U.S. patent application number 14/820682 was filed with the patent office on 2015-12-03 for bottom based balancing in lithium ion system.
This patent application is currently assigned to BLACK & DECKER INC.. The applicant listed for this patent is BLACK & DECKER INC.. Invention is credited to Nathan Cruise, Daniel J. White.
Application Number | 20150349551 14/820682 |
Document ID | / |
Family ID | 40303669 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150349551 |
Kind Code |
A1 |
White; Daniel J. ; et
al. |
December 3, 2015 |
Bottom Based Balancing in Lithium Ion System
Abstract
A method comprises discharging each of a plurality of cells of a
battery pack, stopping the discharging of a selected cell of the
plurality of cells when the selected cell reaches a predetermined
capacity, and charging the plurality of cells after the discharging
has stopped for all of the plurality of cells.
Inventors: |
White; Daniel J.;
(Baltimore, MD) ; Cruise; Nathan; (Phoenix,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BLACK & DECKER INC. |
Newark |
DE |
US |
|
|
Assignee: |
BLACK & DECKER INC.
Newark
DE
|
Family ID: |
40303669 |
Appl. No.: |
14/820682 |
Filed: |
August 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12250673 |
Oct 14, 2008 |
9136716 |
|
|
14820682 |
|
|
|
|
60999024 |
Oct 15, 2007 |
|
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Current U.S.
Class: |
320/112 |
Current CPC
Class: |
Y02T 10/7044 20130101;
H01M 10/441 20130101; H02J 7/0021 20130101; Y02T 10/70 20130101;
H02J 7/0045 20130101; H01M 2/30 20130101; H01M 10/0525 20130101;
B60L 58/15 20190201; Y02P 70/54 20151101; Y02P 70/50 20151101; Y02T
10/7011 20130101; H01M 2200/00 20130101; H01M 2220/30 20130101;
H02J 7/0016 20130101; Y02E 60/10 20130101; H01M 2010/4271 20130101;
H02J 7/0026 20130101; Y02E 60/122 20130101; Y02T 10/705 20130101;
H01M 10/482 20130101; H01M 2/34 20130101 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1. A battery system comprising: a battery comprising: N cells
arranged in series and each having a positive terminal and a
negative terminal; and N+1 external electrical contacts
corresponding to the positive terminals of each of the N cells and
the negative terminal of one of the N cells, respectively; and a
battery charger comprising: a plurality of terminals that
electrically connect to the N+1 external electrical contacts of the
battery; a capacity determination device that determines a capacity
for each of the N cells; and N discharge devices that are
selectively applied to each of the N cells respectively via the
plurality of terminals.
2. The battery system of claim 1 wherein the battery further
comprises a charging protection device that stops conducting when a
current through the charging protection device exceeds a first
threshold, wherein the charging protection device is connected
between one of the N+1 external electrical contacts and one of the
positive terminal and the negative terminal of one of the N
cells.
3. The battery system of claim 2 wherein the battery further
comprises: an additional external electrical contact for connection
to a tool; and a short-circuit protection device that stops
conducting when a current through the short-circuit protection
device exceeds a second threshold, wherein the short-circuit
protection device is connected between the additional external
electrical contact and the one of the positive terminal and the
negative terminal of the one of the N cells.
4. The battery system of claim 3 wherein the first threshold is
greater than the second threshold.
5. The battery system of claim 1 wherein the battery further
comprises a temperature measurement device that measures a
temperature of the battery.
6. The battery system of claim 1 wherein the N discharge devices
each selectively apply a first load at a first time and a second
load at a second time.
7. The battery system of claim 1 wherein the capacity determination
device comprises: a measurement device; and a multiplexer that
selectively connects two of the plurality of terminals to the
measurement device.
8. The battery system of claim 7 wherein the measurement device
comprises: a voltage measurement device; and an analog-to-digital
converter that converts a voltage measured by the voltage
measurement device to a digital value.
9. The battery system of claim 7 wherein the battery charger
further comprises a balancing capacitor that is selectively
connected to an output of the multiplexer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Non-Provisional
application Ser. No. 12/250,673, filed on Oct. 14, 2008, which
claims priority to Provisional Application No. 60/999,024, filed on
Oct. 15, 2007. The disclosure of the above application is
incorporated herein by reference in its entirety.
