Technical Field
The present invention relates to technology of removing sulfation
(desulfation) on electrodes of a lead-acid battery.
Background Art
Sulfation on a positive electrode and a negative electrode of a
lead-acid battery is known as one reason of degrading the performances of
the lead-acid battery. The sulfation occurs on both the electrodes by the
following electrochemical reactions of a diluted sulfuric acid electrolyte
solution with the positive electrode (lead oxide electrode) and with the
negative electrode Qead electrode) during operation (discharging) of the
lead-acid battery. The electrochemical reactions proceed in the reverse
direction during charging:
Pb02 + 4H+ + S042- + 2e- -> PbS04 + 2H2O (positive electrode)
Pb + SO42 -^ PbS04 -t- 2e (negative electrode)
Sulfation Qead sulfation) on the surfaces of the positive electrode and
the negative electrode (electrode surfaces involved in charging) interferes
with the desired electrochemical reactions between the respective electrodes
and the electrolyte solution and thereby degrades the charging performance
and the discharging performance of the lead-acid battery.
Application of a pulse current to the lead-acid battery is known as the
technique of recovering the performances of the lead-acid battery, which are
degraded by sulfation.
This known technique takes account of reduction of performance
degradation of the lead-acid battery during discharging but does consider
removal of sulfation on the electrodes of the used lead-acid battery or
recovery of performances of the lead-acid battery. This known technique
also does not take account of shortening a period of time required for removal
of sulfation or reducing a temperature increase of a removal apparatus
during removal of sulfation.
There is accordingly a requirement to shorten a period of time
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required for removal of sulfation, while reducing heat regeneration during
removal of the sulfation in the lead-acid battery.
SUMMARY OF INVENTION
In order to achieve at least part of the above requirement, the
invention provides various aspects described below.
According to a first aspect, there is provided a desulfation device
applicable to a lead-acid battery. The desulfation device of the first aspect
includes: an electrode connector connected with an electrode of the lead-acid
battery; a drive signal generator configured to generate a pulse wave drive
signal by using electric current extracted from the electrode of the lead-acid
battery via the electrode connector; a resistor configured to regulate the
electric current extracted from the electrode of the lead-acid battery via the
electrode connector to electric current of not less than 300 mA; and a
switcher connected with the drive signal generator and with the resistor and
operated in response to the generated pulse wave drive signal to supply a
back electromotive force and a reverse current to the lead-acid battery in
synchronism with a falling edge of the pulse wave drive signal.
The desulfation device of the first aspect supplies a back
electromotive force and a reverse current to the lead-acid battery in
synchronism with a falling edge of the pulse wave drive signal, thus
shortening the period of time required for removal of sulfation.
In the desulfation device of the first aspect, the drive signal
generator may generate the pulse wave drive signal of a specific pulse width
that causes a temperature increase of the desulfation device to be equal to or
less than a predetermined temperature value. This aspect shortens the
period of time required for removal of sulfation, while reducing heat
generation during removal of sulfation in the lead-acid battery.
In the desulfation device of the first aspect, the drive signal
generator may generate the pulse wave drive signal of a pulse width that is
equal to or less than a pulse width Pwmax calculated by an equation given
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below when Tbase represents a known temperature increase corresponding
to a known pulse width Pwbase and Tmax represents an allowable
temperature increase.
Pw
max max rp
base
This aspect causes the temperature increase of the desulfation device to be
equal to or less than the allowable temperature increase.
In the desulfation device of the first aspect, the drive signal
generator may generate the pulse wave drive signal having a smaller pulse
width with an increase in output voltage of the lead-acid battery. This
aspect effectively reduces heat generation during removal of sulfation in the
lead-acid battery according to the output voltage of the lead-acid battery.
The desulfation device of the first aspect may further include a wave
shaper configured to generate a sawtooth wave drive signal from the pulse
wave drive signal generated by the drive signal generator. This aspect
improves the efficiency of removal of sulfation.
