U.S. patent application number 09/746226 was filed with the patent office on 2001-07-05 for method of fast-charging of a rechargeable battery.
Invention is credited to Yamashita, Takahiro.
Application Number | 20010006338 09/746226 |
Document ID | / |
Family ID | 18492769 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006338 |
Kind Code |
A1 |
Yamashita, Takahiro |
July 5, 2001 |
Method of fast-charging of a rechargeable battery
Abstract
In the method of fast-charging of a rechargeable battery,
full-charge state is determined on the basis of a peak battery
voltage or a decrease .DELTA.V in the battery voltage after the
peak voltage. At the beginning of the fast-charge process, an
initial battery voltage is measured. In case where the initial
voltage is higher than a preselected voltage, the battery is
fast-charged with a normal fast-charge current. In case where the
initial voltage is lower than the preselected voltage, the battery
is fast-charged with a restricted fast-charge current that is
weaker than the fast-charge current.
Inventors: |
Yamashita, Takahiro;
(Sumoto-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K Street, N.W., Suite 800
Washington
DC
20006
US
|
Family ID: |
18492769 |
Appl. No.: |
09/746226 |
Filed: |
December 26, 2000 |
Current U.S.
Class: |
320/160 |
Current CPC
Class: |
H02J 7/0072 20130101;
H01M 10/44 20130101; Y02E 60/10 20130101; H02J 7/0086 20130101;
H02J 7/007182 20200101; H02J 7/007194 20200101; H02J 7/0069
20200101 |
Class at
Publication: |
320/160 |
International
Class: |
H01M 010/44 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1999 |
JP |
368792/1999 |
Claims
What is claimed is:
1. A method of fast-charging of a rechargeable battery, wherein
full-charge state is determined on the basis of a peak battery
voltage or a decrease .DELTA.V in the battery voltage after the
peak voltage, includes a step for detecting the battery's initial
voltage at the beginning of the charging process, a step for
fast-charging with a normal fast-charge current of the battery
whose initial voltage is higher than a preset voltage and a step
for fast-charging with a restricted fast-charge current which is
smaller than the fast-charge current of the battery whose initial
voltage is lower than the preset voltage.
2. A method of fast-charging of a rechargeable battery as recited
in claim 1, wherein said restricted fast-charge current is
50.about.90% of the normal fast-charge current.
3. A method of fast-charging of a rechargeable battery as recited
in claim 1, wherein a preliminary charging is performed with a
preliminary charge current which is smaller than the restricted
fast-charge current before the fast-charge operation in the event
of the initial voltage being higher than the preset voltage but
lower than the preliminary charge voltage at the initial voltage
measurement.
4. A method of fast-charging of a rechargeable battery as recited
in claim 1, wherein a preliminary charging is performed with the
preliminary charge current in the event of the initial voltage
being lower than the preset voltage at the initial voltage
measurement before the fast-charge operation with a restricted
fast-charge current.
5. A method of fast-charging of a rechargeable battery as recited
in claim 4, wherein a preliminary charging is performed with the
preliminary charge current in the event of the initial voltage
being lower than the preset voltage at the initial voltage
measurement, said preliminary charging being followed by the
fast-charge operation with a restricted fast-charge current in case
where the battery temperature is lower than a predetermined level
at the completion of the preliminary charge.
6. A method of fast-charging of a rechargeable battery as recited
in claim 3 wherein the preliminary charging is performed with the
preliminary charge current for a predetermined period of time in
the event of the initial voltage being higher than the preset
voltage but lower than the preliminary charge voltage at the
initial voltage measurement, said preliminary charging being
followed by the fast-charge operation with normal fast-charge
current.
7. A method of fast-charging of a rechargeable battery as recited
in claim 1, wherein the battery is either a nickel-cadmium battery
or a nickel-metal hydride battery.
8. A method of fast-charging of a rechargeable battery, wherein
full-charge state is determined on the basis of a peak battery
voltage or a decrease .DELTA.V in the battery voltage after the
peak voltage, includes a step for detecting the battery's initial
voltage as well as the battery temperature at the beginning of the
charging process, a step for fast-charging with a normal
fast-charge current in the event of the initial voltage being
higher than a preset voltage or the battery temperature being
higher than a preset level and a step for fast-charging with a
restricted fast-charge current that is weaker than the fast-charge
current in the event of the initial voltage as well as the battery
temperature being lower than the preset level.
