Method for determining capacity of lead-acid batteries of various specific gravities

• US 20060226845A1
• Filed: 03/31/2005
• Published: 10/12/2006
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell (Honeywell International Inc.)
• Inventors: Atehortua, Hector M., Palanisamy, Thirumalai G., Singh, Harmohan N., Hoenig, Steven
• Granted Patent: US 7,471,090 B2
• Time in Patent Office: Days
• US Class Current: 324/433
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/379 for lead-acid batteries

Abstract

In accordance with various embodiments, there is a method for determining the capacity of a battery. Various embodiments include applying a predetermined current ramp to a fully charged lead-acid battery while measuring a battery terminal voltage. An I_up can be determined, where the I_up is a transition from charging to overcharging. A specific gravity of the lead-acid battery can also be determined. The capacity of the lead-acid battery can then be determined from the I_up using a correlation function that describes the relationship of the I_up to the capacity, where the correlation function depends on the specific gravity of the lead-acid battery.

Claims

1. A method of determining a capacity of a lead-acid battery comprising:

applying a predetermined current ramp to a fully charged lead-acid battery while measuring a battery terminal voltage;

determining an I_up, wherein the I_up is a transition current from charging to overcharging;

determining a specific gravity of the lead-acid battery;

determining the capacity of the lead-acid battery from the I_up using a correlation function that describes the relationship of the I_up to the capacity, wherein the correlation function depends on the specific gravity of the lead-acid battery.

2. The method of claim 1, wherein the step of applying a predetermined current ramp to the lead-acid battery while measuring a battery terminal voltage comprises:

applying a linearly increasing current ramp to the lead-acid battery while measuring a battery terminal voltage, wherein the increasing current ramp has a slope; and

applying a decreasing current ramp to the lead-acid battery while measuring a battery terminal voltage after the battery terminal voltage reaches a safe limit, wherein the decreasing current ramp has a same slope as an absolute value of the increasing current ramp.

3. The method of claim 2, wherein the slope of the linearly increasing current ramp is about 0.33 A/sec.

4. The method of claim 3, wherein the specific gravity is about 1.30 and wherein the correlation function is:

Capacity=(I_up ×

27.58)−

45.35.

5. The method of claim 3, wherein the specific gravity is about 1.28 and wherein the correlation function is:

Capacity=(I_up ×

28.95)−

36.97.

6. The method of claim 1, wherein determining an I_up comprises:

calculating a slope (dV/dt) of the battery terminal voltage in response to the increasing current ramp and the decreasing current ramp; and

determining I_up where I_up is a current corresponding to a local maximum of the slope of the battery terminal voltage.

7. The method of claim 1, further comprising determining the correlation function for a known specific gravity.

8. The method of claim 1, further comprising determining the correlation function for another predetermined slope.

9. An apparatus for determining a capacity of a lead-acid battery comprising:

a power supply;

a control module comprising an analog-to-digital converter, a digital-to-analog converter, and an electronics control system, wherein the control module controls the power supply to apply a current to a lead-acid battery;

a control relay electrically connected to the power supply;

a sensor that detects a battery voltage response to a current ramp, the sensor electrically connected to the control relay; and

a processor configured to determine I_up, where I_up is a current at a gassing point;

the processor further configured to determine a capacity of the lead-acid battery based on the I_up and a specific gravity of the lead-acid battery.

10. The apparatus of claim 9, wherein the processor is further configured to determine the number of gas points of the lead-acid battery.

11. The apparatus of claim 9, wherein the processor is further configured to determine the specific gravity of the lead-acid battery by comparing a maximum battery voltage detected in the battery voltage response divided by a number of cells of the battery, to an SG_Lim, where the SG_Lim is an upper limit of the maximum measured battery voltage for a low specific gravity battery divided by the number of cells of the low specific gravity battery.

12. The apparatus of claim 9, wherein the control module controls application of the current ramp to the lead-acid battery.

13. The apparatus of claim 9, wherein the current ramp comprises:

a linearly increasing current of about 0.33 A/sec to a predetermined limit; and

a linearly decreasing current of about 0.333 A/sec after reaching the predetermined limit.

14. A computer readable medium for determining a capacity of a battery, the computer readable medium comprising:

program code for applying a current ramp to a fully charged battery;

program code for measuring an battery terminal voltage response to the current ramp;

program code for determining an I_up, wherein the I_up is a transition from charging to overcharging;

program code for determining a specific gravity of the lead-acid battery;

program code for determining the capacity of the lead-acid battery from the I_up using a correlation function, wherein the correlation function depends on the specific gravity of the lead-acid battery.

15. The computer readable medium of claim 14, wherein the current ramp is about 0.33 A/sec, the specific gravity is about 1.28, and the correlation function is:

Capacity=(I_up ×

28.95)−

36.97.

16. The computer readable medium of claim 14, wherein the current ramp is about 0.33 A/sec, the specific gravity is about 1.30, and the correlation function is:

Capacity=(I_up×

27.58)−

45.35.

17. The computer readable medium of claim 14, wherein the program code for determining a specific gravity of the lead-acid battery comprises:

program code for detecting gas points;

program code for calculating a maximum voltage per cell of the battery; and

program code for comparing a maximum battery voltage detected in the battery voltage response to the current ramp divided by the number of cells of the battery, to an SG_Lim, where the SG_Lim is an upper limit of a maximum measured battery voltage of a low specific gravity battery divided by the number of cells of the low specific gravity battery.

18. The computer readable medium of claim 14, further comprising program code for indicating the capacity of the battery.

19. The computer readable medium of claim 14, further comprising program code for fully charging the lead acid battery.