U.S. patent application number 12/368735 was filed with the patent office on 2009-06-11 for protection methods, protection circuits and protection devices for secondary batteries, a power tool, charger and battery pack adapted to provide protection against fault conditions in the battery pack.
This patent application is currently assigned to Black & Decker Inc.. Invention is credited to R. Roby Bailey, Daniele C. Brotto, David Carrier, Jeffrey J. Francis, Steve Phillips, Andrew E. Seman, Jr., Danh Thanh Trinh, Christopher R. Yahnker.
Application Number | 20090146614 12/368735 |
Document ID | / |
Family ID | 34467964 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090146614 |
Kind Code |
A1 |
Carrier; David ; et
al. |
June 11, 2009 |
Protection Methods, Protection Circuits and Protection Devices for
Secondary Batteries, a Power Tool, Charger and Battery Pack Adapted
to Provide Protection Against Fault Conditions in the Battery
Pack
Abstract
In a cordless power tool system, protection methods, circuits
and devices are provided to protect against fault conditions within
a battery pack that is operatively attached to a power tool or
charger, so as to prevent internal or external damage to the
battery pack or attached tool or charger. The exemplary methods,
circuits and devices address fault conditions such as over-charge,
over-discharge, over-current, over-temperature, etc.
Inventors: |
Carrier; David; (Aberdeen,
MD) ; Phillips; Steve; (Ellicott City, MD) ;
Francis; Jeffrey J.; (Nottingham, MD) ; Bailey; R.
Roby; (New Park, PA) ; Trinh; Danh Thanh;
(Parkville, MD) ; Seman, Jr.; Andrew E.; (White
Marsh, MD) ; Yahnker; Christopher R.; (Raleigh,
NC) ; Brotto; Daniele C.; (Baltimore, MD) |
Correspondence
Address: |
THE BLACK & DECKER CORPORATION
701 EAST JOPPA ROAD, TW199
TOWSON
MD
21286
US
|
Assignee: |
Black & Decker Inc.
Newark
DE
|
Family ID: |
34467964 |
Appl. No.: |
12/368735 |
Filed: |
February 10, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10949193 |
Sep 27, 2004 |
7418322 |
|
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12368735 |
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60510128 |
Oct 14, 2003 |
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60551803 |
Mar 11, 2004 |
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Current U.S.
Class: |
320/152 ;
320/162; 320/163 |
Current CPC
Class: |
H02J 7/0029 20130101;
H01M 6/42 20130101; B60L 53/18 20190201; H01M 50/209 20210101; B25F
5/00 20130101; H01M 50/581 20210101; Y02T 90/12 20130101; H01M
10/443 20130101; H01M 10/488 20130101; H01M 10/482 20130101; H02J
7/0031 20130101; H02J 7/0014 20130101; H01M 50/572 20210101; H01M
10/441 20130101; H02J 7/0026 20130101; H01M 2200/106 20130101; H02J
7/00309 20200101; H01M 50/213 20210101; Y02T 10/7072 20130101; H01M
10/486 20130101; Y02E 60/10 20130101; H01M 10/42 20130101; H01M
50/20 20210101; H01M 10/425 20130101; H02J 7/00308 20200101; Y02T
10/70 20130101; Y02T 90/14 20130101 |
Class at
Publication: |
320/152 ;
320/162; 320/163 |
International
Class: |
H02J 7/04 20060101
H02J007/04; H02J 7/06 20060101 H02J007/06 |
Claims
1-24. (canceled)
25. A method of providing over-voltage protection in a battery pack
removably attachable to a cordless power tool and a charger, the
battery pack operatively attached to the charger charging the pack,
comprising: sensing an over-voltage fault condition in the pack;
and terminating charge current in the battery pack or charger based
on the sensed fault condition.
26. The method of claim 25, wherein terminating includes generating
a control signal in the pack to turn off a semiconductor device in
the pack that is adapted to limit or interrupt current in a charge
path of the pack.
27. The method of claim 25, wherein terminating further includes
generating a control signal in the pack, and communicating the
control signal to the charger to turn off a semiconductor device in
the charger that is adapted to limit or interrupt current in a
charge path of the charger to terminate current flow in the battery
pack.
28. A watchdog circuit of a charger, the charger operatively
attached to a battery pack for charging the battery pack, the
watchdog circuit monitoring parameters in both the battery pack and
the charger for one or more control signals from the battery pack
or charger to terminate current flow in the battery pack.
29. The watchdog circuit of claim 28, wherein the parameters
include one or more of battery pack temperature, individual cell
voltages, battery stack voltage, a charge current reset pulse from
the battery pack, and a clock reset pulse from the battery pack,
and/or a charge current reset pulse from the charger.
30. In a charger adapted to charge a battery pack, the charger and
battery pack part of a cordless power tool system, the charger
comprising: a charge current interruption circuit monitoring
parameters in both the battery pack and the charger for one or more
control signals from the battery pack or charger to terminate
current flow in the battery pack.
31. The charge current interruption circuit of claim 30, wherein
the parameters include one or more of battery pack temperature,
individual cell voltages, battery stack voltage, a charge current
reset pulse from the battery pack, a clock reset pulse from the
battery pack, and/or a charge current reset pulse from the
charger.
32-49. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims domestic priority under 35 U.S.C.
.sctn.120 to the following related U.S. Provisional patent
applications filed in the United States Patent & Trademark
Office: U.S. Provisional Application Ser. No. 60/510,128, filed
Oct. 14, 2003, and U.S. Provisional Application Ser. No.
60/551,803, filed Mar. 11, 2004. The entire contents of the
disclosures for each of these provisional applications are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to protection methods,
protection circuits and protective devices for rechargeable
batteries, to a power tool and charger adapted to provide
protection for cells of an attached battery pack, and to a battery
pack including protection control therein, each protecting the
battery back against various potential fault conditions.
[0004] 2. Description of Related Art
[0005] Over the past few years, lithium-ion (Li-ion) batteries have
begun replacing nickel-cadmium (NiCd), nickel-metal-hydride (NiMH),
and lead-acid batteries in low-voltage, portable electronic devices
such as notebook-type personal computers. As compared to NiCd and
NiMH batteries, Li-ion batteries are lighter but have a larger
capacity per unit volume. For this reason, the Li-ion batteries
have been typically suitable to low-voltage devices that are
preferably light and which are required to endure continuous use
for a long time. In an over-discharged state, however, the Li-ion
batteries deteriorate rapidly, thus Li-ion batteries require
over-discharge protection.
[0006] A battery pack used in a portable electronic device
typically has a plurality of battery cells connected in series. The
maximum number of battery cells connected in series in one battery
pack is determined by the output voltage of the battery pack. For
instance, the typical output voltage of one NiCd battery cell or
one NiMH battery cell is 1.2 V. Assuming that an 18V output voltage
from a battery pack is suitable for most general purpose electronic
devices, the maximum number of NiCd or NiMH battery cells connected
in series in the battery pack is 15. On the other hand, the typical
output voltage of one Li-ion battery cell is approximately 3.6 V.
Accordingly, the maximum number of Li-ion battery cells connected
in series in one fictional 18V Li-ion battery pack would be 5.
[0007] Unlike a NiCd battery pack and a NiMH battery pack, the
Li-ion battery pack may include functionality to protect against
fault conditions inside and outside the Li-ion battery pack. This
prevents cells in the Li-ion battery pack from deteriorating and
shortening useful life of the pack. For instance, if a fault
condition such as short-circuiting occurs inside or outside the
Li-ion battery, a fuse may be provided to cut off an
over-discharging current or an overcharging current, if the
discharging current or charging current becomes larger than a given
current level.
[0008] Currently, protection circuits in battery packs such as
Li-ion battery packs are designed primarily for low-voltage
portable electronic devices such as notebook-type personal
computers, cellular phones, etc., which require voltage generally
on the order of 2 to 4 volts. Such devices are characterized by
using battery packs composed of cells (such as Li-ion, NiCd, NiMH
cells) that provide a maximum output voltage of about 4.2
volts/cell. For Li-ion battery cells, care must be taken to prevent
damage from electrical and mechanical stresses, since lithium is a
highly reactive substance.
