Apparatus and method for indicating state of charge of a battery

• US 5,130,658 A
• Filed: 08/29/1990
• Issued: 07/14/1992
• Est. Priority Date: 02/28/1990
• Status: Expired due to Term

• Current Assignee: DISPLAY MATRIX CORPORATION
• Original Assignee: DISPLAY MATRIX CORPORATION
• Inventors: Bohmer, William
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Regan, Maura K.
• Application Number:
  US07/574,661
• Time in Patent Office: 685 Days
• Field of Search: 324/435, 340/636, 340/722, 331/113 R, 307/264, 320/48, 350/332 R
• US Class Current: 324/435
• CPC Class Codes: G01R 13/403 using passive display devices, e.g. liquid crystal display or Kerr effect display devices
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3646 for indicating electrical conditions or variables, e.g. visual or audible indicators

Abstract

A device for indicating the state of charge of an electrochemical cell or battery includes a regulated-voltage generating circuit having an input connectable to the cell and an output providing a regulated reference voltage, an amplifying circuit having an input connectable to the cell and an output having a predetermined relation to a voltage within a predetermined range applied to the input of the amplifying unit, and a solid state analog display unit having a reference input connected to the output of the regulated-voltage generating circuit and an address input connected to the amplifying circuit. The relation between the address voltage output of the amplifying circuit and the cell voltage input is such that the address voltage corresponds to the state of charge of the cell in the predetermined range of cell voltages and falls within the range of the most negative and most positive values of the reference voltage. The device is adaptable for use as an integral state of charge indicator for a battery-operated tool or appliance or as a charge tester for different sizes and types of consumer batteries. One such battery tester has a housing shell provided with a plurality of shaped recesses, each recess receiving a single type or size of battery for test. A number of recesses are aligned so that a single spring-biased metal contact strip can be used for the number of recesses. The spring backing for the contact strip is a resilient pad of plastic foam material.

Claims

1. A device for indicating the state of charge of an electrochemical cell as a function of an output voltage appearing across negative and positive output terminals of the cell, the output voltage lying in a predetermined range and having a predetermined relation to the state of charge of the cell, the device comprising

an amplifying circuit having an input to be connected to the negative and positive terminals of a cell of which the state of charge is to be indicated and an output, the amplifying circuit including means for producing a voltage at the output of the amplifying circuit that is a predetermined function of an output voltage of the cell in said predetermined range;

a regulated-voltage generating circuit having an input to be connected to the negative and positive terminals of the cell to be tested and an output, the regulated-voltage generating circuit including means for producing at the output of the regulated-voltage generating circuit a predetermined fixed regulated reference voltage in response to an output voltage of the cell falling within said predetermined range applied to the input of the regulated-voltage generating circuit; and

an analog solid state display unit having a first input connected to the output of the amplifying circuit and a second input connected to the output of the reference-voltage generating circuit, the display unit producing a visual analog indication of the state of charge of a cell being tested when an output voltage of the cell falling within said predetermined range is applied to the inputs of the amplifying and regulated-voltage generating circuits.

2. An indicating device according to claim 1 wherein the means of the amplifying circuit for producing a voltage at the output of the amplifying circuit that is a function of the output voltage of the cell comprises means for producing a voltage that is a linear function of the output voltage of the cell when the output voltage of the cell falls within said predetermined range.

3. An indicating device according to claim 2 wherein the voltage produced at the output of the amplifying circuit when the output voltage of a cell connected to the input of the amplifying circuit falls within said predetermined range is not greater than the regulated reference voltage produced at the output of the reference-voltage generating circuit when said cell is connected to the input of the reference-voltage generating circuit.

4. An indicating device according to claim 1 wherein the amplifying circuit comprises:

a transistor having a collector, an emitter, and a control electrode;

a load resistor having a first end connected to one of the collector and emitter of the transistor and a second end connected to the output of the reference-voltage generating circuit; and

a current-limiting resistor having a first end connected to the other of the collector and emitter of the transistor and a second end, the control electrode of the transistor and the second end of the current-limiting resistor being connected to the input of the regulated-voltage generating circuit.

