U.S. patent application number 09/892443 was filed with the patent office on 2002-01-03 for rechargeable battery pack.
This patent application is currently assigned to TOSHIBA BATTERY CO., LTD.. Invention is credited to Ishitsuka, Kiyoshi, Sano, Yoshinao, Shiojima, Nobuo.
Application Number | 20020000790 09/892443 |
Document ID | / |
Family ID | 18695036 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000790 |
Kind Code |
A1 |
Sano, Yoshinao ; et
al. |
January 3, 2002 |
Rechargeable battery pack
Abstract
A rechargeable battery pack provided with a battery voltage
detector for detecting a terminal voltage of a rechargeable battery
cell, a -.DELTA.V detection circuit or other full charge detecting
means for detecting a full charge state when charging the
rechargeable battery cell, a switch device interposed in a charge
current circuit of the rechargeable battery cell and opening the
charge current circuit when detecting a full charge state, a memory
for storing a closed circuit voltage of the rechargeable battery
cell immediately before the charge current circuit is opened, an
internal resistance detection circuit for finding a value
corresponding to an internal resistance of the rechargeable battery
cell from an open circuit voltage and the closed circuit voltage
stored in the memory after the charge current circuit is opened,
and a lifetime indicating means for referring to a battery lifetime
table in accordance with a value corresponding to the internal
resistance of the rechargeable battery cell to predict the lifetime
of the rechargeable battery cell and outputting information on the
lifetime. This enables accurate determination of the lifetime of
the rechargeable battery cell under stable conditions without
wastefully consuming the charging capacity.
Inventors: |
Sano, Yoshinao; (Tokyo,
JP) ; Shiojima, Nobuo; (Tokyo, JP) ;
Ishitsuka, Kiyoshi; (Kanagawa, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TOSHIBA BATTERY CO., LTD.
|
Family ID: |
18695036 |
Appl. No.: |
09/892443 |
Filed: |
June 28, 2001 |
Current U.S.
Class: |
320/162 |
Current CPC
Class: |
G01R 31/392 20190101;
G01R 31/3648 20130101; G01R 31/3835 20190101; G01R 31/389 20190101;
G01R 31/3647 20190101 |
Class at
Publication: |
320/162 |
International
Class: |
H02J 007/04; H02J
007/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2000 |
JP |
2000-196566 |
Claims
What is claimed is:
1. A rechargeable battery pack comprising: at least one
rechargeable battery cell, a battery voltage detecting means for
detecting a terminal voltage of said rechargeable battery cell, a
full charge detecting means for detecting a full charge state when
charging said rechargeable battery cell, a switch device interposed
in a charge current circuit of said rechargeable battery cell and
turned off to open said charge current circuit when said full
charge detecting means detects a full charge state, a memory for
storing a closed circuit voltage Von of said rechargeable battery
cell detected by said battery voltage detecting means immediately
before said charge current circuit is opened, an internal
resistance detecting means for finding a value corresponding to an
internal resistance Rin of said rechargeable battery cell from an
open circuit voltage Voff of said rechargeable battery cell
detected by said battery voltage detecting means and the closed
circuit voltage Von stored in said memory after said charge current
circuit is opened,. and a lifetime indicating means for predicting
the lifetime of said rechargeable battery cell in accordance with
the value corresponding to the internal resistance of said
rechargeable battery cell and outputting information L on the
lifetime.
