Method and apparatus for indicating electric charge remaining in batteries based on electrode weight and center of gravity

• US 5,580,675 A
• Filed: 08/11/1994
• Issued: 12/03/1996
• Est. Priority Date: 08/11/1994
• Status: Expired due to Fees

• Current Assignee: Lockheed Idaho Technologies Company
• Original Assignee: Lockheed Idaho Technologies Company
• Inventors: Rouhani, S. Zia
• Primary Examiner(s): Skapars, Anthony
• Application Number:
  US08/289,164
• Time in Patent Office: 845 Days
• Field of Search: 420/90, 420/91, 420/92, 420/93, 320/48, 320/30, 320/31, 324/425, 324/435, 73/32 R, 73/451, 73/291
• US Class Current: 429/90
• 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: H01M 50/569 Constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals battery terminal connectors with integrated measuring arrangements G01R31/364
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

In most electrochemical batteries which generate electricity through the reaction of a battery electrode with an electrolyte solution, the chemical composition, and thus the weight and density, of the electrode changes as the battery discharges. The invention measures a parameter of the battery which changes as the weight of the electrode changes as the battery discharges and relates that parameter to the value of the parameter when the battery is fully charged and when the battery is functionally discharged to determine the state-of-charge of the battery at the time the parameter is measured. In one embodiment, the weight of a battery electrode or electrode unit is measured to determine the state-of-charge. In other embodiments, where a battery electrode is located away from the geometrical center of the battery, the position of the center of gravity of the battery or shift in the position of the center of gravity of the battery is measured (the position of the center of gravity changes with the change in weight of the electrode) and indicates the state-of-charge of the battery.

Claims

1. Apparatus for determining the charge of a battery of a type which generates electricity through the reaction of a battery electrode with an electrolyte which causes a change in the chemical composition of the electrode and therefore a change in the weight and density of the electrode as the charge of the battery changes, comprising:

means for measuring the value of a parameter indicative of the weight of a battery electrode at a time when it is desired to measure the charge remaining in the battery; and

means relating the value of the measured parameter indicative of the weight of the electrode to the value of that parameter indicating a weight of the electrode when the battery is fully charged and a value of that parameter indicating a weight of the electrode when the battery is functionally discharged to determine the charge of the battery.

2. Apparatus for determining the charge of a battery according to claim 1, wherein the parameter measured is the weight of the electrode.

3. Apparatus for determining the charge of a battery according to claim 1, wherein the parameter measured is indicative of the position of the center of gravity of the battery.

4. Apparatus for determining the charge of a battery according to claim 1, wherein the battery has an electrode of one polarity and an electrode of opposite polarity, and wherein the parameter measured is a relative change in the weight of the electrode of one polarity in relation to the weight of the electrode of opposite polarity.

5. Apparatus for determining the charge of a battery according to claim 1, wherein the means for measuring the value of a parameter produces an electrical signal representative of the value of the measured parameter, and the means relating the value of the measured parameter is electronic circuitry including a microprocessor and a visual output which displays the relationship of the measured parameter value to the value of the parameter when the battery is fully charged and the value of the parameter when the battery is functionally discharged.

43. Apparatus for determining the charge of a battery according to claim 1, wherein a plurality of batteries with identical chemical compositions are connected in electrical parallel, and wherein the charge of a single battery of the plurality is determined as representative of the charge in all batteries of the plurality.

6. Apparatus for measuring the charge of a battery of the type which generates electricity through the reaction of a battery electrode with an electrolyte which causes a change in the chemical composition of the electrode and therefore a change in the weight and density of the electrode as the charge of the battery changes, and wherein the electrolyte is a liquid, comprising:

means for suspending at least one battery electrode in the battery electrolyte, said at least one electrode having a weight when the battery is fully charged and a different weight when the battery is functionally discharged;

means for measuring the weight of the at least one suspended battery electrode; and

means for relating the measured weight to the weight of the at least one electrode when the battery is fully charged and the weight of the at least one electrode when the battery is functionally discharged to thereby provide an indication of the amount of charge remaining in the battery.

7. Apparatus for determining the charge of a battery according to claim 6, wherein the battery includes a set of electrodes of one polarity and a set of electrodes of opposite polarity, wherein each set of electrodes has a true weight and a sensible weight, the sensible weight being the difference between the true weight of a set of electrodes and the buoyancy force of the electrolyte acting on the set of electrodes;

and wherein the parameter measured is the sensible weight of one set of electrodes.