In the desulfation device of the first aspect, the drive signal
generator may generate the pulse wave drive signal having a frequency of
15000 Hz to 20000 Hz and a pulse width of 1 jiisec to 2 ^isec, and the resistor
may regulate the electric current extracted from the electrode of the
lead-acid battery to electric current of 300 to 500 mA. This aspect
effectively shortens the period of time required for removal of sulfation,
while reducing heat generation during removal of sulfation in the lead-acid
battery.
According to a second aspect, there is provided a desulfation method
for a lead-acid battery. The desulfation method of the second aspect
includes the steps of: generating a pulse wave drive signal by using electric
current extracted from an electrode of the lead-acid battery; regulating the
electric current extracted from the electrode of the lead-acid battery to
electric current of not less than 300 mA; and suppl5dng a back electromotive
force and a reverse current, which are attributed to the electric current of not
less than 300 mA, to the lead-acid battery in synchronism with a falling edge
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of the pulse wave drive signal, wherein the respective steps are performed
repeatedly
The desulfation method of the second aspect has the similar
functions and advantageous effects to those of the desulfation device of the
first aspect and may be implemented by any of various aspects as in the
desulfation device of the first aspect.
The desulfation method of the second aspect may be implemented in
the form of a sulfation removing program or in the form of a computer
readable medium in which the sulfation removing program is stored.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a block diagram illustrating the functional circuit structure
of a desulfation device according to one embodiment;
Fig. 2 illustrates an equivalent circuit to a waveform shaping circuit
provided in the desulfation device according to the embodiment;
Fig. 3 illustrates one example of a pulse wave drive signal generated
by a pulse generating circuit provided in the desulfation device according to
the embodiment;
Fig. 4 illustrates one example of a sawtooth wave drive signal
generated by the waveform shaping circuit provided in the desulfation device
according to the embodiment;
Fig. 5 illustrates one exemplary connection mode of the desulfation
device of the embodiment with a lead-acid battery;
Fig. 6 schematically illustrates a variation in electric current
between the desulfation device of the embodiment and the lead-acid battery;
Fig. 7 illustrates the results of a test with respect to the performance
recovery of the lead-acid battery by a desulfation device of a comparative
example;
Fig. 8 illustrates the results of a test with respect to the performance
recovery of the lead-acid battery by the desulfation device of the
embodiment;
Fig. 9 illustrates a temperature change during operation of the
desulfation device of the comparative example; and
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Fig. 10 illustrates a temperature change during operation of the
desulfation device of to the embodiment.
DESCRIPTION OF THE EMBODIMENTS
The following describes some embodiments of the desulfation device
and the desulfation method according to the invention with reference to the
accompanied drawings.
Fig. 1 is a block diagram illustrating the functional circuit structure
of a desulfation device (sulfation removal apparatus) according to one
embodiment. The desulfation device 10 of the embodiment includes a power
circuit 110, a pulse generating circuit 120, a waveform shaping circuit 130, a
switching circuit 140, a protective circuit 150, an indication Light 11, a
positive terminal Tl and a negative terminal T2. The positive terminal Tl
is connected with a positive electrode of a lead-acid battery (not shown).
The positive terminal Tl is also connected with the power circuit 110 via a
drive signal current line Ld arranged to supply the electric current extracted
from the positive electrode of the lead-acid battery, to the power circuit 110,
while being connected with the switching circuit 140 via a power current line
Lp arranged to supply the electric current extracted from the positive
electrode of the lead-acid battery, to the switching circuit 140. The drive
signal current line Ld is provided with a diode Dl serving to prevent the
reverse flow of electric current from the power circuit 110 to the positive
terminal Tl. The power current line Lp is provided with a diode D2 serving
to prevent the reverse flow of electric current from the switching circuit 140
to the positive terminal Tl and with a resistor Rl serving to regulate the
electric current that is to be supplied to the switching circuit 140, to a
predetermined value. The indication light 11 is lit on during power supply
(during operation) of the desulfation device 10. For example, a
light-emitting diode may be used for the indication light 11. The respective
circuits included in the desulfation device 10 of the embodiment may be
provided in the form of an integrated circuit or may alternatively be provided
in the form of discrete circuits.