2. A rechargeable battery pack comprising: at least one
rechargeable battery cell, a battery voltage detecting means for
detecting a terminal voltage of said rechargeable battery cell, a
current detecting means for detecting a charge/discharge current
with respect to said rechargeable battery cell, a full charge
detecting means for detecting a full charge state when charging
said rechargeable battery cell, a switch device interposed in a
charge current circuit of said rechargeable battery cell and turned
off to open said charge current circuit when said full charge
detecting means detects a full charge state, a memory for storing a
closed circuit voltage Von of said rechargeable battery cell
detected by said battery voltage detecting means and a battery
charge current Ion detected by said current detecting means
immediately before said charge current circuit is opened, an
internal resistance detecting means for finding a value
corresponding to an internal resistance Rin of said rechargeable
battery cell from an open circuit voltage Voff of said rechargeable
battery cell detected by said battery voltage detecting means and a
current Ioff detected by said current detecting means after said
charge current circuit is opened and the closed circuit voltage Von
and battery charge current Ion stored in said memory, and a
lifetime indicating means for predicting the lifetime of said
rechargeable battery cell in accordance with the value
corresponding to the internal resistance of said rechargeable
battery cell and outputting information L on the lifetime.
3. A rechargeable battery pack as set forth in claim 1 or 2,
wherein said internal resistance detecting means is comprised with
a timer means for measuring a time elapsed from the time of
detecting the full charge state of the rechargeable battery cell
and finds an open circuit voltage Voff of said rechargeable battery
cell when the elapse of a predetermined time from the time of
detecting the full charge state of the rechargeable battery cell is
measured by the timer means.
4. A rechargeable battery pack as set forth in claim 1 or 2,
further comprised with a means for prohibiting processing for
calculating the internal resistance of the rechargeable battery
cell by the internal resistance detecting means when a discharge
current of said rechargeable battery cell is detected by said
current detecting means.
5. A rechargeable battery pack as set forth in claim 1 or 2,
further comprised with: a battery temperature detecting means for
detecting a temperature T of said rechargeable battery cell and a
correcting means for correcting the value corresponding to the
internal resistance of the rechargeable battery cell found by the
internal resistance detecting means in accordance with the battery
temperature detected by said battery temperature detecting
means.
6. A rechargeable battery pack as set forth in claim 1 or 2,
further comprised with a switch control means for operating said
switch device to repeatedly close and open a charge current circuit
for said rechargeable battery cell, wherein said internal
resistance detecting means detects the states of the rechargeable
battery cell immediately before the charge current circuit is
opened and after the charge current circuit is opened to evaluate
the lifetime of the rechargeable battery cell.
7. A rechargeable battery pack as set forth in claim 1 or 2,
wherein the rechargeable battery cell is comprised of a
nickel-metal halide (Ni-MH) type cell.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a rechargeable battery pack
provided with a function enabling accurate judgement of the
lifetime of a nickel-metal halide type battery (Ni-MH type battery)
or other rechargeable battery cell.
[0003] 2. Description of the Related Art
[0004] In recent years, extensive use has been made of rechargeable
battery cells as sources of power for various types of electronic
devices. Rechargeable battery cells however deteriorate in
performance due to repeated charging and discharging or along with
the elapse of time. Therefore, when using a rechargeable battery
cell as a backup power supply to deal with service interruptions of
commercial power such as seen in the uninterruptible power supplies
for servers in network systems, it is important to obtain an
accurate grasp of the battery performance and in turn the battery
lifetime.
[0005] In the past, as a means for evaluating the performance of
rechargeable battery cells (degree of cycle deterioration), for
example, Japanese Unexamined Patent Publication (Kokai) No.
11-329512 discloses to measure the charge time required for
reaching a full charge state when charging a rechargeable battery
cell by a constant current and compare it with the charge time at
the time of new product so as to determine the degree of
deterioration of performance. It is difficult however to ensure
uniform charging conditions of rechargeable battery cells at all
times. Further, the charge time required for charging a
rechargeable battery cell to the full charge state differs
according to the temperature of the battery cell.
[0006] As opposed to this, Japanese Unexamined Patent Publication
(Kokai) No. 2000-12104 discloses a method of finding the residual
battery capacity by determining the battery life from the internal
resistance, battery voltage, and battery temperature of a
rechargeable battery cell measured using a constant current load.