8. Apparatus for determining the charge of a battery according to claim 7, wherein two parameters are measured, and wherein the two parameters measured are the separate sensible weights of each set of electrodes.

9. Apparatus for determining the charge of a battery according to claim 7, wherein the parameter measured is the combined sensible weights of both sets of electrodes.

10. Apparatus for determining the charge of a battery according to claim 6, wherein the suspended at least one electrode has a true weight and a sensible weight, the sensible weight being the difference between the true weight of the at least one electrode and the buoyancy force of the electrolyte acting on the at least one electrode;

wherein the means for measuring the weight of the suspended at least one battery electrode measures the sensible weight of the at least one electrode and is a load cell.

11. Apparatus for determining the charge of a battery according to claim 10, wherein the load cell outputs an electrical signal indicative of the sensible weight of the at least one electrode.

12. Apparatus for determining the charge of a battery according to claim 10, wherein the load cell is hydraulic and has fluid therein having a pressure, and wherein the pressure of the fluid in the load cell is indicative of the sensible weight of the at least one electrode.

13. Apparatus for determining the charge of a battery according to claim 12, wherein the means for relating the measured weight of the at least one electrode to the weight of the at least one electrode when the battery is fully charged and the weight of the at least one electrode when the battery is functionally discharged is a fluid pressure gauge which reads the pressure of the fluid in the hydraulic load cell and wherein the gauge is marked to show the reading of the gauge when the battery is fully charged and the reading when the battery is functionally discharged.

14. Apparatus for determining the charge of a battery according to claim 6, wherein the at least one electrode has a true weight and a sensible weight, the sensible weight being the difference between the true weight of the at least one electrode and the buoyancy force of the electrolyte acting on the at least one electrode, wherein the electrolyte has a density and the buoyancy force of the electrolyte varies depending upon the density of the electrolyte, and additionally including means for determining the density of the battery electrolyte, and means for correcting the sensible weight of the at least one electrode for the buoyancy effects of the electrolyte density.

15. Apparatus for determining the charge of a battery according to claim 14, wherein the means for determining the density of the battery electrolyte includes a body of known mass and volume suspended in the battery electrolyte, the body of known mass and volume having a true weight and a sensible weight, the sensible weight being the difference between the true weight of the body of known mass and volume and the buoyancy force of the electrode acting on the body of known mass and volume, and a load cell supporting the body of known mass and volume which measures the sensible weight of the body in the electrolyte and produces an electrical signal representative of the sensible weight of the body, the sensible weight of the body in the electrolyte being related to the density of the electrolyte.

16. Apparatus for determining the charge of a battery according to claim 15, wherein the electrolyte has a temperature, including means for measuring the temperature of the electrolyte, and wherein the means relating the measured weight corrects the sensible weight for effects of the temperature of the electrolyte.

17. Apparatus for determining the charge of a battery according to claim 9, wherein the set of electrodes of one polarity are anodes and the set of electrodes of opposite polarity are cathodes, wherein the sets of electrodes are bound together as an electrode package, wherein the means suspending the electrode package includes two hangers extending from the electrode package, one of the hangers being connected to the anodes in the electrode package and serving as one cell terminal and the other of the hangers being connected to the cathodes in the electrode package and serving as the another cell terminal, and wherein flexible conductors are in electrical contact with the hangers.

18. Apparatus for determining the charge of a battery according to claim 17, wherein the battery includes a battery casing and battery casing extension and means securely attaching respective ends of the flexible conductors to the battery casing extension to prevent sensible weight measurement distorting tensions on the cell terminals.

19. Apparatus for determining the charge of a battery according to claim 17, wherein the battery includes a battery casing having a top and wherein each hanger extends from the electrode package through the battery casing top and is supported by a separate load cell positioned on the battery casing top for measuring the portion of the electrode package sensible weight supported by the hanger.

20. Apparatus for determining the charge of a battery according to claim 17, wherein the battery includes a battery casing having a top, a rigid beam positioned above the battery casing top, hinge means hingedly securing one end of the rigid beam to the battery casing, a load cell positioned between the rigid beam and the battery casing top spaced along the beam from the hinge means, and wherein each hanger extends from the electrode package through the battery casing top to connection to the rigid beam whereby the load cell measures the sensible weight of the electrode package.

