Battery charge gauge with current integrator and method for guaging battery charge

• US 5,648,717 A
• Filed: 12/22/1995
• Issued: 07/15/1997
• Est. Priority Date: 12/22/1995
• Status: Expired due to Term

• Current Assignee: Amperex Technology Limited (TDK Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Uskali, Bob
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/577,402
• Time in Patent Office: 571 Days
• Field of Search: 320/5, 320/21, 320/30, 320/39, 320/43, 320/44, 320/48, 340/635, 340/636, 429/61, 429/90
• US Class Current: 324/428
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A method for gauging battery charge in which current flowing from a battery (11) is integrated (25) and a charge counter counts charge. Voltage (Vb) across the battery is measured (16) and compared (26) with a voltage threshold (28). The counter (27) is reset to a predetermined value (29) when the measured voltage crosses the voltage threshold.

Claims

1. A method for gauging battery charge comprising the steps of:

integrating current flowing from a battery;

counting a counter in response to the step of integrating;

measuring voltage across the battery; and

comparing measured voltage with a voltage threshold and resetting the counter to a predetermined value when the measured voltage crosses the voltage threshold.

2. A method according to claim 1 wherein the battery has a characteristic exhibiting an elbow and the voltage threshold is representative of the elbow in the characteristic.

3. A method according to claim 1 wherein the battery has a voltage-current characteristic for constant current during discharge and wherein the characteristic has a substantially flat region extending from a maximum charge for a major portion of battery charge where battery charge is relatively high and a rapidly falling region in a minor portion of battery charge where battery charge is relatively low and where the voltage threshold is set in the rapidly falling region of the characteristic.

4. A method according to claim 1 wherein the battery has a maximum charge and the predetermined value is set at approximately 10% of maximum charge.

5. A method according to claim 1 comprising the step of comparing the counter with a predetermined charge level and, during battery discharge:

if the counter exceeds the predetermined charge level and the measured voltage falls below the voltage threshold, setting the counter to the predetermined value;

else

if the counter is below the predetermined charge level and the measured voltage is above the voltage threshold, setting the counter to the predetermined value;

else

if the counter is below the predetermined charge level and the measured voltage is below the voltage threshold, decrementing the counter in response to the step of integrating.

6. A battery charge gauge comprising:

a current integrator for integrating current flowing from a battery;

a counter responsive to the current integrator for counting a value representative of battery charge;

a voltage measurement element for measuring voltage across the battery to provide a measured voltage;

a comparator for comparing the measured voltage with a threshold; and

a counter resetting element for resetting the counter to a calibration value when the measured voltage crosses the threshold.