Methods of charging battery packs for cordless power tool systems

• US 7,656,131 B2
• Filed: 10/27/2006
• Issued: 02/02/2010
• Est. Priority Date: 10/31/2005
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Embrey, Janet M., Trinh, Danh T.
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): OMAR, AHMED H
• Application Number:
  US11/553,742
• Publication Number:
  US 20070103113A1
• Time in Patent Office: 1,194 Days
• Field of Search: 320/127, 320/128, 320134-137, 320/148, 320/150, 320/152, 320/153, 320/155, 320157-158, 320/160, 320/162, 320/163
• US Class Current: 320/162
• CPC Class Codes: H01M 10/4257 Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0036 using connection detecting circuits H02J7/0034 takes precedence
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

In a method of charging a battery pack, the pack is inserted in a charger and an initial set of checks of cell voltage and pack temperature is performed. Once the initial set of checks is satisfied, the cells may be charged at a first constant current level. The first constant current level is adjusted to one or more lower levels of constant current until cell voltages of all the cells are within a full charge voltage window. The voltage window is defined between a minimum full charge cell voltage level and a maximum full charge cell voltage level. The charge may be terminated once all of the cells are within the full charge voltage window.

Claims

1. A method of charging a battery pack having a plurality of battery cells, comprising:

inserting the battery pack into a charger,

performing an initial set of checks of cell voltage and pack temperature,

charging the cells at a first substantially constant current level once the initial set of checks are satisfied,

adjusting the first constant current level to one or more lower levels of substantially constant current until cell voltages of all the cells are within a full charge voltage window between a minimum full charge cell voltage level and a maximum full charge cell voltage level wherein during the charge, after the initial set of checks are performed, all of the subsequent change levels applied to the cells are substantially constant charge levels and are lower than the immediately proceeding substantially constant current level except if the charge is interrupted, then the substantially constant current level following the interruption is brought to the substantially constant current level immediately before the interruption, and

terminating the charge once all cells are within the full charge voltage window.

2. The method of claim 1, wherein the cells are not held at a substantially constant voltage level for a fixed duration to allow current to gradually decrease to complete the charge, upon one or more of the cells reaching a given voltage setpoint during the charge.

3. The method of claim 1, wherein adjusting the constant current level further includes:

determining whether a first charge current transition limit has being reached, and

reducing charge current to a substantially second constant current level lower than the first upon reaching the first transition limit,

determining whether a second charge current transition limit being reached, and

reducing charge current to a substantially third constant current level lower than the second upon reaching the second transition limit.

4. The method of claim 1,

wherein determining whether the first and second transition limits have been reached includes monitoring individual cell and total pack voltage throughout the charge.

5. The method of claim 1, further comprising:

monitoring pack temperature throughout the charge to determine if a control limit based on high pack temperature has been reached,

interrupting the charge if the control limit has been reached or exceeded, and

resuming the charge once monitored pack temperature has fallen below the control limit.

6. The method of claim 1, wherein performing an initial set of checks of cell voltage and pack temperature includes,

checking that pack temperature is within a temperature window between minimum and maximum temperature limits and delaying charging the cells at the first substantially constant current level until pack temperature is within the temperature window, and

checking that all initial individual cell voltages are above a cell low voltage threshold, where if one or more cell voltages are below the cell low voltage threshold,

pre-charging the cells at a charge current less than 200 mA until all initial cell voltages exceed the low voltage threshold,

wherein the initial set of checks are satisfied with pack temperature within the temperature window and no cell voltage below the cell low voltage threshold.

7. The method of claim 3, wherein

the first transition limit is reached if an individual cell reaches 3.7 volts or total pack voltage reaches 37.0 volts, and

the second transition limit is reached if an individual cell reaches 3.8 volts, cell voltage of all cells is ≧

3.6 volts, or total pack voltage reaches 38.0 volts.

8. The method of claim 7, further comprising:

selectively balancing individual cells that reach 3.8 volts during charging at the third substantially constant current level by discharging those cells reaching 3.8V during charging at the third constant substantially current level, until all cells have reached or exceeded 3.6 volts.

9. The method of claim 1, wherein terminating charge further includes terminating the charge once all cells are within the full charge voltage window and a voltage differential between any of the cells is 0.20 or less.

10. The method of claim 3,

wherein the first transition limit is reached if an individual cell reaches 3.6 volts, and the second transition limit is reached if an individual cell reaches 3.75 volts.

11. The method of claim 10, further comprising:

selectively discharging individual cells with a cell voltage≧

3.6 volts and continuing to charge cells with a cell voltage<

3.6 voltage at the third substantially constant current level, and

terminating the charge further includes terminating the charge once all cells are within the full charge voltage window or once a cell having the maximum cell voltage in the pack is greater than a given voltage level for a fixed duration of time at the third substantially constant current level.

12. The method of claim 11, wherein terminating charge includes securing charge current to the cells at the third substantially constant current level if the maximum individual cell voltage of all the cells≧

3.75 volts, or if the minimum individual cell voltage of all the cells≧

3.6 volts, or if the cell in the pack having the maximum cell voltage in the pack has been at a voltage greater than 3.6 volts for 40 minutes.

13. The method of claim 1, wherein the plurality of cells have a lithium metal phosphate cell chemistry.

14. The method of claim 13, wherein the battery pack of lithium metal phosphate cells is configured to provide an output voltage of at least 18 volts.

15. A method of charging a battery pack having a plurality of battery cells, comprising:

inserting the battery pack into a charger,

performing an initial set of checks of cell voltage and pack temperature with zero charge current,

charging the cells at an initial charge current level once the initial set of checks is satisfied to perform a second set of voltage and temperature checks,

charging the cells at a first substantially constant current level once the second set of checks is satisfied, the first substantially constant current level being substantially higher relative to the initial charge current level used for the second checks,

reducing charge current to a second substantially constant current level lower than the first upon reaching a first transition limit,

reducing charge current to a third substantially constant current level lower than the second upon reaching a second transition limit,

selectively discharging individual cells while continuing to charge other cells at the third substantially constant current level wherein during the charge, after the second set of checks is satisfied, all of the subsequent change levels applied to the cells are substantially constant charge levels and are lower than the immediately proceeding substantially constant current level except if the charge is interrupted, then the substantially constant current level following the interruption is brought to the substantially constant current level immediately before the interruption, and

terminating the charge once all cells are within a full charge voltage window between a minimum full charge cell voltage level and a maximum full charge cell voltage level.

16. The method of claim 15, wherein pack voltage is not maintained at a constant voltage level once a cell reaches a given voltage setpoint, as the current gradually decreases to a lower level so as to complete the charge.

17. The method of claim 15, wherein

the first transition limit is reached if an individual cell reaches 3.6 volts, and

the second transition limit is reached if an individual cell reaches 3.75 volts.

18. The method of claim 17, wherein terminating the charge further includes terminating the charge once all cells are within the full charge voltage window or once a cell having the maximum cell voltage in the pack is greater than a given voltage level for a fixed duration of time at the third substantially constant current level.

19. The method of claim 18, wherein terminating charge includes securing charge current to the cells at the third substantially constant current level if the maximum individual cell voltage of all the cells≧

3.75 volts, or if the minimum individual cell voltage of all the cells≧

3.6 volts, or if the cell having the maximum cell voltage in the pack has been at a voltage greater than 3.6 volts for 40 minutes at the third substantially constant current level.

20. The method of claim 15, wherein the plurality of cells have a lithium metal phosphate cell chemistry.