21. Apparatus for determining the charge of a battery according to claim 20, wherein the battery casing additionally includes an extension thereof extending over the rigid beam, and spring means positioned between the extension and the rigid beam to prevent free upward movement of the rigid beam and electrode package suspended therefrom.

22. Apparatus for determining the charge of a battery according to claim 21, additionally including a body of known mass and volume suspended in the battery electrolyte, the body of known mass and volume having a true weight and a sensible weight, the sensible weight being the difference between the true weight of the body of known mass and volume and the buoyancy force of the electrolyte acting on the body of known mass and volume, a load cell supporting the body of known mass and volume which measures the sensible weight of the body in the electrolyte and produces an electrical density signal representative of the sensible weight of the body, the sensible weight of the body in the electrolyte being related to the density of the electrolyte, spring means urging the body of known mass and volume downwardly to prevent free upward movement of said body, and means for correcting the sensible weight of the electrode package for effects of electrolyte density.

23. Apparatus for determining the charge of a battery according to claim 22, additionally including means to prevent lateral movements of the electrode package with respect to the battery housing during movement of the battery, and means for preventing lateral movements of the body of known mass and volume with respect to the battery housing during movement of the battery.

24. Apparatus for determining the charge of a battery according to claim 23, wherein the hangers each pass through a round opening in the casing top and including flexible diaphragms sealing each opening, said flexible diaphragms offering minimal resistance against small vertical movements of the hangers but preventing any expulsion of the liquid electrolyte during movement of the battery.

25. Apparatus for determining the charge of a battery according to claim 23, including means for time averaging the electrical signals representative of the sensible weight of the electrode package, and for time averaging the electrical signals representative of the sensible weight of the body of known mass and volume, whereby erroneous signals caused by battery vibration and movement are filtered out and a filtered density corrected signal representative of electrode package weight is obtained.

26. Apparatus for determining the charge of a battery according to claim 25, wherein the battery includes at least one cell having vertical walls and is mounted on a battery base support, and further including a compensation compartment mounted on the battery base support and having vertical walls parallel to the vertical walls of the at least one cell, a fixed mass having a true weight positioned in the compensation compartment, said fixed mass also having an axial and a transverse weight component, spring means urging the fixed mass axially downwardly with a spring force in the compensation compartment, the axial component of the weight of the fixed mass being the difference between the sum of the total axial force and spring force and the transverse component of the true weight transferred to the compensation compartment vertical walls when the battery is not level, a load cell supporting the fixed mass in the compensation compartment which produces electrical signals representative of the axial weight component of the fixed mass, means for time averaging the electrical signals representative of the axial weight component of the fixed mass to produce a filtered compensation signal, and means for comparing the filtered density corrected signal and the filtered compensation signal to calculate the true weight of the electrode package.

27. Apparatus for determining the charge of a battery according to claim 25, wherein the means for comparing the filtered density corrected signal and the filtered compensation signal calculates the true weight of the electrode package by multiplying the filtered density corrected signal with a ratio of the true weight of the fixed mass to the filtered compensation signal.

28. Apparatus for determining the charge of a battery according to claim 27, wherein the means for comparing the filtered density corrected signal and the filtered compensation signal produces an output signal calibrated to indicate the charge of the battery by comparing the signal to a similar signal representative of the weight of the electrode package when the battery is fully charged and resting on a horizontal surface and the weight of the electrode package when the battery is functionally discharged and resting on a horizontal surface.

29. Apparatus for determining the charge of a battery according to claim 28, herein the battery includes a plurality of similar individual cells connected in electrical series for producing a higher voltage than produced by an individual cell, wherein a plurality of the individual cells are equipped with the charge indicating apparatus according to claim 28, and including a single read-out device to sequentially display the charge information from different cells along with an indication of the cell for which the charge information applies.

30. Apparatus for determining the charge of a battery according to claim 29, wherein the read-out device includes means to compare the indicated charge of the different cells and display the smallest value with a simultaneous warning signal.

