JPH07270504A - Battery life judging device - Google Patents

Abstract

PURPOSE:To surely judge the life of a battery by detecting a battery voltage after initial charging with a specific current for a specific time and judging that the battery life is exceeded when the detection voltage is equal to or more than a specific life judging voltage value. CONSTITUTION:A set of batteries 2 where a plurality of chargeable element batteries are connected in series incorporate a battery temperature detection means 2A consisting of, for example, a thermistor, and the means 2A detects a battery temperature coming into contact with or closer to the element battery. Also, a current detection means 3 detects charge current flowing to the set of batteries 2. Then, the temperature of the set of batteries 2 when starting changing is detected and charge current Ialpha and Ibeta charge time talpha and tbeta are properly set according to the detection temperature for initial charging. By detecting whether the battery voltage after initial charging is equal to or more than life judging reference voltages Vralpha and Vrbeta with a battery voltage detection means 40, a microcomputer 50 discriminates whether the set of batteries 2 are the set of normal batteries or the set of batteries whose life has expired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a life determining device for a secondary battery such as a nickel-cadmium battery (hereinafter referred to as a nicad battery).

[0002]

2. Description of the Related Art Generally, a rechargeable battery is used as a power source for a portable device, and is removed from the device every time the battery capacity runs out, charged by a charging device, and then mounted on the device again for use. It can be used repeatedly and many times. However, these batteries deteriorate as compared with the initial characteristics as shown in FIG. 3 as they are repeatedly charged and discharged, and there is a limit to the number of times that they can be repeatedly used and charged. Conventionally, such a judgment of battery life has been made individually by the user of the device based on experience and the like.

As for the life of the battery, a mode in which the internal impedance increases due to the leakage of the electrolytic solution from the inside of the battery and the capacity decreases as shown in FIG. 3, and the deterioration of the organic material such as the separator inside the battery and the electrode plate. There is an internal short circuit caused by a decrease in strength, but especially in a battery group in which a plurality of unit cells are connected in series, the unit cells with the smallest capacity in the assembled battery are overcharged due to the capacity variation of each unit cell, Over-discharged,
In most cases, the former mode will last the life.

[0004]

However, when the battery life is judged based on the experience of the user, when the user notices the decrease in the capacity, the single cell in the battery set is continuously overcharged and overdischarged. During the charging, there is a problem that the electrolytic solution in the battery is discharged into the charging device, corrodes electronic parts and the like, and causes the failure of the charging device. In addition, a device such as an electric tool that is used under a high load consumes a lot of battery and needs to know when to replace the battery, but this cannot be fully satisfied. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to reliably determine the life of the battery. Another object of the present invention is to make it possible to reliably determine the battery life according to the battery temperature and the number of unit cells.

[0005]

In order to achieve the above object, in the battery life discriminating apparatus of the present invention, a battery whose life has begun to decrease has a sudden voltage at the initial stage of charging as shown in FIG. Focusing on the rise, the battery voltage after initial charging at a predetermined current and a predetermined time is detected, and when the detected voltage value is equal to or higher than a predetermined life determination voltage value, the battery life is determined or charging is performed at a predetermined current. The maximum battery voltage value at that time is detected and stored, and when the detected and stored maximum battery voltage value is equal to or higher than a predetermined life voltage value, the battery life is determined.
Further, by changing the current and time at the time of the initial charging according to the battery temperature, it becomes possible to accurately determine the life. Further, by changing the predetermined voltage value for the life judgment according to the number of unit cells in the battery group, it becomes possible to judge the life of a plurality of battery groups.

[0006]

In the battery life determining device, the battery life is determined based on whether or not the battery voltage at the initial stage of charging is equal to or higher than the predetermined life determining voltage value.

