Methods of discharge control for a battery pack of a cordless power tool system, a cordless power tool system and battery pack adapted to provide over-discharge protection and discharge control

Abstract

In a cordless power tool system, a battery pack which may removably attachable to a cordless power tool and to a charger may include at least one battery cell and a power limiting device. The power limiting device may be arranged in series with the at least one battery cell for limiting power output of the battery pack based on the component that is connected to the pack. Current and hence power out of the battery pack may be controlled as a function of total internal impedance in the battery pack, which may be adjusted depending on the component that is connected to the pack.

1 . A battery pack removably attachable to a cordless power tool and to a charger, comprising: 
 at least one battery cell; and    at least one power limiting device arranged in series with the at least one battery cell for limiting at least one of power and current output of the battery pack based on the component that is connected to the pack.    
   
   
       2 . The battery pack of  claim 1 , wherein 
 the component is a cordless power tool, and    the battery pack is adapted to provide a one of a first current and power to drive a first power tool that is designed to operate with the battery pack and for driving a second power tool configured to ‘operate at one of a second current and power lower than the first current or power, the second power tool designed for operation with a second battery pack.    
   
   
       3 . The battery pack of  claim 2 , wherein the power limiting device is adapted to raise internal impedance of the battery pack to match an internal impedance of the second battery pack, when operatively connected and providing power to the second power tool, thereby limiting one of a maximum current within the battery pack and a maximum power that can be output by the battery pack to the second power tool.  
   
   
       4 . The battery pack of  claim 1 , wherein the component is a charger.  
   
   
       5 . The battery pack of  claim 1 , further comprising: 
 an identification device for identifying the battery pack upon connection to an external component.    
   
   
       6 . The battery pack of  claim 1 , further comprising: 
 a discharge control circuit for restricting at least one of a maximum power and a maximum current that can be output from the battery pack.    
   
   
       7 . The battery pack of  claim 6 , wherein the discharge control circuit is configured to monitor battery voltage, battery current and battery temperature.  
   
   
       8 . The battery pack of  claim 6 , further comprising: 
 a temperature sensor for sensing cell temperature to output a sensed signal to the discharge control circuit; and    a current sensor for sensing battery current to output a sensed signal to the discharge control circuit.    a voltage monitor circuit for sensing one of individual cell voltage and total pack voltage of the pack to output a sensed signal to the discharge control circuit.    
   
   
       9 . The battery pack of  claim 6 , further comprising: 
 at least one communication terminal for communicating information to, and sensing information from, an attached external component.    
   
   
       10 . The battery pack of  claim 1 , wherein at least one cell has a lithium-ion cell chemistry.  
   
   
       11 . A cordless power tool system, comprising: 
 a power tool; and    a battery pack removably attachable to the power tool, the pack including at least one battery cell and at least one power limiting device arranged in series with the at least one battery cell for limiting one of power output and current output from the battery pack.    
   
   
       12 . In a cordless power tool system including a battery pack that is removably attachable to a power tool and to a charger, a method of limiting one of power and current out of a battery pack, comprising: 
 limiting one of power and current output of the battery pack as a function of the component that is connected to the pack.    
   
   
       13 . The method of  claim 12 , wherein 
 the component is embodied a power tool, and    the battery pack is adapted to provide one of a first current and first power to drive a first power tool that is designed to operate with the battery pack and for driving a second power tool configured to operate at one of a second current and second power lower than the first current or power, the second power tool designed for operation with a second battery pack.    
   
   
       14 . The method of  claim 13 , wherein limiting one of power and current output of the battery pack further comprises: 
 raising internal impedance of the battery pack to match an internal impedance of the second battery pack, when operatively connected and providing power to the second power tool, thereby limiting one of a maximum current within the battery pack and a maximum power that can be output by the battery pack to the second power tool.    
   
   
       15 . The method of  claim 13 , wherein limiting one of power and current output of the battery pack further comprises: 
 maintaining internal impedance of the battery pack when operatively connected and providing power to the first power tool.    
   
