Quiescent battery testing method and apparatus

• US 4,514,694 A
• Filed: 07/23/1982
• Issued: 04/30/1985
• Est. Priority Date: 07/23/1981
• Status: Expired due to Term

• Current Assignee: Curtis Instruments Incorporated
• Original Assignee: Curtis Instruments Incorporated
• Inventors: Finger, Eugene P.
• Primary Examiner(s): Tokar, Michael J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/401,383
• Time in Patent Office: 1,012 Days
• Field of Search: 324/426, 324/428, 324/429, 324/430, 324/427, 324/433, 340/636, 320/39, 320/48
• US Class Current: 324/429
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 3/12 Recording operating variables ; Monitoring of operating variables
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: G01R 31/36 Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

The invention relates to apparatus for determining the state of charge of electric storage batteries.

The apparatus makes use of known quiescent battery (16) terminal voltage recovery characteristics after a prior energy transfer to predict the ultimate steady state terminal voltage as a measure of state of charge. In one embodiment, this is accomplished by using a voltage-controlled oscillator (18) and a reversible counter (20) to measure a first battery (16) terminal voltage over a fixed time interval, storing that measurement in a register (24), measuring a second terminal voltage by reversing the counter (24) and counting the counter down for an identical fixed interval of time, and then determining the slope of the voltage recovery (at) (26) (30) based upon the difference between the two voltage measurements as evidenced by the count remaining in the counter (20) and adding a factor (at) (74) to the first voltage measurement based upon the voltage difference measurement to determine a predicted steady state voltage as an indication (28) of the charge on the battery.

Claims

1. A method for testing a battery which is in a quiescent condition comprising the steps of

taking a first battery terminal voltage measurement, storing said first measurement, taking a second terminal voltage measurement at a subsequent time, and comparing said second measurement with said first measurement to determine the direction of voltage change from said first measurement to said second measurement generating at least one signal indicating the direction of voltage change and providing a visual indication of the direction of voltage change to indicate whether the battery was last subjected to charge or discharge.

2. A method for testing a battery which is in a quiescent condition comprising the steps of taking a first battery terminal voltage measurement, noting said first measurement, taking a second terminal voltage measurement at a subsequent time, measuring the time interval from the first battery terminal voltage measurement to the second battery terminal voltage measurement and comparing said second voltage measurement with said first voltage measurement in relation to the time interval measurement to determine the rate of voltage change from said first voltage measurement to said second voltage measurement, and then using the combination of the value of one of said voltage measurements and the direction and the rate of voltage change to determine a quantity which is a function of a predicted steady-state open circuit voltage as a determination of the battery state-of-charge.

3. A method as claimed in claim 2 wherein said measured time interval between said first measurement and said second measurement is a fixed time interval.

4. A method as claimed in claim 3 comprising taking said first battery terminal voltage measurement by connecting a voltage controlled oscillator to receive the voltage to be measured and then counting the number of oscillations from the voltage controlled oscillator over a fixed interval of time, taking the second voltage measurement in the same manner, and then subtracting the counted number of oscillations for the second measurement from the counted number of oscillations for the first measurement to determine the direction and rate of voltage change from the first measurement to the second measurement.

5. A method as claimed in claim 4 wherein the oscillation count from the first voltage measurement is recorded and the oscillation count for the second voltage measurement is then later subtracted from the recorded first count.

6. A method as claimed in claim 4 wherein the voltage measurements and the subtraction of the counts are obtained by connecting a reversible counter to the voltage controlled oscillator and counting the counter up in response to the oscillations of the voltage controlled oscillator during the fixed time interval for the first voltage measurement, and then reversing the counter to count down during the fixed interval of time during the second voltage measurement so that any residue count remaining in the counter represents the difference between the two voltage count measurements.