[0007]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a battery set in which a plurality of rechargeable unit cells are connected in series, and a battery temperature detecting means, such as a thermistor, for detecting the battery temperature in contact with or in proximity to the unit cells Built-in 2A.
3 is a current detecting means for detecting a charging current flowing in the battery set 2, 4 is a charging control signal transmitting means for transmitting a signal for controlling the start and stop of charging, and 5 is a charging for feeding back the signal of the charging current to the PWM control IC 23. It is a current signal transmission means. The charging control transmission signal means 4 and the charging current signal transmission means 5 are composed of, for example, a photo coupler or the like. 10 is a full-wave rectifier circuit 1
A rectifying and smoothing circuit composed of 1 and a smoothing capacitor 12,
Is a switching circuit including a high frequency transformer 21, a MOSFET 22, and a PWM control IC 23. The PWM control IC 23 is a switching power supply IC that changes the drive pulse width of the MOSFET 22 to adjust the output voltage of the rectifying and smoothing circuit 10. Reference numeral 30 is a rectifying / smoothing circuit including diodes 31, 32, choke coil 33, and smoothing capacitor 34, and 40 is a battery voltage detecting means including resistors 41 and 42, which divides the terminal voltage of the battery set 2. Reference numeral 50 denotes an arithmetic means (CPU) 51, a ROM 52, a RAM 53, a timer 5
4, an A / D converter 55, an output port 56, and a reset input port 57. The RAM 53 includes a battery voltage storage unit 531 and a battery temperature storage unit 532 that store the sampled battery voltage and battery temperature, respectively. Reference numeral 60 is an operational amplifier 61, 62 and resistors 63 to 6
6, charging current control means 70, power transformer 7
1, a full-wave rectifier circuit 72, a smoothing capacitor 73, a three-terminal regulator 74, a reset IC 75, which is a constant voltage power source, and serves as a power source for the microcomputer 50, the charging current control means 60, and the like. The reset IC 75 outputs a reset signal to the reset input port 57 in order to initialize the microcomputer 50. Reference numeral 80 denotes a battery life display unit that includes an LED 81 and a resistor 82 and that displays the life of the battery group 2. Reference numeral 90 denotes a charging current setting means 90 for setting a charging current, and a charging current setting reference voltage value applied to the inverting input terminal of the operational amplifier 62 corresponding to a signal from the output port 56, that is, a charging current value to flow. Is what changes.

Before describing the discrimination operation of the present invention, the battery voltage characteristics during charging of a normal battery group 2 (hereinafter referred to as a normal battery group) and a battery group 2 having a limited life (hereinafter referred to as a life battery group) will be described. .

FIG. 4 shows the battery voltage when the battery pack 2 with a life is charged with the charging current Iα, and shows that the battery voltage has risen above the life judgment reference voltage Vrα at the beginning of charging. Figure 5
Indicates the battery voltage when the normal battery group 2 having a low temperature is charged with the charging current Iα, and indicates that the battery voltage is equal to or higher than the life determination reference voltage Vrα at the initial stage of charging. FIG. 6 shows the charging current Iβ (Iα> I) when the temperature of the normal battery group 2 is low and the temperature is low.
It shows the battery voltage at the time of charging in β) and shows that the battery voltage is not higher than the life determination reference voltage Vrβ at the initial stage of charging. FIG. 7 shows the battery voltage when the normal battery set 2 which has been left for a long period of time but has a low temperature is charged with the charging current Iα,
Although the voltage rise occurs at the initial stage of charging, it is smaller than the voltage rise of the battery pack 2 with a limited life. FIG. 8 shows the battery voltage when the battery pack 2 whose life is not low is charged with the charging current Iα, and shows that the battery voltage rises above the life determination reference voltage Vrα at the initial stage of charging. FIG. 9 shows the battery voltage when the battery pack 2 having a low temperature is charged with the charging current Iβ at a low temperature, and shows that the battery voltage rises above the life determination reference voltage Vrβ at a low temperature at the initial stage of charging. . FIG. 10 shows the battery voltage when the normal battery set 2 whose temperature is not low is charged with the charging current Iα, and shows that the battery voltage has not risen to the life determination reference voltage Vrα or more in the initial stage of charging. As described above, the temperature of the battery group 2 at the start of charging is detected,
The charging currents Iα, Iβ and the charging times tα, tβ are appropriately set according to the detected temperature to perform the initial charging, and it is detected whether the battery voltage after the initial charging is equal to or higher than the life determination reference voltages Vrα, Vrβ. By doing so, it becomes possible to determine whether the battery group 2 is a normal battery group or a life battery group. The life determination will be described below with reference to the flowcharts of FIGS. 1 and 2.

