Method and device for monitoring battery cells of a battery pack and method and arrangement for balancing battery cell voltages during charge

• US 20060071643A1
• Filed: 09/30/2005
• Published: 04/06/2006
• Est. Priority Date: 10/04/2004
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Carrier, David A., Brotto, Daniele C., Seman, Andrew E. Jr., Howard, Geoffrey S., Trinh, Danh T.
• Granted Patent: US 7,417,405 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/4257 Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery monitoring device of a battery pack configured for powering a cordless power tool may include an integrated circuit connected to a microprocessor of the pack that is external to the integrated circuit, and which is connected to each of N battery cells of the pack. The integrated circuit may be configured to take, singly or sequentially, a sampled reading comprising one of an individual cell voltage or a total pack voltage for all cells in the pack. The sampled reading is filtered in the integrated circuit prior to being read by the microprocessor.

Claims

1. A battery monitoring device of a battery pack configured for powering a cordless power tool, comprising:

an integrated circuit connected to an microprocessor of the pack that is external to the integrated circuit, and connected to each of N battery cells of the pack, the integrated circuit configured to take, singly or sequentially, a sampled reading comprising one of an individual cell voltage or a total pack voltage for all cells in the pack, wherein the sampled reading is filtered in the integrated circuit prior to being read by the microprocessor.

2. The device of claim 1, wherein the integrated circuit is further configured to selectively discharge one or more of the N cells as the battery pack is being charged.

3. The device of claim 2, wherein the microprocessor issues commands to sequentially and periodically measure individual cell voltages and total pack voltage, compare the measured individual cell voltage values received from the integrated circuit to a given threshold as the pack is being charged, and selectively discharge those cells not satisfying the threshold.

4. The device of claim 3, wherein the threshold is an average cell voltage value for all cells that is determined from the total pack voltage measured by the integrated circuit, the average cell voltage value being stored and updated over the duration of charge in the microprocessor.

5. The device of claim 4, wherein the cell having a maximum differential voltage above the average cell voltage is discharged during the charge until its measured cell voltage has dropped to equal the average cell voltage.

6. The device of claim 4, wherein any cells exceeding the average cell voltage are discharged during the charge until their respective measured cell voltage has dropped to equal the average cell voltage.

7. The device of claim 3, wherein the threshold is set as the highest voltage cell measured in a given cycle of measurements, and the microprocessor issues a command to the integrated circuit to discharge the highest voltage cell as evident from the given cycle of measurements.

8. The device of claim 3, wherein the threshold is set as the X highest voltage cells as measured in a given cycle of measurements, and the microprocessor issues a command to the integrated circuit to discharge the X highest voltage cells until these cells measured voltages evident from the given cycle of measurements.

9. The device of claim 3, wherein the threshold is an integer Y (Y≧

1) multiplied by a minimum voltage for the cell that is set in advance, and the microprocessor issues a command to the integrated circuit to discharge those cells exceeding Y*preset minimum voltage.

10. The device of claim 1, wherein N is greater than or equal to 5.

11. The device of claim 1, wherein the integrated circuit includes a logic controller in communication with the microprocessor and configured to process a given serial data command received from the microprocessor for taking sampled readings from one or more of the N cells, or to direct selective discharging of one or more of the N cells.

12. The device of claim 11, wherein

the integrated circuit is operatively connected to a corresponding channel of each cell in the battery pack, each channel having a channel input from its cell to the integrated circuit, and

the integrated circuit further includes gate drive circuitry in communication with the logic controller for controlling one or more of a plurality of field-effect transistors (FETs), each FET corresponding to a given channel and operable to selectively discharge its corresponding cell, based on a given data command received from the microprocessor.

13. The device of claim 11, wherein

the integrated circuit is operatively connected to a corresponding channel of each cell in the battery pack, each channel having a channel input from its cell to the integrated circuit, and the integrated circuit further includes:

a switch matrix connected to each of the channels and in communication with the logic controller, and which is adapted to select given channels to output the sampled reading based on a control signal from the logic controller, and

a capacitor connected to the output of the switch matrix for storing the sampled reading, wherein the sampled reading is digitally filtered as the capacitor is being charged so that an average voltage value is stored in the capacitor, and wherein, after a controlled delay to allow the capacitor to charge, the average voltage value stored on the capacitor is output from the integrated circuit for reading by the microprocessor.

14. The device of claim 13, wherein, based on a data command received for measuring a given cell voltage or a total pack voltage, the logic controller sends control signals to close the switch matrix and select given channels for taking the sampled reading, and to align switch positions for a group of switches such that the capacitor becomes part of an RC filtering circuit at the output of the switch matrix to filter the output as the capacitor charges up with the sampled reading.

15. The device of claim 13, wherein the integrated circuit further includes an auxiliary circuit thereon that is connected to the output of the switch matrix for connection to an external differential amplifier, wherein the external amplifier can be selectively connected to the switch matrix output to provide an alternative to the capacitor for taking sampled readings.

16. The device of claim 1, wherein the cells of the battery pack have a lithium-ion cell chemistry.

17. The device of claim 1, wherein a nominal voltage rating of the battery pack is at least 18V.

18. A method of monitoring battery cells of a battery pack that is configured for powering a cordless power tool, comprising:

receiving a first serial data command from a microprocessor of the pack to take a voltage measurement from channels connected to one or more of the cells, the voltage measurement embodied as a differential voltage value measured across an individual cell or a differential voltage value measured across all cells to reflect a total pack voltage,

storing the voltage measurement in a capacitor, wherein the voltage measurement is filtered so that the capacitor charges up to an average of the differential voltage value for a given cell or across all cells of the pack, and

receiving a second serial data command to connect the capacitor to a buffer amplifier so that the microprocessor can read the average voltage value off the capacitor.