31. Apparatus for use with a battery to indicate the charge in the battery wherein the battery is of the type which generates electricity through the reaction of a battery electrode with an electrolyte which causes a change in the chemical composition of the electrode and therefore a change in the weight and density of the electrode as the charge of the battery changes, and wherein the battery electrode is positioned in the battery so that as the charge of the battery changes and the weight of the electrode changes, the center of gravity of the battery moves between a position representing a fully charged battery to a position representing a functionally discharged battery, comprising:

means for mounting a battery therein; and

means for producing an indication responsive to the position of the center of gravity of the battery mounted in the apparatus, the position of the center of gravity being indicative of the charge of the battery.

32. Apparatus for determining the charge of a battery according to claim 31, wherein the apparatus includes a base, wherein the means for mounting the battery therein is a balance arm pivotally mounted to the base to rotate about the pivot axis with respect to the base and come to rest at a position indicative of the position of the center of gravity of the battery mounted therein, and wherein the means for producing an indication provides a calibrated visual indication of the position of the balance arm relative to the base calibrated to indicate the charge in the battery.

33. Apparatus for determining the charge of a battery according to claim 31, wherein the means for mounting the battery therein includes a substantially vertically oriented resilient member, a battery holder mounted on the resilient member and positioned to hold a battery in a position to exert a bending torque on the resilient member to cause the resilient member to bend, and wherein a change in the center of gravity of the held battery causes a change in the bending torque applied to the resilient member and a change in the bend of the resilient member, and wherein the means for producing an indication provides a calibrated visual indication of the bend of the resilient member calibrated to indicate the charge in the battery.

34. Apparatus for determining the charge of a battery according to claim 31, wherein the means for mounting the battery therein includes a substantially vertically oriented resilient member, a battery holder mounted on the resilient member and positioned to hold a battery in a position to exert a bending torque on the resilient member to cause the resilient member to bend, and wherein a change in the center of gravity of the held battery causes a change in the bending torque applied to the resilient member and a change in the bend of the resilient member, and electrically conductive traces on the resilient member leading to the battery holder and to terminals of the battery held in the holder to connect the battery in a battery circuit while held in the holder, and wherein the means for producing an indication includes a strain-gauge formed on the resilient member to provide an electrical signal indicative of the bend of the resilient member.

35. Apparatus for determining the charge of a battery according to claim 34, wherein the means for providing an indication includes means for producing an electrical signal representative of the temperature of the resilient member, electronic circuitry connected to receive the electrical signals from the strain-gauge and the electrical signal representative of the temperature of the resilient member and to produce an output signal representative of the bend of the resilient member, and display means for displaying the output signal representative of the bend of the resilient member in terms of the charge of the battery.

36. Apparatus for determining the charge of a battery according to claim 31, wherein the apparatus includes a base, wherein the means for mounting the battery includes means pivotally mounting the battery to the base, and a load cell positioned between the battery and the base, spaced from the pivotal mounting, to resist and measure pivoting force of the battery about its pivotal mounting, the battery being positioned with respect to the battery so that the pivoting force will depend upon the position of the center of gravity of the battery and the measure of the pivoting force will be indicative of the position of the center of gravity of the battery and amount of charge in the battery, electronic circuitry for receiving electrical signals from the load cell and producing output signals representative of the position of the center of gravity of the battery, and display means for displaying the output signals in terms of the charge of the battery.

37. Apparatus for use with a battery to indicate the remaining charge in the battery according to claim 31, wherein the apparatus includes a curved surface adapted to be placed on a flat surface and to rock thereon, and wherein the means for mounting the battery is positioned so that with the apparatus placed on a flat surface and the battery mounted therein, the apparatus will rock to and come to rest at a position indicative of the position of the center of gravity of the battery.

42. Apparatus for determining the charge of a battery according to claim 36, for use in weightless environments, additionally including a support platform to which the base is secured, means for causing oscillatory movement of the support platform which thereby subjects the base and everything attached thereto to oscillatory acceleration forces which cause the load cell to produce electrical output signals representative of sensible weight measured during the oscillations, and wherein the electronic circuitry includes means to filter out all components of negative acceleration and to time average components of positive acceleration to thereby calculate the position of the center of gravity of the battery and produce output signals representative of the position of the center of gravity of the battery.

