Method for detecting low battery state without precise calibration

• US 5,268,845 A
• Filed: 02/14/1991
• Issued: 12/07/1993
• Est. Priority Date: 02/14/1991
• Status: Expired due to Term

• Current Assignee: Dell USA LP (Dell Technologies Inc.)
• Original Assignee: Dell Corporate Services Corporation
• Inventors: Stewart, Gregory N., Startup, Warren W.
• Primary Examiner(s): Cosimano, Edward R.
• Application Number:
  US07/656,262
• Time in Patent Office: 1,027 Days
• Field of Search: 323/275, 324/158 R, 340/636, 364/483, 364/550
• US Class Current: 323/275
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G06F 1/1616 with folding flat displays, e.g. laptop computers or notebooks having a clamshell configuration, with body parts pivoting to an open position around an axis parallel to the plane they define in closed position
• CPC Class Codes: G06F 1/1635 Details related to the integration of battery packs and other power supplies such as fuel cells or integrated AC adapter
• CPC Class Codes: G06F 1/1677 for detecting open or closed state or particular intermediate positions assumed by movable parts of the enclosure, e.g. detection of display lid position with respect to main body in a laptop, detection of opening of the cover of battery compartment
• CPC Class Codes: G06F 1/28 Supervision thereof, e.g. detecting power-supply failure by out of limits supervision
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

A portable electronic system, which can accurately predict impending battery failure, without using expensive comparators, by using voltage and current measurements to determine the source impedance of a battery. Preferably two banks of batteries are used, with a load-switching relay; the voltage and current of both banks is monitored, so that voltage drop under load can be monitored. Alternatively, the voltage variation of a single battery bank can simply be correlated to the current drawn by a changing load.

Claims

1. A portable electronic system, comprising:

at least one microprocessor;

at least one battery power connection, and a ground terminal;

a voltage-sensing interface, connected so that said microprocessor can detect the voltage drop across said battery connection; and

a current-sensing interface, connected so that said microprocessor can detect the current flow through said battery connection;

said microprocessor being configured to repeatedly compare the voltage and current at said battery connection, at an instant when the current through said connection is small, with the voltage and current at said battery connection at another substantially contemporaneous instant when the current through said connection is larger; and

to indicate imminent battery failure when the source impedance seen at said battery connection is accordingly detected to have risen in a pattern corresponding to the internal impedance of a battery which is imminently failing.

2. The system of claim 1, wherein said microprocessor is a microcontroller.

3. The system of claim 1, wherein said microprocessor is a microcontroller, and includes on-chip analog interface circuits.

4. The system of claim 1, wherein said system is a portable computer.

5. The system of claim 1, wherein said system is a portable computer, and said microprocessor is separate from the CPU thereof.

6. A portable electronic system, comprising:

at least one microprocessor;

first and second battery power connections;

a voltage-sensing interface, connected so that said microprocessor can detect the voltage drop across said first battery connection, and also, independently thereof, can detect the voltage drop across said second battery connection; and

a current-sensing interface, connected so that said microprocessor can detect the current flow through said first battery connection, and also, independently thereof, can detect the current flow through said second battery connection;

said microprocessor being configured to repeatedly compare the voltage and current at said first battery connection, at an instant when the current through said first battery connection is small, with the voltage and current at said first battery connection at another substantially contemporaneous instant when the current through said first battery connection is larger, and

to repeatedly compare the voltage and current at said second battery connection, at an instant when the current through said second battery connection is small, with the voltage and current at said second battery connection at another substantially contemporaneous instant when the current through said second battery connection is larger; and

to indicate imminent battery failure when the source impedance seen at said battery connection is accordingly detected to have risen in a pattern corresponding to the internal impedance of a battery which is imminently failing.

7. The system of claim 6, wherein said microprocessor is a microcontroller, and includes on-chip analog interface circuits.

8. The system of claim 6, wherein said system is a portable computer.

9. The system of claim 6, wherein first battery connection includes a ground terminal, and said second battery connection also includes a ground terminal which is common with the ground terminal of said first battery connection.

10. The system of claim 6, wherein said system is a portable computer, and said microprocessor is separate from the CPU thereof.

11. A method for automatic battery management, in a portable electronic system, comprising the operations of:

repeatedly measuring the voltage and current of a battery bank, under changing load conditions;

making a calculation, in a microprocessor, which is substantially equivalent to estimating the internal impedance of the battery bank; and

indicating imminent battery failure when the internal impedance of the battery bank is accordingly estimated to have risen in a pattern corresponding to a battery which is approaching failure.

12. The method of claim 11, wherein said microprocessor is a microcontroller.

13. The method of claim 11, wherein said microprocessor is a microcontroller, and includes on-chip analog interface circuits.

14. The method of claim 11, wherein said system is a portable computer, and said microprocessor is separate from the CPU thereof.

15. A method for automatic battery management, in a portable electronic system, comprising the operations of:

repeatedly measuring the battery voltage and load current of a battery bank, under changing load conditions;

making a calculation, in a microprocessor, of how the battery voltage responds when the load current changes; and

indicating imminent battery failure when an observed change in load current causes a change in battery voltage which is sufficiently large, in relation to the observed change in load current, to approximate the voltage-change-to-current-change ratio of a battery which is approaching failure.

16. The method of claim 15, wherein said microprocessor is a microcontroller, and includes on-chip analog interface circuits.

17. The method of claim 15, wherein said system is a portable computer, and said microprocessor is separate from the CPU thereof.