19. A method of balancing cell voltages while charging of a plurality of cells in a battery pack, comprising:

periodically measuring the cell voltage across each cell of the pack and a total pack voltage in a sequential manner,

determining, based on the measured total pack voltage, a current average cell voltage for all cells in the pack, the current average cell voltage representing a threshold value,

comparing each measured cell voltage to the threshold value, and

discharging one or more cells having a measured cell voltage which exceeds the threshold value for a given duration during the charge.

20. The method of claim 19, wherein the given duration is defined as a time elapsed until the measured cell voltage of a discharging cell has dropped to equal the determined average cell voltage.

21. The method of claim 19, further comprising repeating the periodic measuring, determining the current average cell voltage as threshold, comparing and discharging functions throughout the charge to maintain individual cell voltages substantially balanced throughout the charge.

22. The method of claim 19, wherein determining the current average cell voltage includes automatically dividing the measured total pack voltage by the number of cells in the pack to calculate the current average cell voltage for all cells.

23. An arrangement in a battery pack for balancing cell voltages during charging of a plurality of cells of the pack, the arrangement comprising:

a microprocessor, and

an integrated circuit in operative communication with the microprocessor and connected to each of the cells,

the microprocessor directing the integrated circuit to periodically measure, throughout the duration of charging, the cell voltage across each cell of the pack and the total pack voltage in a sequential manner,

the integrated circuit communicating the measured individual cell voltage and a current average cell voltage for all cells to the microprocessor, wherein the measured total pack voltage automatically divided by the number of cells within the integrated circuit to determine the current average cell voltage, and

the microprocessor controlling balancing of each of the cell voltages based on each measured individual cell voltage and the determined current average cell voltage.

24. The arrangement of claim 23, wherein

the microprocessor controls the balancing of cell voltages by comparing each measured individual cell voltage to the current average cell voltage, and

directs the integrated circuit to discharge one or more cells which have a measured individual cell voltage exceeding the current average cell voltage for a given duration during the charge.

25. The arrangement of claim 23, wherein

the integrated circuit includes a plurality of semiconductor devices, each connected to a corresponding cell in the pack, and

the integrated circuit energizes a semiconductor device to enable discharging of its corresponding cell for the given duration, if the corresponding cell has a measured individual cell voltage greater than the current average cell voltage.

26. The arrangement of claim 24, wherein the given duration is defined as a time elapsed until the measured cell voltage of a discharging cell has dropped to equal the determined average cell voltage.

27. The arrangement of claim 23, wherein the periodic measuring, determining of average cell voltage, comparing and balancing functions performed by the microprocessor or integrated circuit are repeated throughout the charge to maintain individual cell voltages substantially balanced throughout the charge.

28. A method of adaptively balancing cell voltages of a plurality of cells in a battery pack during charging of the battery pack, comprising:

continuously monitoring cell voltages for each cell in the pack in a sequential manner,

detecting a voltage differential for one or more cells, the voltage differential represented as the difference a given measure cell voltage exceeds a current average cell voltage value calculated from the continuously monitoring step, and

balancing cell voltages during the charge by discharging those cells which have a detected voltage differential, until a measured cell voltage for the discharging cell has dropped to equal the average cell voltage.

29. A battery pack configured to monitor voltages of cells therein, the battery pack operatively attachable to a cordless power tool, comprising:

a microprocessor;

an integrated circuit in operative communication with the microprocessor for monitoring cell voltages of at least N individual cells and total pack voltage during discharge of the pack, based on commands received from the microprocessor, and

a motor control semiconductor device operatively controlled by the microprocessor,

wherein as the battery pack is engaged to a cordless power tool, and upon an initial actuation of a trigger of the power tool, the microprocessor directs the integrated circuit to sequentially measure the individual cell voltages of all the cells, and

wherein the microprocessor energizes the motor control semiconductor device to enable battery current to flow to a motor of the power tool, if the determined individual cell voltages are acceptable as compared to a given voltage threshold.

30. The battery pack of claim 29, wherein

as the trigger is re-actuated, the integrated circuit is directed by the microprocessor to sequentially monitor each individual cell voltage in the pack as the cells discharge current to the tool, and

the tool motor remains enabled with current from the battery pack until a cell voltage measured by the integrated circuit and communicated to the microprocessor is at or below a given cut-off voltage.

31. The battery pack of claim 30, wherein the microprocessor de-energizes the motor control semiconductor device to terminate current flow to the tool motor, if any individual cell voltage measured by the integrated circuit is at or below a given cut-off voltage.

32. The battery pack of claim 29, wherein

if the trigger is re-actuated and left in an actuated, active state, the microprocessor continues to direct the integrated circuit to sequentially monitor each individual cell voltage in the pack as the cells discharge current to the tool, and

once total pack voltage reduces below a given cut-off voltage, the microprocessor places the integrated circuit in a sleep mode to reduce internal power consumption within the battery pack.

33. The battery pack of claim 29, wherein N is greater than or equal to 5.