JP3508254B2 - Rechargeable battery charger - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for secondary batteries such as nickel-cadmium batteries, nickel-hydrogen batteries and sealed lead-acid batteries.

[0002]

2. Description of the Related Art In recent years, with the development of portable equipment, the use of secondary batteries has been increasing as a power source for cassette tape recorders, VTRs, electronic equipment such as computers, communication equipment such as mobile phones, and power equipment such as electric tools. It has increased significantly. In charging these secondary batteries, 0.1 to 1.0
A method of charging with a constant current of about C is common. Since this charging method requires a long time for charging, recently, rapid charging with a constant current of 1.0 C or more is predominant. Therefore, in order to reduce gas generation due to charging even in quick charging and to improve charging efficiency, Japanese Patent Laid-Open No. 64-8 has been proposed.
As disclosed in Japanese Patent No. 1628, a charging method has been proposed in which charging is performed with a current having a pulse waveform.

[0003]

In the secondary battery, the electrodes are inactivated when left standing for a long time. The secondary battery that has been deactivated has a higher internal impedance than a normal one. Further, even when the ambient temperature is lower than the room temperature, the internal impedance of the battery becomes high. In addition, the battery at the end of its life has a high internal impedance even in a normal state where it is not left for a long time.
When a battery having a high internal impedance is attempted to be rapidly charged by the above-mentioned conventional charging device, the battery heats up and electric energy is converted into heat, resulting in a decrease in charging efficiency. Moreover, there is a risk that the internal pressure of the battery rises and the liquid leaks. A first object of the present invention is to provide a charging device that can charge a battery as quickly as possible without causing the battery to generate a dangerous state during a charging operation regardless of the internal impedance of the battery. . The second object of the present invention is to provide the above-mentioned first object.
It is an object of the present invention to provide a charging device capable of notifying a user that a battery is at the end of its life, in the charging device that has achieved the above object.

[0004]

In order to achieve the above first object, a charging device according to the present invention comprises a pulse charging means for charging a secondary battery with a current having a pulse waveform and a current during a pulse charging operation. battery voltage V _on the supply interval, and means for detecting a battery voltage V _off of the current blocking section, V _on,
V _off , a means for calculating the internal impedance Z of the secondary battery by the current value I at the time of current supply during pulse charging operation,
And a means for increasing at least one of I and the current supply section t ₁ in response to the decrease of Z.
In order to achieve the above-mentioned second object, the charging device in the present invention is characterized by including means for displaying a relative value of the impedance Z on a display unit.

[0005]

First, the operation of the invention corresponding to claim 1 will be described. The charging device according to the present invention charges the secondary battery with a current having a pulse waveform. Therefore, even in rapid charging, gas generation due to charging is reduced, and charging efficiency is good. During pulse charging, the battery voltage V _on in the current supply section,
Also, the internal impedance Z of the secondary battery is calculated from the battery voltage V _{off in the} current interruption section and the current value I when the current is supplied during the pulse charging operation. The internal impedance Z is obtained by the following equation (1).

Z = (V _on -V _off ) / I (1) When Z is larger than a predetermined value, I is set to a low value, or
The current supply time in the pulse waveform is set to a small value without changing I. Alternatively, by using both means, the battery can be charged while suppressing the temperature rise. Further, even when Z is larger than the predetermined value, Z is gradually lowered during the charging operation by gently charging the initial stage of charging by the above means. Therefore, I is gradually increased during the charging operation so that the temperature of the battery does not rise to a dangerous state, or the current supply time in the pulse waveform is increased without changing I. Alternatively, both means are used. As a result, the temperature rise of the battery can be suppressed and the battery can be charged as quickly as possible.

Next, taking an AA type nickel-hydrogen battery for explaining the operation of the invention corresponding to claim 2, as an example, the internal impedance is about 20 to 40 mΩ in a normal state, but 100 mΩ at the end of life. Over. Therefore,
The measured internal impedance Z of the battery is, for example, 40 m
When less than Ω, 3 LEDs of charging device, 40-100m
Two LEDs when less than Ω, LE when more than 100 mΩ
A means for lighting one D on the display unit of the charging device is provided.
When a battery having a high internal impedance at the end of its life is charged, the internal impedance does not decrease even if charging proceeds. Therefore, only one LED is lit at any time during charging. By doing so, the user can be made aware of the battery life period. As described above, the battery with increased internal impedance due to long-term storage will have a decrease in internal impedance as charging progresses, and the number of LEDs that light up during charging will increase. Can be distinguished.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An outline of a charging device of this embodiment will be described below with reference to the drawings.