The power circuit 110 is connected with the pulse generating circuit
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120 via a signal line, and the pulse generating circuit 120 is connected with
the waveform shaping circuit 130 via a signal line. The waveform shaping
circuit 130 is connected with the switching circuit 140 via a signal line, and
the switching circuit 140 is connected with the power current line Lp as
described above. The protective circuit 150 is connected to the waveform
shaping circuit 130. The negative terminal T2 is signal-grounded.
Although signal-grounding of only the switching circuit 140 is explicitly
illustrated in Fig. 1, the respective other circuits are similarly
signal-grounded.
The power circuit 110 is provided in the form of a DC-DC converter
serving to reduce the voltage level (12V to 48 V) supplied from the lead-acid
battery to lOV that is the voltage for drive signal (control circuit voltage).
The current for drive signal subjected to the voltage step-down by the power
circuit 110 is supphed to the pulse generating circuit 120. The pulse
generating circuit 120 is provided as a circuit serving to use the current for
drive signal supplied from the power circuit 110 and thereby generate a
pulse signal wave for driving the switching circuit 140. The pulse
generating circuit 120 internally has an oscillator and outputs a pulse wave
drive signal including a predetermined number of rectangular waves of a
specified pulse width corresponding to a predetermined frequency. In other
words, the pulse generating circuit 120 continually outputs a rectangular
wave signal of a specified pulse width at a predetermined cycle (l/frequency).
The pulse generating circuit 120 of this embodiment generates a
pulse wave drive signal of a specific pulse width that causes the temperature
increase of the desulfation device 10 to be equal to or less than a
predetermined temperature value. More specifically, the pulse generating
circuit 120 generates a pulse wave drive signal of a pulse width that is equal
to or less than a pulse width Pwmax calculated by an equation given below
when Tbase represents a known temperature increase corresponding to a
known pulse width Pwbase at the frequency of 15000 to 20000 Hz and Tmax
represents an allowable temperature increase:
Pw,
max max rp
base
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The pulse width of the generated pulse wave drive signal is
specifically 1 to 2 |isec and is more specifically about 1.4 to 1.7 ^isec. For
example, the maximum allowable pulse width is about 3.4 usee when the
known pulse width Pwbase is equal to 1.6, the known temperature increase
Tbase is equal to 28°C and the allowable temperature increase Tmax is equal
to 60°C.
The waveform shaping circvdt 130 shapes the pulse wave drive signal
generated by the pulse generating circuit 120 to a sawtooth waveform and
outputs as a sawtooth wave drive signal. Fig. 2 illustrates an equivalent
circuit to the waveform shaping circuit provided in the desulfation device
according to the embodiment. Fig. 3 illustrates one example of the pulse
wave drive signal generated by the pulse generating circuit provided in the
desulfation device according to the embodiment. Fig. 4 illustrates one
example of the sawtooth wave drive signal generated by the waveform
shaping circuit provided in the desulfation device according to the
embodiment.
The waveform shaping circuit 130 is a known circuit and includes, for
example, two resistors R21 and R22 connected in parallel to each other, a
capacitor CI connected in parallel to the resistor R22 and a diode D3
connected in series with the resistor R22. The waveform shaping circuit
130 enables the pulse waveform shown in Fig. 3 to be shaped to the sawtooth
waveform shown in Fig. 4, i.e., waveform having gentle rises and abrupt falls.
Such wave shaping allows a quick switching action of a circuit that is
actuated at a falUng edge as the trigger, for example, the switching circuit
140.
The switching circuit 140 is provided as a circuit switched on and off
in response to the shaped pulse wave drive signal. According to this
embodiment, the switching circuit 140 is switched on to allow extraction of
electric current from a battery via the power current line Lp, while being
switched off to stop the extraction of electric current from the battery. The
switching circuit 140 thus enables the pulse current to be flowed out of the
battery. For example, a field-effect transistor (FET) or another switching
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element may be adopted for the switching circuit 140.