When the power is turned on, the microcomputer 50 enters a standby state for connecting the battery group 2 (step 101). Battery set 2
, The microcomputer 50 discriminates the connection of the battery group 2 from the signal of the battery voltage detecting means 40, and the temperature of the battery group 2, that is, the output signal of the battery temperature detecting means 2A is A / D converted by the A / D converter 55. The battery temperature Tin before the start of charging is fetched (step 102), and the battery temperature Tin before the start of charging
The battery low temperature discrimination reference temperature Tref is subtracted from this to determine whether it is positive or negative (step 103).

If positive, it is determined that the battery temperature is not low, and the charging current setting reference voltage V corresponding to the charging current Iα is set.
α, the life determination reference voltage Vrα (Vrα corresponds to the charging current Iα, Vrα increases when the charging current is set large, and Vrα decreases when the charging current is set small), and the initial charging time tα is set (step 104). ), PWM control I from the output port 56 via the charge control signal transmission means 4
The charge start signal is transmitted to C23, and charging is started with the charge current Iα (step 105). At the same time as charging is started, the charging current flowing through the battery set 2 is detected by the current detecting means 3, and the difference between the voltage corresponding to the detected charging current and the reference voltage Vα from the charging current setting means 90 corresponding to the output of the output port 56 is calculated. From the charging current control means 60 via the signal transmission means 5,
Feedback is applied to the PWM control IC 23. That is, when the charging current is large, the pulse width is narrowed, and in the opposite case, the pulse whose pulse width is widened is given to the high frequency transformer 21 to be smoothed into a direct current by the rectifying / smoothing circuit 30 to keep the charging current constant. That is, the current detection unit 3, the charging current control unit 60, the charging current signal transmission unit 5, the switching circuit 20, the rectifying / smoothing circuit 3
The charging current is controlled to reach the predetermined current value Iα via 0.

Next, battery life determination is performed. Initially set the initial charging maximum battery voltage value Vm to 0 (step 10
6) Then, the latest battery voltage value Vx is input from the start of the initial charging (step 107), the battery voltage value Vx is stored in the battery voltage storage means 531, and the latest battery voltage value Vx and the battery voltage storage means 531 are stored. The comparison calculation is performed with the initial charging maximum voltage value Vm stored in the memory until the previous input (step 10).
8). If positive in step 108, the Vx value is Vm
As a result, the initial charging maximum voltage value of the battery voltage storage means 531 is rewritten (step 109), and it is checked whether or not the initial charging time tα has elapsed (step 110).
If the time has not elapsed, the processes of step 107 to step 110 are performed again. If the result is negative in step 108, the process of step 109 is not performed and the process jumps to step 110. When the time tα has elapsed in step 110, the difference between the initial charging maximum battery voltage value Vm and the life determination reference voltage Vrα is compared and calculated (step 111). If the difference is positive, it is determined that the charged battery group 2 is the battery life. Then, the microcomputer 50 generates an output of the battery life from the output port 56 and causes the LED 81 of the battery life display means 80 to emit light (step 113), and the charge stop signal is PWMed from the output port 56 via the charge control signal transmission means 4. It is transmitted to the control IC 23 and charging is stopped (step 114). Next, battery group 2
Is taken out (step 115), and if it is decided that the battery set 2 is taken out, the process returns to step 101 and stands by for charging the next battery set 2A.