   
       16 . In a cordless power tool system having a power tool and a battery pack removably attachable to the power tool, a method of controlling discharge rate of a plurality of serially connected cells in the battery pack, comprising: 
 raising total internal pack impedance of a first battery pack to match an internal impedance of a second battery pack designed for a given power tool so as to control discharge rate of the serially-connected cells in the first battery pack to prevent one or more cells in the first battery pack from reaching one of an over-discharge state and an over-current condition, when the first battery pack is operatively connected and providing power to the given power tool.    
   
   
       17 . The method of  claim 16 , wherein raising total internal pack impedance includes adding a series resistance between a series connection of the cells in the first battery back and a terminal connection point of the first battery pack to increase total internal impedance of the first battery pack.  
   
   
       18 . The method of  claim 16 , wherein raising total internal pack impedance includes lengthening connecting wires extending between each cell and a terminal connection point to increase total internal impedance of the first battery pack.  
   
   
       19 . The method of  claim 16 , wherein raising total internal pack impedance includes modifying a cross-sectional area of battery straps that connect the cells so as to increase total impedance of the first battery pack.  
   
   
       20 . The method of  claim 16 , wherein raising total internal pack impedance includes dynamically adding, as a function of power tool load on the first battery pack, a series resistance between a series connection of the cells and a terminal connection point of the first battery pack, so as to increase total internal impedance of the first battery pack.  
   
   
       21 . The method of  claim 20 , wherein the dynamically adding of resistance is implemented by at least one semiconductor device of the first battery pack performing a current limiting function.  
   
   
       22 . The method of  claim 20 , wherein the dynamically adding of resistance is implemented by a positive temperature coefficient (PCT) element of the first battery pack.  
   
   
       23 . A cordless power tool system, comprising: 
 a power tool; and    a battery pack removably attachable to the power tool,    the battery pack including one or more serially-connected cells therein and at least one power limiting device in series with at least one of the serially-connected cells, the at least one power limiting device adapted to raise total internal pack impedance of the battery pack to match an internal impedance of a second battery pack that is designed for operation with the power tool, so as to control discharge rate of the serially-connected cells and prevent one or more cells from reaching one of an over-discharge state and an over-current state, when the battery pack is operatively connected and providing power to the power tool.    
   
   
       24 . The system of  claim 23 , wherein 
 the power tool encompasses a first power tool designed for operation with the first battery pack and a second power tool designed for operation with the second battery pack, and    first battery pack is characterized as providing a higher current and a higher power at a lower total internal pack impedance than the second battery pack.    
   
   
       25 . A battery pack operatively attachable to differently-rated cordless power tools, the battery pack adapted for controlling discharge rate therein, comprising: 
 at least one or more serially-connected battery cells for providing one of a first current and first power to drive a first power tool that is designed to operate with the battery pack and for driving a second power tool configured to operate at one of a second current and second power lower than the first current or power; and    at least one power limiting device for raising internal impedance of the battery pack to match an internal impedance of another, second battery pack that is designed to operate with the second power tool to control discharge rate of cells in the battery pack, so as to prevent one or more cells from reaching one of an over-discharge state and an over-current state during operation with the second power tool.    
   
   
       26 . The battery pack of  claim 25 , wherein the at least one power limiting device includes a passive resistance device to raise total internal impedance of the battery pack.  
   
   
       27 . The battery pack of  claim 26 , wherein the passive resistance device is a resistor placed in series with the battery cells between one of the battery cells and a terminal of the battery pack.  
   
   
       28 . The battery pack of  claim 26 , wherein the passive resistance device is embodied by connecting wires extending between each cell and a terminal, the connecting wires being lengthened to increase total internal impedance of the battery pack.  
   
   
       29 . The battery pack of  claim 26 , wherein the passive resistance device is embodied by modifying battery straps connecting the cells to increase total internal impedance of the battery pack.  
   
   
       30 . The battery pack of  claim 25 , wherein the at least one power limiting device includes an active resistance device to increase total internal impedance of the battery pack.  
   
