Method and apparatus for analyzing an AgZn battery

• US 6,215,312 B1
• Filed: 11/09/1999
• Issued: 04/10/2001
• Est. Priority Date: 11/09/1999
• Status: Expired due to Fees

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Alliedsignal Inc.
• Inventors: Palanisamy, Thirumalai G., Hoenig, Steven, Singh, Harmohan, Rudai, Patrick M.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US09/437,886
• Time in Patent Office: 518 Days
• Field of Search: 324/427, 324/430, 324/432, 324/433
• US Class Current: 324/427
• CPC Class Codes: G01R 31/2853 Electrical testing of internal connections or -isolation, e.g. latch-up or chip-to-lead connections G01R31/31717 takes precedence; test of chip-to-PCB or lead-to-PCB connections G01R31/66
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

A method and apparatus for diagnosing the status of a battery having high and low voltage plateau states corresponding to its state of charge in which the battery open circuit voltage is measured (S106) to determine its voltage state and its internal resistance also is measured (S114). A battery having a low voltage state (S116) is tested to determine if its internal resistance is greater than a predetermined maximum resistance (S118) and if it does the battery is considered as possibly having a low electrolyte level, and if it does not the battery is subjected to a current ramp test to determine from the voltage response a point of current transition (S130) due to a battery chemical gassing reaction. The battery state of charge (S132) is determined from curves or algorithms of state of charge versus current transition. Each of a battery of high voltage state (S116) whose internal resistance is less than the maximum internal resistance and one whose internal resistance is greater than the maximum internal resistance and has been subjected to reconditioning by applying successive current pulses (S124, S126) to reduce its internal resistance is subjected to a current ramp test (S134) to determine the point of current transition and the state of charge of such battery is determined (S136) from a different set of curves or algorithms of state of charge versus current transition. Capacity of a battery of the two voltage state types is determined by charging it to its capacity (S144), applying a current ramp (S144) to determine the point of current transition and determining capacity from curves or algorithms of battery capacity versus current transition (S150).

Claims

1. A method for diagnosing a battery having high and low open circuit voltage states corresponding to state of charge conditions of the battery, comprising:

measuring the internal resistance (IR) of the battery;

measuring the battery open circuit voltage (OCV);

comparing the battery'"'"'s measured internal resistance to a predetermined maximum internal resistance (IR_MAX) for the battery; and

subjecting a battery having an internal resistance less than said predetermined maximum internal resistance to a type of state of charge (SOC) test depending on the existence of the high or low voltage state of the battery as determined by the measuring of the battery open circuit voltage.

2. The method of claim 1 further comprising:

determining a battery defect in the form of a low electrolyte level by the measurement of the open circuit voltage indicating the low voltage state and an internal resistance greater than said maximum internal resistance for the battery.

3. The method of claim 1 further comprising:

determining the need for reconditioning of a battery by the measurement of an open circuit voltage of the high state and an internal resistance greater than said maximum internal resistance for the battery.

4. The method of claim 1 wherein the step of measuring the battery internal resistance comprises:

applying to the battery a pulse of current of value A amperes having a leading edge and a trailing edge;

measuring the voltage change (dV) produced on the trailing edge of the applied current pulse (dl) to determine dV/dl; and

computing the battery internal resistance from dV/dl.

5. The method of claim 1 wherein the step of measuring the battery internal resistance comprises:

applying to the battery a pulse of current of value I having a leading edge and a trailing edge;

measuring the voltage of the battery at the time of the maximum value of the trailing edge of the current pulse (V_FALL) and the open circuit voltage after termination of the current pulse (OCV_AFT); and

computing the internal resistance (IR) as IR=(V_FALL−

OCV_AFT)/I.

6. The method of claim 1 wherein the step of subjecting a battery having an internal resistance less than maximum internal resistance and an open circuit voltage of one of the low state or the high state to a state of charge test comprises:

applying a current ramp having a positive rising portion and a negative falling portion over a period of time (t) to the battery and measuring the battery voltage response (V);

computing from the measured voltage response a current value I_TRAN corresponding to an onset of a gassing reaction in the battery; and

determining the value of state of charge as a function of I_TRAN.

7. The method of claim 6 wherein I_TRAN is computed on the positive rising portion of the measured voltage response as a maximum $\frac{{}^{}}{}$

2

V

t2.

8. The method of claim 7 wherein for a battery of a low voltage state I_TRAN is computed as the maximum positive value of $\frac{{}^{}}{}$

2

V

t2.