FIELD
[0002] The present disclosure relates to battery charging, and more
particularly to bottom based balancing in lithium ion
batteries.
BACKGROUND
[0003] Referring now to FIG. 1, a functional block diagram of a
battery pack 100 according to the prior art is presented. The
battery pack 100 includes multiple cells 106-1, 106-2, 106-3, and
106-4, each having a positive and a negative terminal. The cells
106 are connected in series, with the positive terminal of one cell
106 connected to the negative terminal of the next cell 106. In
various implementations, the cells 106 may be lithium ion (Lilon)
charge storage cells.
[0004] The negative terminal of the cell 106-4 is connected to an
external contact, which may interface with a power tool or a
charger. The positive terminal of the cell 106-1 is connected to a
switch 110. When the switch 110 is conducting, the positive
terminal of the cell 106-1 is connected to an external contact,
which may interface with the power tool or the charger. The switch
110 is controlled by a protection system 114. The protection system
114 monitors voltages at the positive and negative terminals of
each of the cells 106.
[0005] The cells 106 may have varying charge storage capacities.
The cells 106 with lower charge storage capacities will decrease in
voltage faster than the cells 106 with larger storage capacities.
The protection system 114 measures the voltages of the cells 106
and instructs the switch 110 to stop conducting when the voltage of
one of the cells becomes too low. In addition, the switch 110 may
stop conducting if the current flowing through it exceeds a safe
operating level.
[0006] Referring now to FIG. 2, a graphical depiction of battery
charging according to the prior art is presented. During battery
charging, each of the cells is charged to a predetermined voltage.
In FIG. 2, four cells are depicted, and they are each charged to
3.6 volts. At 3.6 volts (V), however, the cells may have varying
capacities. For example, the first three cells may have a fully
charged capacity of 1.1 ampere-hours (Ah), while the fourth cell
has a capacity of 1.0 Ah. This imbalance causes problems during
discharging, as shown in the next figure.
[0007] Referring now to FIG. 3, a graphical depiction of battery
discharging according to the prior art is presented. As the battery
pack is discharged, the voltages of the cells decrease. After 1.0
Ah has been drawn from the cells, the first three cells have 0.1 Ah
remaining, and may be at a voltage of approximately 2.5 V. However,
the fourth cell has zero capacity remaining, and may be at a lower
voltage, such as 1.8 V, or even a negative voltage.
[0008] Battery cells, and especially Lilon cells, may be
permanently damaged, and may even become unstable, when driven to
low or negative voltages. The voltage of the fourth cell may be too
low after 1.0 Ah has been drawn from the battery pack. For this
reason, the protection system 114 of FIG. 1 monitors the voltage of
each of the cells. Without this monitoring, the user may continue
using the battery pack even as one or more of the cells 106 runs
out of capacity. As current is drawn from the first three cells,
the fourth cell may even be driven to a negative voltage, which is
likely detrimental to the fourth cell. The protection system 114
can prevent this from happening, but is expensive and complicated
to include in each battery pack.
[0009] The background description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent it is described in
this background section, as well as aspects of the description that
may not otherwise qualify as prior art at the time of filing, are
neither expressly nor impliedly admitted as prior art against the
present disclosure.
SUMMARY
[0010] A method comprises discharging each of a plurality of cells
of a battery pack, stopping the discharging of a selected cell of
the plurality of cells when the selected cell reaches a
predetermined capacity, and charging the plurality of cells after
the discharging has stopped for all of the plurality of cells.
[0011] A battery charger comprises a discharging device, a charging
device, and a control module. The discharging device discharges
each of a plurality of cells of a battery pack. The charging device
charges the plurality of cells. The control module selectively
instructs the discharging device to discharge the plurality of
cells. The control module selectively instructs the discharging
device to stop discharging a selected cell of the plurality of
cells when the selected cell reaches a predetermined capacity. The
control module selectively instructs the charging device to begin
charging the plurality of cells after discharging is stopped for
all the plurality of cells.
