U.S. patent application number 09/768227 was filed with the patent office on 2001-08-02 for method of charging a plurality of batteries.
Invention is credited to Fukuda, Tomoya, Kaite, Osamu.
Application Number | 20010010456 09/768227 |
Document ID | / |
Family ID | 18545105 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010456 |
Kind Code |
A1 |
Kaite, Osamu ; et
al. |
August 2, 2001 |
Method of charging a plurality of batteries
Abstract
The method of charging a plurality of batteries uses a charging
power supply to pulse charge a plurality of batteries to full
charge by time-division switching of the battery being charged.
Further, this charging method moves timing intervals forward to
begin charging the next battery when charging of a fully charged
battery is stopped.
Inventors: |
Kaite, Osamu; (Tsuna-gun,
JP) ; Fukuda, Tomoya; (Mihara-gun, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
18545105 |
Appl. No.: |
09/768227 |
Filed: |
January 25, 2001 |
Current U.S.
Class: |
320/125 |
Current CPC
Class: |
H02J 7/0019
20130101 |
Class at
Publication: |
320/125 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2000 |
JP |
018232/2000 |
Claims
What is claimed is:
1. A method of charging a plurality of batteries which uses a
charging power supply to pulse charge a plurality of batteries to
full charge by time-division switching of the battery being
charged, and which moves timing intervals forward to begin charging
the next battery when charging of a fully charged battery is
stopped.
2. A method of charging a plurality of batteries as recited in
claim 1 wherein batteries to be charged are divided into a
plurality of channels, batteries are attached to each channel in a
detachable fashion, channels with batteries attached and without
batteries attached are detected, and channels without batteries
attached are skipped over and not charged.
3. A method of charging a plurality of batteries as recited in
claim 2 wherein battery attachment is detected by charging
switches.
4. A method of charging a plurality of batteries as recited in
claim 2 wherein battery attachment is detected by charging
current.
5. A method of charging a plurality of batteries as recited in
claim 1 wherein the plurality of batteries are connected to power
supply circuit via switching devices, and any one of the switching
devices is turned on to charge the batteries in sequence.
6. A method of charging a plurality of batteries as recited in
claim 1 wherein batteries near full charge are charged first.
7. A method of charging a plurality of batteries as recited in
claim 1 wherein one pulse width in time for pulse charging
batteries is from 50 msec to 10 sec.
8. A method of charging a plurality of batteries as recited in
claim 1 wherein one pulse width in time for pulse charging
batteries is from 0.1 sec to 5 sec.
9. A method of charging a plurality of batteries as recited in
claim 1 wherein one pulse width in time for pulse charging
batteries is from 0.3 sec to 2 sec.
10. A method of charging a plurality of batteries as recited in
claim 1 wherein trickle charging with a small current is performed
after the batteries are fully charged.
11. A method of charging a plurality of batteries as recited in
claim 1 wherein when switching the battery to be pulse charged, the
instant charging of any battery is stopped, charging of the next
battery to be charged is started and charging current is not
cut-off.
12. A method of charging a plurality of batteries as recited in
claim 11 wherein the instant charging of a fully charged battery is
stopped, charging of the next battery to be charged is started and
charging current is not cut-off.
13. A method of charging a plurality of batteries as recited in
claim 1 wherein a plurality of batteries with different battery
capacities are pulse charged in sequence, and one pulse width in
time for pulse charging low capacity batteries is shorter than one
pulse width in time for pulse charging high capacity batteries.
Description
[0001] This application is based on application No.018232/2000
filed in Japan on Jan. 27, 2000, the content of which incorporated
hereinto by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a method of charging a plurality
of batteries sequentially with pulse charging. The batteries
charged by the method of this invention are from one to four single
rechargeable batteries, or a single battery or plurality of
batteries contained in a battery pack.
