U.S. patent application number 09/963515 was filed with the patent office on 2002-05-23 for battery charger capable of accurately determining fully charged condition regardless of batteries with different charge chracteristics.
This patent application is currently assigned to HITACHI KOKI CO., LTD.. Invention is credited to Harada, Hidekazu, Ishimaru, Kenrou, Takano, Nobuhiro.
Application Number | 20020060552 09/963515 |
Document ID | / |
Family ID | 18823894 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020060552 |
Kind Code |
A1 |
Harada, Hidekazu ; et
al. |
May 23, 2002 |
BATTERY CHARGER CAPABLE OF ACCURATELY DETERMINING FULLY CHARGED
CONDITION REGARDLESS OF BATTERIES WITH DIFFERENT CHARGE
CHRACTERISTICS
Abstract
To provide a battery charger capable of fully charging both an
active battery and an inactive battery, which have different
charging characteristics near the peak level, a voltage across the
battery is periodically sampled during charging the battery. A
voltage change is obtained by subtracting a voltage that has been
sampled previously from the newly sampled voltage. Determination of
the fully charged condition of the battery is made when a voltage
change falls below a critical value (S1, S2) after identifying that
the battery being charged is an active or inactive battery using
another critical values (K1, K2 or K1', K2') The critical values S1
and S2 and another critical values K1 and K2 (or K1' and K2') are
selectively referred to depending to the battery voltage
change.
Inventors: |
Harada, Hidekazu;
(Hitachinaka-shi, JP) ; Ishimaru, Kenrou;
(Hitachinaka-shi, JP) ; Takano, Nobuhiro;
(Hitachinaka-shi, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Assignee: |
HITACHI KOKI CO., LTD.
|
Family ID: |
18823894 |
Appl. No.: |
09/963515 |
Filed: |
September 27, 2001 |
Current U.S.
Class: |
320/106 |
Current CPC
Class: |
H02J 7/0003 20130101;
H02J 7/0049 20200101; H02J 2207/20 20200101; H02J 7/022 20130101;
H02J 7/04 20130101; H02J 7/00047 20200101; H02J 7/007182 20200101;
H02J 7/02 20130101; H02J 7/045 20130101 |
Class at
Publication: |
320/106 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2000 |
JP |
2000-350718 |
Claims
What is claimed is:
1. A battery charger comprising: supplying means for supplying a
charge current to a battery; battery voltage detection means for
periodically detecting a battery voltage across the battery; a
memory storing data on at least one battery voltage that is
detected by said battery voltage detection means; updating means
for updating the data stored in said memory whenever the battery
voltage is newly detected by said battery voltage detection means;
calculating means for calculating a difference between the newly
detected battery voltage and the battery voltage stored in said
memory, said calculating means calculating the difference whenever
the battery voltage is newly detected by said battery voltage
detection means; first detection means for detecting that a value
of the difference calculated by said calculating means has become
equal to or exceeded a first critical value and a second critical
value greater than the first critical value; second detection means
for detecting that the value of the difference has become equal to
or less than a third critical value after the difference had become
equal to or exceeded the first critical value and that the value of
the difference has become equal to or less than a fourth critical
value greater than the third critical value after the difference
had become equal to or exceeded the second critical value; and
determining means for determining that the battery has reached a
fully charged condition when said second detection means detects
that the value of the difference has become equal to or less than
the third critical value after said first detection means detects
that the value of the difference has become equal to or exceeded
the first critical value, or when said second detection means
detects that the value of the difference has become equal to or
less than the fourth critical value after said first detection
means detects that the value of the difference has become equal to
or exceeded the second critical value.
2. The battery charger according to claim 1, wherein said first
detection means first detects that the value of the difference has
become equal to or exceeded the first critical value, and
thereafter detects that the value of the difference has become
equal to or exceeded the second critical value.
3. The battery charger according to claim 1, further comprising
first indication means for indicating that the battery is an
inactive battery when detection implemented by said first detection
means indicates that the value of the difference has become equal
to or exceeded the first critical value but has not become equal to
or exceeded the second critical value, and a second indicating
means for indicating that the battery is an active battery when
detection implemented by said first detection means indicates that
the value of the difference has become equal to or exceeded the
second critical value.
4. A battery charger comprising: supplying means for supplying a
charge current to a battery; battery voltage detection means for
periodically detecting a battery voltage across the battery; a
memory storing data on at least one battery voltage that is
detected by said battery voltage detection means; updating means
for updating the data stored in said memory whenever the battery
voltage is newly detected by said battery voltage detection means;
first calculating means for calculating a first difference between
the newly detected battery voltage and the battery voltage stored
in said memory, said first calculating means calculating the first
difference whenever the battery voltage is newly detected by said
battery voltage detection means; second calculating means for
calculating a second difference between the first difference and an
ever occurring minimum value of the voltage change, said second
calculating means calculating the second difference whenever the
battery voltage is newly detected by said battery voltage detection
means; first detection means for detecting that a value of the
second difference calculated by said second calculating means has
become equal to or exceeded a first critical value and a second
critical value greater than the first critical value; second
detection means for detecting that a value of the first difference
has become equal to or less than a third critical value after the
second difference had become equal to or exceeded the first
critical value and that the value of the first difference has
become equal to or less than a fourth critical value greater than
the third critical value after the second difference had become
equal to or exceeded the second critical value; and determining
means for determining that the battery has reached a fully charged
condition when said second detection means detects that the value
of the first difference has become equal to or less than the third
critical value after said first detection means detects that the
value of the second difference has become equal to or exceeded the
first critical value, or when said second detection means detects
that the value of the first difference has become equal to or less
than the fourth critical value after said first detection means
detects that the value of the second difference has become equal to
or exceeded the second critical value.