The protective circuit 150 is provided as a circuit serving to protect
the resistor Rl from a potential failure^ such as burning-out, when the pulse
wave drive signal output from the waveform shaping circuit 130 is kept
continuously at a high level (i.e., signal level that provides instruction for
switch-on operation to the switching circuit 140). The protective circuit 150
may be implemented by a circuit using a Zener diode and a transistor as is
known to one skilled in the art.
The resistor Rl is used to regulate the value of the power current
that is to be supplied to the switching circuit 140. The resistance value is
selected according to the voltage of a battery BT as the processing object, in
order to regulate the power current to a current value of 300 to 500 mA.
The following description is on the assumption of using the electric current of
500 mA.
The following describes the operations of the desulfation device 10
according to the embodiment. Fig. 5 illustrates one exemplary connection
mode of the desulfation device of the embodiment with a lead-acid battery.
Fig. 6 schematically illustrates a variation in electric current between the
desulfation device of the embodiment and the lead-acid battery. The
desulfation device 10 is used in connection with a battery BT. More
specifically, a positive cable LI connected with the positive terminal Tl of the
desulfation device 10 is connected to a positive electrode T+ of the battery BT,
whereas a negative cable L2 connected with the negative terminal T2 is
connected to a negative electrode T- of the battery BT. The desulfation
device 10 operates with the electric current supplied from the battery BT.
In other words, the electric current extracted from the battery BT via the
positive terminal Tl is supplied to the respective circuits via the drive signal
current line Ld.
As described above, the desulfation device 10 is configured to extract
the electric current in the form of pulses from the battery BT in response to
the pulse wave drive signal. More specifically, the switching circuit 140 is
switched on in response to the pulse wave drive signal to allow the electric
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current regulated to 500 mAby the resistor Rl to flow from the switching
circuit 140 into the ground. The switching circuit 140 is switched off in
response to the pulse wave drive signal to stop the flow of the electric current
regulated to 500 mAinto the ground. This series of operations enable the
electric current in the form of pulses to be extracted from the battery BT.
When the desulfation device 10 (switching circuit 140) stops the extraction of
electric current at a falling edge of the pulse wave drive signal, there are a
back electromotive force and a reverse current, which are attributed to
inductance components including the positive cable LI, the negative cable L2
and the battery BT. The voltage and electric current in the form of spikes,
which are negative with respect to the desulfation device 10, are then
applied to the battery BT (on the assumption that the electric current
extracted from the battery BT is positive). For example, electric current in
the form of spikes as shown in Fig. 6 is apphed to the battery BT. According
to this embodiment, the pulse wave drive signal input into the switching
circuit 140 is shaped to have the sawtooth waveform by the waveform
shaping circuit 130. The switching circuit 140 thus relatively gently shifts
to the ON state when being switched on, but instantaneously shifting to the
OFF state when being switched off. As a result, the electric current and
voltage in the form of spikes having the high peak (large height) and the
small width are provided to the battery BT. The value of the reverse
current in the form of spikes supplied to the battery BT is, for example, 2 to 3
A and increases with an increase in service current (power current). The
current waveform shown in Fig. 6 is obtained by connecting a resistor to an
electrode of the battery BT in series and measuring voltage waveforms at
both ends of the resistor.
The electric current and voltage in the form of spikes acting on the
positive electrode and the negative electrode of the battery enable sulfation
or sulfate layers depositing on the positive electrode and the negative
electrode (lead sulfate layers in the lead-acid battery) to be molecularly
peeled off and separated from the respective electrodes and recovers the
charging area involved in charging out of sulfatexovered surface area of each
of the electrodes to its initial charging area. The molecular sulfate layer
separated into an electrolyte solution is decomposed during charging of the
lead-acid battery and is dissolved in the form of lead ion and sulfate ion into
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the electrolyte solution. Generation of H2O, which proceeds during
discharging of the lead-acid battery, stops during charging. As a result, the
specific gravity of the electrolyte in the battery BT, i.e., lead-acid battery, is
recovered to approach a favorable value of 1.280.
