Method and apparatus for charging a rechargeable battery with monitoring of battery temperature rate of change

• US 20010001533A1
• Filed: 12/22/2000
• Published: 05/24/2001
• Est. Priority Date: 03/24/1998
• Status: Abandoned Application

• Current Assignee: Chartec Laboratories A/S
• Original Assignee: Chartec Laboratories A/S
• Inventors: Stuck Andersen, Kim Arthur, Ostergaard, Kim, Rasmussen, Kim
• Application Number:
  US09/747,507
• Publication Number:
  US 20010001533A1
• Time in Patent Office: Days
• US Class Current: 320/150
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery charger monitors an open-circuit voltage across the battery and the rate of change of temperature of the battery to determine a time to terminate the process of charging the battery. Charging proceeds in four stages. In the first stage the open-circuit voltage of the battery is monitored until such voltage crosses a threshold value. In the second stage, the rate of change of battery temperature is monitored to determine a reference value, for example, a minimum of the monitored rate. In the third stage, the rate of change of battery temperature is again monitored to identify a time when such rate exceeds the reference value by a predetermined amount. In the fourth stage, power supplied to charge the battery is limited immediately after stage three or a predetermined time after stage three for example by reducing the charging current to a trickle-charge level or by reducing the voltage by about 100 mV. The predetermined time may be a function of the elapsed charging time, for example a predetermined percentage of about 25%.

Claims

1. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to charge the battery;

measuring values of rate of change of temperature of the battery to provide a first plurality of values and to provide further values of the measured rate of change of battery temperature;

determining a reference value in response to the first plurality of values;

comparing the further values of the rate of change of temperature of the battery with the reference value; and

limiting the supplied power in response to this comparison.

2. The method of

claim 1

wherein the supplied power is limited when the comparison shows that the measured rate of change of temperature differs from the reference value by a predetermined amount.

3. The method of

claim 1

wherein the reference value is determined in further response to a minimum of the first plurality of values.

4. The method of

claim 1

wherein the step of limiting the supplied power comprises reducing a charging current supplied to the battery.

5. The method of

claim 1

wherein the step of limiting the supplied power comprises:

determining a time period duration; and

after lapse of the time period, reducing a charging current supplied to the battery to no more than a trickle-charge current.

6. The method of

claim 5

wherein the step of determining a time period duration comprises:

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

7. The method of

claim 6

wherein the step of determining the time period duration comprises setting the time period duration to a duration in the range of 5% to 50% of the charging time lapsed when the step of limiting the supplied power is initiated.

8. The method of

claim 5

wherein the step of determining a time period duration comprises setting the time period duration to a constant.

9. The method of

claim 1

wherein the step of limiting the supplied power comprises reducing a voltage across the battery.

10. The method of

claim 9

wherein the voltage across the battery is reduced at least 100 mV.

11. The method of

claim 1

wherein the step of providing a supplied power is performed for a predetermined period prior to performing the step of measuring.

12. The method of

claim 1

wherein performance of the step of measuring is deferred until a voltage across the battery crosses a threshold value.

13. The method of

claim 1

wherein:

a. the method further comprises the steps of reducing a charging current supplied to the battery, measuring a battery voltage across the battery when the charging current is reduced; and

b. performance of the step of comparing measured rates of change of temperature with the reference value is deferred until the battery voltage crosses a threshold value.

14. The method of

claim 1

further comprises providing no more than a trickle-charge current to the battery after performing the step of limiting the supplied power.

15. An apparatus for charging a rechargeable battery, the apparatus comprising:

a. a power supply that provides a supplied power to charge the battery; and

b. a circuit that;

provides indicia of a temperature of the battery;

measures rate of change of the temperature of the battery in response to the indicia to provide a first plurality of values and to provide further values of rate of change of the battery temperature;

determines a reference value in response to the first plurality of values;

compares the further provided values with the reference value; and

provides a signal to the power supply in response to this comparison, wherein the power supply, in response to the signal, limits the supplied power.

16. The apparatus of

claim 15

wherein the circuit comprises:

a. a signal conditioning circuit, responsive to the indicia of the temperature of the battery, for providing an analog signal responsive to the temperature of the battery;

b. an analog to digital converter responsive to the analog signal for providing a digital signal; and

c. control logic responsive to the digital signal for providing the signal to the power supply.

17. The apparatus of

claim 16

wherein the analog to digital converter and the control logic are integral to an integrated circuit.

18. The apparatus of

claim 15

wherein the circuit comprises:

a. a measurement circuit that measures the rate of change; and

b. a control circuit that determines the reference value, compares the further values, and provides the signal to the power supply.