5. The battery charger according to claim 4, wherein said first
detection means first detects that the value of the second
difference has become equal to or exceeded the first critical
value, and thereafter detects that the value of the second
difference has become equal to or exceeded the second critical
value.
6. The battery charger according to claim 4, further comprising
first indication means for indicating that the battery is an
inactive battery when detection implemented by said first detection
means indicates that the value of the second difference has become
equal to or exceeded the first critical value but has not become
equal to or exceeded the second critical value, and a second
indicating means for indicating that the battery is an active
battery when detection implemented by said first detection means
indicates that the value of the second difference has become equal
to or exceeded the second critical value.
7. A battery charger comprising: supplying means for supplying a
charge current to a battery; battery voltage detection means for
periodically detecting a battery voltage across the battery; a
memory storing data on at least one battery voltage that is
detected by said battery voltage detection means; updating means
for updating the data stored in said memory whenever the battery
voltage is newly detected by said battery voltage detection means;
first calculating means for calculating a first difference between
the newly detected battery voltage and the battery voltage stored
in said memory, said first calculating means calculating the first
difference whenever the battery voltage is newly detected by said
battery voltage detection means; second calculating means for
calculating a second difference between the first difference and an
ever occurring minimum value of the voltage change, said second
calculating means calculating the second difference whenever the
battery voltage is newly detected by said battery voltage detection
means; first detection means for detecting that a value of the
second difference calculated by said second calculating means has
become equal to or exceeded a first critical value and a second
critical value greater than the first critical value; second
detection means for detecting that a value of the second difference
has become equal to or less than a third critical value after the
second difference had become equal to or exceeded the first
critical value and that the value of the second difference has
become equal to or less than a fourth critical value greater than
the third critical value after the second difference had become
equal to or exceeded the second critical value; and determining
means for determining that the battery has reached a fully charged
condition when said second detection means detects that the value
of the second difference has become equal to or less than the third
critical value after said first detection means detects that the
value of the second difference has become equal to or exceeded the
first critical value, or when said second detection means detects
that the value of the second difference has become equal to or less
than the fourth critical value after said first detection means
detects that the value of the second difference has become equal to
or exceeded the second critical value.
8. The battery charger according to claim 7, wherein said first
detection means first detects that the value of the second
difference has become equal to or exceeded the first critical
value, and thereafter detects that the value of the second
difference has become equal to or exceeded the second critical
value.
9. The battery charger according to claim 7, further comprising
first indication means for indicating that the battery is an
inactive battery when detection implemented by said first detection
means indicates that the value of the second difference has become
equal to or exceeded the first critical value but has not become
equal to or exceeded the second critical value, and a second
indicating means for indicating that the battery is an active
battery when detection implemented by said first detection means
indicates that the value of the second difference has become equal
to or exceeded the second critical value.
10. A battery charger comprising: supplying means for supplying a
charge current to a battery; battery voltage detection means for
periodically detecting a battery voltage across the battery; a
memory storing data on at least one battery voltage that is
detected by said battery voltage detection means; updating means
for updating the data stored in said memory whenever the battery
voltage is newly detected by said battery voltage detection means;
calculating means for calculating a difference between the newly
detected battery voltage and the battery voltage stored in said
memory, said calculating means calculating the difference whenever
the battery voltage is newly detected by said battery voltage
detection means, said memory further storing an ever occurring
maximum value of the difference; first detection means for
detecting that the maximum value has become equal to or exceeded a
first critical value and a second critical value greater than the
first critical value; second detection means for detecting that the
difference has fallen a third critical value or a fourth critical
value greater than the third critical value from the maximum value;
and determining means for determining that the battery has reached
a fully charged condition when said second detection means detects
that the difference has fallen the third critical value from the
maximum value after said first detection means detects that the
maximum value had become equal to or exceeded the first critical
value but not exceeded the second critical value, and when said
second detection means detects that the difference has fallen the
fourth critical value from the maximum value after said first
detection means detects that the maximum value had become equal to
or exceeded the second critical value.
11. The battery charger according to claim 10, wherein said first
detection means first detects that the maximum value has become
equal to or exceeded the second critical value, and thereafter
detects that the maximum value has become equal to or exceeded the
first critical value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a battery charger for
charging batteries, such as nickel-cadmium batteries and
nickel-hydrogen batteries, which are used as power sources for
hand-held electric devices, such as cordless power tools.