[0009] Conventional protection circuits for these low-voltage
battery packs may monitor cell voltages to prevent a given cell
from over-charging or over-discharging, and may monitor current to
keep current from rising too high. Other protection circuits may
have one or more temperature inputs to disable current during
charge or discharge until the battery pack cools down. Still other
protection circuits may be designed to help maintain the balance of
charge on the cells, commonly known as equalization circuits. A
typical protection circuit may be connected to a given battery cell
or group of cells in the battery pack to avoid these situations.
For example, a conventional protection circuit may typically
include a pair of MOSFET's or other semiconductors that can stop
current flow in either direction.
[0010] However, much higher voltages than described above are
required for higher-power electronic devices such as cordless power
tools. Accordingly, higher-power battery packs may be in the
process of being developed for cordless power tools. Such
"high-power" battery packs may provide higher voltage outputs than
conventional NiCd and NiMH battery packs (and substantially higher
power than conventional Li-ion packs used for PCs and cell phones),
and at a much reduced weight (as compared to conventional NiCd or
NiMH battery packs used as power sources in conventional cordless
power tools). A characteristic of these battery packs is that the
battery packs may exhibit substantially lower impedance
characteristics than conventional NiCd, NiMH and/or even the lower
power Li-ion packs.
[0011] Further, as these battery technologies advance, the
introduction of lower impedance chemistries and construction styles
to develop secondary batteries generating substantially higher
output voltages (of at least 18 V and up, for example) may possibly
create several additional protection issues. Battery packs having
lower impedance also means that the pack can supply substantially
higher current to an attached electronic component, such as a power
tool. As current through a motor of the attached power tool
increases, demagnetization forces (e.g., the number of armature
turns of the motor times the current, ampere-turns) could
substantially increase beyond a desired or design limit in the
motor. Such undesirable demagnetization could thus potentially burn
up the motor.
[0012] For example, a lower impedance electrical source could cause
damage to a tool's motor when the tool is held at stall condition.
During motor stall, the motor and battery impedances are the only
mechanisms to limit the current since there is no back-EMF created
by the motor. With a lower impedance pack, the currents would be
higher. Higher currents through the motor will increase the
likelihood of de-magnetization of the permanent magnets within the
tool's motor.
[0013] Additionally, start-up of the tool could produce excessive
starting currents and cause demagnetization of the motor. Thermal
overload could also be a result of using a low impedance electrical
source in an existing power tool, as the new batteries may be
designed to run longer and harder than what the original cordless
tool system was designed.
[0014] Accordingly, different protection controls may need to be in
place to address potential fault conditions that could occur in
high power battery packs that are adapted for use with both
existing cordless power tools, and developing lines of power tools
that are manufactured for use with these higher power battery
packs. In particular, protection controls need to be developed to
handle fault conditions such as over-charge, over-discharge,
over-current, over-temperature and cell imbalance which could occur
in one or more cells of a battery pack (such as a Li-ion or NiCd
pack), so as to prevent internal or external damage to the pack, an
attached device such as a charger or tool or to a user in the
vicinity of a pack connected to a charger or tool.
SUMMARY OF THE INVENTION
[0015] In a cordless power tool system including a battery pack,
exemplary embodiments of the present invention are directed to
protection methods, protection arrangements and/or devices designed
to protect against fault conditions in the battery pack operatively
attached to the power tool or charger, so as to prevent internal or
external damage to the battery pack or attached tool or charger.
The exemplary methods, circuits and devices address fault
conditions in the battery pack such as over-charge, over-discharge,
over-current, over-temperature, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The exemplary embodiments of the present invention will
become more fully understood from the detailed description given
herein below and the accompanying drawings, wherein like elements
are represented by like reference numerals, which are given by way
of illustration only and thus are not limitative of the exemplary
embodiments of the present invention.
[0017] FIG. 1 illustrates a partial block diagram of a protection
circuit arrangement in accordance with an exemplary embodiment of
the present invention.
[0018] FIG. 2 illustrates a partial block diagram of a protection
circuit arrangement in accordance with another exemplary embodiment
of the present invention.
[0019] FIG. 3A is a block diagram illustrating components and
connections between an exemplary battery pack and an exemplary
battery charger in accordance with an exemplary embodiment of the
present invention.
[0020] FIG. 3B is a block diagram illustrating components and
connections between an exemplary battery pack and an exemplary
power tool in accordance with an exemplary embodiment of the
present invention.
[0021] FIG. 4 is a partial block diagram of connections between a
battery pack and charger to illustrate over-charge protection in
accordance with an exemplary embodiment of the present
invention.
[0022] FIG. 5 is a partial block diagram of connections between a
battery pack and charger to illustrate over-charge protection in
accordance with another exemplary embodiment of the present
invention.
[0023] FIG. 6 is a graph of voltage versus time to illustrate an
automatic shutdown for over-discharge protection invoked by a
protection circuit in accordance with an exemplary embodiment of
the present invention.
[0024] FIG. 7 is a graph of voltage versus time to illustrate a
modified threshold for over-discharge protection in accordance with
an exemplary embodiment of the present invention.
[0025] FIGS. 8A and 8B illustrate exemplary devices used for
over-current protection in accordance with an exemplary embodiment
of the present invention.
[0026] FIG. 9 illustrates a device providing over-temperature
protection in accordance with the exemplary embodiments of the
present invention.
[0027] FIG. 10 illustrates a connection arrangement for a
thermistor in accordance with an exemplary embodiment of the
present invention.
[0028] FIG. 11 is a flow diagram illustrating a method of alerting
an operator of a power tool of an impending fault condition in the
battery pack.
[0029] FIG. 12 is a block diagram illustrating an exemplary
arrangement for determining SOC and varying motor current switching
frequency in accordance with an exemplary embodiment of the present
invention.
[0030] FIG. 13A is an isometric view of a single laminate battery
cell.
[0031] FIGS. 13B and 13C illustrate a device for protecting against
an overcharge condition in accordance with an exemplary embodiment
of the present invention.
[0032] FIGS. 14A and 14B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention.
[0033] FIGS. 15A and 15B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention.
[0034] FIGS. 16A and 16B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention.
[0035] FIGS. 17-19 illustrate exemplary cordless power tools of a
cordless power tool system in accordance with an exemplary
embodiment of the present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0036] With general reference to the drawings, a system of cordless
power tools constructed in accordance with the teachings of
exemplary embodiments of the present invention is illustrated.
Exemplary cordless power tools of the system are shown to include,
by way of examples, a circular power saw 10 (FIG. 17), a
reciprocating saw 20 (FIG. 18) and a drill 30 (FIG. 19). The tools
10, 20 and 30 each may include a conventional DC motor (not shown)
adapted to be powered by a power source having a given nominal
voltage rating. In the exemplary embodiments, the tools 10, 20 and
30 may be driven by a removable power source having a nominal
voltage rating of at least 18 volts. It will become evident to
those skilled that the present invention is not limited to the
particular types of tools shown in the drawings nor to specific
voltages. In this regard, the teachings of the present invention
may be applicable to virtually any type of cordless power tool and
any supply voltage.
[0037] With continued reference to the drawings, the removable
power source which may be embodied as a battery pack 40. In the
exemplary embodiments illustrated, the battery pack may be a
rechargeable battery pack 40. Battery pack 40 may include a
plurality of battery cells connected in series, and/or a plurality
of serially-connected strings of cells, in which the strings are in
parallel with one another. For purposes of describing the exemplary
embodiments of the present invention, battery pack 40 may be
composed of cells having a lithium-ion cell chemistry. As the
exemplary embodiments are directed to the cordless power tool
environment, which requires power sources having much higher
voltage ratings than conventional low voltage devices using Li-ion
battery technology, (such as laptop computers and cellular phones)
the nominal voltage rating of the battery pack 40 may be at least
18V.
[0038] However, pack 40 may be composed of cells of another
lithium-based chemistry, such as lithium metal or lithium polymer,
or other chemistry such as nickel cadmium (NiCd), nickel metal
hydride (NiMH) and lead-acid, for example, in terms of the
chemistry makeup of individual cells, electrodes and electrolyte of
the pack 40.