FIG. 2 is a block diagram showing a schematic configuration of a charging device according to an embodiment of the present invention. The charging current having the pulse waveform shown in FIG. 3 is supplied from the DC power supply device 1 to the secondary battery 5 via the switch circuit 2 for turning the charging current on and off. In this embodiment, the current supply section t ₁ shown in FIG.
Was set to 8 msec, and the current interruption section t ₂ was set to 2 msec. The control circuit 3 that controls ON and OFF of the switch circuit 2 is
It receives the output signal from the microcomputer 4.
The microcomputer 4 has a CPU (central processing unit) 41, a memory 42, an output port 43, an A / D converter (analog / digital converter) 44 for an input port, and the like built therein. The measured voltage signal of the secondary battery is input to the A / D converter 44. This input is processed by the CPU 41 and the memory 42, and an output signal is output from the output port 43 to the control circuit 3. The display unit 6 displays the start of charging, the end of charging, and the state of the secondary battery 5 with LEDs. FIG. 4 is a partial detailed view of the DC power supply device 1 of FIG. In the DC power supply device 1, a power supply 8, resistors 9 _{a to} 9 _d , and FET (field effect transistor) 10 are arranged. The FET 10 is operated by the signal from the output port 43 of the microcomputer,
The current value is changed by passing the current from the power source 8 through the resistors 9 _{a to} 9 _d . The pulse current was supplied to the secondary battery 5 by turning on and off the generated current in the switch circuit 2 by the control circuit 3. In this embodiment, a constant voltage DC power supply of 15V is used as the power supply 8 in FIG. The resistance values of the resistors 9 _{a to} 9 _d are 9 _a = 10Ω, 9 _b = 12Ω, and 9 _c.
= 15Ω and 9 _d = 25Ω. The charging current value output from the DC power supply device 1 was set to 1.25 A through the resistor 9 _b from immediately after the start of charging until the first charging current was determined. After the charging current is determined, when the internal impedance of the battery 5 is less than 40 mΩ, the resistance is passed through the resistor 9 _a ,
When a current of 1.50 A is supplied to the battery 5 and the internal impedance of the battery 5 is 40 mΩ to less than 60 mΩ, the resistance is 9 _c.
A current of 1.00 A is supplied to the battery 5 via the resistor, and when the internal impedance of the battery 5 is less than 60 mΩ to 100 mΩ, a current of 0.60 A is supplied to the battery 5 via the resistor 9 _d. When the internal impedance of the battery was 100 mΩ or more, a current of 0.30 A was supplied to the battery 5 through the resistors 9 _a , 9 _c and 9 _d . The obtained current value is output in one cycle (10 msec) of the pulse waveform when the charging period t ₁ in the pulse waveform in FIG. 3 is 8 msec and the rest period t ₂ is 2 msec as in the present embodiment. The calculated current was calculated as a value (hereinafter, referred to as an effective value) averaged by the following equation (2), and the relation between the internal impedance and the current value was controlled as shown in FIG.

[0010]

[Equation 1]

In other words, when a single cell is used as the battery 5, the value is 1.0 from immediately after the start of charging until the first charging current is determined.
0 A, after the charging current is determined, 1.20 A when the internal impedance of the battery 5 is less than 40 mΩ, 0.80 A when the internal impedance of the battery 5 is less than 40 mΩ to 60 mΩ, the battery 5 Internal impedance is 60mΩ ~
A current of 0.48 A was supplied to the battery 5 when it was less than 100 mΩ, and a current of 0.24 A was supplied when the internal impedance of the battery 5 was 100 mΩ or more.