Results of Verification
The following describes results of various tests using the desulfation
device 10 according to the embodiment and a desulfation device according to
a comparative example.
Recovery of Battery Performances
Fig. 7 illustrates the results of a test with respect to the performance
recovery of the lead-acid battery by the desulfation device of the comparative
example. Fig. 8 illustrates the results of a test with respect to the
performance recovery of the lead-acid battery by the desulfation device of the
embodiment. The following conditions were adopted for the test:
Comparative Example^ pulse frequency: 20000 Hz, current value' 200
mA, battery: 48 volt battery manufactured by GS Yuasa Corporation
Embodiment: pulse frequency: 20000 Hz, current value: 500 mA,
battery: 48 volt battery manufactured by GS Yuasa Corporation
The results of this test prove the recovery of the specific gravity by
the desulfation device 10 of the embodiment and verify the mechanism of
removing and dissolving the sulfate layers by using the electric current in
the form of spikes as described above.
According to the comparative example shown in Fig. 7, the average
specific gravity of the electrolyte solution was 1.255 as its initial value and
was changed to 1.266 after a lapse of 34 days since the start of connection
and was further changed to 1.280 after a lapse of 87 days since the start of
connection. The favorable value of the specific gravity in the lead-acid
battery is generally thought to be about 1.28, which was achieved after the
lapse of 87 days. The improvement rate of the average specific gravity to
the initial value, i.e., the increase rate of the specific gravity, was 1.0087
after the lapse of 34 days and was 1.0199 after the lapse of 87 days. The
increase rate of the specific gravity accordingly remained at the value of
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1.0199 after a lapse of approximately three months. According to the
embodiment, on the other hand, the average specific gravity of the
electrolyte solution was 1.219 as its initial value and was changed to 1.268
after a lapse of 20 days since the start of connection. The improvement rate
of the average specific gravity to the initial value was 1.040 after the lapse of
20 days. The increase rate of the specific gravity accordingly achieved the
value of 1.040 after a lapse of only about half a month.
The primary difference between the embodiment and the
comparative example is the value of electric current. The desulfation device
10 of the embodiment using the larger current value can recover the
performances of the battery within a time period of about 1/3 - 1/4 of the
recovery time by the desulfation device of the comparative example. When
a long period of time, such as three to four months, is required to achieve the
sufficient improvement of the battery performances, it is rather difficult for
the user of the apparatus to effectively verify the improvement effect. The
desulfation device 10 of the embodiment, on the other hand, allows
verification of the improvement effect in a relatively shorter period of time,
such as about half a month to one month and can thus meet the demand of
the user of the apparatus.
These results of the test prove that the larger electric current applied
to the battery BT provides the better improvement effect. The simple
increase in value of electric current applied to the battery BT, however,
causes a problem of increasing the operating temperature of the desulfation
device (that may damage the circuit elements, such as resistor).
Temperature Change
Fig. 9 illustrates a temperature change during operation of the
desulfation device of the comparative example. Fig. 10 illustrates a
temperature change during operation of the desulfation device of the
embodiment. For the purpose of verification, the temperature of the casing
body of the desulfation device and the temperature of the resistor for
regulating the electric current were measured with an infrared thermometer.
Fig. 9 shows a temperature change of the comparative example obtained by
increasing the electric current supphed to the switching circuit of the
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desulfation device from 200 mA to 500 mA under the conditions of the pulse
frequency of 20000 Hz and the pulse width of 4 ^sec of the pulse wave drive
signal. The results of Fig. 9 show that the casing temperature increased
with an increase in value of electric current and that the casing temperature
reached 47°C and the temperature increase reached 19°C at 500 mA. The
temperature of the resistor as the heat source reached 114°C at 500 mA. In
an application of the desulfation device in connection with a battery located
in an engine room of an automobile, the operating environment temperature
is about 60 to 70°C, so that the temperature of the resistor significantly
exceeds 150°C. There is accordingly a high possibility that the resistor for
general purpose is damaged.