[0039] FIG. 1 illustrates a partial block diagram of a protection
circuit arrangement in accordance with an exemplary embodiment of
the present invention. FIG. 1 illustrates a portion of a battery
circuit and in particular illustrates an individual protection
device 102 for each cell 105 of a battery pack such as battery pack
40 in FIGS. 17-19. In FIG. 1, each protection device 102 may be
adapted to perform a current limiting function. In an example, the
protection devices 102 may be embodied as thermistor devices, where
a thermistor device is part of or contained inside the cell.
[0040] A thermistor is a term used to describe a range of
electronic components whose principle characteristic is that their
electrical resistance changes in response to changes in their
temperature, a `thermally sensitive resistor`. Thermistors may be
further classified as `Positive Temperature Coefficient` devices
(PTC devices) or `Negative Temperature Coefficient` devices (NTC
devices). PTC devices are devices whose resistance increases as
their temperature increases. NTC devices are devices whose
resistance decreases as their temperature increases. NTC
thermistors are typically manufactured from proprietary
formulations of ceramic materials based on transition metal
oxides.
[0041] In FIG. 1, the protection devices 102 may be embodied as PTC
devices, which may protect the string of cells from thermal
overload. If any cell becomes hot, the PTC device within that cell
increases in resistance to limit the current through the entire
string. This method of protection of battery cells may have a
drawback in that it requires many devices (PTC's in this example)
performing a current limiting function as protection device
102.
[0042] FIG. 2 illustrates a partial block diagram of a protection
circuit arrangement in accordance with another exemplary embodiment
of the present invention. An alternative approach to using multiple
protection devices 102 is to include a dedicated protection circuit
210 for each cell that senses one or more battery pack parameter in
a pack such as battery pack 40, for example. These parameters
include, but are not limited to current temperature, voltage and
impedance through the pack. A protection circuit 210 may be
operatively connected to a corresponding driver circuit 220. The
level-shifting circuits 220 may be connected to a plurality of AND
gates (shown by box 230) to link the protection circuit(s) 210 to a
master device 240 which performs a current limiting or current
interrupting function. If any protection circuit detects a problem
it can change from an output high to an output low state. The AND
gates ensure that all protection circuit outputs are high (OK) to
turn master device 240 on. Additionally, it is envisioned that the
reverse logic could be used with the protection devices output to
be normally low and using NOR gates instead. The master device 240
may be embodied as semiconductor device such as a metal-oxide
semiconductor field effect transistor (MOSFET), as shown in FIG. 2.
Accordingly, if a battery pack has multiple cells 105 in series,
then an exemplary configuration envisions a set of protection
circuits 210 (apportioned one per cell) connected to and
controlling a master device 240 that enables/disables current flow,
such as a MOSFET.
[0043] As discussed above, using multiple, dedicated protection
circuits 210 may require a corresponding level-shifting circuit 220
that drops the voltage changes from the highest potential cells
down to normal levels to switch the master semiconductor device
240, as shown in FIG. 2 for example. If monitoring each cell is
excessive, then groups of cells or the entire battery pack may be
monitored with a single protection circuit 210 and a single master
device 240 for limiting or interrupting current.
[0044] FIG. 3A is a block diagram illustrating components and
connections between an exemplary battery pack and an exemplary
battery charger in accordance with an exemplary embodiment of the
present invention. FIG. 3A is merely an exemplary circuit
configuration and is provided as a context for more clearly
describing the various protection methods, circuits and devices in
accordance with the exemplary embodiments.
[0045] Referring to FIG. 3A, battery pack 100 may include a
plurality of battery cells 105 connected in series (six shown for
simplicity, pack 100 could include more or less than six cells or
may be composed of serial strings of cells with the serial strings
in parallel with each other). For purposes of describing the
exemplary embodiments of battery pack 100 may be composed of cells
having a lithium-ion cell chemistry. As the exemplary embodiments
are directed to the cordless power tool environment, which requires
much higher voltage ratings than conventional devices using Li-ion
battery technology, the nominal voltage rating of the battery pack
100 may be at least 18V.
[0046] Thus, battery pack 100 in FIG. 3A (and in FIG. 3B) may be
applicable to and/or designed for cordless power tool systems
comprising at least a cordless power tool, the battery pack and a
charger. Pack 100 may be understood as a removable power source for
high-power, power tool operations. In an example, battery pack 100
may have a nominal voltage rating of at least 18 volts and/or have
a maximum power output of at least about 385 Watts. However, it
should be evident to those skilled in the art that the present
invention is not necessarily limited to the particular types of
tools shown in FIGS. 17-19 nor to specific voltage ratings and/or
power output specifications described above.
[0047] Pack 100 may further be composed of cells of another
lithium-based chemistry, such as lithium metal or lithium polymer,
or other chemistry such as nickel cadmium (NiCd), nickel metal
hydride (NiMH) and lead-acid, for example, in terms of the
chemistry makeup of individual cells, electrodes and electrolyte of
the pack 100.
[0048] In FIG. 3A, seven terminal (terminals 1-7) are shown.
However, the exemplary embodiments should not be limited to this
terminal configuration, as more or less terminals could be included
depending on the desired information passed between, or parameters
monitored by, the pack 100 or charger 150.
[0049] The pack 100 may also include a Pack ID 110 connected to an
output terminal (terminal 1) for identification of the pack 100
when inserted into a charger 150. The Pack ID 110 may include the
model number, version, cell configuration and the battery type
(chemistry), such as lithium-ion, NiCd or NiMH, for example. The
Pack ID 110 may be embodied as one or more communication codes
received from output terminal 1 of the battery pack 100 by an
asynchronous full duplex communication system in the pack 100, such
as is described in U.S. Pat. No. 5,680,027 to Hiratsuka et al.
However, this is only one example, as the pack ID 110 may also be
embodied by an ID resistor, LED display that displays
identification data of the pack, serial data sent upon engagement
and sensed by the tool/charger via terminal 2 for example, and/or a
field in an frame of data sent over an air interface to the
tool/charger, etc.
[0050] The pack 100 may further include one or more temperature
sensors 120. Temperature sensor 120 may be embodied as NTC or PTC
thermistors, Temperature sensing Integrated Circuits, or
thermocouples. The temperature sensor 120 may communicate the
temperature inside the battery pack 100 to intelligence in the
battery pack 100 and/or to intelligence in a connected charger 150,
for example, via terminal 3. As the function of such temperature
sensors are known, a detailed explanation of functional operation
is omitted for purposes of brevity. Power connections for charging
and discharging are represented as terminals 1 and 7.
[0051] A battery electronic control unit 125 may be responsible for
the protection of the cells 105 for any fault condition exposed on
the terminals by the user (via charger 150, an attached tool,
and/or due to user tampering). The battery electronic control unit
125 may be embodied in hardware or software as a digital
microcontroller, a microprocessor or an analog circuit, a digital
signal processor or by one or more digital ICs such as application
specific integrated circuits (ASICs), for example.
[0052] The discharge current and charge current can be clamped or
discontinued by the use of semiconductor devices 130a (discharge
FET) and 130b (charge FET), under the control of battery electronic
control unit 125. The battery electronic control unit 125 may be
powered by an internal power supply 135 as shown, and the
semiconductor devices 130a and 130b may be linked through a driver
circuit 140.
[0053] Battery pack 100 may further include a current sensor 145
which senses current and provides a signal to battery electronic
control unit 125. Current sensor 145 may be embodied as known
components for current sensors, such as a shunt resistor, current
transformer, etc. which may provide a signal representing sensed
current in pack 100 to battery electronic control unit 125.
Semiconductor devices 130a may include a pull down resistor 147
which acts to bypass the semiconductor device 130a when device 130a
is off and the pack 100 is dormant.
[0054] Pack 100 may also include a voltage monitor circuit 115.
Voltage monitor circuit 115 may be embodied by any known voltage
monitor circuit, for example, and may be configured to sense
individual cell voltage and/or sense total pack voltage of the
string of cells 105 (`stack voltage`) to provide a signal
representing the individual cell or stack voltage to battery
electronic control unit 125. As a variant, and instead of a single
voltage monitor circuit 115 configured to sense both individual
cell and total stack voltage, pack 100 could include a voltage
monitor circuit as shown in FIG. 3A, comprising a first plurality
of voltage monitor circuits (shown generally as 115A) for sensing
individual cell voltage and a second voltage monitor circuit 115B
for sensing total stack voltage of the cells 110 for example.