[0003] Prior art methods of fully charging a plurality of batteries
include methods of charging all batteries at once, and methods
which sequentially fully charge batteries by time-division
switching. Methods of charging all batteries at once include
methods which connect batteries in series for charging, and methods
which connect batteries in parallel for charging. Since the same
charging current flows through all batteries connected in series,
series connected methods cannot charge all batteries to full charge
if there are differences in remaining battery capacity when
charging is initiated. This is because batteries with large
remaining battery capacity will be over-charged, and batteries with
small remaining battery capacity won't reach full charge. In
methods which connect a plurality of batteries in parallel,
charging current cannot be uniformly distributed to charge all
batteries in an ideal fashion. For example, larger currents will
flow in low voltage batteries than in high voltage batteries making
it impossible to uniformly distribute charging current. Therefore,
all batteries cannot be fully charged under ideal conditions.
[0004] This drawback can be eliminated by providing special purpose
charging circuitry to establish optimum charging current for each
battery. However, battery charger cost for this method of charging
becomes high. For example, to charge four batteries under ideal
conditions four sets of charging power supplies are required.
[0005] As a method of charging a plurality of parallel connected
batteries with one charging power supply, it is theoretically
possible to distribute charging current to each battery in an ideal
fashion by connecting current control circuits in series with each
battery. However, practical realization is difficult because each
current control circuit itself adjusts internal resistance to
control battery charging current, and thus has the drawback of high
power consumption. It is necessary to design current control
circuits able to control high currents and power making parts cost
expensive. In addition, since the current control circuits consume
wasted power, it is necessary to design the charging power supply
to output higher power. Further, large amounts of heat are
generated by the current control circuits requiring a large cooling
fan and increasing the parts cost.
[0006] These drawbacks can be eliminated by a method which charges
a plurality of batteries by sequentially switching from one battery
to the next. Since this method charges by sequentially switching
from a fully charged battery to the next battery, it has the
characteristic capability of fully charging a plurality of
batteries with a single charging power supply while controlling
charging current to ideal values.
[0007] This method of charging is described in Japanese
Non-examined Patent Publications No. 4-105521 issued on Apr. 7,
1992 and No. 3-164034 issued on Jul. 16, 1991. The method cited in
these and other patent applications initially supplies charging
current to only the first battery and charges that battery to full
charge. Then, after the first battery reaches full charge, charging
of the first battery is cut-off and charging current is supplied to
only the second battery which is charged to full charge. In this
fashion, charging is switched from the first, second, third, and
subsequent batteries to fully charge all batteries.
[0008] A method of charging a plurality of batteries by switching
from one to the next can fully charge batteries sequentially while
keeping the charging current small. However, this charging method
has the drawback that it takes too much time to fully charge all
batteries. If charging current is increased to reduce the time to
full charge, battery performance is degraded. This is because the
maximum current for acceptable battery charging is limited. If
charging is performed extremely rapidly with large currents,
battery temperature rises or the battery is adversely affected
causing degradation in electrical performance.
[0009] As shown in FIG. 1, this drawback can be eliminated with a
method of pulse charging a plurality of batteries by sequential
time-division switching. FIG. 1 shows pulse charging of a first,
second, third, and fourth battery by repeated time-division
switching through the charging order. Further, FIG. 1 shows the
first battery reaching full charge first and the third battery
reaching full charge next. Since charging stops for a fully charged
battery, charging is cut-off to that battery.
[0010] As shown in FIG. 1, a time-division pulse charging method
can reduce charging time for a plurality of batteries compared to a
method which switches charging after each battery is fully charged.
However, since timing is temporarily interrupted when a battery
reaches full charge, all batteries cannot be quickly charged under
the most ideal conditions.
[0011] The present invention was developed to eliminate these types
of drawbacks, It is thus a primary object of the present invention
to provide a method of charging that can fully charge a plurality
of batteries in a shorter time.
[0012] It is yet another important object of the present invention
to provide a method of charging a plurality of batteries which can
rapidly charge all batteries to full charge without causing battery
performance degradation.