To measure battery information (internal resistance) using a
constant current load, however, a constant current load
constituting an extra load on the rechargeable battery cell becomes
necessary and therefore the configuration becomes bulkier and more
expensive. Further, at the time of measurement, the current (charge
current) of the rechargeable battery cell is wastefully
consumed.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a
rechargeable battery pack of a simple configuration enabling
accurate judgement of the lifetime of the rechargeable battery cell
under stable conditions without wasteful consumption of the charge
capacity of the rechargeable battery cell, that is, without
discharge of the rechargeable battery cell.
[0008] The present invention takes note of the facts that the
closed circuit voltage Von when charging a rechargeable battery
cell and the open circuit voltage Voff of a rechargeable battery
cell when opening the charge current circuit differ and that the
voltage difference between them is closely related to the internal
resistance of the rechargeable battery cell.
[0009] Therefore, the rechargeable battery pack according to the
present invention is provided with a rechargeable battery cell
comprised of for example a nickel-metal halide type battery, a
battery voltage detecting means for detecting a terminal voltage of
the rechargeable battery cell, a full charge detecting means for
detecting a full charge state when charging the rechargeable
battery cell, a switch device interposed in a charge current
circuit of the rechargeable battery cell and turned off to open the
charge current circuit when the full charge detecting means detects
a full charge state, a memory for storing a closed circuit voltage
Von of the rechargeable battery cell detected by the battery
voltage detecting means immediately before the charge current
circuit is opened, an internal resistance detecting means for
finding a value corresponding to an internal resistance of the
rechargeable battery cell from an open circuit voltage Voff of the
rechargeable battery cell detected by the battery voltage detecting
means and the closed circuit voltage Von stored in the memory after
the charge current circuit is opened, and a lifetime indicating
means for predicting the lifetime of the rechargeable battery cell
in accordance with a value corresponding to the internal resistance
of the rechargeable battery cell and outputting information L on
the lifetime.
[0010] That is, the rechargeable battery pack according to the
present invention detects the full charge state of the rechargeable
battery cell when charging the rechargeable battery cell and
measures the closed circuit voltage Von immediately before stopping
the charging and the open circuit voltage Voff after stopping the
charging to ensure uniform measurement conditions (battery state)
and finds the value Rin corresponding to the internal resistance of
the rechargeable battery cell as
R.sub.in=A(Von-Voff)
[0011] from the closed circuit voltage Von immediately before
stopping the charging and the open circuit voltage Voff after
stopping the charging to accurately judge the lifetime L of the
rechargeable battery cell.
[0012] The rechargeable battery pack according to the present
invention may further be provided with a current detecting means
for detecting a charge current with respect to the rechargeable
battery cell, store in the memory a closed circuit voltage Von of
the rechargeable battery cell detected by the battery voltage
detecting means and a battery charge current Ion detected by the
current detecting means immediately before the charge current
circuit is opened, and find a value corresponding to an internal
resistance of the rechargeable battery cell as
Rin=B(Von-Voff)/(Ion-Ioff)
[0013] from an open circuit voltage Voff of the rechargeable
battery cell detected by the battery voltage detecting means and a
current Ioff detected by the current detecting means after the
charge current circuit is opened and the closed circuit voltage Von
and battery charge current Ion stored in the memory.
[0014] At this time, it is preferable for the internal resistance
detecting means to use a timer circuit to measure a time elapsed
from the time of detecting the full charge state of the
rechargeable battery cell and find an open circuit voltage Voff of
the rechargeable battery cell or its current Ioff when a
predetermined time elapses from the time of detecting the full
charge state. Further, it is preferable to provide a means for
prohibiting processing for calculating the internal resistance of
the rechargeable battery cell by the internal resistance detecting
means when a discharge current of the rechargeable battery cell is
detected by the current detecting means so as to prevent erroneous
judgement of the battery life.