38. A battery of the type which generates electricity through the reaction of a battery electrode with an electrolyte solution which causes a change in the chemical composition of the electrode and therefore a change in the weight and density of the electrode as the charge in the battery changes, and which battery has a cylindrical housing with a cylindrical axis and is adapted to display its state of charge, comprising:

at least one electrode within the housing located eccentrically with respect to the cylindrical axis so that as the battery discharges from a fully charged condition to a functionally discharged condition the center of gravity of the battery changes as the weight of the electrode changes; and

visual indications applied to the battery housing;

whereby when the battery is placed on a flat surface with its cylindrical axis parallel to the surface, the center of gravity of the battery will cause the battery to come to rest on the surface in a particular orientation and the visual indications in that orientation will display the amount of charge remaining in the battery.

39. A battery according to claim 38, wherein the visual indications include a marking representing fully charged condition positioned on the battery housing to be on top of the battery housing when the battery comes to rest on the surface and is in fully charged condition, and a marking representing discharged condition positioned on the battery housing to be on top of the housing when the battery comes to rest on the surface and the battery is in functionally discharged condition, and gradations therebetween.

40. A battery according to claim 38, wherein the at least one electrode located eccentrically within the housing includes a zinc powder anode with zinc metal insert therein wrapped in an electrolyte soaked separator material, said separator wrapped zinc material being located in an axially eccentric position within the cylindrical housing, a cathode mixture of oxygen-rich chemicals partially surrounding the separator wrapped zinc material and having an outer surface away from the wrapped zinc material, said zinc material oxidizing during discharge of the battery, an electric collector of conductive carbon in contact with the outer surface of the cathode mixture and contoured to fit inside the cylindrical housing, a thin layer of insulating material separating the electric collector from the cylindrical housing, a metal cathode button at the top of the cylindrical housing connected to the conductive carbon and insulated from the cylindrical housing, a metal anode cap at the bottom of the cylindrical housing connected to the zinc metal insert and insulated from the housing, and a longitudinal cavity of cross sectional area of at least 10% of the cross sectional area of the separator wrapped zinc material located immediately adjacent a side of the separator wrapped zinc material away from the cylindrical axis and between the separator wrapped zinc material and the thin layer of insulating material to provide an expansion space for the separator wrapped zinc material during oxidation and discharge of the battery, the location of the longitudinal cavity being such to amplify the shift in the center of gravity of the battery as the zinc material oxidizes during discharge of the battery.

41. A battery according to claim 40, including a light, porous, and shrinkable material filling the longitudinal cavity.

44. A method for determining the charge of a battery of a type which generates electricity through the reaction of a battery electrode with an electrolyte solution which causes a change in the chemical composition of the electrode and therefore a change in the weight of the electrode as the battery discharges, comprising the steps of:

determining the value of a parameter indicative of the weight of the electrode when the battery is substantially fully charged;

determining the value of the parameter indicative of the weight of the electrode when the battery is substantially functionally discharged;

determining at any time when it is desired to measure the charge remaining in the battery the value of the parameter indicative of the weight of the electrode at that time; and

relating the value of the parameter indicative of the weight of the electrode at that time to the values of the parameter indicative of the weights when fully charged and when functionally discharged to determine the remaining charge in the battery.

46. A method for determining the charge of a battery according to claim 44, wherein the determined value of the parameter is linearly related to the value of the parameter indicating a weight of the electrode when the battery is fully charged and a weight of the electrode when the battery is functionally discharged.

47. A method for determining the charge of a battery according to claim 44, wherein the parameter determined is the weight of the electrode.

48. A method for determining the charge of a battery according to claim 44, wherein the parameter determined is the position of the center of gravity of the battery.

49. A method for determining the charge of a battery according to claim 44,wherein the parameter determined is the change in the position of the center of gravity of the battery.

50. A method of determining the charge of a battery according to claim 44, wherein the parameter measured is a relative change in the weight of the electrode in relation to a second battery electrode.

45. A method for determining the charge of a battery of a type which generates electricity through the reaction of a battery electrode with an electrolyte solution which causes a change in the chemical composition of the electrode and therefore a change in the weight and density of the electrode as the battery discharges, comprising the steps of:

determining the value of a parameter indicative of the weight of the electrode at a time when it is desired to measure the charge remaining in the battery; and

relating the value of the parameter indicative of the weight of the electrode at that time to the value of the parameter indicating a weight of the electrode when the battery is fully charged and a value of the parameter indicating a weight of the electrode when the battery is functionally discharged to determine the remaining charge in the battery.