Method for Li-Ion safety switch fault detection in smart batteries

• US 6,268,713 B1
• Filed: 02/26/1999
• Issued: 07/31/2001
• Est. Priority Date: 02/26/1999
• Status: Expired due to Fees

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Thandiwe, Iilonga P.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/258,730
• Time in Patent Office: 886 Days
• Field of Search: 320/132, 320/134, 320/136, 361/86
• US Class Current: 320/134
• CPC Class Codes: H02J 7/0029 with safety or protection devices or circuits
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A method for testing safety circuitry in rechargeable battery packs is provided herein by which the operation and integrity of circuits associated with rechargeable cells may be verified. A controller 103 senses current flow during cell 108 charge or discharge. The controller 103 then activates the safety circuitry and once again senses current to ensure high circuit impedance. If a fault is detected, the controller 103 notifies the user or host device. The controller 103 then decides if the fault warrants isolating the cell 108 from the terminals of the battery pack 111, 112. If such action is warranted, the controller 103 clears the current carrying path 104, 105, creating a fail condition that does not endanger the user or associated equipment.

Claims

1. A method of testing safety circuits in battery charging systems, comprising:

a) providing a power source with a return line for supplying or dissipating energy;

b) providing a battery pack with one or more cells for storing or supplying energy;

c) providing a fuse means connected in series between said power supply and said cell(s);

d) providing a control switch whereby the switch, when closed, shorts either the power supply or cell(s) to ground through said fuse means;

e) providing one or more power switches connected in series between said power supply and said cell(s);

f) providing a series resistor for sensing current;

g) providing an indicating means;

h) providing a controller with memory which will, at either the onset of charging or the onset of discharging, verify the integrity of the protection circuit with these steps;

1) measure the sense voltage across said sense resistor with said power switch closed;

2) open said power switch;

3) measure the voltage across said sense resistor again;

whereby, when the sense voltage described is above a predetermined limit, the controller will record an error in said memory, notify the user through said indicating means, and when desired, close said control switch clearing said fuse and thus disabling said battery pack, and

whereby, when the sense voltage is below a predetermined limit, the controller will close said power switch.

2. A method of testing safety circuits in battery charging systems as described in claim 1, further comprising steps of:

1) Measure the voltage across said sense resistor with said power switch closed;

2) If the voltage across said sense resistor is above a predetermined limit, proceed to step 8. Otherwise, proceed to step 3;

3) Open said power switch;

4) Measure the voltage across said sense resistor with said power switch open;

5) If the voltage across said sense resistor is above a predetermined limit, proceed to step 8. Otherwise, proceed to step 6;

6) Close said power switch;

7) Wait for next charge or discharge cycle to begin. Once the next charge or discharge cycle has begun, proceed to step 1;

8) Record failure in said controller memory;

9) Notify user with said indicating means;

10) Determine whether or not to disable circuit. If circuit disable is required, proceed to step 11. Otherwise proceed to step 6;

11) Close said control switch, causing said fuse means to clear. Circuit is now disabled.

3. A method of testing safety circuits in battery charging systems comprising the steps of:

1) A controller with memory activating the safety circuits;

2) Said controller deactivating said safety circuits prior to the onset of charging or discharging;

3) Said controller reactivating said safety circuits;

4) Said controller comparing parameters associated with said safety circuits in steps 2 and 3;

Whereby when said parameters associated with steps 2 and 3 are adequately different, said controller determines said safety circuits are functioning properly;

Further whereby when said parameters associated with steps 2 and 3 are not adequately different, said controller notifies the user and then terminates circuit operation.