[0055] Referring back to FIG. 2, for example, protection circuit
210 may include at least battery electronic control unit 125,
current sensor 145, a voltage monitor circuit 115 and temperature
sensor 120, and optionally may further include pack ID 110 and an
internal power supply such as power supply 135. Driver circuit 140
may be analogous to driver circuit 220 in FIG. 2 and semiconductor
devices 130a and 130b may singly or together represent a master
device 240 having a current limiting/interrupting functionality
under the control of the protection circuit 210.
[0056] Referring to FIG. 3A, during discharge, the battery
electronic control unit 125 may output pulse width modulation (PWM)
control signals to drive the driver circuit 140. For example, a
pulsing semiconductor (pulse width modulator (PWM)) is commonly
used in the electronics industry to create an average voltage that
is proportional to the duty cycle. PWM is modulation in which the
duration of pulses is varied in accordance with some characteristic
of the modulating signal. Alternatively pulse frequency modulation
could be used to create this average voltage. In either case, the
semiconductor devices 130a and 130b (which may be embodied as a
discharge FET and charge FET respectively) may be switched between
ON and OFF states to create an average voltage that is proportional
to the duty cycle at which it is switched.
[0057] During discharge, the driver circuit 140 level shifts the
PWM output of battery electronic control unit 125 to drive the gate
of semiconductor device 130a, cycling the semiconductor devices
130a on and off depending on sensed conditions. Since the
semiconductor device 130b is reverse-biased, the device 130b passes
current with only a diode drop in voltage. If the current were at
20 Amps and device 130b had a forward voltage of 0.6 Volts the
power loss would be only 12 watts. If lower losses are desired, the
battery electronic circuit 125 may output a state to the driver
circuit 140 which commands the semiconductor device 130b to remain
on during the PWM action on semiconductor device 130a. Now, the
power lost into device 130b would be its on resistance time the
current squared (I.sup.2R.sub.ON)+Today's MOSFETs typically have an
on-resistance (R.sub.ON) of 10 milliohms, so at 20 Amps the power
loss would only be 4 watts. The result is a controlled discharge
and lower losses through the semiconductor device.
[0058] During charge, the reverse logic can be applied.
Semiconductor device 130a is reversed-biased with respect to
current flow and even though it conducts in the OFF state, device
130a should remain ON for the least amount of losses. Semiconductor
device 130b may control the charge current based on information
from the battery electronic control 125 going through the driver
circuit 140. The component arrangement that comprises driver
circuit 140 is known in the art and is not described herein for
reasons of brevity.
[0059] When battery pack 100 is connected to charger 150, a charger
electronic control unit 155 in the charger 150 may be powered from
the battery's internal power supply 135 through terminals 1 and 6.
This is only an exemplary connection scheme, as other means for
powering the charger electronic control unit 155 can be employed.
The charger 150 could have its own supply or derive it directly
from the battery voltage. The charger electronic control unit 155
may also be embodied in hardware or software as a digital
microcontroller, microprocessor, analog circuit, digital signal
processor, or by one or more digital ICs such as application
specific integrated circuits (ASICs), for example. Battery and
charger data and control information may be exchanged through
serial data paths on terminals 4 and 5. The charger electronic
control unit 155 may drive a power controller 160 with a set
voltage and a set current to deliver the desired voltage and
current from a power source 165 to the battery pack 100 via
terminals 1 and 7.
[0060] FIG. 3B is a block diagram illustrating components and
connections between an exemplary battery pack and an exemplary
power tool in accordance with an exemplary embodiment of the
present invention. FIG. 3B is merely an exemplary circuit
configuration and is provided as a context for more clearly
describing the various protection methods, circuits and devices in
accordance with the exemplary embodiments. The battery pack and
tool configuration of FIG. 3B may be applicable to the exemplary
cordless tool systems, and equivalents, in any of FIGS. 17-19. In
FIG. 3B, a `smart` power tool 170 is illustrated, it being
understood that battery pack 100 may be adapted for powering a
`dumb` power tool, i.e., a power tool without an intelligent device
or microelectronic component control such as a microprocessor.
[0061] Referring to FIG. 3B, power tool 170 may be powered from the
internal battery power supply 135 via terminals 1 and 6. The tool
170 may include a mechanical switch 175 that pulls terminal 7 high
when the semiconductor device 130a (discharge FET) is off. If
semiconductor device 130a is left off while the battery pack 100 is
dormant, the voltage at terminal 7 is low because of the pull down
resistor 147. This resistor value should have a substantially high
resistance since it acts to bypass the semiconductor device 130a.
With this pull down resistor 147 in place and the semiconductor
device 130a in the off state, the voltage at terminal 7 remains low
until a switch 175 in tool 170 is activated. The result is that
power terminal 7 immediately increases in voltage and the signal
through power terminal 7 could be used to wake the battery pack 100
from a dormant mode of operation. Tool 170 may include a tool
electronic control unit 180. Tool electronic control unit 180 may
also be embodied in hardware or software as a digital
microcontroller, microprocessor, analog circuit, digital signal
processor, or by one or more digital ICs such as application
specific integrated circuits (ASICs), for example.
[0062] The tool electronic control unit 180 may be programmable so
as to read a trigger position of a trigger 181 and report the
trigger position to the battery electronic control unit 125 via
serial data paths at terminals 4 and 5. Based on the trigger
position data, the battery electronic control unit 125 may vary the
PWM duty cycle through semiconductor device 130a to obtain the
desired motor speed in tool motor 190. While semiconductor device
130a is off, a diode 195 in the toot 170 may re-circulate residual
inductive motor current to prevent voltage spikes from occurring
therein. The forward/reversing switch 185 is typical for cordless
tools and will not be described here.
[0063] A dumb tool (not shown) may just have a trigger 181
configured as a potentiometer and connected to one of terminals 1,
4 or 5, and to terminal 6. The battery electronic control unit 125
may recognize the lack of serial data communications and perform an
analog analysis of the voltage at terminals 4 or 5. Based on the
analysis, the battery electronic control unit 125 may send PWM
control signals via driver circuit 140 to cause semiconductor
device 130a to switch at the desired duty cycle, so as to create an
intended motor speed. Even dumber tools could exist as on/off
tools. These tools require only the connection to terminals 1 and 7
for operation.
Over-Charge Protection
[0064] There are two basic types of battery chargers used for
recharging battery packs: trickle chargers and fast chargers.
Trickle chargers are significantly less expensive than fast
chargers; however a trickle charger requires approximately a 1/2
day for recharging a battery pack. A fast charger can recharge a
battery pack within about an hour. An over-charge fault condition
may occur because of some fault condition or system failure in
either the charger or battery pack. Typically, a protection circuit
in the battery pack can detect an over-charge fault condition by
monitoring voltage across the battery pack. During charge, the
voltage reaches a particular threshold. The charger thus considers
the battery pack `fully charged` and the charge current is
terminated. If the charger was locked-on due to a component
failure, it is desirable for the battery pack to be able to disable
the charging current with its own semiconductor device, such as
charge FET (semiconductor device 130b) under the control of battery
electronic control unit 125.
[0065] Over-charge control may be provided by use of a charge
lock-on detection circuit (also known as a `hardware watchdog
circuit`) between the battery pack and the charger. In general, if
the charger locked-on and pulsing data (e.g., a clock provided from
pack to charger via a suitable serial data path) stopped, then the
hardware watchdog may automatically turn off the current flow.
[0066] A conventional hardware watchdog circuit is typically
located in the charger. This circuit monitors the charge current
and looks for a 10 ms current off reset pulse in the charging
current. In a typical charging scenario, a microprocessor in the
charger (such as charger electronic control unit 155) may generate
this reset pulse using the charge control line I.sub.CTRL. In an
abnormal situation (e.g., the charger microprocessor has locked the
current solid on or the charger power supply has locked the current
solid on), the hardware watchdog circuit would timeout and turn the
charge current off using a charge FET. However, in the conventional
arrangement, it is still possible to overcharge the battery pack if
the microprocessor in the charger were to continually generate the
reset pulse without ever terminating the fast charge (due to
improper microprocessor behavior, for example).