Embodiment 1 (corresponding to claim 1) FIG. 1 is a flowchart showing a charge control algorithm according to an embodiment of the present invention. When a secondary battery for charging is connected to the charging device and charging is started, the microcomputer reads and stores the battery voltage V _off before the charging current is supplied by the voltage measuring unit. Next, the switch circuit is turned on to supply a charging current of a predetermined value to the secondary battery. Then, the switch circuit is in the ON state, that is, the battery voltage V _on when the pulse waveform current is supplied is read. Next, the microcomputer turns V _off ,
Internal impedance Z of the secondary battery from V _on and charging current I
Is calculated. The internal impedance is obtained by the above-mentioned formula (2). The current value to be charged is determined by the obtained internal impedance of the secondary battery. In this embodiment,
The measurement of V _off and V _on in FIG. 1 was performed once in every 20 cycles of the flowchart, and the rest was passed through. V _off , V in one cycle of the waveform passing during measurement
_{The on} was measured four times, and the average value of the four times was used as the measured value to perform impedance calculation. At this time, if the obtained internal impedance is large, the charging current is reduced, and conversely, if the impedance is small, the charging current is greatly changed. FIG. 5 shows an example of the relationship between the impedance and the charging current when determining the current value. Normal AA type nickel
The internal impedance of the hydrogen battery is about 20-40 mΩ. In this embodiment, 1100 mAh of AA type nickel.
Using a battery pack in which five hydrogen batteries are connected in series, the charging current is 1.2 A (effective value) when the internal impedance is less than 200 mΩ, and 0.8 A (effective value) when the internal impedance is less than 200 to 300 mΩ, When it was less than 300 to 500 mΩ, it was 0.48 A (effective value), and when it was 500 mΩ or more, it was 0.24 A (effective value). The charging current at the start of charging was set to 1.0 A (effective value). Hereinafter, all the current values shown in the description of this embodiment are effective values. Next, it is determined whether charging is completed. In this embodiment, a sealed nickel-hydrogen battery is used as the secondary battery to be charged, and it is detected that the battery voltage change amount appearing at the end of charging shifts from a positive value to a negative value and then a predetermined value of the battery voltage decreases. The completion of charging was detected by the so-called -ΔV method. That is, the maximum battery voltage value of the detected V _off is loaded into the memory,
The voltage drop from there -ΔV was detected and controlled. If charging is complete, stop charging. If charging is not completed, the switch circuit is turned _off and the process returns to the measurement of the battery voltage V _off when the current is cut off in the pulse waveform. The operation of loading the maximum battery voltage value of V _off into the memory was started after the initial current value was determined. The method of determining whether or not the charging is completed is different depending on the type of battery and whether the battery is a sealed type or an open type. Therefore, a method suitable for the battery to be used is used. For example, in the case of a sealed nickel-cadmium battery, the method may be the same as in the present embodiment, and in the case of a sealed lead-acid battery, a method may be used in which it is detected that the battery voltage hardly changes at the end of charging.

(Embodiment 1a) FIG. 6 shows an internal impedance of 250 m when left for a long time using the above-mentioned charging device.
Ambient temperature of 20 using a battery pack in which 5 AA type nickel-hydrogen batteries of 1100 mAh that have become Ω are connected in series.
The changes over time in the battery voltage V, the charging current I, the battery temperature increase amount T, and the internal impedance Z (hereinafter referred to as charging characteristics) when charged at 0 ° C. are shown. Charging current I at the start of charging
Is 1.0 A, it is detected that the calculated internal impedance Z is 250 mΩ, and the charging current I is 0.8 A.
Go down to. The internal impedance Z is decreasing as the charging progresses, and 200 mΩ 10 minutes after the start of charging.
And the charging current I has risen to 1.2A. The battery temperature increase amount T was almost 0 at the beginning of charging and increased by about 20 ° C. at the end of charging.

(Comparative Example 1a) FIG. 7 shows the charging characteristics when charged under the same conditions as in Example 1a except that the charging current value I was not changed by the value of the internal impedance and pulse charging was performed at 1.2A. The battery temperature increase amount T increased from the beginning of charging and exceeded 30 ° C. at the end of charging.

(Embodiment 1b) FIG. 8 shows the charging characteristics when a battery pack in which five AA type nickel metal hydride batteries of 1100 mAh at an ambient temperature of 0 ° C. are connected in series using the battery charger of this embodiment. Show. At the start of charging, the internal impedance Z of the battery exceeds 200 mΩ, and the charging current I drops from 1.0 A to 0.8 A. Even if charging proceeds, the internal impedance Z is not significantly reduced because of the low temperature environment, but it becomes less than 200 mΩ 30 minutes after the start of charging, and the charging current rises to 1.2 A. The battery temperature rise amount T hardly increased, and was 20 ° C. or lower even at the end of charging.

(Comparative Example 1b) FIG. 9 shows the charging characteristics when charging was performed under the same conditions as in Example 1b except that pulse charging was performed at 1.2 A without changing the charging current value I depending on the internal impedance value. The battery temperature increase amount T increased from the beginning of charging and exceeded 30 ° C. at the end of charging.

(Embodiment 1c) FIG. 10 shows a battery pack in which five 1100 mAh AA nickel-metal hydride batteries having high internal impedance at the end of life are connected in series at an ambient temperature of 20 ° C. by the charging device according to the present invention. The charging characteristics at the time of performing are shown. Internal impedance at the start of charging is 400
Since it is mΩ or more, the charging current is 0.48 A, which suppresses heat generation due to charging.

(Comparative Example 1c) FIG. 11 shows the charging characteristics when the same battery as in Example 1c was pulse-charged at 1.2 A without changing the charging current. Since the battery having a high internal impedance is charged with a large charging current, the temperature rises significantly, and the temperature rises nearly twice as much as in Example 1c. Therefore, the charging efficiency was poor due to the heat generation, and at the end of the charging, the internal pressure of the battery increased and the electrolyte leaked.

In the examples described above, the time required for charging was comparable to that of the comparative examples, and charging could be performed while suppressing an increase in battery temperature. Further, in this embodiment, the current value was changed according to the impedance value, but the same effect was obtained even if the time of the charging section of the pulse waveform was changed.