9. The method of claim 7 wherein for a battery of a high voltage state I_TRAN is computed as the maximum negative value of $\frac{{}^{}}{}$

2

V

t2.

10. The method of claim 1 further comprising:

selecting a battery in which the state of charge exceeds a predetermined value; and

determining the Amp.hour capacity of the battery.

11. The method of claim 10 wherein the step of determining the capacity of a battery comprises:

charging the battery at a constant current to a predetermined charge state;

applying a ramp current of positively increasing slope to the battery;

measuring the battery voltage (V) response to the applied ramp current;

computing I_TRAN as the point on the voltage response curve where on the positive position of the current ramp the slope of the voltage dV/dt either remains constant or begins increasing after a period of decreasing $\left(\frac{{<br><br>}^2<br><br>V}{<br><br>t^2}\ge <br><br>0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{after}<br><br>\text{\hspace{1em}<br><br>}<br><br>a<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{period}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>V/<br><br>t<<br><br>0\right);<br><br>$

after a period of dV/dt<

0); and

determining the battery capacity as a function of I_TRAN.

12. The method of claim 11 further comprising stopping the ramp current when either the applied ramp current has reached a predetermined value or the voltage response thereto reaches a predetermined limit.

13. The method of claim 11 wherein the step of determining the battery capacity as a function of I_TRAN comprises:

preparing one of a curve equation and algorithm corresponding to the I_TRAN versus capacities of batteries having different measured values of I_TRAN; and

determining the capacity of the battery under test from the curve equation or algorithm.

16. The method of claim 1 further comprising the step of reconditioning a battery having a high state open circuit voltage state and an internal resistance greater than said predetermined maximum internal resistance before subjecting the battery to the state of charge test.

17. The method of claim 16 wherein said step of reconditioning comprises applying successive pulses of current to the battery to lower its internal resistance.

18. The method of claim 6 further comprising determining the Amp.hour capacity of the battery by

charging the battery at a constant current to a predetermined charge state;

applying a ramp current of positively increasing slope to the battery;

measuring the battery voltage (V) response to the applied ramp current;

computing I_TRAN as the point on the voltage response curve where on the positive position of the current ramp, the slope of the voltage dV/dt either remains constant or begins increasing after a period of decreasing $\left(\frac{{<br><br>}^2<br><br>V}{<br><br>t^2}\ge <br><br>0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{after}<br><br>\text{\hspace{1em}<br><br>}<br><br>a<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{period}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>V/<br><br>t<<br><br>0\right);<br><br>$

after a period of dV/dt<

0); and

determining the battery capacity as a function of I_TRAN by preparing one of a curve equation and algorithm corresponding to the I_TRAN versus capacities of batteries having different measured values of I_TRAN and determining the capacity from the curve equation or algorithm.

14. A method of determining the Amp.Hour capacity of a battery comprising:

charging the battery at a constant current to a predetermined charged state;

applying a pulse of current to the battery and monitoring the battery response voltage to determine a V limit at the time before the current pulse returns to a minimum value;

applying a ramp current of positively increasing slope to the battery and monitoring the battery response voltage V;

terminating the ramp current at one of a predetermined current limit or the response voltage reaching V limit;

computing I_TRAN corresponding to an onset of battery gassing reaction as the point on the voltage response curve where on the positive portion of the current ramp the slope of the voltage V response curve either remains substantially constant or begins increasing after a period of decrease; and

determining the battery capacity as a function of I_TRAN.

15. The method of claim 14 wherein the step of determining the battery capacity as a function of I_TRAN comprises:

preparing one of a curve equation and algorithm corresponding to the I_TRAN versus capacities of batteries having different measured values of I_TRAN; and

determining the capacity from the curve or algorithm.

19. A system for diagnosing a battery having high and low open circuit voltage states corresponding to state of charge conditions of the battery comprising:

computer means including a control program for

(a) controlling the application of a ramp current from a current supply source to a battery and measuring the voltage response,

(b) determining the point of current transition due to battery chemical reaction in response to the applied ramp current, and

(c) computing the battery state of charge from one of at least one algorithm of transition current point versus state of charge and the Amp.hour battery capacity from at least one algorithm of transition current versus Amp.hour battery capacity.

20. The system of claim 19 wherein said computer means further comprising:

means for measuring the battery open circuit voltage (OCV);

means for measuring the internal resistance (IR) of the battery; and

wherein said computer means determines the point of current transition in a manner based upon the measured open circuit voltage which determines its voltage state and its measured internal resistance.