Battery charger and charging method

• US 6,433,517 B2
• Filed: 02/13/2001
• Issued: 08/13/2002
• Est. Priority Date: 02/28/1998
• Status: Expired due to Fees

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Sakakibara, Kazuyuki
• Primary Examiner(s): Toatley, Gregory
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/781,318
• Publication Number:
  US 20010009362A1
• Time in Patent Office: 546 Days
• Field of Search: 320/153, 320/150, 320/128, 320/137
• US Class Current: 320/153
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A battery charger and a charging method capable of charging a battery for a short period of time while suppressing battery temperature from rising. The current temperature of the battery is detected (in step S12) and a temperature rise is calculated from the detected temperature (in step S14). An allowable current map is then retrieved from the detected temperature and the obtained temperature rise, an allowable current with which the battery can be charged while suppressing battery temperature from rising is obtained (in step S16) and the battery is charged with the allowable current (in step S20). Since the allowable current which the battery can be charged with, while suppressing battery temperature from rising is retrieved using the map which the allowable current is mapped, based on battery temperature and battery temperature rise, and charging current is controlled, it is possible to charge the battery for a short period of time while suppressing battery temperature from rising.

Claims

1. A method for charging a battery comprising:

supplying a charging current to the battery while monitoring battery temperature and battery temperature increase rate,

changing the charging current based upon the battery temperature and the battery temperature increase rate in order to avoid overheating the battery; and

terminating the supply of charging current to the battery based upon a determination that a relatively low charging current has been repeatedly supplied to the rechargeable battery over a series of intervals.

2. The method as in claim 1, wherein the current is terminated when a relatively low current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

3. A method of charging a battery comprising:

monitoring battery temperature and battery temperature increase rate of the battery,

selecting a charging current from a look up table using the battery temperature and battery temperature increase rate as indices for the look up table,

supplying the selected charging current to the battery while continuing to monitor the battery temperature and battery temperature increase rate at frequent intervals,

selecting a new charging current from the look up table when the battery temperature and/or the battery temperature increase rate changes; and

terminating the charging when the battery temperature increase rate is relatively high and a relatively low charging current has been supplied to the battery at relatively high frequency.

4. The method as in claim 3, wherein a lower charging current is selected if the battery temperature and/or battery temperature increase rate increases.

5. The method as in claim 4, wherein a higher charging current is selected if the battery temperature increase rate decreases.

6. The method as in claim 5, wherein the supply of charging current to the battery is terminated based upon a determination that a relatively low charging current has been repeatedly supplied to the rechargeable battery over a plurality of consecutive intervals.

7. The method as in claim 6, wherein the current is terminated when a relatively low current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

8. An apparatus adapted to charge a removable battery pack having a battery temperature sensor and a charging terminal comprising:

a controller adapted to couple to the battery temperature sensor and charging terminal of the removable battery pack, wherein the controller terminates a supply of charging current to the battery when the battery temperature increase rate is relatively high and a relatively low charging current has been supplied to the battery at a relatively high frequency.

9. The apparatus as in claim 8, wherein the controller comprises instructions for stopping the supply of current to the battery if the current being supplied to the battery falls below a predetermined current value over a series of consecutive intervals.

10. The apparatus as in claim 8, further comprising a look up table comprising a set of allowable charging current values and having battery temperature and battery temperature increase rates as indices, wherein the controller further comprises instructions for selecting an allowable charging current value based upon a present battery temperature and present battery temperature increase rate.

11. An apparatus adapted to supply current to a rechargeable battery comprising:

a first terminal adapted to couple to a battery temperature sensor,

a power supply,

a second terminal coupled to the power supply and adapted to supply current to the battery and

a controller coupled to the first terminal and the power supply, wherein the controller is adapted to terminate the supply of current to the battery based upon a determination that a relatively low charging current has been repeatedly supplied to the rechargeable battery over a series of intervals.

12. The apparatus as in claim 11, further comprising a look up table comprising a set of allowable charging current values and having battery temperature and battery temperature increase rates as indices, wherein the controller further comprises instructions for selecting an allowable charging current value based upon a present battery temperature and present temperature increase rate.

13. The apparatus as in claim 12, wherein the controller comprises instructions for stopping the supply of current to the battery if the current being supplied to the battery falls below a predetermined current value over a plurality of consecutive intervals.

14. A battery charging system, comprising:

means for detecting a battery temperature and battery temperature increase rate,

means for storing a map of allowable current values based upon the detected battery temperature and a battery temperature increase rate,

means for supplying a selected allowable charging current to the battery selected from the storing means, wherein the allowable charging current is selected based upon the detected battery temperature and battery temperature increase rate; and

means for terminating the supply of charging current to the battery based upon a determination that a relatively low charging current has been repeatedly supplied to the battery over a series of intervals.

15. A method for charging a battery, comprising:

using a processor to select an allowable current value from a look up table based upon a detected battery temperature and detected battery temperature increase rate;

supplying the selected allowable current to the battery while continuing to detect the battery temperature and the battery temperature increase rate,

selecting a new allowable current value when the battery temperature and/or battery temperature increase rate changes; and

terminating the supply of current to the battery when the battery temperature is relatively high and a relatively low charging current has been supplied to the battery over a plurality of consecutive intervals.