19. The apparatus of

claim 18

wherein the measurement circuit comprises an analog to digital converter.

20. The apparatus of

claim 15

wherein the signal is provided when the comparison shows that the measured rate of change of temperature differs from the reference value by a predetermined amount.

21. The apparatus of

claim 15

wherein the reference value is determined in response to a minimum of the first plurality of values.

22. The apparatus of

claim 15

wherein the power supply, in response to the signal, limits the supplied power by reducing a charging current supplied to the battery.

23. The apparatus of

claim 15

wherein the signal is provided to the power supply so that a charging current supplied by the power supply to the battery for charging the battery is reduced to no more than a trickle-charge current after lapse of a time period duration beginning from an identified point in time, the circuit determining the time period duration and the identified point in time according to a method comprising:

comparing the further provided values with the reference value to identify the point in time;

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

24. The apparatus of

claim 15

wherein the power supply, in response to the signal, limits the supplied power by reducing a voltage across the battery.

25. The apparatus of

claim 15

the wherein measurements for providing the first plurality of values are made after a predetermined period of time during which supplied power is being provided to charge the battery.

26. The apparatus of

claim 15

wherein the circuit further measures a voltage across the battery and determines the reference value in further response to the first plurality of values being measured after the voltage across the battery crosses a threshold value.

27. The apparatus of

claim 15

wherein:

a. the circuit comprises a device for reducing current supplied to the battery; and

b. the circuit measures the voltage across the battery when current supplied to the battery is reduced.

28. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to quickly charge the battery;

measuring a first characteristic of the battery;

measuring values of a second characteristic of the battery; and

limiting the supplied power in response to values of the second battery characteristic being measured after the first battery characteristic crosses a threshold.

29. The method of

claim 28

further comprising:

selecting the first battery characteristic from a group consisting of battery terminal voltage, charging current, battery temperature, rate of change of battery terminal voltage, rate of change of charging current, and rate of change of battery temperature; and

selecting the second battery characteristic from a group consisting of battery terminal voltage, charging current, battery temperature, rate of change of battery terminal voltage, rate of change of charging current, and rate of change of battery temperature, wherein the second battery characteristic is not the same characteristic as the first battery characteristic.

30. The method of

claim 28

wherein the step of measuring values of the second battery characteristic comprises measuring a rate of change of a battery temperature.

31. The method of

claim 28

wherein the step of measuring the first battery characteristic comprises measuring a voltage across the battery.

32. The method of

claim 28

wherein:

the method further comprises determining a reference value in response to the values of the second battery characteristic; and

the step of limiting the supplied power comprises limiting in further response to the reference value.

33. The method of

claim 32

wherein:

the method further comprises after determining the reference value, further measuring values of the second battery characteristic; and

the step of limiting the supplied power comprises limiting in further response to comparing the reference value and the further measured values of the second battery characteristic.

34. The method of

claim 32

wherein the step of determining comprises setting the reference value in response to a minimum of a plurality of the values of the second battery characteristic.

35. The method of

claim 33

wherein the step of comparing the reference value and the further measured values comprises:

forming a difference between the reference value and the further measured values; and

comparing the difference to a predetermined value to provide the comparison of the reference value and the further measured values.

36. The method of

claim 28

wherein the step of limiting the supplied power comprises reducing a charging current supplied to the battery.

37. The method of

claim 28

wherein the step of limiting the supplied power comprises:

determining a time period duration; and

after lapse of the time period, reducing a charging current supplied to the battery to no more than a trickle-charge current.

38. The method of

claim 37

wherein the step of determining a time period duration comprises:

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

39. An apparatus for charging a rechargeable battery, the apparatus comprising:

a. a power supply that provides a supplied power to quickly charge the battery; and

b. a circuit that;

measures a first characteristic of the battery;

measures a second characteristic of the battery; and

provides a signal to the power supply in response to the second characteristic being measured after the first characteristic crosses a threshold, wherein the power supply, in response to the signal, limits the supplied power.

40. The apparatus of

claim 39

wherein the second characteristic is responsive to a rate of change of a battery temperature.

41. The apparatus of

claim 39

wherein the first characteristic is responsive to a voltage across the battery.

42. The apparatus of

claim 39

wherein the circuit:

measures the second characteristic to provide a plurality of values and to provide further values; and

provides the signal in further response to comparing the plurality of values and the further values.

43. The apparatus of

claim 39

wherein the circuit:

measures the second characteristic to provide a plurality of values and to provide further values; and

determines a reference value in response to the plurality of values, compares the reference value to the further values, and provides the signal in further response to the comparison.

44. The apparatus of

claim 43

wherein the circuit determines the reference value in response to a minimum of the plurality of values.

