Electronic battery tester with automatic compensation for low state-of-charge

• US 5,585,728 A
• Filed: 06/29/1995
• Issued: 12/17/1996
• Est. Priority Date: 05/01/1992
• Status: Expired due to Term

• Current Assignee: Keith S Champlin
• Original Assignee: Keith S Champlin
• Inventors: Champlin, Keith S.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): BROWN, GLENN WARNER
• Time in patent office: 537 Days
• Field of Search: 320/48, 324/427, 324/430, 324/433, 324/436, 324/442, 340/636
• US Class Current: 324/427
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

Three embodiments of an improved electronic device for testing or monitoring storage batteries that may be only partially charged are disclosed. The device determines the battery'"'"'s small-signal dynamic conductance in order to provide either a proportional numerical readout, displayed in appropriate battery measuring units, or a corresponding qualitative assessment of the battery'"'"'s relative condition based upon its dynamic conductance and electrical rating. Without additional user intervention, the device also determines the battery'"'"'s terminal voltage in an essentially unloaded condition and utilizes this information to automatically correct the measured dynamic conductance. By virtue of this automatic correction, the quantitative or qualitative information displayed to the user conforms with that of a fully-charged battery even though the battery may, in actual fact, be only partially charged. If the battery'"'"'s state-of-charge is too low for an accurate assessment to be made, no information is displayed. Instead, an indication is made to the user that the battery must be recharged before testing.

Claims

1. An electronic device for assessing the condition of an electrochemical cell or battery having a dynamic conductance and an open-circuit voltage comprising:

means operably connected to said cell or battery for detecting said dynamic conductance and for generating a signal proportional thereto;

means operably connected to said cell or battery for sensing said open-circuit voltage;

correction means coupled to said means for detecting said dynamic conductance and directly electrically coupled to said means for sensing said open-circuit voltage, said correction means for responding to said open-circuit voltage by adjusting the level of said signal in accordance with said open-circuit voltage; and

,

means for displaying an assessment of said cell or battery in accordance with the adjusted level of said signal.

2. An electronic device as in claim 1 wherein said correction means adjusts said level of said signal in inverse correspondence with the value of said open-circuit voltage relative to a fully-charged value.

3. An electronic device as in claim 2 wherein said correction means comprises a correction amplifier having an input voltage and an output voltage, said input voltage being derived from said open-circuit voltage and said output voltage being proportional to said adjusted level of said signal.

4. An electronic device as in claim 3 wherein said correction amplifier comprises a reference voltage, a plurality of operational amplifier, a plurality of diodes, and a plurality of resistors interconnected to provide a piece-wise linear transfer function relating said output voltage to said input voltage.

5. An electronic device for assessing the condition of an electrochemical cell or battery having an internal resistance and a dc terminal voltage comprising:

means directly electrically coupled to said electrochemical cell or battery for generating a time-varying first signal inversely related to said dc terminal voltage;

current generating means coupled to said electrochemical cell or battery and to said means for generating a time-varying first signal, said current generating means for producing a second signal directly proportional to said first signal and inversely proportional to said internal resistance; and

means coupled to said current generating means for sensing said second signal and for relating said second signal to said condition of said electrochemical cell or battery.

6. An electronic device as in claim 5 wherein said means for generating a time-varying first signal includes a nonlinear dc amplifier means for amplifying said dc terminal voltage and further includes a chopper means for chopping a dc output of said nonlinear dc amplifier means to produce said time-varying first signal.

7. An electronic device as in claim 6 wherein said nonlinear dc amplifier means has a piecewise-linear transfer function.

8. An electronic device for assessing the condition of an electrochemical cell or battery having a dc terminal voltage comprising:

means directly electrically coupled to said electrochemical cell or battery for generating a time-varying input signal inversely related to said dc terminal voltage;

high-gain amplifier means for providing an output signal;

internal feedback means including low-pass filter means for coupling said output signal to the input of said high-gain amplifier means;

external feedback means including feedback resistor means for coupling said output signal to said electrochemical cell or battery;

capacitive coupling means for coupling said input signal and a time-varying voltage across said electrochemical cell or battery to said input of said high-gain amplifier means; and

,

means coupled to said high-gain amplifier means for sensing said output signal and for relating said output signal to said condition of said electrochemical cell or battery.

9. An electronic device as in claim 8 wherein said means for generating a time-varying input signal includes a nonlinear dc amplifier means for amplifying said dc terminal voltage and further includes a chopper means for chopping a dc output of said nonlinear dc amplifier means to produce said time-varying input signal.

10. An electronic device as in claim 9 wherein said nonlinear dc amplifier means has a piecewise-linear transfer function.

11. An electronic device for assessing the condition of an electrochemical cell or battery having a dynamic parameter and an open-circuit voltage comprising:

means operably connected to said cell or battery for measuring said dynamic parameter;

means operably connected to said cell or battery for sensing said open-circuit voltage;

correction means coupled to said means for measuring said dynamic parameter and directly electrically coupled to said means for sensing said open-circuit voltage, said correction means for responding to said open-circuit voltage by adjusting a measured dynamic parameter value in accordance with said open-circuit voltage to obtain a corrected dynamic parameter value; and

means for displaying an assessment of said condition of said electrochemical cell or battery in conformance with said corrected dynamic parameter value.