[0003] 2. Description of the Related Art
[0004] It is essential for battery chargers to determine, during a
charging process, that a battery has reached a fully charged
condition and to stop charging the battery at the time thereof. One
method of determining the fully charged condition is a so-called
"-.DELTA.V detection method", in which the battery is determined to
be fully charged when the battery voltage drops a predetermined
voltage (.DELTA.V) from the peak level. To this end, the voltage
V.sub.in across the battery is sampled at every predetermined
period, and whenever the detected battery voltage V.sub.in exceeds
the ever occurring maximum voltage, the data recorded as the
maximum voltage is updated. When the battery voltage V.sub.in drops
the predetermined voltage .DELTA.V from the maximum voltage, the
battery is determined to be fully charged.
[0005] Japanese Patent Application Publication (Kokai) No.
HEI-7-184329 describes a "two-step detection method", in which the
battery is determined to be fully charged when the battery voltage
change exceeds a first predetermined critical value K, and
thereafter falls below a second predetermined critical value S. To
this end, the voltage across the battery is sampled at every
predetermined period, and a previously detected voltage is
subtracted from the newly detected voltage to obtain a gradient of
the battery voltage, i.e., a battery voltage change. Generally, as
the charging progresses, the battery voltage change increases,
reaches the peak, and then goes down. The peak of the battery
voltage appears at some point while the battery voltage change
gradually goes down after having reached the peak of the voltage
change. Therefore, by identifying the point with a particular value
of the battery voltage change (i.e., the second predetermined
critical value) corresponding to the peak of the battery voltage,
the fully charged condition of the battery can be known.
[0006] Generally, there is less danger that the batteries will be
overcharged with the two-step detection method than with the
-.DELTA.V detection method. However, the accuracy in detection of
the fully charged condition with the two-step detection method is
not assured if there is a change in the charge characteristics of
the batteries.
[0007] Batteries subject to charging with the charger include
active batteries and inactive batteries, which are classified in
terms of the use circumstance. Batteries that are normally
discharged through the use with electrically powered products are
herein referred to as active batteries. Inactive batteries are such
batteries that have been left unused for a long period of time,
causing the battery to discharge. Active and inactive batteries
exhibit different charge characteristics. Further, nickel-hydrogen
batteries and nickel-cadmium batteries also exhibit different
charge characteristics.
[0008] When the battery charger with the first and second critical
values K and S set for the inactive battery is used for charging
the active battery, the fully charged condition of the active
battery will be detected after the battery voltage peak level has
passed, resulting in overcharging the active batteries. On the
other hand, when the inactive battery is charged with the first and
second critical values K, S set for the active batteries, there is
a possibility that the voltage change never reaches the first
critical value K, resulting in overcharge of the inactive
batteries. Even if the first critical value K is reached, the
second critical value S may be reached before the battery voltage
reaches the peak level, resulting in undercharging the inactive
batteries.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
battery charger capable of reliably and accurately charging
batteries to a fully charged condition regardless of the type and
kind of the battery.
[0010] In order to achieve the above and other objects, there is
provided a battery charger that includes supply means, battery
voltage detection means, memory, updating means, calculating means,
first detection means, second detection means, and determining
means. The supplying means is provided for supplying a charge
current to a battery. Generally, the battery voltage increases as
the charging progresses. The battery voltage detection means is
provided for periodically detecting the battery voltage. At least
one battery voltage that has been previously detected by the
battery voltage detection means is stored in the memory. The data
stored in the memory is updated by the updating means whenever the
battery voltage is newly detected by the battery voltage detection
means. The difference between the newly detected battery voltage
and the battery voltage stored in the memory is calculated by the
calculating means whenever the battery voltage is newly detected by
the battery voltage detection means. The difference is calculated
by subtracting the previously detected battery voltage from the
newly detected battery voltage.
[0011] The first detection means is provided for detecting that the
value of the difference calculated by the calculating means has
become equal to or exceeded a first critical value and a second
critical value greater than the first critical value. The second
detection means is provided for detecting that the value of the
difference has become equal to or less than a third critical value
after the difference had become equal to or exceeded the first
critical value. The second detection means further detects that the
value of the difference has become equal to or less than a fourth
critical value greater than the third critical value after the
difference had become equal to or exceeded the second critical
value. The determining means determines that the battery has
reached a fully charged condition (1) when the second detection
means detects that the value of the difference has become equal to
or less than the third critical value after the first detection
means detects that the value of the difference has become equal to
or exceeded the first critical value, or (2) when the second
detection means detects that the value of the difference has become
equal to or less than the fourth critical value after the first
detection means detects that the value of the difference has become
equal to or exceeded the second critical value
[0012] According to another aspect of the invention, there is
provided a battery charger that includes supplying means, battery
voltage detection means, memory, and updating means as described
above. The charger further includes first calculating means, second
calculating means, first detection means, second detection means,
and determining means.
[0013] The first calculating means calculates a first difference
between the newly detected battery voltage and the battery voltage
stored in the memory, and calculates the first difference whenever
the battery voltage is newly detected by the battery voltage
detection means. The second calculating means calculates a second
difference between the first difference and an ever occurring
minimum value of the voltage change, and calculates the second
difference whenever the battery voltage is newly detected by the
battery voltage detection means.