16. A controller adapted to provide instructions for charging a battery, comprising:

instructions to terminate battery charging when a relatively high battery temperature is detected and a relatively low charging current has been supplied to the battery over a plurality of consecutive intervals.

17. The controller as in claim 16, further comprising:

a look up table comprising a set of allowable current values and having detected battery temperature and detected battery temperature increase rate as indices; and

instructions for selecting an allowable current value from the look up table based upon the detected battery temperature and detected battery temperature increase rate.

18. A method for charging a rechargeable battery comprising:

supplying a charging current to the rechargeable battery, and

terminating a supply of charging current to the rechargeable battery based upon repeated detection over a series of intervals that relatively low charging current has been supplied to the rechargeable battery.

19. A method as in claim 18, wherein the charging current is terminated when a relatively low charging current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

20. A method as in claim 18, wherein the rechargeable battery comprises nickel metal hydride battery cells and further comprising adjusting the supply of charging current in order to prevent the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

21. A method as in claim 18, further comprising:

supplying the charging current to the rechargeable battery while monitoring battery temperature and battery temperature increase rate and

adjusting the charging current to a current selected from the group consisting of;

(i) a relatively high current, if the battery temperature and battery temperature increase rate are relatively low,

(ii) an intermediate current, if the battery temperature is relatively low and the battery temperature increase rate is relatively high, or if the battery temperature is relatively high and the battery temperature increase rate is relatively low, and

(iii) a relatively low current, if the battery temperature and battery temperature increase rate are relatively high.

22. A method as in claim 21, wherein the rechargeable battery comprises nickel metal hydride battery cells and the supply of charging current is adjusted so as to prevent the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

23. A method as in claim 22, wherein the charging current is terminated when a relatively low charging current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

24. A battery charger comprising:

a processor programmed to terminate a supply of charging current to a rechargeable battery based upon repeated detection over a series of intervals that relatively low charging current has been supplied to the rechargeable battery, and

means for establishing electrical communication between the processor and the rechargeable battery.

25. A battery charger as in claim 24, wherein the processor is programmed to terminate the charging current when a relatively low charging current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

26. A battery charger as in claim 24, wherein the rechargeable battery comprises nickel metal hydride battery cells and the processor is further programmed to adjust the supply of charging current in order to prevent the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

27. A battery charger as in claim 24, wherein the processor is further programmed to:

supply the charging current to the rechargeable battery while monitoring battery temperature and battery temperature increase rate and

adjust the charging current to a current selected from the group consisting of;

(i) a relatively high current, if the battery temperature and battery temperature increase rate are relatively low,

(ii) an intermediate current, if the battery temperature is relatively low and the battery temperature increase rate is relatively high, or if the battery temperature is relatively high and the battery temperature increase rate is relatively low, and

(iii) a relatively low current, if the battery temperature and battery temperature increase rate are relatively high.

28. A method as in claim 27, wherein the rechargeable battery comprises nickel metal hydride battery cells and the processor is further programmed to adjust the supply of charging current so as to prevent the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

29. A method as in claim 28, wherein the processor is further programmed to terminate the charging current when a relatively low charging current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.

30. A method of charging a battery comprising:

monitoring battery temperature and battery temperature increase rate of the battery,

adjusting charging current supplied to the battery to a current selected from the group consisting of;

(i) a relatively high current, if the battery temperature and battery temperature increase rate are relatively low,

(ii) an intermediate current, if the battery temperature is relatively low and the battery temperature increase rate is relatively high, or if the battery temperature is relatively high and the battery temperature increase rate is relatively low, and

(iii) a relatively low current, if the battery temperature and battery temperature increase rate are relatively high, and

terminating the charging current when the battery temperature increase rate is relatively high and relatively low charging current has been supplied to the battery at a relatively high repetition rate.

31. A method as in claim 30, wherein the battery comprises nickel metal hydride battery cells and the supply of charging current is adjusted so as to prevent the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

32. A method as in claim 30, wherein the charging current is terminated when a relatively low charging current is supplied to the battery in 8 out of 10 intervals and in 5 consecutive intervals.

33. An apparatus comprising:

means for monitoring battery temperature and battery temperature increase rate of a rechargeable battery,

means for adjusting charging current supplied to the battery to a current selected from the group consisting of;

(i) a relatively high current, if the battery temperature and battery temperature increase rate are relatively low,

(ii) an intermediate current, if the battery temperature is relatively low and the battery temperature increase rate is relatively high, or if the battery temperature is relatively high and the battery temperature increase rate is relatively low, and

(iii) a relatively low current, if the battery temperature and battery temperature increase rate are relatively high, and

means for terminating the charging current when the battery temperature increase rate is relatively high and relatively low charging current has been supplied to the rechargeable battery at a relatively high repetition rate.

34. An apparatus as in claim 33, wherein the rechargeable battery comprises nickel metal hydride battery cells and the charging current adjusting means prevents the temperature of the nickel metal hydride battery cells from exceeding 50°

C.

35. An apparatus as in claim 33, wherein the charging current terminating means terminates the supply of charging current when relatively low charging current is supplied to the rechargeable battery in 8 out of 10 intervals and in 5 consecutive intervals.