[0012] Further areas of applicability of the present disclosure
will become apparent from the detailed description provided
hereinafter. It should be understood that the detailed description
and specific examples, while indicating the preferred embodiment of
the disclosure, are intended for purposes of illustration only and
are not intended to limit the scope of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present disclosure will become more fully understood
from the detailed description and the accompanying drawings,
wherein:
[0014] FIG. 1 is a functional block diagram of a battery pack
according to the prior art;
[0015] FIG. 2 is a graphical depiction of battery charging
according to the prior art;
[0016] FIG. 3 is a graphical depiction of battery discharging
according to the prior art;
[0017] FIGS. 4A-4B are graphical depictions of bottom based
balancing according to the principles of the present
disclosure;
[0018] FIG. 5 is a graphical depiction of charging from a bottom
balanced state according to the principles of the present
disclosure;
[0019] FIG. 6 is a flowchart depicting exemplary steps performed by
a battery charger according to the principles of the present
disclosure;
[0020] FIG. 7 is a flowchart depicting exemplary steps performed in
bottom balancing and charging according to the principles of the
present disclosure;
[0021] FIGS. 8A-8B are functional block diagrams of exemplary
charging systems according to the principles of the present
disclosure;
[0022] FIG. 9 is a functional block diagram of another exemplary
battery charging system according to the principles of the present
disclosure;
[0023] FIG. 10 is a functional block diagram of an exemplary
battery pack according to the principles of the present
disclosure;
[0024] FIG. 11 is a functional block diagram of another exemplary
battery pack according to the principles of the present disclosure;
and
[0025] FIG. 12 is a functional block diagram of another exemplary
battery pack according to the principles of the present
disclosure.
DETAILED DESCRIPTION
[0026] The following description is merely exemplary in nature and
is in no way intended to limit the disclosure, its application, or
uses. For purposes of clarity, the same reference numbers will be
used in the drawings to identify similar elements. As used herein,
the phrase at least one of A, B, and C should be construed to mean
a logical (A or B or C), using a non-exclusive logical or. It
should be understood that steps within a method may be executed in
different order without altering the principles of the present
disclosure.
[0027] As used herein, the term module refers to an Application
Specific Integrated Circuit (ASIC), an electronic circuit, a
processor (shared, dedicated, or group) and memory that execute one
or more software or firmware programs, a combinational logic
circuit, and/or other suitable components that provide the
described functionality.
[0028] In prior art methods of battery charging, each cell is
charged to a predetermined voltage, regardless of the resulting
capacity in the cell. According to the principles of the present
disclosure, each of the battery cells is discharged to a
predetermined low capacity. Once the cells are balanced at this low
capacity, an equal amount of capacity is added to all of the cells.
To accomplish this, the cells may be charged from the predetermined
low capacity until any of the cells reaches a maximum voltage. At
this point, charging of all the cells can be stopped. FIGS. 4A-B
and 5 graphically depict charging according to these
principles.
[0029] FIG. 6 depicts exemplary steps performed by a battery
charger that implements bottom balanced charging according to the
principles of the present disclosure. FIG. 7 illustrates exemplary
steps performed in discharging the cells to a balanced low (bottom)
level. FIGS. 8A-9 depict exemplary charging systems for performing
these methods, while FIGS. 10-12 depict exemplary battery packs
that can be used in these battery charging systems.
[0030] Referring now to FIG. 4A, a graphical depiction of bottom
based balancing is shown. Four cells from an exemplary battery pack
are depicted, although battery packs according to the principles of
the present disclosure may have more or fewer cells. Each of the
four cells is discharged to a predetermined bottom capacity. For
example, in FIG. 4A, the predetermined bottom capacity is shown as
0.1 Ah.
[0031] In order to achieve this bottom capacity in each cell, the
voltage of the cell can be measured and its capacity determined
from known voltage decay characteristics. FIG. 4B depicts exemplary
voltage curves for two cells as they discharge. For example, a
fully charged cell may have a voltage above 3 V, and the voltage
may initially decrease fairly slowly as the cell is discharged.
Once the cell's capacity reaches a low level, the voltage will
begin to drop quickly. This change in voltage decrease rate may be
referred to as a knee. The voltage knee may correspond to a certain
capacity that is fairly consistent across the cells. For example
only, the voltage knee may correspond to 0.15 Ah.