9. A method of fast-charging of a rechargeable battery as recited
in claim 8, wherein said restricted fast-charge current is
50.about.90% of the normal fast-charge current.
10. A method of fast-charging of a rechargeable battery as recited
in claim 8, wherein a preliminary charging is performed in the
event of the initial voltage being higher than the preset voltage
but lower than the preliminary charge voltage at the initial
voltage measurement with a preliminary charge current which is
smaller than the restricted fast-charge current before the
fast-charge operation.
11. A method of fast-charging of a rechargeable battery as recited
in claim 8, wherein a preliminary charging is performed with the
preliminary charge current in the event of the initial voltage
being lower than the preset voltage at the initial voltage
measurement before the fast-charge operation with a restricted
fast-charge current.
12. A method of fast-charging of a rechargeable battery as recited
in claim 11, wherein a preliminary charging is performed with the
preliminary charge current in the event of the initial voltage
being lower than the preset voltage at the initial voltage
measurement, said preliminary charging being followed by the
fast-charge operation with a restricted fast-charge current in case
where the battery temperature is lower than a predetermined level
at the completion of the preliminary charge.
13. A method of fast-charging of a rechargeable battery as recited
in claim 10, wherein the preliminary charging is performed with the
preliminary charge current for a predetermined period of time in
the event of the initial voltage being higher than the preset
voltage but lower than the preliminary charge voltage at the
initial voltage measurement, said preliminary charging being
followed by the fast-charge operation with normal fast-charge
current.
14. A method of fast-charging of a rechargeable battery as recited
in claim 8 wherein the battery is either a nickel-cadmium battery
or a nickel-metal hydride battery.
Description
[0001] This application is based on application No.11-368792 filed
in Japan on Dec. 27, 1999, the content of which incorporated
hereinto by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates mainly to a method of charging
a rechargeable battery such as nickel-cadmium (Ni--Cd) battery or
nickel-metal hydride (Ni--MHD) battery, which shows a decrease
.DELTA.V in voltage from the peak voltage after it is fully
charged.
[0003] In order to charge a rechargeable battery, it is important
to detect the full-charge state and to stop supplying charging
current on the completion of full capacity charge (100%), because
overcharging causes reduced battery quality on one side, and
incomplete charge, i.e. less than 100% capacity charge and leads to
a shorter service time on the other. But it is not easy to charge a
rechargeable battery to the full capacity under various
conditions.
[0004] A rechargeable battery such as Ni--Cd battery or Ni--MHD
battery shows a decrease .DELTA.V from the peak voltage when the
charging continues after it has benn fully charged. This
characteristic is utilized to detect the full-charge state of a
rechargeable battery.
[0005] Under normal conditions, the full charge state can be
detected accurately by detecting the peak voltage or a decrease
.DELTA.V in voltage. The rechargeable battery with an unduly low
output voltage caused by overdischarge shows charge voltage
characteristics different from normal characteristics, when it is
fast-charged. Some rechargeable batteries with unduly low output
voltage are no longer usable because of an internal short circuit.
In order to discriminate batteries between usable ones and unusable
ones, weak charging current is supplied in the first step of
fast-charging until the output voltage reaches a predetermined
voltage, for example 1V, then fast-charging begins.
[0006] FIG. 1 shows a voltage curve in a fast-charging process of a
battery with overdischarge. As shown in the figure, the charge
voltage shows a sharp rise immediately after the fast-charge
process begins following the preliminary charge then the charge
voltage decreases. Thus a characteristic curve shows a decrease
.DELTA.V in voltage after it reaches a peak value. When the charge
voltage changes in the similar curve pattern, the battery charger
determines the completion of the charging process and terminates
the charging process. Thus charging process is terminated before
the battery has been fully charged. The rise to the peak and
decrease .DELTA.V in the charge voltage is remarkable when the
battery temperature is low.