5. An indicating device according to claim 4 wherein the reference-voltage generating circuit comprises first and second transistors connected as a multivibrator, a resistor connected in one of a collector leg and an emitter leg of the first transistor, an inductor connected in one of a collector leg and an emitter leg of the second transistor so that current flows through the inductor when the second transistor is turned on, a storage capacitor connected in circuit with the inductor so as to be charged by the collapsing field of the inductor when the second transistor is shut off, and a combination charging diode and voltage limiting device connected in circuit with the capacitor to limit the charge voltage of the capacitor to the value of the predetermined regulated reference voltage.

6. An indicating device according to claim 5 wherein the combination charging diode and voltage limiting device is a zener-effect element.

7. An indicating device according to claim 6 wherein the zener-effect element is selected from the group consisting of a zener diode and a transistor connected as a diode.

8. An indicating device according to claim 7 wherein the input of the regulated-voltage generating circuit comprises a negative bus and a positive bus, the inductor being connected between one of the collector and emitter of the second transistor and one of the negative and positive buses, a control grid of the zener-effect transistor being connected to the junction between the inductor and the second transistor, one of a collector and emitter of the zener-effect transistor being connected to one side of the capacitor, and the other side of the capacitor being connected to the other of the negative and positive buses.

9. An indicating device according to claim 1 wherein the analog display unit comprises:

first and second plates, at least one of which is transparent, the plates being spaced apart by a small gap and having respective first and second inner surfaces facing each other across the gap;

a field-effect visual display dielectric material disposed in the gap between the first and second plates;

an address electrode disposed on the first inner surface of the first plate, the address electrode being conductively connected to the output of the amplifying circuit; and

a reference electrode disposed on the second inner surface of the second plate, the reference electrode being conductively connected to the output of the reference-voltage generating circuit.

10. A device according to claim 1 wherein the analog display device comprises:

first and second plates, at least one of which is transparent, the plates being spaced apart by a small gap and having respective first and second inner surfaces facing each other across the gap;

a field-effect visual display dielectric material disposed in the gap between the first and second plates;

a non-resistive address electrode disposed on the first inner surface and having an area corresponding to a preselected area of a visual analog display, the address electrode being conductively connected to the first input of the display unit;

a series of non-resistive conductor strips disposed in spaced parallel relation on the second inner surface across the area of the analog visual display;

an elongated resistive element disposed along a side of the second plate perpendicularly to the conductor strips, the resistive element being connected across the second input of the display unit, and the conductor strips being electrically connected to the resistive element at spaced-apart locations along the length of the resistive element, such that each conductor assumes a different incremental voltage when the regulated reference voltage is applied to the second input of the display unit.

11. An indicating device according to claim 10 wherein the field-effect visual display dielectric material requires a minimum actuating voltage for changing from a first visual state to a second visual state such that when the value of an output voltage of the amplifying circuit applied to the first input of the display unit is between the most negative and most positive values of the regulated reference voltage applied to the second input of the display unit, the resulting display shows a bar having the appearance of the first visual state at a region of the display area where the voltages on the conductor strips differ from the output voltage of the amplifying circuit applied to the address electrode by less than the actuating voltage, and the remainder of the display area has the appearance of the second visual state of the field-effect dielectric material.

12. An indicating device according to claim 11 wherein the width of the bar having the appearance of the first visual state is a function of the magnitude of the regulated reference voltage.

13. An indicating device according to claim 1 wherein the means for producing the predetermined regulated reference voltage at the output of the regulated-voltage generating circuit comprises;

means for converting the output voltage of the cell into a succession of pulses;

means for shaping each pulse into a high-voltage short duration pulse;

a storage device;

means for delivering each shaped pulse to the storage device; and

means for limiting the voltage of the storage device to the preselected value of the regulated reference device.

14. An indicating device according to claim 13 wherein the means for converting the output voltage of the cell comprises a multivibrator circuit having an input corresponding to the input of the regulated-voltage generating circuit and an output for delivering the succession of pulses;

and

the means for shaping each pulse into a high-voltage short duration pulse comprises an inductor for producing the high-voltage short duration pulses.

15. An indicating device according to claim 1 wherein the analog solid state display unit provides a bar graph presentation.

16. An indicating device according to claim 1 wherein the analog solid state display unit is a liquid crystal display unit.