[0015] Further, preferably the rechargeable battery pack is further
provided with a battery temperature detecting means for detecting a
temperature T of the rechargeable battery cell and a correcting
means for correcting the value corresponding to the internal
resistance of the rechargeable battery cell found by the internal
resistance detecting means in accordance with the detected battery
temperature and the battery lifetime is judged by anticipating
changes in the battery characteristics due to the battery
temperature. Further, it is possible to operate the switch device
to repeatedly close and open a charge current circuit for the
rechargeable battery cell and detect the states of the rechargeable
battery cell immediately before the charge current circuit is
opened and after the charge current circuit is opened to eliminate
variations in the measurement data at the time of detection of the
status and evaluate the lifetime of the rechargeable battery cell
with a high accuracy.
[0016] In addition, various techniques proposed in the past can be
suitably employed for the full state detecting means. Various
modifications can be made within the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] These and other objects and features of the present
invention will be more apparent from the following description
given with reference to the accompanying drawings, wherein:
[0018] FIG. 1 is a view of the general configuration of a
rechargeable battery pack according to a first embodiment of the
present invention;
[0019] FIG. 2 is a view of timing of control for stopping charging
of the rechargeable battery cell and changes in the battery voltage
and current;
[0020] FIG. 3 is a view of the general relationship between the
internal resistance and battery lifetime of a rechargeable battery
cell;
[0021] FIG. 4 is a view of the overall flow of an operation for
detecting the battery lifetime in the rechargeable battery pack
shown in FIG. 1;
[0022] FIG. 5 is a view of the overall flow according to another
embodiment of an operation for detecting the battery lifetime in
the rechargeable battery pack shown in FIG. 1;
[0023] FIG. 6 is a view of processing for temperature correction
for detection of internal resistance; and
[0024] FIG. 7 is a view of an example of control for prohibiting an
internal resistance detection operation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Below, an embodiment of the present invention will be
explained with reference to the drawings taking as an example a
rechargeable battery pack able to be used as a backup power source
of a server in a network system.
[0026] FIG. 1 is a view of the general configuration of a
rechargeable battery pack according to this embodiment. Reference
numeral 1 indicates an rechargeable battery cell comprised of a
nickel-metal halide battery etc. The rechargeable battery cell 1 is
comprised of for example a plurality of battery cells connected in
series and having a predetermined terminal voltage (battery
voltage) and predetermined design capacity. The rechargeable
battery cell 1 is charged by connection to an internal power source
of a not shown outside apparatus (server). By discharging the
charging capacity to the above outside apparatus, it supplies the
apparatus with power.
[0027] A switch device 2 comprised of a field effect transistor
(FET) etc. is interposed in series in the charge current circuit of
the rechargeable battery cell 1. The switch device 2 selectively
closes/opens the charge current circuit by being turned on/off by a
switch control circuit 7. The rechargeable battery cell 1 is
controlled in charging through the switch device 2. The switch
control circuit 7 is controlled in operation by the output of a
charge control device which monitors the terminal voltage of the
rechargeable battery cell 2 and controls its charging, that is, a
-.DELTA.V detection circuit 3.
[0028] Further, here, the explanation will be given assuming
detecting the full charge state of the rechargeable battery cell 1
by -.DELTA.V detection to control the charging of the rechargeable
battery cell 1, but it is also possible to suitably employ the
system of detecting the full charge state from the rate of rise of
temperature of the rechargeable battery cell 1 at the time of
charging for control of the charging, the system of detecting the
peak voltage of the rechargeable battery cell 1 for control of the
charging, and various other systems for control of charging
proposed in the past.
[0029] The charge current circuit of the rechargeable battery cell
1, however, has serially interposed in it a charge/discharge
measurement circuit 4 for measuring the charge current of the
rechargeable battery cell 1--one of the parameters for evaluating
the battery performance of the rechargeable battery cell 1.
Further, between the two terminals of the rechargeable battery cell
1 is provided a battery voltage measurement circuit 5 for measuring
the terminal voltage of the rechargeable battery cell 1--another
parameter for evaluating the battery performance of the
rechargeable battery cell 1. Further, in the figure, reference
numeral 6 is a temperature sensor for monitoring the battery
temperature of the rechargeable battery cell 1. This is adhered
etc. to the outside of the rechargeable battery cell 1.