[0007] In order to overcome the drawback, a new method has been
proposed in which detection of the voltage decrease is nullified
for a certain period of time after the quick charge process begins
following the preliminary charge. But the method has the difficulty
of setting the time period during which the voltage detection is
nullified. In the case where an unduly long time period is
predetermined, overcharging which tends to reduce battery quality
often occurs due to the failure in detecting the full-charge
state.
[0008] In the case where an unduly short period time is
predetermined, charging is no longer possible for the battery which
shows the voltage decrease .DELTA.V before the full-charge state
has been reached.
[0009] The present invention has been developed to overcome these
drawbacks. The main objective of the present invention is to
propose a method of fast-charging of overdischarged rechargeable
batteries capable of accurately charging to the full-charge
state.
[0010] The above and further objectives and features of the
invention will more fully be apparent from the following detailed
description with accompanying drawings.
SAMMARY OF THE INVENTION
[0011] The method of present invention for fast-charging a
rechargeable battery resides in that the completion of charging
operation is determined by detecting a peak voltage or decrease in
battery voltage from the peak voltage. The method of the present
invention for fast-charging further includes a step for detecting
the initial battery voltage at the beginning of charging process.
If the initial voltage is higher than a predetermined level, the
battery is fast-charged with a preselected fast-charge current. If
the initial voltage is lower than the predetermined level, the
battery is fast-charged with a restricted fast charge current which
is smaller than the fast-charge current.
[0012] The present method of fast-charging has the advantage that
it enables to fast-charge a normally discharged battery on one
hand, and to charge an overdischarged battery to the full charge
state on the other. An overdischarged battery shows a peak voltage
followed by a decrease .DELTA.V in voltage before the battery is
fully charged, when it undergoes a fast-charge operation with
normal fast-charge current. In the method of the present invention,
an overdischarged battery is fast-charged with restricted
fast-charge current which prevents the battery from showing a peak
battery voltage or a decrease .DELTA.V before it is fully charged.
The method enables to detect the completion of the fast-charge
operation for an overdischarged battery on the basis of peak
voltage or a decrease .DELTA.V in voltage.
[0013] The method of the present invention for fast-charging
preferably includes steps for detecting the battery voltage as well
as the battery temperature at the beginning of the charging. If the
initial battery voltage is higher than the predetermined level and
the battery temperature is higher than a predetermined level, the
battery is fast-charged with fast-charge current. But, if the
initial battery voltage is lower than the predetermined level and
the battery temperature is below the predetermined level, the
battery is fast-charged with the limited and smaller fast-charge
current.
[0014] The limited fast-charge current is set, for example, at
50.about.90% of the fast-charge current. The smaller the limited
fast-charge current, the fewer is the incidents of false detection
of full-charge state. But smaller restricted fast-charge currents
lead to a longer full charge time. The restricted fast-charge
current is therefore determined at a larger possible level as long
as incidents of false detection of full-charge state can be
avoided.
[0015] Yet another embodiment of the present invention for
fast-charging a rechargeable battery preferably includes a step for
preliminary charge with preliminary charge current smaller than
restricted fast-charge current preceding the fast-charge in the
case where the initial battery voltage is higher than the
predetermined level and lower than a level which is predetermined
for the preliminary charge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a diagram of a battery voltage characteristics
of a overdischarged rechargeable battery during the fast-charging
operation.
[0017] FIG. 2 shows a circuit of fast-charging device set forth as
means for fast-charge of the present invention.
[0018] FIG. 3 shows a diagram of a battery voltage characteristics
of a overdischarged rechargeable battery during the fast-charging
with restricted current.
[0019] FIG. 4 shows a flow chart of steps of fast-charge operation
carried out by the fast-charge device as set forth in FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 2 is a block diagram showing a circuit for practicing
the method of fast-charge of the invention. The battery charging
circuit includes a power source 2 for supplying voltage and current
to a rechargeable battery 1, a charge switch 3 connected to the
output terminals of the power source, a charge control circuit 4
for controlling the charge switch 3, a voltage detection circuit 5
for detecting the battery voltage of the rechargeable battery 1, a
temperature detection circuit 6 for detecting the battery
temperature and a current switching circuit 7 controlled by the
charge control circuit for controlling the output of the power
source 2.
[0021] The fast-charge circuit shown in the drawings is designed
for charging a rechargeable battery such as Ni--Cd battery or
Ni--MHD battery, which has the characteristics that a decrease in
the battery voltage occurs if the charging continues after the peak
voltage appears at the time when the battery is fully charged.