[0014] The first detection means is provided for detecting that a
value of the second difference calculated by the second calculating
means has become equal to or exceeded a first critical value and a
second critical value. The second critical value is greater than
the first critical value. The second detection means is provided
for detecting that a value of the first difference has become equal
to or less than a third critical value after the second difference
had become equal to or exceeded the first critical value. Further,
the second detection means detects that the value of the first
difference has become equal to or less than a fourth critical value
greater than the third critical value after the second difference
had become equal to or exceeded the second critical value. The
determining means determines that the battery has reached a fully
charged condition (1) when the second detection means detects that
the value of the first difference has become equal to or less than
the third critical value after the first detection means detects
that the value of the second difference has become equal to or
exceeded the first critical value, or (2) when the second detection
means detects that the value of the first difference has become
equal to or less than the fourth critical value after the first
detection means detects that the value of the second difference has
become equal to or exceeded the second critical value.
[0015] According to still another aspect of the invention, there is
provided a battery charger that includes supplying means, battery
voltage detection means, memory, and updating means as described
above. The charger further includes first calculating means, second
calculating means, first detection means, second detection means,
and determining means.
[0016] The first calculating means calculates a first difference
between the newly detected battery voltage and the battery voltage
stored in the memory. The first calculating means calculates the
first difference whenever the battery voltage is newly detected by
the battery voltage detection means. The second calculating means
calculates a second difference between the first difference and an
ever occurring minimum value of the voltage change. The second
calculating means calculates the second difference whenever the
battery voltage is newly detected by the battery voltage detection
means.
[0017] The first detection means detects that a value of the second
difference calculated by the second calculating means has become
equal to or exceeded a first critical value and a second critical
value greater than the first critical value. The second detection
means detects that a value of the second difference has become
equal to or less than a third critical value after the second
difference had become equal to or exceeded the first critical value
and that the value of the second difference has become equal to or
less than a fourth critical value greater than the third critical
value after the second difference had become equal to or exceeded
the second critical value. The determining means determines that
the battery has reached a fully charged condition (1) when the
second detection means detects that the value of the second
difference has become equal to or less than the third critical
value after the first detection means detects that the value of the
second difference has become equal to or exceeded the first
critical value, or (2) when the second detection means detects that
the value of the second difference has become equal to or less than
the fourth critical value after the first detection means detects
that the value of the second difference has become equal to or
exceeded the second critical value.
[0018] According to further aspect of the invention, there is
provided a battery charger that includes supplying means, battery
voltage detection means, memory, and updating means as described
above. The charger further includes calculating means, first
detection means, second detection means, and determining means.
[0019] The calculating means calculates a difference between the
newly detected battery voltage and the battery voltage stored in
the memory. The calculating means calculates the difference
whenever the battery voltage is newly detected by the battery
voltage detection means. The memory further stores an ever
occurring maximum value of the difference.
[0020] The first detection means detects that the maximum value has
become equal to or exceeded a first critical value and a second
critical value greater than the first critical value. The second
detection means detects that the difference has fallen a third
critical value or a fourth critical value greater than the third
critical value from the maximum value. The determining means
determines that the battery has reached a fully charged condition
(1) when the second detection means detects that the difference has
fallen the third critical value from the maximum value after the
first detection means detects that the maximum value had become
equal to or exceeded the first critical value but not exceeded the
second critical value, and (2) when the second detection means
detects that the difference has fallen the fourth critical value
from the maximum value after the first detection means detects that
the maximum value had become equal to or exceeded the second
critical value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features and advantages of the
invention will become more apparent from reading the following
description of the preferred embodiment taken in connection with
the accompanying drawings in which:
[0022] FIG. 1 is a block diagram showing a battery charger
according to the present invention;
[0023] FIG. 2 is a flowchart illustrating operations executed
according to a first embodiment of the present invention;
[0024] FIG. 3 is a flowchart illustrating operations executed
according to a second embodiment of the present invention;
[0025] FIG. 4(a) is a graphical representation showing a battery
voltage charge characteristic curve of an inactive battery;
[0026] FIG. 4(b) is a graphical representation showing a battery
voltage charge characteristic curve of an active battery;
[0027] FIG. 4(c) is a graphical representation showing a battery
voltage change characteristic of the inactive battery; and
[0028] FIG. 4(d) is a graphical representation showing a battery
voltage change characteristic of the active battery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Next, preferred embodiments of the present invention will be
described while referring to the accompanying drawings.
[0030] FIG. 1 shows a hardware arrangement of the battery charger
according to a preferred embodiment of the present invention. To
charge a battery 2 with the battery charger 100, the battery 2 is
loaded into connection terminals, one being connected to the output
of a rectifying/smoothing circuit 30 (to be described later), and
the other to ground. The battery 2 consists of a plurality of cells
connected in series.
