Method for monitoring battery discharge by determining the second derivative of battery voltage over time

• US 5,278,509 A
• Filed: 02/03/1992
• Issued: 01/11/1994
• Est. Priority Date: 02/03/1992
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T, Inc.
• Inventors: Haynes, Richard, Levy, Robert B.
• Primary Examiner(s): Strecker, Gerard R.
• Assistant Examiner(s): DO, DIEP N
• Application Number:
  US07/829,635
• Time in Patent Office: 708 Days
• Field of Search: 324/426, 324/433, 324/427, 324/429, 340/636, 320/48, 320/21, 320/31, 320/39, 429/197
• US Class Current: 324/427
• CPC Class Codes: G01R 31/378 specially adapted for the type of battery or accumulator

Abstract

The state of charge of a rechargeable battery (12), such as those made from lithium, nickel-cadmium or metal hydrides, can be accurately determined by monitoring the rate of change of battery voltage over time (dv/dt), which parameter has empirically been found to change dramatically as the battery reaches complete discharge.

Claims

1. A method for monitoring the state of charge of a battery undergoing discharge in an electronic system, comprising the steps of:

monitoring the rate of change of battery voltage (dv/dt) over time;

establishing the rate at which dv/dt for the battery changes;

determining from the rate at which dv/dt for the battery changes, the time interval before dv/dt reaches a prescribed level corresponding to a critical value of battery charge; and

cutting off battery discharge, at the end of said time interval, when the value of dv/dt reaches the level corresponding to a critical value of battery charge.

2. The method according to claim 1 wherein the electronic system undertakes at least one termination operation within the time interval before the battery charge reaches a critical level.

3. The method according to claim 1 wherein the battery discharge is cut off prior to the absolute value of dv/dt exceeding a value corresponding to 95% discharge of the battery.

4. The method according to claim 1 wherein the battery is undergoing pulsed discharge.

5. The method according to claim 1 wherein the pulsed discharges are periodic.

6. The method according to claim 1 wherein the battery is undergoing constant discharge.