[0032] All the cells may then be discharged to the point at which
their respective voltage knee is observed, at which time they will
have approximately equal capacities. However, monitoring voltage
rates quickly and determining derivatives in order to precisely
determine the knee may require additional circuitry, adding
complexity and cost to an implementation. Instead, the position of
the knee can be approximately determined by monitoring when the
cell crosses a voltage threshold that is less than the knee
voltage.
[0033] After the knee voltage is reached, the voltage will decrease
fairly rapidly. The voltage threshold should therefore be reached
fairly soon after the voltage knee, and the point at which the cell
voltage crosses the voltage threshold may be a reliable indicator
of where the knee voltage was. At the threshold voltage, the
capacity of the cell may be slightly lower than at the knee
voltage. For example, the cell capacity may be 0.1 Ah.
[0034] In FIGS. 4A-B, a threshold voltage of 2.5 V is shown. When
approximately determining the knee voltage, each cell can be
discharged until it reaches 2.5 V. Once the cell reaches 2.5 V,
discharging can be stopped for that cell. The threshold voltage of
2.5 V is for example only. Alternative threshold voltages may be
chosen. In addition, threshold voltages may vary based on cell
chemistry and construction. The cells may be discharged by applying
a load across each cell. For example, the load may be a constant
current load, such as a transistor, or may be a resistive load.
[0035] To achieve fast discharging, and therefore fast charging,
large loads may be applied to the cells. The large load may
discharge the cells quickly, but may not allow for an accurate
determination of capacity. To combine the fast discharge of a large
load with the accuracy of a small load, the large load can be
applied until the cell reaches a second threshold voltage. Once the
cell has reached the second threshold voltage, a smaller load can
be applied to the cell until it reaches the threshold voltage, such
as 2.5 V in FIGS. 4A-B. The cells may all be discharged
simultaneously, with the discharging of each cell stopped when it
reaches the threshold voltage.
[0036] In various implementations, the second threshold voltage may
be set approximately equal to the threshold voltage. In such
implementations, once the cell reaches the threshold voltage, the
large load can be removed from the cell. When the large load is
removed, the cell voltage may rebound to a level above the
threshold. The cell is then discharged using the smaller load until
it once again reaches the threshold voltage.
[0037] Once the cells have all reached the threshold voltage, a
balancing capacitor or capacitors may optionally be sequentially
applied across the battery cells. The capacitors can precisely
equalize the voltages across the cells. Once the cells have been
discharged to a common capacity, charging from this bottom balanced
condition can begin.
[0038] Referring now to FIG. 5, a graphical depiction of charging
from a bottom balanced state is presented. The four exemplary
cells, which are arranged in series, may be charged by a common
current. As the cells increase in capacity, the voltages of the
cells may begin to diverge. Once one of the cells reaches a
predetermined maximum voltage, charging can be stopped across all
cells. At this point, each of the cells should have approximately
the same capacity.
[0039] For example only, in FIG. 5, the four cells are charged
until the time when the fourth cell reaches 3.6 V. At this point,
each of the cells has approximately 1.0 Ah of capacity. The first
three cells, however, only have a voltage of 3.2 V at 1.0 Ah of
capacity. The threshold voltage of 3.6 V may be chosen, similarly
to FIG. 4B, as a voltage that will be crossed during a rapid rise
in voltage, which indicates a maximum cell capacity. The threshold
voltage may be chosen
[0040] When a battery pack including cells charged in this manner
is used in a tool, the cells will reduce in capacity at the same
rate. As capacity decreases, the user will notice the power
reduction from the tool and charge the battery before any cells can
be damaged. This is in contrast to the prior art method of battery
charging, where there may be enough power to run the tool even as
one of the cells is driven to low voltages.
[0041] In applications where the user may not notice decreasing
power, such as in a work light, the electronics in the battery pack
or the tool may disconnect battery power once the total voltage of
the battery pack decreases to a low level. Because the cells are
balanced in terms of capacity, no one cell will see a markedly
reduced or even negative voltage.
[0042] Referring now to FIG. 6, a flowchart depicts exemplary steps
performed by a battery charger according to the principles of the
present disclosure. Control begins in step 200, where a timer is
reset. Control continues in step 202, where cell voltages are
measured. For example only, the cell voltages may be measured
serially using a single measurement device. For example only, a
multiplexer may output the positive and negative terminals of each
cell to an analog-to-digital converter (ADC). The multiplexer may
then select each of the cells, whose voltage can be measured by the
ADC.