   
       31 . The battery pack of  claim 30 , wherein the active resistance device dynamically adds a series resistance as a function of tool load between a series connection of the cells and a terminal connection point of the battery to increase total internal impedance of the battery pack.  
   
   
       32 . The battery pack of  claim 30 , wherein the active resistance device is at least one semiconductor device with current limiting function in series with at least one of the one or more serially-connected cells.  
   
   
       33 . The battery pack of  claim 30 , wherein the active resistance device is at least two semiconductor devices with current limiting function operating in parallel to form a parallel combination in series with at least one of the one or more serially-connected cells.  
   
   
       34 . The battery pack of  claim 30 , wherein the active resistance device is a positive temperature coefficient (PCT) element.  
   
   
       35 . The battery pack of  claim 25 , wherein the battery pack is a lithium-ion battery pack, and the second battery pack having an internal impedance to be matched is a nickel cadmium or nickel metal hydride battery pack.  
   
   
       36 . A battery pack adapted to power one of a first power tool and a second power tool, the first power tool configured to operate at a higher current or power than the second power tool, the battery pack characterized as providing a higher current and a higher power at a lower internal impedance than that of a second battery pack designed for operation with the second power tool, the battery pack comprising: 
 a sensor adapted to selectively add internal impedance in the battery pack based on a indicator signal indicating that the battery pack is connected to one of the first or second power tools, and    an active resistance device for dynamically adding a series resistance to increase total internal impedance of the battery pack, depending on the indicator signal.    
   
   
       37 . The battery pack of  claim 36 , wherein the active resistance device is bypassed when the indicator signal indicates that the first power tool is connected to the battery pack.  
   
   
       38 . The battery pack of  claim 36 , wherein the active resistance device is activated to add internal impedance in the battery pack the indicator signal indicates that the second power tool is connected to the battery pack, facilitating raising of the internal impedance in the battery pack to match an internal impedance of the second battery pack that is designed to operate with the second power tool.  
   
   
       39 . The battery pack of  claim 36 , wherein the sensor is embodied as one of an inductive pick-up sensor, magnetic sensor, radio frequency sensor and optical sensor for sensing a corresponding induction signal, magnetic signal, RF signal or optical signal that is generated based on engagement of one of the first and second power tools with the battery pack.  
   
   
       40 . A battery pack adapted to power a first power tool configured to operate at one of a higher current and power than a second power tool, comprising: 
 a positive terminal;    a negative terminal;    a third terminal for sensing power operation of the first or second power tool to provide a sensed signal, when the pack is attached thereto; and    a control circuit for determining a desired internal impedance mode for the battery pack based on the sensed signal received from an attached one of the first and second power tools via the third terminal.    
   
   
       41 . The battery pack of  claim 40 , wherein the battery pack is adapted to a higher current and a higher power at a lower total internal pack impedance than a second battery pack that is designed to operate with the second power tool.  
   
   
       42 . The battery pack of  claim 41 , wherein 
 the third terminal is a thermistor contact terminal that is open when the pack is connected to the second power tool, and    the control circuit sets a high impedance mode based on lack of receipt of the sensed signal, adding resistance to raise the internal impedance of the pack to match an internal impedance of the second battery pack that is designed to operate with the second power tool.    
   
   
       43 . The battery pack of  claim 42 , wherein 
 the thermistor contact terminal senses a signal from the first power tool when the pack is connected to the first power tool, and    the control circuit sets a low impedance mode based on the received sensed signal.    
   
   
       44 . The battery pack of  claim 41 , wherein 
 the third terminal is an additional power contact terminal, and    the control circuit is a current limiting device configured to selectively add resistance to raise total internal pack impedance based on connective engagement of the additional power contact terminal with a corresponding power contact terminal on one of the first and second power tools.    
   
   
       45 . The battery pack of  claim 44 , wherein 
 only the first power tool has a corresponding power contact terminal, and    the current limiting device maintains a low impedance mode based on a signal received via the corresponding power contact terminal of the first power tool.    
   