[0031] The battery charger 100 includes a resistor 3 serving as a
current detection means for detecting a charge current flowing in
the battery 2. A rectifying/smoothing circuit 10 is connected to an
A.C. power source 1 for converting the A.C. voltage to D.C.
voltage. The circuit 10 includes a full-wave rectifier 11 and a
smoothing capacitor 12. A switching circuit 20 is connected to the
output of the rectifying/smoothing circuit 10 and includes a high
frequency transformer 21, a MOSFET 22, and a PWM (pulse width
modulation) control IC 23. This IC 23 changes the width of driving
pulses applied to the MOSFET 22. With the switching actions
performed by the MOSFET 22, pulsating voltage is developed at the
secondary side of the transformer 21. Another rectifying/smoothing
circuit 30 is connected to the secondary side of the transformer
21. The circuit 30 includes diodes 31, 32, a choke coil 33, and a
smoothing capacitor 34. A battery voltage detection section 40,
which is made up of two resistors 41 and 42 connected in series, is
connected in parallel to the battery 2. With this configuration,
the voltage across the battery 2 can be obtained from the voltage
developed across the resistor 42.
[0032] The battery charger 100 further includes a microcomputer 50
having a CPU 51, a ROM 52, a RAM 53, a sampling timer 54, an A/D
converter 55, an output port 56, and a reset input port 57, which
are mutually connected by a bus. A charge current control section
60 is connected between the current detection section (resistor) 3
and the switching circuit 20 to maintain the charge current at a
predetermined level. The charge current control section 60 includes
cascade-connected operational amplifiers 61 and 62, and resistors
63 through 66.
[0033] A constant voltage power supply 70 is provided for supplying
constant voltages to the microcomputer 50 and the charge current
control section 60. The constant voltage power supply 70 includes a
transformer 71, a full-wave rectifier 72, a smoothing capacitor 73,
a three-terminal voltage regulator 74, and a reset IC 75. The reset
IC 75 outputs a reset signal to the reset input port 57 to reset
the microcomputer 50. A charge current setting section 80 is
connected between the output port 56 of the microcomputer 50 and
the inverting input terminal of the operational amplifier 62. The
charge current setting section 80 is provided for setting the level
of the charge current. This can be done by changing the voltage
applied to the inverting input terminal of the operational
amplifier 62 in response to the signal output from the
microcomputer 50.
[0034] A photo-coupler 4 is connected between the output port 56 of
the microcomputer 50 and the IC 23 of the switching circuit 20. The
photo-coupler 4 is provided for transmitting a charge start signal
and a charge stop signal fed from the output port 56 of the
microcomputer 50 to the PWM control IC 23. Another photo-coupler 5
is connected between the output of the charge current control
section 60 and the PWM control IC 23 for feeding the charge current
signal back to the PWM control IC 23.
[0035] With the arrangement shown in FIG. 1, the fully charged
condition of the battery 2 is detected as will be described below.
In the following embodiments, an improved two-step detection method
is used to detect the fully charged condition of the battery. The
improved two-step detection method takes into account difference in
the battery voltage charge characteristic of, for example, active
and inactive batteries.
[0036] FIGS. 4(a) and 4(b) are charge characteristics of the
inactive batteries and the active batteries, respectively, wherein
the axis of abscissa represents charge time, and the axis of
ordinate battery voltage. FIGS. 4(c) and 4(d) are voltage change
characteristics of the inactive batteries and the active batteries,
respectively, wherein the axis of abscissa represents charge time,
and the axis of ordinate the amount of the voltage change expressed
by the number of bits.
[0037] As shown in FIGS. 4(c) and 4(d), the voltage change of the
inactive batteries and the active batteries reaches the peak before
the battery voltage reaches the peak level. However, the peak level
of the voltage change is different between the inactive batteries
and the active batteries. In this example, the inactive batteries
have a peak of 3 bits on the graph of FIG. 4(c) and the active
batteries have a peak of 9 bits on the graph of FIG. 4(d).
[0038] In the conventional two-step detection method, the voltage
change of the battery is first compared with a first critical value
K. When the voltage change has exceeded the first critical value K,
then it is compared with a second critical value S. The battery is
determined to be fully charged when the voltage change of the
battery falls below the second critical value S.
[0039] In the improved two-step detection method according to the
invention, two critical values K1 and S1 are specifically set for
inactive batteries. When the voltage change of the battery falls
below the critical value S1 after having exceeded the critical
value K1, the inactive battery is determined to be fully charged.
Likewise, two critical values K2 and S2 are specifically set for
active batteries. When the voltage change of the battery falls
below the critical value S2 after having exceeded the critical
value K2, the active battery is determined to be fully charged.
With the voltage change characteristics of the inactive and active
batteries in mind, the critical value K1 is set smaller than K2,
and the critical value S1 is set smaller than S2.
[0040] More specifically, in the following embodiments, the
critical value K1 for the inactive batteries is set to 3 (bits). To
identify that the battery to be charged is an active battery, the
critical value K2 for the active batteries needs to be greater than
3 (bits) but less than 9 (bits) as can be appreciated from the
graphs of FIGS. 4(c) and 4(d). Accordingly, in the following
embodiments, 6 (bits) is selected as the critical value K2 for the
active batteries.
