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

• US 7,471,090 B2
• Filed: 03/31/2005
• Issued: 12/30/2008
• Est. Priority Date: 03/31/2005
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Palanisamy, Thirumalai G., Singh, Harmohan N., Hoenig, Steven, Atehortua, Hector M.
• Primary Examiner(s): Ullah; Akm E
• Assistant Examiner(s): RAMADAN, RAMY O
• Application Number:
  US11/094,444
• Publication Number:
  US 20060226845A1
• Time in Patent Office: 1,370 Days
• Field of Search: 320/134, 324/426, 324/427
• US Class Current: 324/427
• 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:

providing a lead-acid battery having at least one cell;

fully charging the lead-acid battery;

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

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, wherein the slope of the linearly increasing current ramp is about 0.33 A/sec;

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

determining a battery specific gravity of the lead-acid battery; and

calculating the capacity of the lead-acid battery dependent upon the determined battery specific gravity using a correlation function, wherein the correlation function is Capacity=(I_up×

27.58)−

45.35 when the full charge specific gravity is about 1.30 or Capacity=(I_up×

28.95)−

36.97 when the battery specific gravity is about 1.28.

2. 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.

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

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

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

program code for determining when a lead-acid battery is fully charged;

program code for applying a current ramp to the fully charged lead-acid battery;

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

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

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

program code for calculating the capacity of the lead-acid battery dependent upon the determined battery specific gravity;

wherein the current ramp is about 0.33 A/sec, wherein the program code for calculating the capacity includes coding for a correlation function wherein the correlation function is Capacity=(I_up×

27.58)−

45.35 when the battery specific gravity is about 1.30 or Capacity=(I_up×

28.95)−

36.97 when the battery specific gravity is about 1.28.

6. The computer readable medium of claim 5, wherein the program code for determining a full charge 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 full charge specific gravity battery divided by the number of cells of the low full charge specific gravity battery.

7. The computer readable medium of claim 5, further comprising program code for indicating the capacity of the battery.

8. The computer readable medium of claim 5, further comprising program code for fully charging the lead acid battery.