   
       46 . The battery pack of  claim 44 , wherein the current limiting circuit selects a high impedance mode for adding resistance to raise the internal impedance of the pack to match an internal impedance of the second battery pack designed to operate with the second power tool, only when the battery pack is connected to the second power tool.  
   
   
       47 . A battery pack adapted to power a first power tool configured to operate at one of a higher current and power than a second power tool, the first and second power tools including a motor, semiconductor device and control circuit, the semiconductor device and control circuit adapted for providing variable speed control in the motor of the first or second power tool, the battery pack comprising: 
 a positive terminal;    a negative terminal;    a third terminal for receiving an indicator from the semiconductor device of one of the first and second power tools; and    a current limiting device connected to the third terminal and configured to select a desired impedance mode to selectively add resistance to raise internal impedance of the battery pack, based on the received indicator.    
   
   
       48 . The battery pack of  claim 47 , wherein the battery pack is configured to provide a higher current and a higher power at a lower internal impedance than a second battery pack that is designed to operate with the second power tool.  
   
   
       49 . The battery pack of  claim 48 , wherein lack of receipt of the indicator signal when the second power tool is attached causes the current limiting device to select a high impedance mode for adding resistance, raising the internal impedance of the pack to match an internal impedance of the second battery pack.  
   
   
       50 . The battery pack of  claim 47 , wherein receipt of the indicator signal causes the current limiting device to select a low impedance mode for the pack, maintaining internal impedance of the pack.  
   
   
       51 . The battery pack of  claim 50 , wherein the indicator generated by the semiconductor device of the first power tool is embodied as one of a given resistance value, polarity setting, torque value, speed, temperature and motor field strength value of the first power tool.  
   
   
       52 . A cordless power tool having a positive terminal, negative terminal, motor, semiconductor device and control circuit, the cordless power tool designed to operate with a battery pack having a positive terminal, negative terminal and a third terminal, the cordless power tool comprising: 
 a third terminal sending an indicator generated by the semiconductor device to the corresponding third terminal of the battery pack indicating an impedance mode to be selected for the cordless power tool.    
   
   
       53 . The cordless power tool of  claim 52 , wherein the indicator is embodied as one of a given resistance value, polarity setting, torque value, speed, temperature and motor field strength value of the cordless power tool.  
   
   
       54 . In a cordless power tool system having a power tool and a battery pack removably attachable to the power tool, a method of controlling discharge rate of one or more serially-connected cells in the battery pack to protect the cells from an over-current condition, comprising: 
 controlling at least one semiconductor device in the pack in series with at least one of the one or more serially-connected cells so as to selectively control total internal battery pack impedance.    
   
   
       55 . The method of  claim 54 , wherein controlling further includes controlling at least two semiconductor devices operating in parallel to form a parallel combination that is in series with at least one of the one or more serially-connected cells.  
   
   
       56 . The method of  claim 55 , further comprising: 
 sensing current in the pack during power tool operations,    wherein controlling further includes maintaining the at least one semiconductor device energized until sensed current meets or exceeds a given maximum current threshold, pulse width modulating the at least one semiconductor device to raise an effective internal pack impedance, as seen by the power tool, until the sensed current has dropped below the given threshold.    
   
   
       57 . A cordless power tool system, comprising: 
 a power tool, and    a battery pack having a plurality of serially-connected cells and removably attached to the power tool, the pack including a discharge control circuit controlling at least one semiconductor device so as to selectively control the average voltage applied to the tool motor so as to control at least one of power and current output from the battery pack.    
   
   
       58 . The system of  claim 57 , wherein the at least one semiconductor device is a field effect transistor in series with at least one of the plurality of serially-connected cells.  
   
   
       59 . The system of  claim 57 , wherein the battery pack includes at least at least two field-effect transistors operating in parallel to form a parallel combination that is in series with at least one of the serially-connected cells.  
   