[0022] The power source 2 is provided with a circuit capable of
limiting the maximum voltage and maximum current, i.e. a
constant-voltage and constant-current circuit. The power source 2
is capable of charging with optimum voltage and current. The power
source is also capable of switching output current either to the
normal fast-charge current or to the restricted fast-charge charge
current in response to the current switching circuit 7. The power
source 2 either fast-charges a normally discharged battery with the
normal fast-charge current or fast-charges an overdischarged
battery with the restricted current.
[0023] The normal fast-charge current is preset at an optimum value
taking the types of the battery into consideration. A rechargeable
battery has its own maximum charge current according to its battery
type. Accordingly, the normal fast-charge current, which is the
output current of the power source 2, is set for an optimum value,
e.g. 0.5.about.2C, with which the battery can be fast-charged as
quickly as possible without reducing battery quality.
[0024] The restricted fast-charge current is set at 50.about.90%,
preferably at 60.about.85%, furthermore preferably at 65.about.85%
or most preferably at 80% of the normal fast-charge current. The
amplitude of the restricted fast-charge current is so selected that
the fast-charge current gives no false signals of full-charge state
in detecting a peak voltage or a decrease from the peak
voltage.
[0025] FIG. 3 shows how the battery voltage changes as the
fast-charge proceeds. As is shown in the FIG. 3, during the
fast-charge operation with the restricted fast-charge current,
which is smaller than the normal fast-charge current, the battery
voltage shows a sharp rise immediately after the normal fast-charge
current is applied. In this case, the battery voltage does not hit
a peak or does not decrease from a peak voltage.
[0026] In charging an overdischarged battery, as the restricted
fast-charge current becomes heavier, a peak voltage tends to appear
immediately after the charge current shifts to the normal
fast-charge current, and then the charge voltage decreases by
.DELTA.V from the peak voltage. In cases where the charge control
circuit 4 is of the type that determines full-charge state not by
the peak voltage, but by the voltage decrease .DELTA.V from the
peak voltage, the restricted fast-charge current can be selected at
such a value that gives a peak voltage at the time of the charge
current shift to fast-charge because full-charge detection is not
based on a peak voltage at the time of the charge current shift to
fast-charge. On the other hand, in cases where the charge control
circuit 4 determines the full-charge state on the basis of peak
voltage, the circuit misjudges the full-charge state upon the peak
voltage at the time of the charge current shift to fast-charge.
Therefore, in cases where the charge control circuit 4 determines
the full-charge state on the basis of peak voltage, the restricted
fast-charge current must be set at the value that yields no peak
voltage at the time when the charge current shifts to fast-charge
current.
[0027] Upon detection of full-charge state of a rechargeable
battery 1, the charge control circuit 4 turns the charge switch 3
from `on` to `off`. The charge control circuit 4 keeps the charge
switch 3 at `on` state to keep charging the battery until the
battery 1 is fully charged. When the rechargeable battery 1 reaches
the full-charge state, the circuit 4 turns the charge switch off to
terminate charging. The charge control circuit 4 detects either the
peak voltage or the charge voltage decrease .DELTA.V, or both of
them during charging operation to determine the full-charge
state.
[0028] The charge control circuit 4 detects initial battery voltage
and battery temperature at the beginning of charging operation to
control the charge current from the power source 2 by means of a
current switching circuit 7. The charge control circuit 4 controls
the charge current from the power source 2 by means of the current
switching circuit 7 such that the normal fast-charge current is
supplied for fast charging in case where the initial battery
voltage or the battery temperature is higher than a predetermined
level. In cases where both initial battery voltage and battery
temperature are lower than a predetermined level, the charge
control circuit controls the current switching circuit 7 to allow
the power source 2 to supply the restricted fast-charge
current.
[0029] The voltage detection circuit 5 detects battery voltage and
inputs the signal to the charge control circuit 4. The temperature
detection circuit 6 detects battery temperature and inputs the
signals to the charge control circuit 4. The temperature detection
circuit 6 is connected to a temperature detection device 8 which is
placed in contact with or close to the battery to be charged to
detect battery temperature.