45. The apparatus of

claim 43

wherein the circuit provides the signal after a measured further value differs from the reference value by a predetermined amount.

46. The apparatus of

claim 39

wherein the power supply, in response to the signal, limits the supplied power by reducing a charging current supplied to the battery.

47. The apparatus of

claim 39

wherein the circuit provides the signal to the power supply so that a charging current supplied by the power supply to the battery for charging the battery is reduced to no more than a trickle-charge current after lapse of a time period duration beginning from an identified point in time, the circuit determining the time period duration and the identified point in time according to a method comprising:

comparing the reference value and the measured further values to identify the point in time;

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

48. The apparatus of

claim 39

wherein:

a. the circuit selects the first characteristic from a group consisting of battery terminal voltage, charging current, battery temperature, rate of change of battery terminal voltage, rate of change of charging current, and rate of change of battery temperature; and

b. the circuit selects the second characteristic from a group consisting of battery terminal voltage, charging current, battery temperature, rate of change of battery terminal voltage, rate of change of charging current, and battery temperature, wherein the second characteristic is not the same characteristic as the first characteristic.

49. A method for charging a rechargeable battery, the method comprising:

supplying a charging current to the battery;

determining a plurality of values of rate of change of temperature of the battery during at least part of the process of charging the battery;

determining and storing a reference value based on the plurality of values;

after the step of determining the plurality, determining further values of rate of change of temperature of the battery;

comparing further values of rate of change of temperature of the battery to the reference value to provide a comparison; and

controlling termination of the charging process based on the comparison.

50. A method for charging a rechargeable battery, the method comprising:

supplying a charging current to the battery;

determining a plurality of values of rate of change of temperature of the battery during at least part of the process of charging the battery;

determining and storing a reference value based on a minimum of the plurality of values;

after the step of determining the plurality, determining further values of rate of change of temperature of the battery;

comparing further values of rate of change of temperature of the battery to the reference value to provide a comparison; and

controlling termination of the charging process based on the comparison.

51. A method for charging a rechargeable battery, the method comprising:

supplying a charging current to the battery;

determining a plurality of values of rate of change of temperature of the battery during at least part of the process of charging the battery;

determining and storing a reference value based on a sum of a minimum of the plurality of values and a constant;

after the step of determining the plurality, determining further values of rate of change of temperature of the battery;

comparing further values of rate of change of temperature of the battery to the reference value to provide a comparison; and

controlling termination of the charging process based on the comparison.

52. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to charge the battery;

measuring rate of change of a temperature of the battery to provide a plurality of measurements and later a second plurality of measurements;

determining a reference value in response to the plurality;

comparing the reference value to each measurement of the second plurality to provide a comparison; and

limiting the supplied power in response to the comparison.

53. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to charge the battery;

measuring rate of change of a temperature of the battery to provide a plurality of measurements and later a second plurality of measurements;

determining a reference value in response to a minimum of the plurality;

comparing the reference value to each measurement of the second plurality to provide a comparison; and

limiting the supplied power in response to the comparison.

54. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to charge the battery;

measuring rate of change of a temperature of the battery to provide a first plurality of measurements and later a second plurality of measurements;

determining a reference value in response to a sum of a minimum of the first plurality and a constant;

comparing the reference value to each measurement of the second plurality to provide a comparison; and

limiting the supplied power in response to the comparison.

55. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to charge the battery;

measuring rate of change of a temperature of the battery to provide a first plurality of values and a second value; and

limiting the supplied power in response to the second value and to a minimum of the first plurality of values.

56. The method of

claim 55

wherein supplied power is limited after a first time when the second value exceeds a sum of a constant and the minimum of the first plurality of values.

57. The method of

claim 56

wherein the step of limiting the supplied power comprises:

determining a time period duration; and

after occurrence of the first time and after lapse of the time period, reducing a charging current supplied to the battery to no more than a trickle-charge current.

58. The method of

claim 57

wherein the step of determining a time period duration comprises:

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

59. The method of

claim 58

wherein the step of determining the time period duration comprises setting the time period duration to a duration in the range of 5% to 50% of the charging duration occurring prior to the first time.

60. The method of

claim 57

wherein the step of determining a time period duration comprises setting the time period duration to a constant.

61. The method of

claim 55

wherein performance of the step of measuring is deferred during a predetermined initial portion of the performance of the step of providing supplied power.

62. The method of

claim 55

wherein performance of the step of measuring is deferred until a voltage across the battery crosses a threshold value.