[0043] Control continues in step 204, where control determines
whether cell voltages are less than a lower threshold. For example,
control can determine whether any of the cell voltages is less than
the lower threshold, or whether an average cell voltage of all the
cells is less than the lower threshold. Alternatively, because the
cell voltages should track together closely, control may measure
only one cell voltage to determine whether it is than lower
threshold.
[0044] If cell voltages are lower than the lower threshold, control
transfers to a bottom balance and charge operation. For example,
the bottom balance and charge operation may be that described in
FIG. 7 below. After this process, control continues in step 208. If
the cell voltages are not less than the lower threshold in step
204, control transfers to step 212.
[0045] In step 212, control determines whether cell voltages are
greater than an upper threshold. If so, control transfers to step
208; otherwise, control transfers to step 216. In step 216, cell
voltages are not below a lower threshold, implying that they do not
need to be fully discharged and recharged. However, they are less
than the upper threshold, and so can be incrementally charged.
[0046] In step 216, control begins charging all cells. Control
continues in step 220, where control determines whether any cell
has reached full capacity. If so, control transfers to step 224;
otherwise, control remains in step 220. Control may determine
whether a cell has reached full capacity by determining whether a
cell has reached a predetermined maximum voltage. In step 224,
control stops charging all cells, and control continues in step
208.
[0047] In step 208, control may determine whether the timer is
greater than the threshold. If so, control transfers to step 228;
otherwise, control remains in step 208. The timer may measure time
in terms of days. After a predetermined number of days, such as 30,
where the battery pack has remained on the charger, a new bottom
balancing charge procedure may be carried out. As such, in step
228, control resets the timer, and then performs bottom balancing
and charging, such as according to FIG. 7.
[0048] Referring now to FIG. 7, a flowchart depicts exemplary steps
performed in bottom balancing and charging according to the
principles of the present disclosure. Control begins in step 302,
where control starts discharging all cells of the battery pack.
Control may begin when a battery pack is inserted into the
charger.
[0049] Control continues in step 306, where control determines
whether any cell has reached a low capacity. If so, control
transfers to step 310; otherwise, control transfers to step 314.
Control may determine that a cell has reached a low capacity by
determining when the voltage across the cell has decreased below a
threshold level.
[0050] In step 310, control determines whether a large load is
applied to the cell that has reached the low capacity. If so,
control transfers to step 318; otherwise, control transfers to step
322. In step 318, the large load is removed from the cell and the
small load is applied to the cell. Control then continues in step
314. Control may be modified by including more than two load sizes.
For example only, three or more loads may be sequentially applied
when discharging a cell. In addition, the load size may be
variable, increasing as the cell capacity decreases.
[0051] In step 322, control stops discharging the cell, and control
continues in step 314. Steps 310 and 318 are optional, and may be
used when both large and small loads are used for discharging. If a
single load is applied to the cells, step 306 may proceed directly
through step 310 to step 322. In step 314, control determines
whether discharging has stopped for all cells. If so, control
returns to step 306; otherwise, control transfers to step 326.
[0052] Step 306 may be easily modified to determine whether a cell
has crossed a first threshold voltage when a large load is applied
or a second threshold voltage when a small load is applied. In step
326, control begins charging all cells, and control continues in
step 330. In step 330, control determines whether any cell has
reached full capacity. If so, control transfers to step 334;
otherwise, control remains in step 330. Control may determine that
a cell has reached full capacity when the voltage across the cell
has reached a predetermined maximum voltage. In step 334, control
stops charging all cells. Control then ends.
[0053] Referring now to FIG. 8A, a functional block diagram of an
exemplary charging system is presented. A battery pack 402 includes
four cells, 404-1, 404-2, 404-3, and 404-4. For purposes of
illustration only, the battery pack 402 is shown with four cells
404, although fewer cells may be present. The battery pack 402 has
been simplified, with no short-circuit protection or any other
features shown.
[0054] A battery charger 410 includes a multiplexer 414 that
receives voltages from the positive and negative terminals of each
of the cells 404. The multiplexer 414 is controlled by a control
module 418. Based on input from the control module 418, the
multiplexer 414 selects the positive and negative terminals of one
of the cells 404-1 and outputs the voltage at the selected
terminals to an analog-to-digital converter (ADC) 422.