[0013] It is a further important object of the present invention to
provide a method of charging a plurality of batteries which can
rapidly charge all batteries to full charge with a charging power
supply that can be inexpensively manufactured.
[0014] The above and further objects and features of the invention
will more fully be apparent from the following detailed description
with accompanying drawings.
SUMMARY OF THE INVENTION
[0015] The method of charging of the present invention charges a
plurality of batteries to full charge with a charging power supply
by pulse charging and time-division switching of batteries.
Further, in the charging method of the present invention, when
charging of a fully charged battery is stopped, timing to begin
charging the next battery is moved up.
[0016] This method of charging has the characteristic that a
plurality of batteries can be fully charged in a shorter time
without causing battery performance degradation. This is because
when time-division switched pulse charging of a fully charged
battery is stopped, timing is moved up to begin charging the next
battery. This charging method does not temporarily interrupt
charging for a fully charged battery, but rather skips that
battery's timing interval and goes to the next battery. Therefore,
a plurality of batteries can be quickly and efficiently fully
charged. Further, this charging method can fully charge a plurality
of batteries in an ideal fashion with a charging power supply which
can be inexpensively manufactured. Therefore, this method also has
the characteristic that battery charger cost can be reduced.
[0017] In the charging method of the present invention, when
switching the battery being pulse charged, it is preferable to
begin charging the next battery the instant charging of any battery
is stopped, avoiding interruption in charging current. Since
charging current is not cut-off in this charging method, it has the
characteristic of reduced in-rush current and noise when the
battery being charged is switched.
[0018] Further, in the charging method of the present invention,
when charging of a fully charged battery is stopped, it is
preferable to begin charging the next battery at that instant
without interrupting the charging current.
[0019] Further, in the charging method of the present invention,
when sequentially pulse charging a plurality of batteries of
different battery capacities, the pulse width in time for charging
low capacity batteries can be made shorter than the pulse width for
high capacity batteries. This controls the average charging current
to lower values for lower capacity batteries.
[0020] This method of charging has the characteristic ability to
pulse charge all batteries in a short time and in an ideal fashion.
This is because the pulse width in time can be changed according to
the capacity of a battery. By varying the pulse charging duty
factor, efficient use of the charging power supply can be increased
without changing the total power supply current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a timing chart showing a prior art method of
charging a plurality of batteries.
[0022] FIG. 2 is a block diagram showing a battery charger used in
an embodiment of the method of charging a plurality of batteries of
the present invention.
[0023] FIG. 3 is a timing chart showing an embodiment of the method
of charging a plurality of batteries of the present invention.
[0024] FIG. 4 is a timing chart showing another embodiment of the
method of charging a plurality of batteries of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Turning to FIG. 2, a block diagram of a battery charger used
in the charging method of the present invention is shown. FIG. 2
shows a battery charger for fully charging four batteries 1
attached in a removable fashion and comprising ch1 through ch4.
However, the charging method of the present invention is a pulse
charging method for a plurality of batteries and is not limited to
charging four batteries. Further, the present invention is also not
limited to a method of charging batteries attached in a removable
fashion. The present invention can also fully charge multiple
batteries divided into a plurality of channels by sequentially
charging batteries in each channel.
[0026] The battery charger shown in FIG. 2 is provided with a power
supply circuit 2, switching devices 3 to connect the power supply
circuit 2 with each battery 1, and a charging control circuit 4 to
control the switching devices 3. Further, the battery charger of
FIG. 2 has charging switches 5 connected to the charging control
circuit 4 to determine whether or not the ch1 through ch4 batteries
1 are attached. This battery charger can detect which battery
channels are attached and which are not attached by the charging
switches 5, and can skip charging channels which are not attached.
Therefore, this battery charger can fully charge all batteries in a
shorter time when the batteries of any channels are not
attached.
[0027] However, determination of whether or a not a battery is
attached to the battery charger does not necessarily have to be
determined by charging switches. This is because battery attachment
or lack of attachment can also be determined by measuring charging
current. In a method of determining battery attachment by measuring
charging current, charging current is measured at the first
charging pulse, and channels with no current flow are judged to
have no battery attached. Subsequently, charging is performed
skipping those channels.