63. A method for charging a rechargeable battery, the method comprising:

providing a supplied power to quickly charge the battery;

measuring a first characteristic of the battery to provide a first value;

after the first value crosses a first threshold, measuring a second characteristic of the battery to provide a second value; and

after the second value crosses a second threshold, limiting the supplied power.

64. The method of

claim 63

wherein:

a. the first characteristic is selected from the group consisting of a battery voltage, a charging current, a battery temperature, rate of change of a battery voltage, rate of change of a charging current, and rate of change of battery temperature;

b. the second characteristic is selected from the group consisting of a battery voltage, a charging current, a battery temperature, rate of change of a battery voltage, rate of change of a charging current, and rate of change of battery temperature; and

c. the second characteristic is not the same characteristic as the first characteristic.

65. The method of

claim 64

wherein the method further comprises:

determining a minimum of the second characteristic; and

determining the second threshold in response to the minimum.

66. The method of

claim 65

wherein the second characteristic is determined to have crossed the second threshold when a difference between the second characteristic and the second threshold exceeds a predetermined amount.

67. The method of

claim 66

wherein the step of limiting the supplied power comprises:

determining a time period duration; and

after lapse of the time period, reducing a charging current supplied to the battery to no more than a trickle-charge current.

68. The method of

claim 67

wherein the step of determining a time period duration comprises:

determining a charging duration during which the charging current had been supplied to the battery; and

determining the time period duration in response to the charging duration.

69. An apparatus for charging a rechargeable battery, the apparatus comprising:

a. a power supply that provides a supplied power to charge the battery; and

b. a circuit that;

measures rate of change of the temperature of the battery;

determines a minimum of the measured rate of change;

determines a present measured rate of change;

provides a comparison of the minimum rate of change and the present rate of change; and

provides a signal to the power supply in response to this comparison, wherein the power supply, in response to the signal, limits the supplied power.

70. The apparatus of

claim 69

wherein the circuit provides the comparison as a difference between the minimum rate of change and the present rate of change and provides the signal when the comparison exceeds a predetermined amount.

71. The apparatus of

claim 70

wherein the circuit provides the signal to the power supply so that a charging current supplied by the power supply to the battery for charging the battery is reduced to no more than a trickle-charge current after lapse of a time period duration beginning from an identified point in time, the circuit determining the time period duration and the identified point in time according to a method comprising:

a. identifying the point in time as the time when the comparison exceeds the predetermined amount;

b. determining a charging duration during which the charging current had been supplied to the battery; and

c. determining the time period duration in response to the charging duration.

72. The apparatus of

claim 71

wherein the power supply, in response to the signal, limits the supplied power by maintaining a reduced voltage across the battery.

73. The apparatus of

claim 72

wherein the reduced voltage is maintained at a constant value during the time period.

74. The apparatus of

claim 73

wherein the battery comprises at least one cell and the voltage is reduced by an amount of about 40 millivolts per cell.

75. The apparatus of

claim 69

wherein determining the minimum rate of change is deferred until after lapse of a period of time during which supplied power is being provided to charge the battery.

76. The apparatus of

claim 69

wherein the lapse of the period of time occurs in response to determining that a voltage across the battery has crossed a threshold value.

77. The apparatus of

claim 76

wherein the threshold value is determined in response to the voltage across the battery compensated for the temperature of the battery.

78. An apparatus for controlling power supplied for charging a rechargeable battery, the battery comprising at least one cell, the apparatus comprising a circuit that:

measures a first characteristic of the cell while power is being supplied to quickly charge the cell;

measures a second characteristic of the cell; and

provides a signal to control supplied power in response to the second characteristic being measured after the first characteristic crosses a threshold.

79. The apparatus of

claim 78

wherein the first characteristic is responsive to a voltage of the cell.

80. The apparatus of

claim 79

wherein the second characteristic is responsive to rate of change of a temperature of the cell.

81. The apparatus of

claim 80

wherein:

a. the circuit decreases a reference value in response to decreasing measurements of the second characteristic made after the first characteristic crosses the threshold; and

b. the circuit provides the signal in response to a measurement of the second characteristic that exceeds the reference value by a predetermined amount.

82. The apparatus of

claim 81

wherein the circuit adjusts the threshold in response to the temperature of the cell.

83. The apparatus of

claim 82

wherein:

a. the supplied power comprises a charging current;

b. the circuit provides the signal for reducing the charging current to no more than a trickle-charge current after lapse of a time period duration beginning from an identified point in time; and

c. the circuit determines the time period duration and the identified point in time according to a method comprising;

identifying the point in time in response to the time when a measurement of the second characteristic that exceeds the reference value by a predetermined amount;

determining a charging duration during which the charging current had been supplied to the cell; and

determining the time period duration in response to the charging duration.