[0030] FIG. 4 is a flowchart of the operation performed by the
charge control circuit 4 which fast-charges a battery with a normal
charge current or restricted charge current supplied via the
current switching circuit 7 from the power source 2. Charging
operation for a rechargeable battery 1 shown in the flowchart is
performed through following steps.
[0031] [Step n=1]
[0032] Battery loading detection. Loading of a battery is detected,
e.g. by measuring voltage by means of the voltage detection circuit
5, or by mechanical means e.g. a limit switch.
[0033] [Step n=2]
[0034] The initial battery voltage is measured and compared with a
predetermined voltage and preliminary charge voltage in order to
put the battery into either of three categories, i.e. an
overdischarged battery that has a lower initial voltage than the
predetermined voltage, a discharged battery that has a initial
voltage between the predetermined voltage and preliminary charge
voltage, and a non-discharged battery whose initial voltage is
higher than the preliminary charge voltage. For a non-discharged
battery, the fast-charged with normal charge voltage is carried out
without preliminary charge.
[0035] The flowchart is shown as performing the charging operation
of a Ni--Cd or Ni--MHD battery, the predetermined voltage and
preliminary charge voltage is set at 0.6V/cell and 1V/cell
respectively. The predetermined voltage and preliminary charge
voltage may vary according to the battery type. For Ni--Cd battery
or Ni--MH battery, the predetermined voltage is set at
0.4.about.0.8V and the preliminary charge voltage at
0.8.about.1.1V. The preliminary charge voltage is always higher
than the predetermined voltage.
[0036] [Step n=3]
[0037] Overdischarged and discharged batteries undergo a
preliminary charge carried out with a weaker current. Non
discharged batteries are fast-charged without preliminary charge.
In the flowchart, the value 0.5A is selected for preliminary
charge, i.e. 25% of the normal fast-charge current. The preliminary
charge current is preferably set at 5.about.30% of the normal
fast-charge current. The preliminary charge is completed when the
battery voltage reaches the preliminary voltage. The preliminary
charge may be interrupted when a timer counts up a preselected
time.
[0038] [Step n=4]
[0039] The battery temperature is measured and compared with
predetermined temperature after preliminary charge of an
overdischarged battery. The predetermined temperature is set at 10
degrees centigrade. The predetermined temperature is so chosen that
the peak voltage and the voltage decease appear when the normal
fast-charge current is supplied.
[0040] [Step n=5]
[0041] If the battery temperature is lower than the preselected
value, the battery is fast-charged with restricted fast-charge
current. In the embodiment shown in the flowchart, the restricted
fast-charge current is set at 1.6A, i.e. 80% of normal fast-charge
current. The fast-charge step with restricted fast-charge current
is completed when battery voltage reaches the peak voltage or
decreases by .DELTA.V from the peak voltage.
[0042] [Step n=6]
[0043] If the battery temperature is higher than the preselected
value, the battery is fast-charged with normal fast-charge current.
The fast-charge step with normal fast-charge current is completed
when battery voltage reaches the peak voltage or decreases .DELTA.V
from the peak voltage.
[0044] In the flowchart described above, the temperature detection
is performed for overdischarged batteries that have the initial
voltage lower than predetermined value, and fast-charge with
restricted fast-charge current is carried out only if the battery
temperature is lower than the preselected value. Within the scope
of the present invention, it is possible to fast-charge
overdischarged batteries with restricted fast-charge current
without battery temperature detection. In this case, the step n=4
is skipped and all the overdischarged batteries which have
undergone the preliminary charge are fast-charged with restricted
fast-charge current.
[0045] In the method of fast-charging described above, the
batteries, which are classified as overdischarged or discharged for
the initial battery voltage lower than predetermined voltage, are
fast-charged after the preliminary charge. With the preliminary
charge included, the present method of fast-charging enables to
find damaged batteries on none hand, and to charge under optimum
conditions batteries used under various conditions on the
other.
[0046] However, another feature of the method of the present
invention includes fast-charging with restricted fast-charge
current of an overdischarged battery without the step of
preliminary charge.
[0047] 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 meets and bounds of the claims, or equivalence of such
meets and bounds thereof are therefore intended to be embraced by
the claims.
* * * * *