Embodiment 2 (corresponding to claim 2) FIG. 12 is a flowchart showing a charge control algorithm according to an embodiment of the present invention. The means described in a) to c) below is added to the flowchart of FIG.

A) When charging is started, R (red)
Turn on the LED.

B) A plurality of (three) regions are set for the impedance value, it is judged which region the calculated impedance value is in, and the result is LE.
Display D. In this embodiment, the impedance is 200 mΩ
LED in Y (yellow) when the area is below
3 lights, 2 lights in the region of 200 mΩ or more and less than 500 mΩ, and 1 light in the region of 100 mΩ or more.

C) When charging is completed, the G (green) LED is turned on. By adding the above means and displaying the above information on the display unit 12 of the charging device 11 shown in FIG. 13, the user can know that charging has started and charging has ended. Furthermore, since the internal impedance of the battery increases as it approaches the end of its life, Y (yes
The life time of the battery can be grasped from the number of lit LEDs. If the internal impedance of the battery is high due to being left for a long time before charging, etc., since one or two Y (yellow) LEDs were lit at the beginning of charging, the internal impedance decreased as the charging progressed. Y (y
Since the number of lit LEDs is increased, it can be distinguished from the end of life.

In this embodiment, a Y (yellow) LED is used.
Although the number of 3 is three, it can be easily increased by subdividing the determination of the impedance value. Naturally, it is easy to reduce the number to two. Further, the impedance value used when determining the impedance value is not limited to the above value.

[0025]

By using the charging device according to the present invention as set forth in claim 1, it is possible to suppress the rise in battery temperature while charging the secondary battery having a high internal impedance as quickly as possible. Further, by using the charging device according to the second aspect of the present invention, the user can grasp the life time of the battery.

[Brief description of drawings]

FIG. 1 is a flowchart showing a charge control algorithm according to an embodiment of the present invention.

FIG. 2 is a block diagram according to the charging device of the present invention.

FIG. 3 is a diagram showing a current waveform and a battery voltage measurement timing according to the present invention.

FIG. 4 is a partial detailed view of the charging device of the present invention.

FIG. 5 is a diagram showing an example of the relationship between impedance and charging current that can be placed in the device of the present invention.

FIG. 6 is a diagram showing charging characteristics of an example according to the present invention.

FIG. 7 is a diagram showing charging characteristics of a comparative example.

FIG. 8 is a diagram showing charging characteristics of an example according to the present invention.

FIG. 9 is a diagram showing charging characteristics of a comparative example.

FIG. 10 is a diagram showing charging characteristics of an example according to the present invention.

FIG. 11 is a diagram showing charging characteristics of a comparative example.

FIG. 12 is a flowchart showing a charge control algorithm according to an embodiment of the present invention.

FIG. 13 is a diagram showing a schematic external view of a charging device according to an embodiment of the present invention.

[Explanation of symbols]

1 ... DC power supply device, 2 ... switch circuit, 3 ... control circuit,
4 ... Microcomputer, 41 ... CPU, 42 ... Memory, 43 ... Output port, 44 ... A / D converter, 5 ... Secondary battery, 6 ... Display unit, 7 ... Battery voltage measuring unit, 8 ... Power supply, 9
... resistor, 10 ... FET, 11 ... charging device, 12 ... LED

Continuation of the front page (56) Reference JP-A-64-81628 (JP, A) JP-A-61-262032 (JP, A) JP-A-58-139080 (JP, A) JP-A-8-182215 (JP , A) JP-A-8-149709 (JP, A) JP-A-5-292675 (JP, A) JP-A-4-125034 (JP, A) JP-A-2-262855 (JP, A) 3-500959 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02J 7/04 H02J 7/10

Claims (2)

(57) [Claims] 1. A pulse charging means for charging a secondary battery with a current having a pulse waveform, a battery voltage Von in a current supply section t1 during a pulse charging operation,
And means for detecting the battery voltage Voff in the current cutoff section t2, and Von, Voff, and the current value I at the time of current supply during the pulse charging operation, the internal impedance Z of the secondary battery is expressed by Z
= (Von-Voff) / I, and when the internal impedance Z is larger than a predetermined value,
At least one of the current value I and the current supply section t1
And the internal impedance Z is smaller than a predetermined value.
In the other case, the rechargeable battery charging device is provided with means for increasing at least one of the current value I and the current supply section t1. 2. The internal impedance Z at the initial stage of charging is
The current value I and the current supply section t1 are larger than a fixed value.
Even if at least one of the
If the impedance Z does not decrease, the secondary battery has reached the end of its life.
It is characterized by having means for displaying that the period is
The rechargeable battery charging device according to claim 1.