[0028] The power supply circuit 2 outputs voltage and current
capable of charging the batteries 1. The charging power supply is
preferably a switching power supply. The switching power supply is
provided with a rectifying circuit to rectify 100V/120V alternating
current (AC), a switching circuit to switch direct current (DC)
output from the rectifying circuit, a transformer to step down AC
voltage output from the switching circuit and input to its primary
side to the battery charging voltage, a rectifying circuit of
diodes to rectify AC output from the transformer to DC, a CV/CC
control circuit to control the switching circuit duty cycle with
rectifying circuit output voltage and signals from the control
circuit, and an isolating PC circuit. However, the power supply
circuit does not necessarily have to be a switching power supply.
Power supply circuitry to step down input 100V/120V AC via a
transformer, rectify the AC to DC, and stabilize the rectified DC
can also be used.
[0029] The switching devices 3 are semiconductor switching devices
such as field effect transistors (FETs) or bipolar transistors.
Each switching device 3 is connected in series with each battery 1
to connect the batteries 1 with the power supply circuit 2.
Batteries 1 connected to the power supply circuit 2 via "ON"
switching devices 3 are supplied with charging current for
charging. Charging current is cut-off from batteries 1 connected to
"OFF" switching devices 3 and those batteries are not charged. One
of the plurality of switching devices 3 is "ON" and all others are
controlled "OFF" to pulse charge a battery 1.
[0030] The charging control circuit 4 controls the switching device
3 connected to each battery 1 "ON" and "OFF". The charging control
circuit 4 outputs charging signals to the switching devices 3 to
control the switching devices 3 "ON" and "OFF". The charging
control circuit 4 determines the order and timing for pulse
charging of the plurality of batteries 1.
[0031] The charging control circuit 4 controls the switching
devices 3 "ON" and "OFF", and the charging current to charge each
battery 1 is as shown in FIG. 3. In FIG. 3, the batteries of ch1
through ch4 are sequentially charged by pulse charging. The
charging order for a plurality of batteries may be, for example,
starting from the battery closest to full charge. This method
minimizes the time to the first fully charged battery. Whether a
battery is near full charge or not is determined by battery voltage
when charging is initiated.
[0032] The width in time of one pulse for pulse charging each
battery is determined by the pulse width of the charging signal
input to the switching device. For example, the width in time of
one pulse may be 1 sec. However, the charging method of the present
invention does not restrict the width in time of one pulse for
pulse charging a battery. The width in time of one pulse is set,
for example, from 50 msec. to 10 sec., preferably 0.1 sec. to 5
sec., more preferably 0.2 sec. to 3 sec., and optimally 0.3 sec. to
2 sec.
[0033] When the battery capacity of all the plurality of batteries
to be charged is the same, the pulse width of a single pulse (tn)
is the same for all batteries. As shown in FIG. 3, all batteries
are charged with the same single pulse width (t1, t2, t3, t4). When
a plurality of batteries of different capacities are charged in
sequence, the single pulse width of low capacity batteries is made
shorter than the single pulse width of high capacity batteries.
This method has the characteristic that low capacity batteries and
high capacity batteries can be fully charged quickly and in an
evenly balanced fashion. This is because the average charging
current for low capacity batteries with shorter pulse width is
lower than the average charging current for high capacity
batteries.
[0034] Turning to FIG. 4, charging current is shown with shorter
pulse width for the low capacity batteries of ch3 and ch4 compared
to the high capacity batteries of ch1 and ch2. In FIG. 4, the pulse
widths (t3, t4) for charging the batteries of ch3 and ch4 are
approximately 1/2 the pulse widths (t1, t2) for the batteries of
ch1 and ch2, and the average charging currents for ch3 and ch4 are
1/2 those for ch1 and ch2. In a method which charges low capacity
batteries with reduced pulse width (t3, t4) and which does not
cut-off charging current, the charging time for low capacity
batteries is reduced and the period for charging all batteries with
a single pulse is shortened. This means average charging current
for high capacity batteries can be increased to reach full charge
in a shorter time. This is because the average charging current for
a high capacity battery is proportional to the width in time of one
pulse divided by the period (T) for charging all batteries with a
single pulse.