[0030] Further, the charging is controlled by the -.DELTA.V
detection circuit 3 in the following way. For example, as shown in
FIG. 2 showing the change in the battery voltage Vb at the time of
constant current charging (and the charge current Ic, the battery
voltage Vb of the rechargeable battery cell 1 is substantially
constant during the charge period, but rises as the full charge
state is approached. When the full charge state is reached, the
battery voltage Vb peaks, then falls. The -AV detection circuit 3
detects the time when the battery voltage Vb falls by exactly a
predetermined voltage (AV) after the peak voltage is reached as the
rechargeable battery cell 1 reaching the full charge state. When
the full charge state is detected, the switch device 2 is turned
off to open the charge current circuit of the rechargeable battery
cell 1.
[0031] This being so, the rechargeable battery cell 1 stopped being
charged settles down to a constant state and the terminal voltage
stabilizes after the elapse of a predetermined time from when the
terminals are opened. At this time, a predetermined trickle current
It derived from the constant current charging flows in the
rechargeable battery cell 1. Whatever the case, the battery voltage
Vb when the state of the rechargeable battery cell 1 stabilizes
after the switch device 2 is opened and the charging of the
rechargeable battery cell 1 is stopped is the open battery voltage
Voff.
[0032] In the rechargeable battery pack controlling the charging of
the rechargeable battery cell 1 as explained above, the
characterizing feature of the present invention lies in the
provision of a memory 11 for storing the closed circuit voltage Von
of the rechargeable battery cell 1 immediately before the charging
is stopped when detecting the full charge state of the rechargeable
battery cell 1 to turn off the switch device 2 and open the charge
current circuit of the rechargeable battery cell 1. The memory 11
operates under the control of the -.DELTA.V detection circuit 3 and
stores the closed circuit voltage Von of the rechargeable battery
cell 1 detected by the battery voltage measurement circuit 5
immediately before the switch device 2 is turned off. The control
output of the -.DELTA.V detection circuit 3 is given to the timer
circuit 12. The timer circuit 12 drives a second memory 13 provided
in parallel with the memory 11 when a predetermined time elapses
from the time when the switch device 2 is turned off (time when
stopping charging of rechargeable battery cell 1). The second
memory 13 stores the battery voltage Vb of the rechargeable battery
cell 1 which the battery voltage measurement circuit 5 detects at
the timing driven by the timer circuit 12. Therefore, the second
memory 13 stores the open circuit voltage Voff at the time of
elapse of a predetermined time after stopping the charging of the
rechargeable battery cell 1.
[0033] The internal resistance detection circuit 14 fetching the
voltages Von and Voff stored in the two memories 11 and 13 finds
the value Rin corresponding to the internal resistance of the
rechargeable battery cell 1 as for example
Rin=A(Von-Voff)
[0034] from the open circuit voltage Von of immediately before the
rechargeable battery cell 1 stops being charged and the closed
circuit voltage Voff of after the charging is stopped. Here, "A" is
a proportional coefficient.
[0035] The value Rin corresponding to the internal resistance is
converted to information L of the battery lifetime through a
battery lifetime table 15 describing the relationship between the
internal resistance Rin of the rechargeable battery cell and the
battery lifetime such as shown in FIG. 3. The information L of the
battery lifetime is output and indicated (displayed) at the
above-mentioned external device. Note that the above battery
lifetime table 15 stands on the fact that the internal resistance
of the rechargeable battery cell 1 has a close correspondence with
the battery lifetime as shown in FIG. 3 and stores the
correspondence between the value Rin corresponding to the internal
resistance and the battery lifetime in a tabular format. Therefore,
by using such a battery lifetime table 15, the information L of the
battery lifetime of the rechargeable battery cell 1 is found from
the value Rin corresponding to the internal resistance of the
rechargeable battery cell 1 calculated in the above way.