12. An electronic device in accordance with claim 11 including means for providing a special indication when said open-circuit voltage is less than a predetermined value and further including means for suppressing said assessment when said open-circuit voltage is less than a predetermined value.

13. An electronic device in accordance with claim 11 wherein said dynamic parameter is dynamic conductance and said correction means includes correction amplifier means having an input voltage and an output voltage, said input voltage being proportional to said open-circuit voltage and said output voltage being proportional to the ratio of said corrected dynamic conductance value to said measured dynamic conductance value.

14. An electronic device in accordance with claim 11 wherein said dynamic parameter is dynamic conductance and said correction means comprises a firmware correction program implemented by microprocessor means and wherein digital representations of said open-circuit voltage and said dynamic conductance are both inputted to said microprocessor and combined algorithmically to obtain said corrected dynamic conductance value based upon said firmware correction program.

15. An electronic device in accordance with claim 11 wherein said dynamic parameter is dynamic resistance and said correction means comprises a firmware correction program implemented by a microprocessor, and wherein digital representations of said open-circuit voltage and said dynamic resistance are both inputted to said microprocessor and combined algorithmically to obtain said corrected dynamic resistance value based upon said firmware correction program.

16. An electronic device in accordance with claim 11 wherein said assessment comprises numbers proportional to said corrected dynamic parameter value.

17. An electronic device in accordance with claim 11 wherein said assessment comprises a qualitative assessment in conformance with said corrected dynamic parameter value relative to a reference dynamic parameter value.

18. An electronic device in accordance with claim 17 wherein said electrochemical cell or battery has an electrical rating, said electronic device includes means for inputting the value of said rating, and said reference dynamic parameter value is determined by the particular value of said electrical rating thus inputted.

19. An electronic device for assessing the condition of an electrochemical cell or battery having a dynamic conductance, an open-circuit voltage, and a state-of-charge comprising:

means operably connected to said cell or battery for determining a digital representation of said dynamic conductance;

means directly electrically connected to said cell or battery for determining a digital representation of said open-circuit voltage;

microprocessor means for implementing a firmware correction program, said microprocessor means directly electrically coupled to said means for determining a digital representation of said dynamic conductance and to said means for determining a digital representation of said open-circuit voltage and algorithmically combining said digital representation of said dynamic conductance with said digital representation of said open-circuit voltage to obtain an assessment result representative of said dynamic conductance corrected to represent its presumed value at 100% state-of-charge based upon said firmware correction program; and

means for displaying said assessment result.

20. An electronic device as in claim 19 wherein said assessment result comprises numbers proportional to said dynamic conductance corrected to represent its presumed value at 100% state-of-charge.

21. An electronic device as in claim 19 wherein said assessment result comprises a qualitative result determined in accordance with the value of said dynamic conductance corrected to represent its presumed value at 100% state-of-charge relative to a reference value.

22. An electronic device as in claim 21 wherein said electrochemical cell or battery has an electrical rating and said electronic device includes means for inputting said electrical rating to said microprocessor means, said reference value being determined by the particular value of said electrical rating thus inputted.

23. An electronic device for assessing the condition of an electrochemical cell or battery having a dynamic resistance, an open-circuit voltage, a state-of-charge, and an electrical rating, comprising:

means operably connected to said cell or battery for determining a digital representation of said dynamic resistance;

means directly electrically connected to said cell or battery for determining a digital representation of said open-circuit voltage;

microprocessor means for implementing a firmware correction program, said microprocessor means directly electrically coupled to said means for determining a digital representation of said dynamic resistance and to said means for determining a digital representation of said open-circuit voltage and algorithmically combining said digital representation of said dynamic resistance with said digital representation of said open-circuit voltage based upon said firmware correction program thereby evaluating a reciprocal dynamic resistance corrected to represent its presumed value at 100% state-of charge;

means for inputting said electrical rating to said microprocessor means for determining a reference quantity therefrom;

means for comparing said reference quantity with said reciprocal dynamic resistance corrected to represent its presumed value at 100% state-of-charge; and

means for displaying a qualitative assessment of said condition of said electrochemical cell or battery in accordance with said comparison.

24. An electronic device as in claim 23 including means for suppressing said qualitative assessment and for providing a special indication when said open-circuit voltage is less than a predetermined value.

25. An electronic device for assessing the condition of an electrochemical cell or battery having a dynamic resistance, an open-circuit voltage, a state-of-charge, and an electrical rating comprising:

means operably connected to said cell or battery for determining a digital representation of said dynamic resistance;

means directly electrically connected to said cell or battery for determining a digital representation of said open-circuit voltage;

microprocessor means for implementing a firmware correction program, said microprocessor means directly electrically coupled to said means for determining a digital representation of said dynamic resistance and to said means for determining a digital representation of said open-circuit voltage and algorithmically combining said digital representation of said dynamic resistance with said digital representation of said open-circuit voltage based upon said firmware correction program thereby evaluating a dynamic resistance corrected to represent its presumed value at 100% state-of-charge;

means for inputting said electrical rating to said microprocessor means for determining a reference quantity therefrom;

means for comparing said reference quantity with said dynamic resistance corrected to represent its presumed value at 100% state-of-charge; and

,

means for displaying a qualitative assessment of said condition of said electrochemical cell or battery in accordance with said comparison.

26. An electronic device as in claim 25 including means for suppressing said qualitative assessment and for providing a special indication when said open-circuit voltage is less than a predetermined value.