[0067] FIG. 4 is a partial block diagram of connections between a
battery pack and charger to illustrate over-charge protection in
accordance with an exemplary embodiment of the present invention.
In FIG. 4 seven terminals and six battery cells are shown for
convenience, it being understood that more or less terminals and
battery cells could be illustrated in the exemplary embodiment.
[0068] In FIG. 4, battery pack 100 includes at least a battery
electronic control unit 125, semiconductor device 130b (such as
charge control FET) and temperature sensor 120. The temperature
sensor 120 may be embodied as an internal NTC thermistor, for
example. The charger 150 may include at least charger electronic
control circuit 155, a charge FET 157 and a hardware watchdog
circuit 158.
[0069] The battery electronic control unit 125 may receive a
battery temperature value from the internal NTC thermistor and may
communicate this information via serial data paths at terminals 3
and/or 4 to the charger electronic control unit 155. In the event
of an extreme battery temperature due to an overcharge condition,
the charge current may be terminated by the battery electronic
control circuit 125 sending a PWM control signal or pulse, via
driver circuit 140, to turn semiconductor device 130b off.
Alternatively, this control signal may be sent via serial data
paths at terminals 3 and/or 4 to charger electronic control circuit
155 to turn off the charge FET 157 in the charger 150. However, it
may still be possible to overcharge the battery pack 100 in the
event of a two-point failure--a shorted semiconductor device 130b
(charge control FET) in the battery pack 100 and improper unit
behavior in one of the battery electronic control unit 125 or
charger electronic control unit 155.
[0070] The dotted arrowhead lines in FIG. 4 show a hardware
watchdog circuit 158 (hereafter watchdog 158) having multiple reset
inputs. In addition to monitoring the charge current reset pulse,
watchdog 158 also monitors the serial communications clock path
(through terminal 3) as a reset pulse. If any of these reset pulses
did not occur, the watchdog would timeout and turn the charge
current off. It may still be possible to overcharge the battery
pack 100 in the event of a 2 point failure--a shorted charge
control FET (e.g., device 130b) in the battery pack 100 and
improper unit behavior in one of the battery electronic control
unit 125 or charger electronic control unit 155.
[0071] In addition to monitoring the charge current reset pulse,
watchdog 158 also monitors the pack temperature at temperature
sensor 120 (such as an NTC thermistor) directly to sense an
overcharge condition. In FIG. 4, a shorted battery charge control
FET (semiconductor device 130b) and any failures in the battery
electronic control unit 125 or charger electronic control unit 155
would not affect the watchdog's 158 ability to monitor the pack
temperature for sensing and terminating an overcharge
condition.
[0072] In addition to monitoring the charge current reset pulse,
watchdog 158 could also monitor the individual cell voltages using
circuits 415A and terminal 6 to sense an over voltage condition
which would indicate an overcharge condition. In FIG. 4, a shorted
battery charge control FET (semiconductor device 130b) and any
failures in the battery electronic control unit 125 or charger
electronic control unit 155 would not affect the watchdog's 158
ability to monitor the individual cell voltages for sensing and
terminating an overcharge condition.
[0073] In addition to controlling the hardware watchdog, the
voltage monitor circuits 41 SA used for monitoring the individual
cell voltages could also directly control the charge FET 130b in
the battery pack 100 through the driver circuit 140 and/or directly
control the charge FET in the charger (157) through the AND logic
(151) and terminal 6. This is shown by the doffed lines between
voltage monitor circuits 415A and driver circuit 140. This control
would allow circuits 415A to stop an overcharge condition due to
overvoltage of the individual cells.
[0074] In addition to monitoring the charge current reset pulse,
watchdog 158 could also monitor the battery stack voltage using
voltage monitor circuit 415B and terminal 7 to sense an overvoltage
condition which would indicate an overcharge condition. In FIG. 4,
a shorted battery charge control FET (semiconductor device 130b)
and any failures in the battery electronic control unit 125 or
charger electronic control unit 165 would not affect the watchdog's
158 ability to monitor the battery stack voltage for sensing and
terminating an overcharge condition.
[0075] In addition to controlling the hardware watchdog, voltage
monitor circuit 415B used for monitoring the battery stack voltage
could also directly control the charge FET in the battery (130b)
(see optional dotted line 425) through the driver circuit (140)
and/or directly control the charge FET in the charger (157) through
the AND logic (151) and terminal (7). This control would allow
voltage monitor circuit 415B to stop an overcharge condition due to
overvoltage of the entire battery stack voltage.
[0076] FIG. 5 is a partial block diagram of connections between a
battery pack and charger of a cordless power tool system to
illustrate over-charge protection in accordance with another
exemplary embodiment of the present invention. FIG. 5 omits the
voltage monitor circuits 415A and 415B for purposes of clarity, it
being understood that both individual cell voltage and total stack
voltage could be inputs to a hardware watchdog circuit 158' in FIG.
5, similar to as shown in FIG. 4.
[0077] FIG. 5 is a hybrid of FIG. 4 to illustrate a watchdog 158'
with multiple inputs. Watchdog 158' monitors the charge reset
pulse, clock reset pulse, and the NTC signal, cell voltage, and/or
battery stack voltage in order to sense a charge lock-on condition.
The charge current could still be shut off even with a shorted
charge control FET 130b in the battery and improper unit behavior
in one of the battery electronic control unit 125 or charger
electronic control unit 155, and may reduce the number of terminals
needed by sharing the NTC output terminal with the clock terminal.
Accordingly, the exemplary hardware watchdog circuit(s) in FIGS. 4
and 5 may prevent battery overcharging by monitoring the condition
of both the battery pack 100 and charger 150. Overcharge prevention
remains available even in the event of a two-point failure such as
a shorted battery charge FET and improper microprocessor behavior
in one (or both) of the battery pack 100 and charger 150.
[0078] Determination of an over-charge fault condition can also be
done by other means. If an accurate current measurement is made by
a current sensor in the battery pack (such as current sensor 145)
during discharge, then a coulomb measurement could be made by the
battery electronic control unit 125 to put back in the amount of
energy taken out. This could be used in conjunction with or without
the voltage measurement that may be made by a protection circuit
210 in the battery pack 100 to detect an over-charge fault
condition.
Over-Discharge Protection
[0079] Various battery technologies can be damaged when discharged
in excess of the manufacturer's recommendations. In accordance with
the exemplary embodiments, the battery pack 100, such as is shown
above in FIG. 3A or 3B, may include circuitry to prevent current
flow when the battery voltage drops below a given voltage
threshold, hence under-voltage lockout. A protection circuit 210 in
the battery pack can sense battery voltage and if the voltage drops
below a given voltage level, the discharge FET (semiconductor
device 130a) is turned off. Battery cells 105 would still be
susceptible to charge, but would not discharge any more. The
threshold may be an absolute threshold set at time of manufacture,
for example, or a threshold that may vary based on a number of
given factors.
[0080] FIG. 6 is a graph of voltage versus time to illustrate an
automatic shutdown invoked by a protection circuit in accordance
with an exemplary embodiment of the present invention. To protect
against an over-discharge fault condition in a battery pack of a
cordless power tool system, an exemplary protection circuit 210
(such as shown in FIG. 2) and/or the battery electronic control 125
in FIGS. 3A-5, could perform an automatic shutdown of current in
pack 100 if the voltage reached a given threshold.
[0081] An improvement to the aforementioned voltage threshold may
be to combine the threshold with a proportion of discharge current
to compensate for the impedance of the battery pack 100. Basing the
threshold on an absolute level and subtracting a portion of the
instant current may provide an alternative method for under-voltage
lockout.
[0082] FIG. 7 is a graph of voltage versus time to illustrate a
modified threshold for over-discharge protection in accordance with
an exemplary embodiment of the present invention. For the purposes
of describing FIG. 7, the protection current 210 of FIG. 2 or the
battery electronic control 125 could be configured to make the
following calculations and/or perform the automatic shutdown. FIG.
7 shows an example of a battery pack at 10% state-of-charge. By
adding in a proportion of discharge current to compensate for the
impedance of the battery pack 100, the battery pack 100 is still
above a given discharge threshold of 2.7 volts.