When the result is negative in step 111, the battery set 2 is determined to be a battery set 2 that can be used normally, and the full charge detection process is subsequently performed. Although there are various detection methods for full charge detection as well known, for example, the battery set 2 is detected by detecting that a predetermined amount ΔV has fallen from the known peak voltage value at the end of charging and then stopping charging −ΔV detection. -ΔV is detected (step 112), and when it is determined that the battery is fully charged, the microcomputer 5
0 transmits a charge stop signal to the PWM control IC 23 to stop charging (step 114), then determines that the battery set 2 is taken out (step 115), and returns to step 101 when it is determined that the battery set 2 is taken out. , Next battery group 2
Wait for charging. When the result in step 112 is negative, the process returns to step 112 again.

If the result of step 103 is negative, it is determined that the battery temperature is low, and the charging current Iβ (Iα> I)
charging current setting reference value Vβ (Vα> V) corresponding to β)
β), the life determination reference voltage Vrβ (Vrβ also corresponds to the charging current Iβ similarly to Vrα, and the magnitude difference from Vrα depends on the values of the charging currents Iα and Iβ) and the initial charging time t.
β (tβ ≧ tα) is set (step 116), and thereafter, the same initial charging, battery life determination and full charge determination as in steps 105 to 112 are performed in steps 116 to 124 to determine the battery set 2 lifetime. In step 113, the LED 81 is caused to emit light, and when the battery set 2 is normal and full charge is detected, charging is stopped in step 114.

In the above embodiment, it is determined whether or not the battery temperature Tin at the start of charging the battery set 2 is lower than the reference temperature Tref to determine whether or not the battery is a low temperature battery, and the detected temperature is dealt with. The judgment reference voltages Vrα, Vrβ and the battery voltage are detected to judge whether or not the battery pack has a life. However, the reference temperature is subdivided, and the judgment reference voltage is subdivided corresponding to the subdivided reference temperature. May be.

The battery set 2 is a battery set 2 having the same number of unit cells.
However, the number of unit cells may be detected and the determination reference voltages Vrα and Vrβ corresponding to the detected number of unit cells may be used. That is, as disclosed in Japanese Patent Application No. Hei 5-93081 “Charge control method for battery charger” previously filed by the present applicant, the battery voltage is detected after charging for a predetermined time with a small current at the initial stage of charging, and the unit cell is detected. The number may be detected and the determination reference voltages Vrα and Vrβ corresponding to the detected number of unit cells may be used.

As a matter of course, in the above embodiment, the discrimination reference voltages Vrα and Vrβ are the charging currents Iα and
Depending on Iβ, if the charging currents Iα and Iβ are set to be large, the discrimination reference voltages Vrα and Vrβ are also set to be large, and if they are set to be small, they are set to be small. That is, the discrimination reference voltages Vrα and Vrβ change according to the charging currents Iα and Iβ and the battery temperature.

Also, there are various types of unit cells that make up the battery group 2, and there are 5 types from the standard type that is charged with a current of 1 C or less.
There are various types and types of rapid charging that can be charged up to about C, and the charging currents Iα and Iβ are set according to the types of these unit cells in the above embodiment.

Table 1 shows an example of the discrimination reference voltage corresponding to the battery temperature, the number of unit cells and the charging current. In addition, assuming that the battery set 2 is composed of a quick charging type unit battery (1700 mAh), the nominal voltage of one unit battery is 1.2 V, and the battery set 2 is 7.2 V (6 unit batteries). ),
There are four types, 9.6V (8 unit cells), 12V (10 unit cells), and 24V (20 unit cells), and the charging current Iα is 4C.

[0020]

[Table 1]

Further, the battery low temperature discrimination reference value Tref is set to 0 ° C.,
Table 2 shows an example of the determination reference voltage corresponding to the number of unit cells when the charging current Iα is 3C and Iβ is 1C. Similar to Table 1, the battery set 2 is a quick charging type unit cell (1700 m
Ah).