7. A method as claimed in claim 3 wherein the following additional step is taken when said second measurement after a fixed time interval does not provide a difference from said first measurement sufficient for an accurate difference determination comprising subsequently taking another second voltage measurement at the end of a variable measured time interval after said first voltage measurement which is determined when a second voltage measurement is achieved which represents a predetermined fixed voltage difference from said first voltage measurement.

8. A method as claimed in claim 2 wherein said measured time interval from said first voltage measurement to said second voltage measurement is variable, with the end of said measured time interval being determined when a second voltage measurement is reached which represents a predetermined fixed voltage difference from said first voltage measurement.

9. A method as claimed in claim 8 wherein said predetermined fixed difference between said second voltage measurement and said first voltage measurement is different when the voltage difference is positive from when the voltage difference is negative.

10. A method as claimed in claim 8 or claim 9 wherein the end of said measured time interval is determined at the second voltage measurement which represents a fixed difference from the first voltage measurement by comparing successive voltage measurements with the sum of the stored first voltage measurement and a fixed difference voltage quantity to determine when one of the successive voltage measurements first more than matches the sum.

11. A method as claimed in claim 2 wherein the determination of the quantity which is a function of a predicted steady state open circuit voltage is based upon known battery terminal voltage recovery characteristics after a battery current exchange for the type of battery under test.

12. A method as claimed in claim 2 wherein the determination of the quantity which is a function of a predicted steady state open circuit voltage is carried out by adding a factor to one of said voltage measurements determined as a function of the rate of change between said voltage measurements.

13. A method as claimed in claim 12 wherein the factor determined as a function of the rate of voltage change is substantially an anti-logarithmic function of voltage change per unit of time.

14. A method as claimed in claim 12 or claim 13 wherein the factor determined as a function of the rate of voltage change is simply derived in a step-wise manner by determining into which range of a group of different voltage change rate ranges the rate of voltage change falls, and then employing a factor previously assigned for the determined range.

15. A method as claimed in claim 12 wherein the factor added to said one voltage measurement which is determined as a function of the rate of voltage change is a combined function of the rate of voltage change and the voltage level to match the prediction of steady state open circuit voltage to known battery terminal voltage recovery characteristics when the slopes of the voltage recovery curves vary for recovery from different voltage levels.

16. A method as claimed in claim 15 wherein the voltage level and the rate of voltage change are combined to produce said combined function by multiplying a signal quantity corresponding to a zero level adjusted voltage level by a factor substantially proportional to an anti-logarithmic function of the rate of voltage change.

17. A method as claimed in claim 2 wherein said second measurement is taken at a fixed time interval after said first measurement or at a fixed voltage difference from said first measurement, whichever occurs first.

18. A method as claimed in claim 3 wherein the following additional step is taken when said second measurement after a fixed time interval does not provide a difference from said first measurement sufficient for an accurate difference determination:

taking another second voltage measurement at the end of a longer fixed time interval after said first voltage measurement.

19. Apparatus for testing a quiescent battery for determining the state of charge of that battery comprising means for taking battery terminal voltage measurements, means for storing a first battery terminal voltage measurement, means for comparing a second battery terminal voltage measurement taken at a subsequent time with said first battery terminal voltage measurement and operable to determine the direction of voltage change of said second voltage measurement from said stored first voltage measurement and to generate at least one signal indicating the direction of voltage change, and visual indicating means connected to said comparison means to receive said direction of voltage change signal for providing a visual indication of the direction of voltage change as an indication as to whether the battery was last subjected to charge or discharge.

20. Apparatus as claimed in claim 19 wherein said means for taking battery terminal voltage measurements comprises a voltage controlled oscillator and a digital counter connected to receive oscillation pulses from said voltage controlled oscillator for counting those pulses as a measurement of voltage, said means for comparing a second battery terminal voltage measurement taken at a subsequent time comprising means for reversing the operation of said reversible counter during said second battery terminal voltage measurement to count said counter in the reverse direction, and said means for comparing said second battery terminal voltage with said first battery terminal voltage measurement including means to determine whether or not said reversible counter is switched into the complement mode to indicate a negative remainder in said reversible counter as an indication of the direction of voltage change.