[0083] For example, if a 10 amp pulse load is placed on the battery
pack 100, the battery impedance would cause the voltage to jump
below the threshold momentarily and return to its resting value
when the current pulse is removed. Even though the battery pack 100
had 10% of charge left, a protection current would have interrupted
current flow. However, if the low-voltage threshold was partially
compensated with current as described in the previous paragraph,
the threshold would be dropped during the heavy current draw and no
shutdown would occur. In other words, the low-voltage threshold may
be varied by subtracting a portion of the instantaneous discharge
current to compensate for pack impedance so as to avoid an unwanted
automatic shutdown.
[0084] Once the impedance of the pack is known, then the portion of
the low-voltage threshold related to current can be calculated.
Additional battery factors that may influence the low voltage
threshold may include battery temperature, battery age, rate of
decrease in battery voltage, etc.
Over-Current Protection
[0085] FIGS. 8A and 8B illustrate exemplary devices that may be
used in the battery pack for over-current protection in accordance
with an exemplary embodiment of the present invention. FIGS. 8A and
8B illustrate only a portion of a battery pack circuit for reasons
of brevity. However, the devices in FIGS. 8A and 8B could be part
of the battery pack 100 as shown in any of FIGS. 3A-5. Another
mechanism that can cause cell damage is over-current. Various
electronic switching methods may have a drawback, in that
electronic switches are prone to failing in a short circuit
condition. When this happens, an operator overload the motor of the
attached tool. For battery pack circuit designs that include
separate impedance branches, a device such as a fuse or fusible
link could be used to limit the maximum current through that
circuit branch.
[0086] Fuses generally are not designed to provide overload
protection, as a fuse's basic function is to protect against short
circuits. However, a dual-element (two-element) fuse or time delay
fuse may provide secondary motor overload protection, although when
blown must be replaced, as these fuses are nonrenewable.
Accordingly, such a fuse could represent a secondary failure and be
intended to prevent further operation, for example.
[0087] Thus, a simple fuse as shown in FIG. 8A may be designed to
limit the current through the cells 105, but may also cause
permanent damage once its rating is exceeded. Other devices such as
Positive Temperature Coefficient (PTC) elements and re-settable
fuses may be substituted for the fuse in FIG. 8A for over-current
protection. As discussed above, PTC devices or elements are known
as protective elements for controlling the current which flows
through circuits to be protected, since their resistance value
increases as they give off heat in over-current conditions. For
example, PTC thermistors have been used as an over-current
protection element. When an electronic circuit gets overloaded,
conductive polymers of a PTC thermistor, which have PTC properties,
emit heat and thermally expand to become high resistance, thereby
reducing the current in the circuit to a safe, relatively small
current level.
[0088] Accordingly, if a PTC device such as described above is
connected in series with the battery, the total pack impedance
would increase with increasing current. If substantially low
impedance is needed and no commercially available single PTC device
can offer the desired low impedance and/or current capability, then
multiple PTC's could be connected in parallel with each other to
share the current, as shown in FIG. 8B, for example.
[0089] If separate charge and discharge paths or branches are
envisioned in the battery pack, then a thermal fuse such as a PTC
element could be placed on each current path. This would be
beneficial in that the charge path would use a low current device
and the discharge path would use a high current device.
[0090] Proximity placement of a fuse nearer the terminals also may
provide an added benefit of isolating the downstream branch of
electrical devices from a non-isolated charger. If a battery pack
100 were to melt sufficiently to expose the cells 105 and
electronics, the fuses (which would have blown) near the terminals
would provide a disconnect of the exposed metal from the
non-isolated charger output, hence electric isolation to possible
preserve electrical components in an attached charger (or tool).
Thus, positioning the fuse (or PTC element) in FIG. 8A nearer the
terminal may provide additional over-current protection in pack
100.
[0091] Using current sensing measures (such as current sensor 145
of FIGS. 3A and 3B) and a semiconductor device (such as
semiconductor devices 130a and 130b) to stop current flow once an
over-current threshold is reached may be a desirable method of
preventing cell-damage. For example, current sensor 145 may be
adapted to sense pack current to generate a control signal based on
sensed current exceeding a given current limit or threshold. A
semiconductor device having a current limiting or current
interrupting function (e.g., semiconductor devices 130a and 130b)
may be directly connected to the current sensor 145. The
semiconductor device may be adapted to limit or interrupt current
based on the control signal received directly from the current
sensor 145 instead of from battery electronic control 125 via
driver 140.
[0092] Current sensing could also be coupled with an averaging
algorithm if momentarily high current loads were acceptable but
steady state high current was not acceptable. A suitable current
limit or threshold could also be variable, and proportional, to the
temperature of the cells. This may be beneficial in that, if the
cells were already hot, the maximum current pulled out would not be
sufficient to overheat the internal cell chemistry.
Over-Temperature Protection
[0093] Some batteries may also be damaged by extreme temperatures
(extreme high or low temperatures) or have reduced performance
(i.e., reduced voltage and/or current output) due to extreme
temperatures. This is particularly relevant to battery packs having
a Li-ion cell chemistry. A battery temperature threshold may be set
to shutdown the battery pack until it cools below a desired or
given temperature. Likewise, a battery temperature threshold may be
set to shutdown the battery pack until it rises above a desired or
given temperature. These thresholds can also be based on a set
limit with a partial dependence on current, voltage, age, and rate
of rise or fall in temperature, for example. As discussed above,
one or more temperature sensors may be used for determining the
state of the battery pack temperature.
[0094] FIG. 9 illustrates a device providing over-temperature
protection in accordance with the exemplary embodiments of the
present invention. An over-temperature fault condition in a battery
cell may cause permanent damage. Thus, a protection circuit
configured to monitor absolute temperature may be useful in
preventing over-temperature conditions. FIG. 9 illustrates only a
portion of a battery pack circuit for reasons of brevity. However,
the devices in FIG. 9 could be part of the battery pack 100 as
shown in any of FIGS. 3A-5.
[0095] As shown in FIG. 9, the protection device 210 may be
embodied as a thermal switch 910 that opens high current contacts
920. These contacts may be located within the circuit to stop any
current flow in or out of the pack 100 until the temperature drops
to an acceptable level. These devices may be typically set to trip
at a pre-determined temperature and are usually found in coffee
makers, for example. Once the water in a coffee maker is boiled off
the heating element temperature rises above 212.degree. F. The
temperature switch senses this and breaks the temperature
controlled switch. When the pack (or a cell) temperature gets too
hot, the charge and/or discharge function in pack 100 is
disabled.
[0096] Alternatively a thermally controlled release mechanism could
`pop` the battery pack 100 out of the tool 170 or charger 150 and
prevent re-insertion, until the pack 100 has cooled off. This
device could be similar to a "pop-up timer" aimed at a latch
mechanism which restrains an ejection device within pack 100) as
will be seen in further detail below. Another device for protecting
against an over-temperature fault condition is the use of a
thermistor. A thermistor may be utilized in the battery pack 100 to
monitor temperature conditions while maintaining full electrical
isolation of the thermistor from the battery cells 105.
[0097] Currently, manufacturers typically may include a thermistor
in battery packs to monitor the temperature of the core pack and to
terminate charge in the event of an over temperature condition.
These thermistors have a connection arrangement in which one end is
connected to a terminal going out to the charger 150, and the other
end is referenced to ground by tying to the negative terminal lead
in the battery pack.
[0098] For high power battery packs adapted for use with both
existing cordless power tools, and developing lines of power tools
that are manufactured for use with these high power battery packs,
such as Li-ion battery packs, this above connection arrangement may
be problematic, since the connection arrangement creates the
potential for a charge path through the thermistor. If a small
amount of current were passed through the thermistor, the battery
pack could potentially be charged outside the protection controls
and circuitry provided in the pack 100 and charger 150. This could
potentially lead to an inadvertent overcharging of the pack 100, a
potentially hazardous condition.
