Apparatus and method for detecting memory effect in nickel cadmium batteries

• US 6,094,051 A
• Filed: 09/15/1998
• Issued: 07/25/2000
• Est. Priority Date: 09/15/1998
• Status: Expired due to Fees

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Alliedsignal Inc.
• Inventors: Patel, Alpesh, Palanisamy, Thirumalai G., Singh, Harmohan, Rudai, Patrick M.
• Primary Examiner(s): Ballato, Josie
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US09/153,401
• Time in Patent Office: 679 Days
• Field of Search: 324/433, 324/426, 324/71.1, 324/431
• US Class Current: 324/426
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm

Abstract

The invention provides for a timesaving method of determining whether a nickel cadmium (NiCd) battery is stricken with memory effect. A fully charged NiCd battery under test ("test battery") 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 maximum measured terminal voltage of the test battery is compared to the measured terminal voltage of a NiCd battery of the same nominal voltage and capacity and known not to have memory effect ("normal"battery). A NiCd battery is determined to have memory effect if the maximum voltage of the test battery exceeds the maximum voltage of the normal battery.

Claims

1. A method for determining whether a fully charged nickel cadmium battery has a memory effect electrical properties defect as opposed to other possible battery defects, said method comprising the steps of:

subjecting said battery to a slowly increasing charge current and then a decreasing charge current;

measuring the battery terminal voltage after subjecting said battery to said slowly increasing and then a decreasing charge current and determining the maximum measured voltage; and

comparing the maximum voltage thus determined to a threshold value;

whereby if the maximum voltage is greater than said threshold value, the battery has a memory effect electrical properties defect.

2. The method of claim 1, wherein said slowly increasing charge current increases as a function of time.

3. The method of claim 1 wherein said slowly increasing charge current comprises current pulses with each subsequent current pulses having a higher current magnitude than the preceding current pulse.

4. The method of claim 1 wherein said decreasing charge current decreases as a function of time at the same rate as said slowly increasing charge current.

5. The method of claim 1 wherein said decreasing charge current comprises current pulses with each subsequent current pulse having a lower current magnitude than the preceding current pulse.

6. The method of claim 2 wherein the rate of said charge current is a 0.22 A/500 millisecond step.

7. A method for determining whether a first fully charged nickel cadmium battery has memory effect electrical properties comprising the steps of:

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

b) subjecting a second, fully charged nickel cadmium battery without memory effect electrical characteristics to a slowly increasing charge current and then a decreasing charge current;

c) measuring the first and second battery terminal voltages during steps (a) and (b) and determining the maximum measured voltage of each battery; and

d) comparing the maximum voltages of the first and second batteries;

whereby if the maximum voltage of the first battery is greater than the maximum voltage of the second battery, the first battery has memory electrical properties.

8. Apparatus for determining whether a fully charged nickel cadmium battery has memory effect electrical characteristics comprising:

current means for generating a slowly increasing charge current applied to the battery and also for generating a decreasing charge current applied to the battery subsequent to the increasing current charge;

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

comparing means for comparing the maximum battery voltage to a threshold value;

whereby if the maximum voltage is greater than said threshold value, the battery has memory effect properties.

9. A method for determining whether a fully charged nickel cadmium battery has memory effect electrical properties comprising the steps of:

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

b) measuring the battery terminal voltage during step (a) and determining the rate of change of the measured voltage with time; and

c) comparing the measured voltage rate of change to a threshold value;

whereby if the measured voltage rate of change is greater than said threshold value, the battery has memory effect electrical properties.

10. A method for determining whether a fully charged nickel cadmium battery with a given nominal voltage rating has memory effect electrical properties comprising the steps of:

a) subjecting said battery to a slowly increasing charge current until the battery reaches a predetermined voltage value greater than the nominal voltage rating and then to a decreasing charge current;

b) measuring the current magnitude during step (a); and

c) comparing the current magnitude to a threshold value;

whereby if the measured current magnitude is less than said threshold value, the battery has memory effect electrical properties.