[0022]

[Table 2]

FIG. 11 is a flow chart showing another embodiment of the present invention. In this embodiment, whether or not the battery set 2 has reached the end of life is detected by detecting whether or not the maximum value of the battery voltage that rises with charging is equal to or higher than a predetermined life determination voltage. In FIG. 11, the same or almost the same steps as those in the flowchart of FIG. 2 have the same step numbers. That is, steps 108 and 12 as in FIG.
At 0, the maximum value Vm of the battery voltage is detected, and steps 111 and 123 detect whether or not the maximum battery voltage value Vm is larger than the life determination voltage values Vrα and Vrβ, and if so, the LED 81 is turned on at step 113. In step 114, charging is stopped. Steps 201 and 202
Is a step of detecting full charge. For example, as in Japanese Patent Application No. 4-156676 filed by the applicant of the present application, it is detected that the second-order differential value of the battery voltage is equal to or lower than a predetermined value, and the full charge is detected. This is a step of detecting by the Δ ² V detection method.
According to this embodiment, it is possible to obtain the effect of being able to quickly detect the battery pack 2 having a limited life.

[0024]

As described above, according to the present invention, it is possible to reliably detect the life of the battery regardless of the battery temperature, the charging current, and the number of unit cells.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a charging device of the present invention.

FIG. 2 is a flowchart showing an embodiment of the present invention.

FIG. 3 is a graph showing cycle life characteristics of a battery.

FIG. 4 is a graph showing charge characteristics when a battery having a limited life is charged.

FIG. 5 is a graph showing charging characteristics when a normal battery having a low battery temperature is charged with a normal charging current.

FIG. 6 is a graph showing charge characteristics when a normal battery is charged at a low battery temperature.

FIG. 7 is a graph showing charge characteristics when a battery left for a long time is charged.

FIG. 8 is a graph showing charge characteristics when a battery whose battery temperature is not low but has a life is charged.

FIG. 9 is a graph showing charge characteristics when a battery having a low battery temperature and a long life is charged.

FIG. 10 is a graph showing the charge characteristics when a normal battery is charged without the battery temperature being low.

FIG. 11 is a flowchart showing another embodiment of the present invention.

[Explanation of symbols]

2 is a battery group, 2A is battery temperature detecting means, 40 is battery voltage detecting means, 50 is a microcomputer for determining battery life, 60 is charging current control means, 80 is battery life displaying means, and 90 is charging current setting means. is there.

Claims (7)

[Claims] 1. A battery voltage detecting means for detecting a battery voltage of a battery to be charged, and a battery life judging means for judging that a charged battery has reached the end of its life when the output of the battery voltage detecting means is equal to or higher than a predetermined life judging voltage. A battery life discriminating apparatus comprising: a battery life discriminating device which discriminates that the battery voltage after charging with a predetermined charging current for a predetermined charging time is equal to or higher than the life discrimination voltage. 2. The battery life determining device according to claim 1, further comprising temperature detecting means for detecting the temperature of the battery at the time of starting charging, and reducing the charging current when the detected temperature is equal to or lower than a predetermined value. . 3. A battery life discriminating apparatus according to claim 1, further comprising temperature detecting means for detecting the temperature of the battery at the start of charging, and the charging time is lengthened when the detected temperature is equal to or lower than a predetermined value. . 4. A temperature detecting means for detecting the temperature of the battery at the start of charging is provided, and the life judging voltage of the battery life judging means is changed according to the detection output of the battery temperature detecting means. The battery life determining device according to claim 1. 5. The battery life discriminating apparatus according to claim 1, wherein the life discriminating voltage of the battery life discriminating means is changed according to the charging current. 6. A battery voltage detecting means for detecting a battery voltage of a battery to be charged, and a battery life judging means for judging that the battery to be charged has reached the end of its life when the output of the battery voltage detecting means is equal to or higher than a predetermined life judging voltage. A battery life determining device characterized by being provided. 7. A battery voltage detecting means for detecting a battery voltage of a battery to be charged, a means for detecting whether or not the output of the battery voltage detecting means is maximum and storing the maximum value, and the stored battery voltage value. A battery life discriminating device that discriminates the life of the battery to be charged when the maximum value of is equal to or higher than a predetermined life discriminating voltage.