[0099] FIG. 10 illustrates a connection arrangement for a
thermistor in accordance with an exemplary embodiment of the
present invention. In FIG. 10, only the positive and negative
terminals of the pack 100 are shown for clarity. FIG. 10
illustrates only a portion of a battery pack circuit for reasons of
brevity. However, the thermistor in FIG. 10 could be part of the
battery pack 100 as shown in any of FIGS. 3A-5. The two leads of
the thermistor (Th+ and Th-) may be brought out of the pack on
independent terminals 2 and 3. These terminals may interface to
temperature monitoring circuitry inside of the charger 150, for
example, such as temperature monitoring circuitry of the charger
electronic control unit 155 (not shown in FIG. 10 for clarity).
This may allow monitoring of pack 100 temperature while keeping the
thermistor completely isolated from the charge path in the pack
100. By doing this, there is no charge path through the thermistor
and no potential to overcharge the battery pack 100 through the
thermistor.
Audible/Visual Warning Mechanisms
[0100] Before shutting down the battery power, it may be desirable
that some kind of warning be provided to the operator of a cordless
tool powered by the attached battery pack. Similar to a scenario
when a fault condition occurs, or is in the process of occurring,
in an owner's car, the owner may be given a warning light on the
dashboard for a given duration of time before the engine breaks
down because of the fault condition (i.e., piston damage due to a
lack of oil).
[0101] Both under-voltage and temperature limitations can be used
as a cut-off, i.e., the battery pack 100 ceases to output current
once a threshold is reached. However, before such a fault condition
occurs (such as an under-voltage or over temperature threshold) is
reached, a warning mechanism in either the battery pack or tool may
warn the operator that the operator is approaching an impending
operating limit in the pack that may automatically shutdown battery
power in the pack. The warning mechanism could be audible (with a
horn or buzzer) or visible using a desired illumination scheme such
as LEDs, for example.
[0102] The audible and/or visible warning mechanism may be tied
into the existing circuitry in the pack 100 or tool 170. As
discussed above, the battery pack 100, tool 170 or charger 150 in
any of FIGS. 3A through 5 and may be controlled by intelligence in
the pack, tool, charger, etc. Such intelligence as battery
electronic control 125 or tool electronic control 180 could be
configured to control warning mechanisms for various impending or
present fault conditions. As an example, a separate audible or
visual warning may be provided to alert the tool operator of an
over-discharge condition in the battery pack 100, an over-current
condition in the battery pack 100, and over-temperature condition
in the pack 100 or in the motor 190 of the attached tool 170,
and/or an under-voltage condition in the battery pack 100 due to an
excessive amount of current being drawn from the battery pack
100.
[0103] As discussed above, the warning mechanism before an
impending automatic battery power shutdown is reached could be
embodied in many different forms. The aforementioned audible
warnings such as horns, buzzers, and speaker sounds might be
acceptable in some working environments, but may not be heard by
the tool operator in loud environments. Visual cues such as
specified illumination(s) and gauges may also be missed by the tool
operator in extremely dark or substantially bright work areas.
[0104] An alternative warning mechanism to alert the tool operator
may be embodied in the motor control of the tool motor. In general,
an electronic circuit in one of the tool or battery pack could
reduce the maximum power output capability of the battery pack and
produce a "fold back" condition. The operator would both hear and
feel this condition as a `weakening` of the tool performance. The
operator would be prompted to back off and avoid an impending fault
condition (e.g., under-voltage, over-temperature, under-temperature
condition, etc.).
[0105] An additional method for alerting the user of an impending
fault condition would be to vary the motor control's pulse width
modulation (PWM) to create a "warble" effect in the speed of the
motor. This mild cyclic change in motor speed is selected as such
it would not adversely affect tool performance. This method
provides the user with both audible and tactile feedback on the
impending fault condition.
[0106] A third method for alerting the user of an impending fault
condition would be to lower the PWM frequency into the audible
frequency range and vary the pitch in a periodic fashion. This will
present an efficient warning mechanism to get the operators
attention. At the very least, the warning mechanism gives the
operator a sense of warning that they may be able to finish the
current job, but may not be able to move on to another job before
resting or recharging the battery pack to eliminate or overcome the
impending fault condition.
[0107] Any of the above warning mechanisms, either singly or in
combination with one or more of the above warning mechanisms, could
potentially enhance the tool functionality or extend tool and/or
battery pack life. The following details the latter warning
mechanism as directed to providing the aforementioned warbling
effect in the motor of the power tool based on a state of charge in
the battery pack.
PWM State of Chare (SOC) Indicator
[0108] The purpose of the PWM State of Charge (SOC) Indicator is to
alert the operator of an impending fault condition which could
cause automatic battery power shutdown, resulting in a `dead`
battery pack. This may be accomplished by directly determining SOC
information in a motor control unit that is part of the battery
pack circuitry. Based on the SOC information, a motor control unit
in the battery pack would vary the motor current switching
frequency to produce the `warbling effect` in the tool motor that
may be heard and/or physically felt by the tool operator.
[0109] FIG. 1 is a flow diagram illustrating a method of alerting
an operator of a power tool of an impending fault condition in the
battery pack. Referring to FIG. 11, a motor control unit (not
shown) in the battery pack may measure various battery pack
parameters to determine state of charge (SOC) information in the
battery pack at a given time instant (S1110). The motor control
unit may be embodied in hardware or software as a digital
microcontroller or microprocessor or an analog circuit, for
example, and/or by a digital IC such as a digital signal processor
or an application specific integrated circuit (ASIC). Based on the
SOC information, the motor control unit determines a desired motor
current switching frequency (S1120) which is imparted to the tool
motor to produce the warbling effect (S1130) to alert the
operator.
[0110] There are a number of ways to evaluate, track and determine
the SOC of the battery pack. For example, battery pack parameters
measured by the motor control unit to determine the SOC information
may include battery pack voltage, Coulomb count
(Ah.sub.in-Ah.sub.out), total battery pack 100 impedance, etc. The
motor control unit would then decide on a motor current switching
frequency based on the SOC information.
[0111] The motor current switching frequency for the tool 170 motor
could be manipulated in a number of ways to alert the user.
Accordingly, adjusting the motor current switching frequency
enables the motor of the tool to communicate to the tool operator.
A switching frequency could be selected in the audible frequency
range, so that the motor would make a noise that is perceptible by
the operator. Exemplary audible frequencies could be a constant
frequency tone emitted by the tool motor, a varying frequency ring
tone, a complex series of multiple frequency tones to mimic a
`voice` speaking to the tool operator, for example. Additionally,
the motor control unit could pulse the motor so as to make the tool
physically shutter or vibrate in a way that would let the operator
know that the battery packing was running out of charge, for
example, or approaching a fault condition requiring attention.
[0112] Methods of pulse-width-modulating the motor to alert the
operator of an impending fault condition such as a low SOC
condition could also be used to communicate other fault conditions.
For example, motor current switching frequency could be adjusted to
alert the tool operator based on sensed information related to an
over temperature condition in the battery pack, over temperature
condition in the tool motor, over-current condition in the pack
and/or under-voltage condition due to an excessive amount of
current being drawn from the battery pack. Current, temperature and
voltage are merely exemplary measurable parameters that could be
tracked for a given fault condition.
[0113] FIG. 12 is a block diagram illustrating an exemplary
arrangement for determining SOC and varying motor current switching
frequency in accordance with an exemplary embodiment of the present
invention. FIG. 12 shows a circuit interface relationship between
battery pack 100' and tool 170' somewhat similar to FIG. 3B,
although only certain components are shown for reasons of
clarity.
[0114] Referring to FIG. 12, IC1, R1, and Q1 contribute to
protection circuitry and cell balancing functionality, as discussed
above in reference to several of the other figures. IC1 could
represent the battery pack electronic control unit 125, for
example, in FIGS. 3A and 3B. DATA3 and DATA4 represent serial data
paths to carry serial data between IC1 and IC2; IC2 in FIG. 12 may
represent the motor control unit. For example, DATA3 could be
dedicated to passing data and control signals between IC1 and IC2,
and DATA4 for sending a clock to synchronize IC1 with IC2 or vice
versa.