[0055] The ADC 422 converts the analog voltage across the selected
cell 404 to a digital value that is output to the control module
418. The ADC 422 may sample periodically or may be triggered to
sample when the control module 418 selects a new cell 404 using the
multiplexer 414. To charge the cells 404, the control module 418
controls a current source 426. The current source 426 outputs a
current to the positive terminal of the cell 404-1 of the battery
pack 402. Alternatively, the current may be output to the negative
terminal of the cell 404-4.
[0056] The current of the current source 426 may pass through an
overvoltage protection module 430. The overvoltage protection
module 430 provides redundant protection to prevent overcharging
the battery pack 402. If the voltage across the battery pack
exceeds a predetermined threshold, the overvoltage protection
module 430 may disconnect the current source 426 from the battery
pack 402.
[0057] The current source 426 may output a predefined current, or
may output a current based upon a value from the control module
418. To discharge the cells 404, load resistors 434-1, 434-2,
434-3, and 434-4 are arranged across the cells 404-1, 404-2, 404-3,
and 404-4, respectively. The load resistors 434-1, 434-2, 434-3,
and 434-4 are controlled by switches 438-1, 438-2, 438-3, and
438-4, respectively.
[0058] The switches 438 are controlled by respective control lines
from the control module 418. The load resistors 434 dissipate
stored energy from the cells 404. While discharging is occurring,
the control module 418 monitors the voltages of the cells 404 via
the multiplexer 414 and the ADC 422. As each cell 404 reaches the
predetermined voltage threshold, the control module 418 instructs
the associated switch 438 to disconnect the associated load
resistor 454.
[0059] Once the control module 418 has disconnected all of the load
resistors 434, the control module 418 may sequentially apply a
capacitor 442 across each of the cells 404. The capacitor may be
switched via first and second switches 446 and 450. The capacitor
442 may be applied to each of the cells 404 by the multiplexer 414.
The capacitor 442 may be quickly applied to each of the cells 404 a
large number of times to precisely balance the voltages across the
cells 404. Alternatively, the ADC 422 may monitor cell voltages to
determine when capacitor-based balancing can end.
[0060] Referring now to FIG. 8B, a functional block diagram of a
battery charging system where various components are located in the
battery pack is presented. One or more of the circuit components of
the battery charger 410 of FIG. 8A may instead be located in the
battery pack 402. For example, the location of circuit components
may be determined based upon commercial decisions regarding the
relative cost of battery packs and battery chargers.
[0061] By locating more components in the battery pack, the number
of electrical contacts on the battery pack may be reduced. In
addition, components in the battery pack may present a consistent
external interface, thereby allowing a single battery charger to
operate with diverse battery packs.
[0062] For example only, FIG. 8B depicts a configuration where the
load resistors 434, the switches 438, 446, and 450, the multiplexer
414, the ADC 422, the capacitor 442, and a control module 460
similar to the control module 418 of FIG. 8A are located in a
battery pack 462. A battery charger 470 includes the current source
426 and the overvoltage protection module 430.
[0063] The battery charger 470 may also include a charging control
module 472 that exchanges data with the control module 460. The
control module 460 may indicate to the control module 472 a desired
charging current. In addition, the control module 460 may indicate
an overvoltage value, which the control module 472 may transmit
(not shown) to the overvoltage protection module 430. The
overvoltage protection module 430 may use the overvoltage value to
determine when an overvoltage condition occurs.
[0064] The control module 460 may receive charging instructions
from the control module 472, which may be controlled by a user
interface (not shown). The control module 472 may also display
charge level information about the battery pack 462 and whether
charging or discharging is currently occurring. The battery pack
462 may include a regulator to provide a stable power voltage for
operation of the control module 460 based on the charging voltage
received. Alternatively, the control module 460 may receive power
along with the data from the control module 472.
[0065] Referring now to FIG. 9, a functional block diagram of
another exemplary battery charging system according to the
principles of the present disclosure is presented. A battery
charger 502 may include components similar to that of the battery
charger 410 of FIG. 8A. The battery charger 502 may include first
and second load resistors 506 and 508 for each of the cells
404.