[0041] As to the inactive batteries, the fully charged condition
will be properly detected when the critical value S1 is set to 0
(bit). Also, the fully charged condition of the active batteries
will be properly detected when the critical value S2 is set to 2
(bits) as can be understood from FIG. 4(d).
[0042] With the use of two sets of critical values in the improved
two-step detection method, the batteries can be charged to a fully
charged condition regardless of whether the battery to be charged
is inactive or active.
[0043] To obtain the battery voltage characteristic as shown in
FIG. 4(a) or FIG. 4(b), the output of the battery voltage detecting
section 40 is periodically sampled and the sampled voltage V.sub.in
is subjected to analog-to-digital conversion in the A/D converter
55. Digital data corresponding to the sampled voltage V.sub.in is
stored in the RAM 53. The RAM 53 also stores previously sampled and
A/D converted six battery voltages V.sub.i-06, V.sub.i-05, . . . ,
V.sub.i-01, which are updated every time the battery voltage
V.sub.in is newly sampled so that the most recent six battery
voltages are stored.
[0044] To obtain the battery voltage change characteristic as shown
in FIGS. 4(c) and 4(d), the microcomputer 50 calculates a voltage
difference between the battery voltage V.sub.in and the battery
voltage V.sub.i-06 that was detected six-sampling times before. The
voltage difference .DELTA.V.sub.i-06 (=V.sub.in-V.sub.i-06)
represents a voltage change in a unit time, that is, gradient of
the battery voltage characteristic curve.
[0045] Alternatively, the microcomputer 50 may further calculate a
difference between the voltage change .DELTA.V.sub.-06 and an ever
occurring minimum voltage change .DELTA.V.sub.min, which will be
referred to as "deviated voltage change"
(=.DELTA.V.sub.-06-.DELTA.V.sub.min), to obtain a deviated voltage
change characteristic. Based on this characteristic, identification
of inactive and active batteries and also determination of the
fully charged condition of the batteries are carried out using four
critical values K1', K2', S1' and S2'. The critical value K1' is
used to identify inactive batteries, and the critical value K2'
active batteries. The critical value S1' is used to determine the
fully charged condition of the inactive batteries, and the critical
value S2' the fully charged condition of the active batteries. As
such, the critical values K1', K2', S1' and S2' correspond to K1,
K2, S1 and S2, respectively, wherein the values K1', K2', S1' and
S2' are set to be smaller values than the values K1, K2, S1 and S2,
respectively.
[0046] Next, operation of the battery charger 100 according to the
first embodiment will be described while referring to the flowchart
shown in FIG. 2. Hereinafter, individual steps will be referred to
with an "S" followed by the step number.
[0047] When the battery charger 100 is powered, the microcomputer
50 goes into a standby condition in which it is determined whether
or not the battery 2 is loaded into the battery charger 100 (S101).
When, by referring to the signal output from the voltage detection
section 40, the microcomputer 50 determines that the battery 2 is
loaded (S101:YES), then charging of the battery 2 is started (S102)
Specifically, the microcomputer 50 outputs the charge start signal
from the output port 56 to the PWM control IC 23 via the
photo-coupler 4. At the same time, the microcomputer 50 applies a
reference voltage V.sub.i to the operational amplifier 62 via the
charge current setting section 80, so that the battery 2 is charged
with a charge current I. At the time when the battery charging is
started, an actual charge current flowing through the battery 2 is
detected at the resistor 3. The reference voltage V.sub.i is
subtracted from the voltage corresponding to the actual charge
current detected at the resistor 3, and the resultant difference
signal is fed back to the PWM control IC 23 via the photo-coupler
5.
[0048] More specifically, the width of the pulse applied to the
high frequency transformer 21 is reduced when the actual charge
current is greater than a reference charge current corresponding to
the reference voltage V.sub.i whereas the width of the pulse
applied to the high frequency transformer 21 is increased when the
actual charge current is less than the reference charge current.
The output from the secondary winding of the high frequency
transformer 21 is subject to rectification and smoothing by the
rectifying/smoothing circuit 30. In this way, a constant charge
current I flows in the battery 2.
[0049] The microcomputer 50 samples the output of the battery
voltage detection section 40 at every predetermined period and
converts the sampled voltages to digital data in the A/D converter
55. The digital data on the most recent six sampled voltages are
stored in the RAM 53. In S103, various values stored in the RAM 53
are initialized. That is, data to be recorded as the most recent
six sampled voltages V.sub.i-06, V.sub.i-05, . . . , V.sub.i-01 are
initialized to zero. The minimum voltage change .DELTA.V.sub.min is
set to infinite. Also, the maximum value in the A/D converter 55 is
set to infinite.
[0050] The RAM 53 also stores a first set of critical values K1'
and S1 for the inactive batteries, a second set of critical values
K2' and S2 for the active batteries, a first
voltage-increase-detection flag F1, and a second
voltage-increase-detection flag F2. Both the first and second flags
F1, F2 initially take value of "0" (S103). However, the first flag
F1 is turned to "1" when detection is so made that the deviated
voltage change has become equal to or exceeded the critical value
K1'. The second flag F2 is turned to "1" when detection is so made
that the deviated voltage change has become equal to or exceeded
the critical value K2'.
