechargeable battery has been in use exceeds a predefined maximum lifetime.

43. The method of claim 40, wherein a critical error is logged by the central processing unit if a program content of the non-volatile memory has become corrupted.

44. The method of claim 40, wherein a critical error is logged by the central processing unit if the rechargeable battery receives a notification from a host device that the smart battery should be discarded.

45. The method of claim 40, wherein a critical error is logged by the central processing unit if a full charge capacity is less than a predefined full charge capacity minimum value.

46. The method of claim 40, wherein the central processing unit displays through the user interface and display an indication of that the rechargeable battery may not be reliable and should be discarded if the central processing unit has logged a critical error.

47. The apparatus of claim 40, wherein a critical error is communicated by the smart battery to a host device via a communication interface.