Apparatus and method for determining the capacity of a nickel-cadmium battery

• US 5,926,008 A
• Filed: 09/15/1998
• Issued: 07/20/1999
• Est. Priority Date: 09/15/1998
• Status: Expired due to Fees

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Alliedsignal Inc.
• Inventors: Palanisamy, Thirumalai G., Patel, Alpesh, Singh, Harmohan, Rudai, Patrick M.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/153,606
• Time in Patent Office: 308 Days
• Field of Search: 320/132, 320/156, 320/161, 320/155
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3835 involving only voltage measurements

Abstract

The invention provides for a timesaving method of determining the capacity of a nickel cadmium (NiCd). A fully charged NiCd battery under is subjected to a positive sloped current charge ramp and then a negative sloped current charge ramp while continuously monitoring the battery terminal voltage. The voltage is plotted and the maximum slope of the measured terminal voltage determines l_gas. The value of I_gas is compared to a temperature calibration curve to determine the capacity of the battery under test.

Claims

1. A method for determining the capacity of a nickel cadmium battery comprising:

a) measuring the ambient temperature of the battery;

b) charging said battery with a current charge;

c) determining the current charge value I_gas when said battery begins to evolve gas; and

d) comparing said I_gas value of c) against a known battery capacity vs. I_gas relationship at said measured temperature.

2. A method for determining the capacity of a nickel cadmium battery comprising:

a) measuring the temperature of said battery;

b) subjecting said battery to an increasing current charge and then a decreasing current charge;

c) measuring the battery terminal voltage during step (a);

d) determining the maximum slope of the measured battery terminal voltage;

e) calculating the current charge value I_gas associated with said maximum slope;

f) comparing said I_gas value of e) against a known battery capacity vs. I_gas relationship at said measured temperature.

3. The method of claim 2 wherein said increasing current charge increases as a function of time.

4. The method of claim 2 wherein said increasing current charge is current pulses with each subsequent current pulse having a higher current magnitude than the preceding current pulse.

5. The method of claim 2 wherein said decreasing current charge decreases at the same, but negative rate as said increasing current charge.

6. The method of claim 3 wherein the rate of said current charge is a 0.22 A/500 millisecond step.

7. Apparatus for detecting the capacity of a nickel cadmium battery comprising:

a) measurement means for measuring the battery temperature;

b) current means for generating an increasing current charge applied to the battery;

c) current means for generating a decreasing current charge applied to the battery subsequent to the increasing current charge;

d) voltage sensing means for sensing the battery terminal voltage during application of the current charge; and

e) calculating means for determining the maximum slope of said battery voltage;

f) first comparing means for determining the current charge value I_gas associated with the calculated maximum voltage slope; and

g) second comparing means for comparing said I_gas value of f) against a known battery capacity vs. I_gas relationship at said measured temperature.