17. A device for indicating the state of charge of a battery in an apparatus powered by the battery, the device comprising:

a solid state display unit having a reference voltage input and first and second address inputs, each address input being connected to respective first and second adjacent analog display elements;

an amplifying circuit having an input and an output, the circuit including means for producing a voltage at the output that has a predetermined characteristic corresponding to values of the battery voltage applied to the input in a preselected range of battery voltages under load that relate directly to the state of charge of the battery;

an input switch for connecting the input of the amplifying circuit to the battery when the battery is supplying power to the apparatus;

an output switch for periodically connecting the output of the amplifying circuit alternately to the first and second address inputs when the battery is connected to the input of the amplifying circuit;

a regulated-voltage generating circuit having an input connected to the battery through the input switch and an output connected to the reference voltage input of the display unit for supplying a reference voltage to both display elements of the display unit when the input of the amplifying circuit is connected to the battery; and

means connected between the output of the amplifying circuit and the first display element for storing at least one of the alternately applied output voltages so that the first display element shows a previous value of the state of charge of the battery when the second display element shows a current value of the state of charge of the battery, whereby the difference in displayed values by the two display elements provides an optical indication of the rate of change of the state of charge of the battery.

18. An indicating device according to claim 17 wherein the display unit comprises first and second parallel plates having a gap between them, at least one of the plates being transparent and being subdivided into first and second side-by-side elongated display regions, the first plate having first and second electrically conductive surfaces facing the gap in the respective first and second display regions and being connected to the respective first and second address inputs, and the second plate having first and second electrically nonconductive surfaces facing the gap in the respective first and second display regions;

a plurality of conductive elements disposed in predetermined spaced-apart relation on the nonconductive surfaces of the second plate in the first and second display regions;

an impedance element connected to the reference voltage input for distributing the reference voltage as a voltage gradient, each of the conductive elements in each display region being connected to the impedance element at a different point of the voltage gradient so that adjacent conductive elements in each display region have incrementally different electrical potentials; and

liquid crystal material disposed in the gap between first and second plates in the two display regions.

19. An indicating device according to claim 18 wherein the impedance element comprises an elongated resistive element having a predetermined resistance per unit length in accordance with said voltage gradient.

20. An indicating device according to claim 19 wherein the plurality of conductive elements disposed on the second plate in each display region comprise a plurality of parallel strips extending transversely to the longitudinal dimension of the display region, and the resistive element extends adjacent a corresponding end portion of each of the conductive strips, the end portion of each of the conductive strips being electrically connected in the order of the plurality of strips to different locations disposed along the length of the resistive element.

21. An indicating device according to claim 20 wherein the voltage gradient along the length of the resistive element is a linear gradient.

22. A method for providing an optical presentation of the state of charge of an electrochemical cell on an analog liquid crystal display unit having a pair of plates spaced apart from one another to form a gap therebetween and a liquid crystal material disposed in the gap, at least one of the plates being substantially transparent, and the unit having a reference voltage input and at least one address voltage input, wherein the method comprises:

deriving a reference voltage having a predetermined fixed value from an output voltage of the cell within a preselected range corresponding to a range of charge states to be optically presented on the display unit;

deriving an address voltage from the output voltage of the cell within the preselected range, the value of the address voltage having a predetermined relation to the state of charge corresponding to the output voltage of the cell and falling within the most negative and most positive values of the reference voltage;

applying the reference voltage to the reference voltage input of the display unit; and

applying the address voltage to the at least one address input of the display unit so as to cause the liquid crystal material to provide an optical presentation corresponding to the state of charge of the cell.

23. A method according to claim 22 wherein the step of deriving a reference voltage comprises:

converting the output voltage of the cell to a succession of voltage pulses, each pulse having a peak value higher than the output value of the cell;

storing the voltage pulses to provide a source of constant voltage; and

limiting the value of the stored constant voltage to the predetermined value of the reference voltage.

24. A method according to claim 22 wherein the step of deriving an address voltage comprises amplifying the output voltage of the cell by a preselected factor depending on the selected magnitude of and the most negative and most positive values of the reference voltage.

25. A method according to claim 22 wherein the display unit has first and second display regions and first and second address inputs, one to each display region, and wherein the step of applying the address voltage to the at least one address input comprises periodically sampling an instantaneous value of the address voltage;

alternately storing a sampled address voltage and applying a sampled address voltage to one of the first and second address inputs; and

periodically applying at least one previously stored sampled address voltage to the other of the first and second address inputs, such that the one of the first and second display regions shows a periodically updated instantaneous state of charge of the cell, the other of the first and second display regions shows a previous value of the state of charge, and the difference between the two displays is an indication of the rate of change of the state of charge.