Battery charging algorithm

• US 6,731,096 B1
• Filed: 08/10/2000
• Issued: 05/04/2004
• Est. Priority Date: 08/10/2000
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Patino, Joseph, Fiske, John Dewey
• Primary Examiner(s): Han, Jessica
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/636,126
• Time in Patent Office: 1,363 Days
• Field of Search: 320/150, 320/153, 701/22, 701/1
• US Class Current: 320/137
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

This invention is a method of charging a battery wherein false dT/dt measurements are identified. When a NiMH battery reaches full charge, the change in temperature per unit time increases. Thus, this dT/dt measurement can be used to properly terminate charging. Initial charging, however, causes a large dT/dt value that may falsely cause charging to terminate. This invention alleviates this condition by adding a wait state and then taking a second dT/dt measurement. As a fully charged battery'"'"'s temperature briefly continues to rise after charging current is removed, a second, positive dT/dt measurement confirms that the battery has been completely charged to ensure proper charge termination.

Claims

1. A method or charging a battery, the method comprising the steps of:

a. providing a rechargeable battery cell;

b. providing a charger;

c. recognizing at least one battery characteristic;

d. testing the battery;

e. reading a first temperature;

f. comparing the first temperature to a threshold;

g. entering a charge mode for a predetermined time;

h. reading a voltage, comparing the read voltage to a predetermined threshold voltage, and entering a second charge mode where the read voltage exceeds the predetermined threshold voltage;

i. reading a second temperature at the end of the predetermined time;

j. calculating a difference between the second temperature and the first temperature divided by the predetermined time;

k. comparing the difference between the second temperature and the first temperature divided by the predetermined time to a predetermined (dT/dt value; and

l. reducing charging current when the difference between the second temperature and the first temperature divided by the predetermined time exceeds the predetermined dT/dt value.

2. The method of claim 1, further comprising the steps of:

a. reading a third temperature;

b. waiting a predetermined wait time;

c. reading a fourth temperature;

d. calculating a difference between the fourth temperature and the third temperature divided by the predetermined wait time;

e. entering a trickle charge mode where the difference between the fourth temperature and the third divided by the predetermined wait time is a positive value.

3. The method of claim 2, further comprising the step of returning to a rapid charge mode where the difference between the fourth temperature and the third divided by the predetermined wait time is a non-positive value.

4. A method of charging a battery, the method comprising the steps of:

a. charging a battery in a rapid charge mode for a predetermined charge time;

b. calculating a change in temperature of the battery during predetermined charge time;

c. calculating a quotient by dividing the change in temperature by the predetermined charge time;

d. comparing the quotient to a threshold;

e. reducing charging current where the quotient exceeds the threshold; and

f. reading a first battery temperature.

5. The method of claim 4, further comprising the steps of:

a. waiting for a predetermined wait period;

b. reading a second battery temperature;

c. subtracting the first battery temperature from the second battery temperature; and

d. entering a trickle charge mode where the difference of the first battery temperature from the second battery temperature is positive.

6. The method of claim 5, further comprising returning to a rapid charge mode where the difference of the first battery temperature from the second battery temperature is non-positive.

7. A method for charging a battery, the method comprising the steps of:

a. providing a rechargeable battery cell;

b. providing a charger;

c. recognizing at least one battery characteristic;

d. reading a first temperature;

e. comparing the first temperature to a threshold; and

f. entering a first charge mode;

g. reading a second temperature at the end of a predetermined charge time;

h. calculating a difference between the second temperature and the first temperature divided by the predetermined charge time;

i. comparing the difference between the second temperature and the first temperature divided by the predetermined charge time to a predetermined dT/dt value; and

j. reducing charging current when the difference between the second temperature and the first temperature divided by the predetermined charge time exceeds the predetermined dT/dt value.

8. The method of claim 7, wherein the first charge mode is a rapid charge mode, further comprising reading a first voltage, comparing the read first voltage to a predetermined threshold voltage, and entering a trickle charge mode where a read voltage exceeds the predetermined threshold voltage.

9. The method of claim 7, further comprising monitoring the first temperature, comparing the first temperature to a predetermined threshold temperature, and entering a trickle charge mode when the first temperature exceeds the predetermined threshold temperature.