The desulfation device 10 of the embodiment is, on the other hand,
driven with the pulse wave drive signal having the pulse width of 1.6 |xsec
and the frequency of 20000 Hz, so as to eHminate this problem. Fig. 10
shows the results of verification with respect to the desulfation device 10
connected to a 36 volt battery and to a 48 volt battery and measured at 200
mA and 500 mA as the value of electric current supphed to the switching
circuit 140.
According to the comparison using the electric current of 200 mA, the
casing temperature was 31°C and 34°C and the temperature increase was
6°C and 8°C for the 36 volt battery and for the 48 volt battery, respectively.
According to the embodiment using the electric current of 500 mA, on the
other hand, the casing temperature was 32°C and 35°C and the temperature
increase was 5°C and 8°C for the 36 volt battery and for the 48 volt battery,
respectively. The temperature increase of this embodiment is accordingly
reduced to 8°C, compared with the temperature increase of 19°C in the
comparative example of Fig. 9. This level of temperature increase is
substantially equivalent to the temperature increase of the comparative
example using the electric current of 200 mA.
The pulse width of 1.6 |j,sec is selected only for the purpose of
reducing the temperature increase to a level equivalent to the conventional
temperature increase. The smaller pulse width should be selected, in order
to achieve a further reduction of the temperature increase. The larger pulse
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width may be selected, on the other hand, for a requirement that satisfies
the less reduction of the temperature increase. At the operating current
that is less than 500 mA, the resistor Rl has the less amount of heat
generation, so that the larger pulse width is allowable. At the operating
current that is not less than 500 mA, on the other hand, the resistor Rl has
the greater amount of heat generation, so that the smaller pulse width is
desirable. The amount of heat generation by the resistor Rl increases with
an increase in voltage of the battery BT,* so that the smaller pulse width may
be used with an increase in voltage of the battery BT.
As described above, the desulfation device 10 of the embodiment
increases the working current from the conventional level of 200 mA to 500
mA, so as to shorten the period of time required for recovery of the
performances of the battery BT to 1/3 - 1/4 of the conventionally required
recovery time. In other words, the desulfation device 10 of the embodiment
can remove the sulfate layers depositing on the electrodes of the battery BT
more effectively than the conventional desulfation device.
Increasing the working current to 500 mA causes a potential problem
of temperature increase of the desulfation device 10 (resistor Rl). Reducing
the pulse width of the pulse wave drive signal to 1.6 |isec that is about 1/2.5
of the conventional pulse width, however, advantageously reduces the
temperature increase of the desulfation device 10 at the working current of
500 mAto the level equivalent to the temperature increase at the working
current of 200 mA.
The desulfation device 10 of the embodiment can thus shorten the
period of time required for removal of sulfation, while reducing heat
generation during removal of sulfation.
Modifications
(l) The foregoing description of the embodiment includes verification
using the pulse wave drive signal having the frequency of 20000 Hz. The
frequency of the signal may, however, be less than 20000 Hz or greater than
20000 Hz.
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(2) The foregoing description of the embodiment includes verification
using the electric current of 500 mA. The value of electric current used may,
however, be in a range of 300 to 500 mA or may be greater than 500 mA.
[0048]
(3) According to the above embodiment, the pulse wave drive signal
generated by the pulse generating circuit 120 has a fixed pulse width. The
pulse width may, however, be variable among a plurality of different values
by switching operation. According to the above embodiment, the resistor Rl
has a fixed resistance value. The resistor Rl may, however, be a variable
resistor where the resistance value is variable among a plurahty of different
values by switching operations. In this modification, varying the resistance
value according to the voltage of the battery BT enables one desulfation
device 10 to be applicable to a plurality of different battery voltages. This
also enables the value of electric current to be adequately changed according
to the voltage of the battery BT and allows the user to determine and set
desired parameters suitable for the operating environment, thus improving
the convenience of the desulfation device 10.
The foregoing has described the invention with reference to the
embodiment and some modifications. The embodiment of the invention
described above is only for the purpose of facilitating the understanding of
the invention and is not intended to limit the invention at all. The
invention may be changed or modified without departing from the scope of
the invention and includes such modifications and equivalents.