   
       60 . The system of  claim 57 , wherein 
 the battery pack includes a current sensor between a terminal of the pack and at least one of the cells for sensing battery current and for outputting a sensed signal to the discharge control circuit, and    as the pack is providing power to a tool motor of the power tool, the discharge control circuit controls the duty cycle of the at least one semiconductor device to selectively control the average voltage applied to the tool motor so as to control at least one of power and current output from the battery pack.    
   
   
       61 . The system of  claim 60 , wherein 
 the at least one semiconductor device is a pulse width modulated field-effect transistor (FET), and    as sensed current approaches a maximum current threshold during pack-tool operations, the discharge control circuit pulse width modulates the FET to selectively reduce the voltage applied to the tool motor so as to cause a gradual drop in voltage and current out-of the pack.    
   
   
       62 . The system of  claim 61 , wherein the gradual reduction in output voltage causes a drop in motor RPM which changes motor noise, informing a user of the tool that the tool is approaching one of a stall and overload condition.  
   
   
       63 . The system of  claim 60 , wherein the discharge control circuit controls the duty cycle of the at least one FET so that the FET remains energized until pack current reaches a maximum current threshold, whereupon the FET is de-energized and current flow, forced by an inductive nature of the tool motor, is returned back to the motor by a recirculation path in one of the battery pack and the power tool.  
   
   
       64 . The system of  claim 63 , wherein the recirculation path is in the battery pack and includes a diode blocking current when the at least one FET is energized but allowing current to pass from a negative terminal of the battery pack to a positive terminal of the pack.  
   
   
       65 . The system of  claim 63 , wherein the recirculation path is in the power tool and includes a diode blocking current when the at least one FET is energized but allowing current to pass from a negative terminal of the power tool to a positive terminal of the power tool.  
   
   
       66 . The system of  claim 60 , wherein 
 the at least one semiconductor device includes first and second pulse width modulated field-effect transistors (FETs), the second FET operating synchronously with the first FET, and    as sensed current approaches a maximum current threshold during pack-tool operations, the discharge control circuit pulse width modulates the first and second FETs to selectively reduce the voltage applied to the tool motor so as to cause a gradual drop in voltage and current out of the pack.    
   
   
       67 . The system of  claim 66 , wherein the discharge control circuit controls the duty cycle of the first and second FETs so that the first FET remains energized and the second FET de-energized until pack current reaches a maximum current threshold, whereupon the first FET is de-energized and the second FET is energized so that current flow, forced by an inductive nature of the tool motor, is returned back to the motor by a recirculation path in the battery pack, the recirculation path including the second FET.  
   
   
       68 . The system of  claim 67 , wherein the first FET reverts to an energized state and the second FET is de-energized once sensed current in the pack drops below the current threshold.  
   
   
       69 . In a cordless power tool system having a power tool and a battery pack removably attachable to the power tool, the battery pack including one or more serially-connected cells, a discharge control circuit, comprising: 
 a current controlled relay arranged in a current path of the pack to provide a current limiting function with hysteresis that limits current out of the pack to a motor of the tool.    
   
   
       70 . The system of  claim 69 , wherein the current controlled relay further comprises: 
 a primary coil having N turns,    a switch, the switch and primary coil in series between a negative terminal of the pack and at least one cell of the pack,    a secondary coil having first and second ends, at least N+1 turns, the first end of the secondary coil magnetically connected to the switch, and    a diode connected between a positive terminal of the pack and the second end of the secondary coil,    wherein the switch has a first state which connects the battery pack to a motor of the tool and a second state which interrupts current to the tool.    
   
   
       71 . The system of  claim 70 , wherein 
 current flow through the pack during power operations with the tool creates a magnetic field between the primary and secondary coils, and    as current increases in the pack to a given maximum current threshold for power tool operations, the magnetic field generated activates the switch to the second state, interrupting current to the tool.    
   
   
       72 . The system of  claim 70 , wherein the additional turns of the secondary coil enable the secondary coil to hold the switch in the second state to enable current within the pack to decay through the secondary coil and diode, until the current drops to a second threshold at which the magnetic field is unable to hold the switch in its second state, the switch returning to the first state to connect the pack to the tool.  
   