[0115] The element REG is a voltage regulator that supplies VCC to
digital devices IC2 and IC3. In FIG. 14, IC3 may represent a tool
electronic control unit 180 as described in FIG. 3B for example,
with DATA1 and DATA2 representing serial data paths for
communication of data and control signals between IC3 and IC2. SW1
represents the tool switch to pull current from the battery pack to
power motor M1. Resistor R6 and potentiometer R7 make up a variable
speed input for the tool. Each of IC1, IC2 and IC3 may be embodied
in hardware or software as a digital microcontroller or
microprocessor or an analog circuit, for example, and/or by a
digital IC such as a digital signal processor or an application
specific integrated circuit (ASIC)
[0116] Motor control unit IC2 drives the gates of Q5 and Q6 (which
may be embodied as MOSFETs) in order to regulate output voltage of
the battery pack and thereby control motor current that powers the
motor M1 of the tool. IC2 may measure one of more battery pack
parameters to determine SOC. For example, IC2 could monitor battery
pack output voltage across nodes N1 and N2, or perform Coulomb
counting by monitoring current at shunt resistor R5 and keeping
track of time (via suitable internal clock). Further, IC2 could
also monitor pack impedance by subtracting loaded battery pack
output voltage (when current is flowing) from unloaded pack voltage
(recorded before current draw) and dividing the result by the
current measurement taken at R5. Any of these measurable parameters
could serve as a SOC measure. IC2 would then use this SOC
information to determine the appropriate switching frequency, and
control Q5 and Q6 to achieve that switching frequency.
Redundancy
[0117] The features described above are designed to prevent damage
to the battery cells from heavy use or failing components in any
part of the control system in the pack 100, charger 150 or tool
170. By adding a secondary form of redundancy, the cells may be
less likely to experience cell damage. For example, in FIG. 12, the
charger 150 and the tool 170 could also monitor battery temperature
and current through external terminals or communications. Battery
voltage may also be monitored during charge by the charger 150. It
could also be checked by the tool during discharge.
[0118] FIGS. 13-16, in general, illustrate various devices for
providing overcharge protection in extreme cases. In the event that
an overcharge condition fails to be addressed by the above
described watchdog circuit of FIGS. 4 and 5, other current sensory
devices, and/or an intelligent device microprocessor in one or more
of the battery pack 100 or charger 150 fails (multi-point failures
in pack or charger), FIGS. 13-16 illustrate potential secondary
protection for the battery pack 100 and/or charger 150.
[0119] FIG. 13A is an isometric view of a single laminate battery
cell, in which cell 1305 (analogous to cell 105 in any of FIGS.
3A-5) has a tab 1303 (also known as a connector) for connection to
an adjacent serially connected cell. FIGS. 13B and 13C illustrate a
device for protecting against an overcharge condition in accordance
with an exemplary embodiment of the present invention.
[0120] FIGS. 13B and 13C illustrate a device which may reduce the
potential for battery cells having a lithium-ion cell chemistry (or
other cell chemistries) from rupturing upon a severe overcharge
condition that is unattended by other protection circuitry in the
pack. In general, during an overcharge event, the laminated
lithium-ion battery cells 1305 may exhibit extensive swelling. If
the overcharge continues, this may result in a rupture of one or
more of the cells 1305. This rupture may result in fire and
potentially severe damage to the battery pack 100 attached
electrical device (charger 150, tool 170) and/or user of the
battery pack 100.
[0121] Accordingly, a battery pack may be designed to take
advantage of this swelling phenomenon. FIG. 13B a side view of a
steady-state or normal condition in the battery pack, and
illustrates tab welds 1306 or similar connections to serially
connect the tabs 1303 of adjacent cells 1305 between positive and
negative power terminals of the battery pack 100. As shown in FIG.
13C, swelling of one or more given cells 1305 in the battery pack
100 may help to prevent a severe overcharge condition from
occurring. The swelling cell(s) 1305 creates a tension pressure
against its tab 1303, such that two tabs 1303 may separate at a tab
weld 1306. In this example, the an opening 1308 is formed in the
circuit, thus removing or interrupting charge current to the cells
1305. Thus, as a cell 1305 expands, it pulls the tab connector 1303
away from an adjacent tab 1303 at the tab weld 1306 to break the
electrical connection between cells 1305, interrupting current flow
in the battery pack 100.
[0122] FIGS. 14A and 14B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention. FIG. 14A illustrates a side
view of normal or steady state conditions in pack 100 to illustrate
another exemplary protection arrangement. In FIG. 14A, the cells
1305 may be serially arranged within a battery housing (shown
generally as housing sidewall 1401a and housing sidewall 1401b,
which may include an intermediate housing wall 1401c, for example.
A plunger 1408 may be provided between the serially connected cells
1305 and the intermediate housing wall 1401c so as to protrude into
a recess 1409 through the walls 1401b, 1401c. In an example, the
plunger may be restrained via a counter force provided by spring
1410, so that there is a channel 1404 formed between housing
sidewall 1401b and intermediate housing wall 1401c. A lead wire
(here shown as a positive terminal wire or circuit trace), may
extend through the channel 1404.
[0123] Referring now to FIG. 14B, showing one cell 1305 in an
overcharged state. As the cell 1305 expands, the expansion force
from the cell assists the plunger 1408 in overcoming the
counterforce spring pressure from spring 1410. Thus, plunger 1408
travels into recess 1409 to sever lead wire 1405 as shown generally
at 1415, thereby interrupting charge current to the cells 1405 of
the battery pack. Note also that the swelling cell 1305 also causes
the tabs 1303 to come apart as shown generally at 1308, providing
further redundancy to sever or break the electrical connections
internal to the battery pack. These protective features may thus
prevent rupture of one or more cells in the pack 100 by
interrupting the current flow.
[0124] FIGS. 15A and 15B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention. FIGS. 15A and 15B illustrate a
plunger designed so as to eject a battery pack from a charger.
[0125] FIG. 15A is similar to FIG. 14A, thus only differences are
discussed for reasons of brevity. As shown in FIG. 15A, in steady
state or normal operations, plunger 1408 is biased against a
counterforce spring pressure of spring 1410, such that the plunger
1408 rests against a charger housing sidewall 1501. Charger housing
sidewall 1501 abuts sidewall 1401b of pack 100. Lead wire 1405 of
the pack and a charger lead wire 1505 are operatively connected at
contacts 1410, 1510.
[0126] Referring now to FIG. 15B, as a cell 1305 expands, plunger
1408 overcomes spring 1410 pressure which causes the plunger 1408
to self-eject the pack 100 from the charger, see gap 1508 between
cell housing sidewall 1501 and pack sidewall 1401b. This action
breaks contacts 1410 and 1510. Accordingly, upon a severe
overcharge condition, the swelling of the pack in combination with
the placement of the plunger 1408 interrupts charging current and
prevents rupture of the pack by ejecting the pack from the charger.
Note also that the swelling cell 1305 also causes the tabs 1303 to
come apart as shown generally at 1308, providing further redundancy
to sever or break the electrical connections internal to the
battery pack. These protective features may thus prevent rupture of
one or more cells in the pack 100 by interrupting the current
flow.
[0127] FIGS. 16A and 16B illustrate a device for protecting against
an overcharge condition in accordance with another exemplary
embodiment of the present invention. FIGS. 16A-B are similar in
some respects to FIGS. 14A-14B, thus the differences are described
for purposes of brevity.
[0128] In FIG. 16A, the charger lead wire or trace 1505 is
connected to pack lead wire at contacts 1405, 1505. Unlike in FIG.
14A, charger lead wire 1505 abuts an inside surface a charger
housing sidewall 1501. Plunger 1408 and spring 1410 are as
described in FIG. 14A. Referring now to FIG. 16B, showing one cell
1305 in an overcharged state. As the cell 1305 expands, the
expansion force from the cell assists the plunger 1408 in
overcoming the counterforce spring pressure from spring 1410. Thus,
plunger 1408 travels into recess 1409 to sever charger lead wire
1505 as shown generally at 1615, thereby interrupting charge
current to the cells 1405 of the battery pack. Note also that the
swelling cell 1305 also causes the tabs 1303 to come apart as shown
generally at 1308, providing further redundancy to sever or break
the electrical connections internal to the battery pack. These
protective features may thus prevent rupture of one or more cells
in the pack 100 by interrupting the current flow.
[0129] The exemplary embodiments of the present invention being
thus described, it will be obvious that the same may be varied in
many ways. Such variations are not to be regarded as departure from
the spirit and scope of the exemplary embodiments of the present
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
* * * * *