21. Apparatus for testing a quiescent battery for determining the state of charge of that battery comprising means for taking battery terminal voltage measurements, means for storing a first battery terminal voltage measurement, means for comparing a second battery terminal voltage measurement taken at a subsequent time with said first battery terminal voltage measurement, means for measuring the time interval from the first battery terminal voltage measurement to the second battery terminal voltage measurement, means for comparing said second voltage measurement with said first voltage measurement in relation to the time interval measurement to generate a quantity corresponding to the rate of voltage change from said first voltage measurement to said second voltage measurement, means connected to receive one of said measurements and said rate of voltage change quantity and operable to determine a quantity which is a function of a predicted steady-state open circuit voltage as a determination of the battery state-of-charge, and display means connected to said last-named means for display of said state-of-charge quantity.

22. Apparatus as claimed in claim 21 wherein said means for measuring said time interval is operable to measure a fixed time interval.

23. Apparatus as claimed in claim 22 wherein said battery terminal voltage measurement means comprises a voltage controlled oscillator connected to receive the voltage to be measured and a reversable counter operable to count the number of oscillations from the voltage controlled oscillator, said counter being operable to count in one direction over a fixed interval of time to take said first voltage measurement, said counter being operable to reverse to count in the other direction to make said second voltage measurement so that any residue count remaining in the counter represents the difference between the two voltage count measurements.

24. Apparatus as claimed in claim 21 wherein said means for comparing said second voltage measurement with said first voltage measurement is operable to determine a a second voltage measurement which represents a predetermined fixed voltage difference from said first voltage measurement.

25. Apparatus as claimed in claim 24 wherein said comparison means comprises a comparison circuit connected to compare successive voltage measurements with the sum of the stored first voltage measurement and a fixed difference voltage quantity to determine when one of the successive voltage measurements more than matches the sum.

26. Apparatus as claimed in claim 21 wherein said means for determining the quantity which is a function of a predicted steady state open circuit voltage comprises means for adding a factor to one of said voltage measurements, and means for determining said last-named factor as a function of the rate of change between said voltage measurements.

27. Apparatus as claimed in claim 26 wherein said factor determining means is operable to determine said last-named factor as a substantially anti-logarithmic function of voltage change per unit of time.

28. Apparatus as claimed in claim 26 wherein said means for determining said factor as a function of the rate of change between said voltage measurements comprises a digital counter for storing a number corresponding to said voltage change and logic gates connected to said counter and operable to determine different ranges of values for said rate of change, and at least one correction function generator connected to said logic gates and operable in response to the determination of the ranges of values for said rate of change to provide a predetermined value for said factor based upon the determined voltage change rate range.

29. Apparatus as claimed in claim 28 wherein said means for determining said factor as a function of the rate of change between said voltage measurements further includes an adder circuit, said adder circuit being connected to receive one of said voltage measurements and to add a fixed quantity to said voltage measurement to provide a zero level adjusted voltage measurement, and wherein said correction function generator comprises a multiplier circuit connected to receive the zero level adjusted voltage measurement from said adder, said multiplier being operable to multiply said zero level adjusted voltage measurement by different selected factors as selected by said different voltage change rate ranges to thereby generate a product output as said factor determined as a function of the rate of change between said voltage measurements.

30. Apparatus as claimed in claim 26 including means for subtracting a fixed factor from said one of said voltage measurements in order to provide for a zero corrected indication of state of charge upon said display means.

31. Apparatus as claimed in claim 21 wherein there is provided a temperature measurement means connected to said predicted steady state open circuit voltage function means to modify the operation of said last named means to compensate for temperature changes.

32. Apparatus as claimed in claim 21 wherein said means for measuring the time interval from the first battery terminal voltage measurement to the second battery terminal measurement comprises a digital counter and a timing oscillator, the lower order stages of said digital counter being operable to provide clock commutator switching functions for said apparatus.