[0036] That is, the rechargeable battery pack, as shown by the flow
of the control routine in FIG. 4, detects the voltage drop
(-.DELTA.V) after the detection of the peak voltage when charging
the rechargeable battery cell 1 (step S1) and judges when the
rechargeable battery cell 1 reaches the full charge state (step
S2). When the full charge state is detected, it detects the
terminal voltage Von of the rechargeable battery cell 1, stores it
in the memory 11 (step S3), then opens the switch device 2 to stop
the charging of the rechargeable battery cell 1 (step S4).
[0037] Next, it uses the timer circuit 12 to judge the elapse of
the predetermined time (step 5) and detects the open terminal
voltage Voff at the time when the state of the rechargeable battery
cell 1 after a predetermined time, that is, when the state of the
rechargeable battery cell 1, stabilizes after the charging is
stopped (step S6). It then calculates the value Rin corresponding
to the internal resistance of the rechargeable battery cell 1 from
the open terminal voltage Voff and the charge voltage Von of the
rechargeable battery cell 1 immediately before the charging is
stopped stored in the memory 11 (step S7), searches through the
battery lifetime table 15 in accordance with this value Rin to find
the information L of the lifetime of the rechargeable battery cell
1 (step S8), then outputs the lifetime information L (step S9).
[0038] Therefore, according to the rechargeable battery pack of the
above configuration, when stopping the charging when the
rechargeable battery cell 1 reaches the full charge state when
charging the rechargeable battery cell 1, the value Rin
corresponding to the rechargeable battery cell 1 after the charging
is stopped is found in accordance with the closed circuit voltage
Von immediately before the charging is stopped and the open circuit
voltage Voff in the state where the rechargeable battery cell 1
stabilizes after the charging is stopped, so it is possible to
accurately judge the battery performance of the rechargeable
battery cell 1 and in turn the battery lifetime. In particular, at
the timings of detection of the battery voltages Von and Voff,
since the battery is in a stable state where the charging of the
rechargeable battery cell 1 reaching the full charge state is
stopped, it becomes possible to evaluate (judge) the battery
lifetime accurately under uniform measurement conditions. Further,
since there is no need to discharge the rechargeable battery cell 1
by a constant current as in the past, there are the effects that
there is no economic waste and the hardware configuration can be
simplified and reduced in price.
[0039] In the above embodiment, the value Rin corresponding to the
internal resistance of the rechargeable battery cell 1 was found
based on the closed circuit voltage Von immediately before stopping
the charging at the time of detection of the full charge state and
the open circuit voltage Voff when a predetermined time elapsed
from when charging was stopped, but it is also possible to detect
the charge current Ib of the rechargeable battery cell 1 at these
detection timings. Specifically, as shown by the flow of processing
in FIG. 5, the closed circuit voltage Von is detected (step S3) and
the charge current Ion is detected (step S3a) immediately before
stopping the charging when detecting the full charge state of the
rechargeable battery cell 1. Further, when a predetermined time
elapses from when the charging was stopped, the open circuit
voltage Voff of the rechargeable battery cell 1 is detected (step
S6) and the charge current (trickle current) Ioff is detected (step
S6a). Further, the internal resistance detection circuit 14 finds
the value Rin corresponding to the internal resistance of the
rechargeable battery cell 1 by for example
Rin=B(Von-Voff)/(Ion-Ioff)
[0040] (step S7a). "B" is a proportional coefficient. By detecting
the currents Ion and Ioff flowing through the rechargeable battery
cell 1 in addition to the battery voltages Von and Voff of the
rechargeable battery cell 1 in this way to find the value Rin
corresponding to the internal resistance, it becomes possible to
evaluate (judge) the battery performance and in turn the battery
lifetime more accurately without regard as to the type of charging
of the rechargeable battery cell 1.