[0066] One terminal of the load resistors 506 and 508 is connected
to a positive terminal of the associated cell 404. The opposite
terminals of the load resistors 506 and 508 are connected to the
negative terminal of the associated cell via switches 510 and 512,
respectively. The load resistors 506 may have a low resistance,
presenting a large load to the corresponding cell 404. The load
resistors 508 may have a higher resistance, presenting a lower load
to the cells 404. In various implementations, both load resistors
506 and 508 may be applied across the cell 404 to create a smaller
parallel resistance and therefore a larger load.
[0067] A control module 520 senses the voltage across each of the
cells 404. The control module 520 may initially apply the large
loads 506 to the cells 404. When a cell 404 reaches a predetermined
voltage threshold, the control module 520 may disconnect the large
load 506 and connect the small load 504. After the small load 504
has been connected, once the cell 404 reaches a second
predetermined voltage threshold, the control module 520 disconnects
the small load 504. Various components of the battery charger 502
may be located within the battery pack 402, similar to the example
of FIG. 8B.
[0068] Referring now to FIG. 10, a functional block diagram of an
exemplary battery pack 600 according to the principles of the
present disclosure is presented. The battery pack 600 includes
multiple cells 602. For purposes of illustration only, the battery
pack 600 is shown with four cells 602-1, 602-2, 602-3, and 603-4,
though more or fewer are possible. The cells 602 each have a
positive and negative terminal.
[0069] The positive terminal of the cell 602-1 is connected to an
external contact that interfaces with a power tool or a battery
charger. The negative terminal of the cell 602-4 is connected to an
external contact that interfaces with the power tool or the battery
charger. The negative terminals of the cells 602-1, 602-2, and
603-3 connect to external contacts that interface with the battery
charger. Because the battery charger bottom balances the cells 602,
and then charges the cells 602 to a common capacity, the battery
pack 600 does not need to have a low voltage protection system.
[0070] Referring now to FIG. 11, a functional block diagram of
another exemplary battery pack 620 according to the principles of
the present disclosure is presented. The battery pack 620 is
similar to the battery pack 600, but includes short-circuit
protection 622. The short-circuit protection may be located between
the positive terminal of the cell and the external contact.
Alternatively, the short-circuit protection 622 may be located
between the negative terminal of the cell 602-4 and the external
contact. The short-circuit protection 622 may stop conducting when
a current above a predetermined threshold is detected.
[0071] Referring now to FIG. 12, a functional block diagram of
another exemplary battery pack 640 according to the principles of
the present disclosure is presented. The battery pack 640 includes
short-circuit protection 622. The short-circuit protection 622 may
be located between the negative terminal of the cell 602-4 and an
external contact that interfaces with the tool. The positive
terminal of the cell 602-1 connects to an external contact that
interfaces with the power tool or the battery charger.
[0072] A charge protection module 624 is located between the
negative terminal of the cell 602-4 and an external contact that
interfaces with the battery charger. The charge protection module
624 may allow a greater amount of current to flow than the
short-circuit protection 622. In this way, the charger can quickly
discharge the cells 602 of the battery pack 640 at a current level
that might appear as a short-circuit to the short-circuit
protection 622.
[0073] The battery pack 640 may also include a temperature sensor
626 that may be located between the negative terminal of the cell
602-4 and an external contact that can interface with the tool and
the charger. In this way, the tool and/or the charger can determine
the temperature of the battery pack 640. In various
implementations, the temperature sensor 626 may include a
thermocouple.
[0074] Battery charging according to the principles of the present
disclosure may allow battery packs to be produced with very limited
electronics, as shown in FIGS. 10-12. Such charging techniques
prevent any one battery cell from prematurely running out of
capacity and risking damage. In this way, battery packs may be
manufactured, without monitoring electronics, at lower expense and
with lower weight. Further, electronics in the battery charger may
be less subject to vibration and impact than electronics in a
battery pack inserted into a cordless power tool. Advantages in
battery life and safety may also be recognized, regardless of
whether electronics are located in the battery or battery pack.
[0075] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the disclosure
can be implemented in a variety of forms. Therefore, while this
disclosure includes particular examples, the true scope of the
disclosure should not be so limited since other modifications will
become apparent to the skilled practitioner upon a study of the
drawings, the specification, and the following claims.
* * * * *