   
       73 . A cordless power tool system, comprising: 
 a power tool including a tool motor, and    a battery pack having a plurality of cells and removably attached to the power tool for providing power to the motor, wherein a control signal related to speed control information for the motor of the tool is an input for controlling the current output from the cells for powering the tool.    
   
   
       74 . The system of  claim 73 , wherein discharge control for current out of the pack and speed control for controlling speed of the tool resides in the battery pack.  
   
   
       75 . The system of  claim 73 , 
 wherein the battery pack further includes: 
 a positive terminal,  
 a negative terminal,  
 a control terminal,  
 at least one semiconductor device between the negative terminal and at least one cell for providing variable speed control for the tool motor,  
 a discharge control circuit operatively connected to the positive terminal and control terminal, and operatively connected to the semiconductor device for controlling the semiconductor device,  
   wherein the power tool further includes: 
 a pair of power terminals, one power terminal connected to the positive terminal and the other to the negative terminals of the pack,  
 a voltage sense device between the power terminals for sensing a voltage value corresponding to a given tool motor speed to generate the control signal, and  
 a third terminal connecting the voltage sense device to the control terminal of the pack, and  
 as the voltage sense device sends the control signal via the third terminal and control terminal to the discharge control device, the discharge control device controls the semiconductor device based on the control signal to control current out of the pack and speed of the tool motor.  
   
   
   
       76 . A cordless power tool system, comprising: 
 a power tool having a tool motor and means for variable speed control of the tool motor, and    a battery pack having a plurality of cells and removably attached to the power tool, the pack including a discharge control device controlling a semiconductor device so as to selectively raise internal battery pack impedance for limiting current out of the cells of the pack.    
   
   
       77 . A cordless power tool system, comprising: 
 a power tool including a tool motor, and    a battery pack having a plurality of cells and removably attached to the power tool for providing power to the motor, wherein discharge control for controlling current out of the pack and speed control for controlling speed of the tool resides in the power tool.    
   
   
       78 . The system of  claim 77 , wherein the tool includes a microprocessor for controlling discharge rate of the cells in the battery pack and for controlling speed of the tool motor.  
   
   
       79 . The system of  claim 78 , 
 wherein the battery pack includes: 
 a current sensor for communicating a signal representing sensed current in the pack to the microprocessor, and  
 a semiconductor device in operative communication with the microprocessor in the power tool and operable to interrupt current in the battery pack, and  
   wherein the microprocessor is operable to send a control signal to de-energize the semiconductor device in the battery pack to interrupt current, based on the sensed current signal received from the current sensor in the battery pack.    
   
   
       80 . The system of  claim 79 , wherein the semiconductor device in the battery pack is further controllable by the microprocessor in the power tool to provide variable speed control for the tool motor.  
   
   
       81 . In a cordless power tool system including a battery pack that is removably attachable to a power tool and to a charger, a method of communicating a fault in the battery pack to the charger, comprising: 
 detecting a fault in the battery pack, and    communicating the fault to the charger upon pack engagement with the charger.    
   
   
       82 . A cordless power tool system, comprising: 
 a charger; and    a battery pack removably attachable to the charger for receiving a charge current and to a power tool of the system for powering the tool, the battery pack including a fault detection device detecting a fault in the battery pack and communicating the fault to the charger upon pack engagement with the charger.    
   
   
       83 . The system of  claim 82 , the battery pack further including: 
 a positive terminal,    a negative terminal,    an active resistance circuit for limiting charge current in the battery pack, the fault detection circuit configured to monitor the active resistance circuit for a fault therein, and    a third terminal operatively attached to the fault detection circuit, wherein the fault detection circuit drives the third terminal to a high or low electrical state if it detects a fault in the active resistance circuit.    
   
   
       84 . The system of  claim 83 , the charger further including a microcontroller in operative communication with the third terminal upon pack to charge engagement to sense the electrical state indicating the fault, so as to prevent the battery pack from being charged.  
   
   
       85 . The system of  claim 83 , wherein the third terminal is a thermistor terminal or a pack identification terminal.