[0041] Further, by making temperature corrections to the battery
characteristics in accordance with the battery temperature T
detected by the temperature sensor 6, it becomes possible to
further improve the measurement accuracy. In this case, as shown by
part of the processing routine in FIG. 6, it is possible to measure
the battery temperature when the charging of the rechargeable
battery cell 1 is stopped (step S11) and make temperature
corrections to the value Rin corresponding to the internal
resistance of the rechargeable battery cell 1 found as explained
above in accordance with the battery temperature measured (step
S12). Next, it is also sufficient to search through the battery
lifetime table 15 in accordance with the temperature corrected
internal resistance.
[0042] More preferably, it is possible to monitor the discharge of
the rechargeable battery cell 1 from the polarity of the current
flowing through the rechargeable battery cell 1 by a discharge
detection circuit 16 and prohibit the storage of the open circuit
voltage Voff in the second memory 13 and prohibit the operation of
the internal resistance detection circuit 14 when detecting
discharge. That is, as shown by part of the processing routine in
FIG. 7, it is judged if the rechargeable battery cell 1 is
discharging from the polarity of the current flowing through the
rechargeable battery cell 1 (step S13). When the rechargeable
battery cell 1 is discharging, the processing for calculating the
internal resistance is prohibited (step S14) and the processing for
estimating the battery lifetime is stopped. By providing this
function for prohibiting the judgement of the battery lifetime in
this way, it is possible to block the judgement (evaluation) of the
processing for calculating the internal resistance and in turn the
battery performance (battery lifetime) based on mistaken
measurement data, so it is possible to easily improve the
reliability of the judgement of the battery lifetime.
[0043] The present invention is not limited to the above
embodiment. For example, it is also possible to repeatedly perform
the processing for detection of the battery voltages Von and Voff
as explained above when detecting the full charge state of the
rechargeable battery cell 1 and evaluate the battery lifetime by
making an overall judgement of the results of the processing. That
is, the full charge state of the rechargeable battery cell 1 is
detected, then the switch device 2 is turned on and off several
times at a predetermined period to repeatedly stop the charging of
the rechargeable battery cell 1. It is also possible to
successively detect the battery voltages Von and Voff at that time
and find the value Rin corresponding to the internal resistance of
the rechargeable battery cell 1 in accordance with the mean values
of the battery voltages Von and Voff. In this case, it is
preferable to eliminate detected values with large deviations to
keep down the fluctuations in detection of the battery voltages Von
and Voff and improve the accuracy of measurement.
[0044] Further, it is possible not to provide the second memory 13
and to perform the processing for calculating the internal
resistance by obtaining the open circuit voltage Voff from the
battery voltage measurement circuit 5 in the internal resistance
detection circuit 14. Further, here, the explanation was made of
the case of use of a nickel-metal halide battery as the
rechargeable battery cell 1, but of course the invention can also
be applied to the use of a Li ion battery or other rechargeable
battery cell. Further, it is possible to turn the switch device 2
on and off to evaluate the battery performance (battery lifetime)
in the end charge state before the rechargeable battery cell 1
reaches the full charge state. Further, it is of course possible to
control the processing for detection of the battery voltages Von
and Voff by software. The present invention can be modified in
various other ways as well within the scope of the invention.
[0045] As explained above, according to the present invention,
since the battery performance is evaluated based on the closed
circuit voltage immediately before control for stopping charging
when charging the rechargeable battery cell and the open circuit
voltage after stopping charging, it becomes possible to accurately
evaluate (judge) the battery lifetime accurately under a stable
state of the battery and uniform measurement conditions. Further,
there is no need to discharge the rechargeable battery cell by a
constant current. Since the lifetime is evaluated under a stable
state of the battery at all times, the battery lifetime can be
easily and accurately judged. Further, there are the tremendously
practical effects of simplification of the configuration and
reduction of the price of the rechargeable battery pack as a
whole.
[0046] While the invention has been described with reference to
specific embodiment chosen for purpose of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
[0047] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2000-19566, filed on Jun. 29,
2000, the disclosure of which is expressly incorporated herein by
reference in its entirety.
* * * * *