[0035] The period (T) for charging all batteries with a single
pulse is equal to the sum of the single pulse widths for charging
each battery, namely, t1+t2+t3+t4. As shown in FIG. 3, when the all
batteries are charged with equal pulse widths, the time for one
period is one pulse width times the number of batteries being
charged. As shown in FIG. 4, for the case of different pulse
widths, the period (T) is shorter than the (long) pulse width times
the number of batteries.
[0036] As shown in FIGS. 3 and 4, in the method of charging of the
present invention, when the battery being pulse charged is
switched, charging current is not cut-off. Specifically, when
charging of the previous battery is stopped and charging of the
next battery is started, charging of the next battery begins the
instant charging of the previous battery ends. As shown in FIGS. 3
and 4, this charging method can charge a plurality of batteries
without changing the current output from the power supply circuit.
Further, the charging method shown in FIGS. 3 and 4 also does not
cut-off charging current when charging of a fully charged battery
is ended and charging of the next battery is started.
[0037] However, in the method of charging of the present invention,
when the battery being charged is switched, a pause in charging may
also be established. The time period for a pause in charging is
made sufficiently shorter than the width in time of one pulse. This
is because a long pause will make the time to fully charge all
batteries longer.
[0038] The method of charging of the present invention skips over
fully charged batteries and begins charging the next battery. In
FIG. 3, when none of the batteries are fully charged, charging is
performed in the order ch1, ch2, ch3, ch4. After the battery of ch1
becomes fully charged, charging of the ch1 battery is skipped and
charging is performed in the order ch2, ch3, ch4. After the battery
of ch3 becomes fully charged, charging is performed in the order
ch2, ch4. Finally, after the battery of ch2 becomes fully charged,
only the battery of ch4 is continuously charged.
[0039] In FIG. 4, when none of the batteries are fully charged,
charging is performed in the order ch1, ch2, ch3, ch4. After the
battery of ch1 becomes fully charged, charging of the ch1 battery
is skipped and charging is performed in the order ch2, ch3, ch4.
After the battery of ch3 becomes fully charged, charging is
performed in the order ch2, ch4. Finally, after the battery of ch4
becomes fully charged, only the battery of ch2 is continuously
charged.
[0040] The charging control circuit 4 detects the fully charged
state of a battery 1, and instead of turning the switching device
connected to the fully charged battery "ON", it turns "ON" the
switching device connected to the next battery to be charged. The
charging control circuit 4 detects the fully charged state of a
battery 1 by different methods depending on the type of battery 1.
For nickel-cadmium and nickel-hydrogen batteries, full charge is
determined by detecting when battery voltage reaches a peak, or by
detecting a DV drop from the peak voltage. For lithium-ion
rechargeable batteries, full charge is determined by detecting when
battery voltage reaches a specified voltage.
[0041] The charging control circuit 4 maintains the switching
device connected to a fully charged battery "OFF", and turns the
switching device connected to the next battery to be charged "ON"
during the interval previously used to charge the fully charged
battery. This carry-forward in timing is continued while non-fully
charged batteries are sequentially charged until al batteries reach
full charge, at which time all switching devices are maintained
"OFF" and charging is complete. After all batteries have reached
full charge, all batteries may be trickle charged by a small
trickle current. Trickle charging may be pulse charging with a
current sufficiently smaller than that used for rapid charging, or
all batteries may be connected in parallel and charged with
constant voltage and constant current.
[0042] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiment is therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within the meets and bounds of the claims or equivalence of
such meets and bounds thereof are therefore intended to be embraced
by the claims.
* * * * *