[0051] Then, the battery voltage sampling timer 54 is started
(S104). When the timer 54 has measured a sampling period of time
.DELTA.t (S105:YES), then the timer 54 is restarted (S106) for
allowing the battery voltage to be sampled.
[0052] During the sampling period, the battery voltage V.sub.in is
detected (S107), and the voltage change .DELTA.V.sub.i-06
(=V.sub.in-V.sub.i-06) is calculated (S108). The voltage change
.DELTA.V.sub.i-06 indicates a difference in the battery voltage
which occurred during six sampling periods (6.DELTA.t). If the
second flag F2 has the value of "1" (S109:YES), the routine
proceeds to S118. However, at the initial stage of charging, the
second flag F2 takes a value of "0" as it is so set in S103.
Therefore, the routine proceeds to S110 where it is determined
whether or not the first flag F1 has the value of "1". If the first
flag F1 has the value of "1" (S110:YES), then the routine proceeds
to S116. The first flag F1 also takes a value of "0" at the initial
stage of charging, so the routine proceeds to S111.
[0053] In S111, if the deviated voltage change
(.DELTA.V.sub.i-06-.DELTA.V- .sub.min) is determined less than the
critical value K1' (S111:NO), then the routine proceeds to S112
where comparison is made between the voltage change
.DELTA.V.sub.i-06 and the minimum voltage change .DELTA.V.sub.min.
If the voltage change .DELTA.V.sub.i-06 is smaller than the minimum
voltage change .DELTA.V.sub.min (S112:YES), then the minimum
voltage change .DELTA.V.sub.min is replaced by the voltage change
.DELTA.V.sub.i-06 to update the minimum voltage change
.DELTA.V.sub.min (S113). Then, data for the detected battery
voltages V.sub.i-06 to V.sub.i-01 are updated (S114). That is,
V.sub.i-06 is replaced by V.sub.i-05, V.sub.i-05 by V.sub.i-04,
V.sub.i-04 by V.sub.i-03, and so on. The V.sub.i-01 is replaced by
V.sub.in. If the voltage change .DELTA.V.sub.i-06 is equal to or
greater than the minimum voltage change .DELTA.V.sub.min (S112:NO),
the routine directly proceeds to S114 without executing S113. Then,
upon execution of S114, the routine returns to S105 where whether
the sampling period of time has expired or not is checked.
[0054] As the charging of the battery progresses, the deviated
voltage change will become equal to or exceed the critical value
K1' (S111:YES), then the process proceeds to S115 where the value
of the first flag F1 is rewritten to "1" (S115) The value "1" of
the first flag F1 assumes, for the time being, that the battery
being charged is an inactive battery. However, this assumption is
denied if the deviated voltage change has become equal to or
exceeded the critical value K2' (S116:YES). That is, the battery 2
is finally determined to be an active battery, not inactive
battery. At this time, the value of the flag F2 is rewritten to "1"
(S117), and then the routine proceeds to S118. On the other hand,
if the deviated voltage change is less than the critical value K2'
(S116:NO), the assumption that the inactive battery is being
charged is correct, and the routine proceeds to S119.
[0055] When it is determined that the active battery is being
charged, the voltage change .DELTA.V.sub.i-06 is compared with the
critical value S2 (S118). The fact that the voltage change
.DELTA.V.sub.i-06 has become equal to or less than the critical
value S2 (S118:YES) indicates that the battery has reached the
fully charged condition. Therefore, the charge stop signal is
applied to the PWM control IC 23 via the charge control signal
transmitting section 4 and the battery charger 100 stops charging
the battery 2 (S120). When the battery 2 is unloaded from the
charger 100 (S121:YES), the routine returns to S101. If the voltage
change .DELTA.V.sub.i-06 is still greater than the critical value
S2 (S118:NO), it is indicated that the fully charged condition has
not yet been reached, so the routine proceeds to S112 to continue
charging the battery.
[0056] In S116, when the deviated voltage change does not exceed
the critical value K2' (S116:NO), the battery 2 is determined to be
an inactive battery and the voltage change .DELTA.V.sub.i-06 is
compared with the critical value S1 (S119). If the voltage change
.DELTA.V.sub.1-06 has become equal to or less than the critical
value S1 (S119:YES), it is determined that the inactive battery 2
has reached the fully charged condition. So the battery charger 100
stops charging the battery (S120). When the battery 2 is unloaded
from the charger 100 (S121:YES), the routine returns to S101. The
fact that the voltage change .DELTA.V.sub.i-06 is still greater
than the critical value S1 (S119:NO) indicates that the inactive
battery has not yet been reached the fully charged condition, so
the routine proceeds to S112.
[0057] As described, when the voltage change .DELTA.V.sub.i-06
falls below the critical value S1 while only the first flag F1 has
the value of "1", the inactive battery is determined to be in the
fully charged condition. On the other hand, when both the first and
second flags F1 and F2 have the value of "1", this means that the
battery 2 is the active battery. In this case, the active battery
is determined to be fully charged when the voltage change
.DELTA.V.sub.i-06 falls below the critical value S2.
[0058] In this manner, the fully charged condition of the battery 2
is reliably and accurately detected regardless of whether the
battery 2 is active or inactive, thereby preventing the batteries
from overcharging and undercharging.
[0059] In the first embodiment, the battery 2 is determined to be
active or inactive based on the deviated voltage change
(.DELTA.V.sub.i-06-.DELT- A.V.sub.min), however, this determination
may be made based on the voltage change .DELTA.V.sub.i-06 while
using the critical values K1 and K2. In this case, the critical
values K1 and K2 to be compared with the voltage change
.DELTA.V.sub.i-06 must be set larger than the critical values K1'
and K2', respectively.
[0060] Next, operation of the battery charger 100 according to the
second embodiment will be described while referring to the
flowchart of FIG. 3. In the first embodiment, detection of the
fully charged condition is made when the voltage change falls below
the critical values S1, S2 after the deviated voltage change has
become equal to or exceeded at least one of the critical values K1'
and K2'. However, according to the second embodiment, the fully
charged condition is determined when the voltage change falls a
predetermined value from the maximum voltage change. In the second
embodiment, critical values P1, P2, Q1 and Q2 are used, wherein
P1<P2, Q1<Q2.
[0061] The processes of S201 through S208 in FIG. 3 are basically
the same as those of S101 through S108 in FIG. 2, and so their
explanation will be omitted to avoid duplicate description. In
S203, a value for the maximum voltage change .DELTA.V.sub.max is
initialized to 0.
[0062] After S209, when the maximum voltage change .DELTA.V.sub.max
is equal to or greater than the critical value P2 (S209:YES), then
the battery 2 is determined to be an active battery, and the
routine proceeds to S215. On the other hand, when the maximum
voltage change .DELTA.V.sub.max is less than the critical value P2
(S209:NO), then the routine proceeds to S210. In S210, when the
maximum voltage change .DELTA.V.sub.max is equal to or greater than
the critical value P1 (S210:YES), it is assumed that the battery 2
is an inactive battery, and the routine proceeds to S214. On the
other hand, if the maximum voltage change .DELTA.V.sub.max is less
than the critical value P1 (S210:NO), then the routine proceeds to
S211.
[0063] In S211, the voltage change .DELTA.V.sub.i-06 is compared
with the maximum voltage change .DELTA.V.sub.max. When the voltage
change .DELTA.V.sub.i-06 is greater than the maximum voltage change
.DELTA.V.sub.max (S211:YES), then the maximum voltage change
.DELTA.V.sub.max is replaced by the voltage change
.DELTA.V.sub.i-06 to update the maximum voltage change
.DELTA.V.sub.max (S212), and the process proceeds to S213. On the
other hand, the maximum voltage change .DELTA.V.sub.max is greater
than the voltage change .DELTA.V.sub.i-06 (S211:NO), then the
routine directly proceeds to S213, wherein the data on the most
recent six battery voltages V.sub.i-06 to V.sub.i-01 are updated in
the same manner as S114 of FIG. 2.
[0064] In S214, when the voltage change .DELTA.V.sub.i-06 falls the
critical value Q1 from the maximum voltage change .DELTA.V.sub.max
(S214:YES), then it is determined that the inactive battery has
reached the fully charged condition, so the charging is stopped
(S216). When the battery 2 is unloaded (S217:YES), the routine
returns to S201. If the voltage change .DELTA.V.sub.i-06 does not
fall the critical value Q1 from the maximum voltage change
.DELTA.V.sub.max (S214:NO), then the process returns to S211.
[0065] In S215, when the voltage change .DELTA.V.sub.i-06 falls the
critical value Q2 from the maximum voltage change .DELTA.V.sub.max
(S215:YES), then it is determined that the active battery has
reached the fully charged condition, so the charging is stopped
(S216). When the battery 2 is unloaded (S217:YES), the routine
returns to S201. If the voltage change .DELTA.V.sub.i-06 does not
fall the critical value Q1 from the maximum voltage change
.DELTA.V.sub.max (S214:NO), then the process returns to S211.
[0066] In the second embodiment, the battery 2 is determined active
or inactive based on the level of the maximum voltage change
.DELTA.V.sub.max reached during charging. Then, the critical values
Q1 and Q2 are selectively used to determine if the battery has
reached the fully charged condition. In the second embodiment, the
fully charged condition can be reliably and correctly detected
regardless of whether the battery 2 is the active or inactive in
the similar manner as in the first embodiment.
[0067] While the invention has been described in detail with
reference to specific embodiments thereof, it would be apparent to
those skilled in the art that various changes and modifications may
be made therein without departing from the spirit of the
invention.
[0068] For example, the above embodiments are described for
charging the active batteries and inactive batteries. However, the
present invention can also be applied to charging other types of
batteries with different charging characteristics, such the
nickel-cadmium batteries and the nickel-hydrogen batteries.
* * * * *