JPH07308030A - Charger for secondary battery - Google Patents

Abstract

PURPOSE:To prevent undercharge or overcharge due to erroneous decision at the time of boosting charge by decreasing the differentiated reference temperature sequentially stepwise as the time elapses after starting the charging operation. CONSTITUTION:When a secondary battery 2 is set in a charger 4 and boosting charge is started, the differentiated reference temperature is set at a relatively high value for a predetermined time after starting the charging operation and then it is set at a lower value. When the differentiated reference temperature is initially set at a relatively high value, erroneous decision of full charge is eliminated and thereby undercharge is prevented. When the differentiated reference temperature is set, upon elapse of a predetermined time after starting the charging operation, lower than the initially set value, the boosting charge is stopped immediately upon full charge and thereby overcharge is prevented.

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 a secondary battery, and more particularly to a charging device suitable for rapid charging of an alkaline secondary battery such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art In a quick charger for charging a secondary battery in a short time, it is judged that the battery is fully charged, and the rapid charging is terminated. Various methods for determining full charge have been considered, one of which is the temperature differential detection method.
This utilizes the temperature differential of the battery, that is, the temperature rise amount per unit time rapidly increases at the end of charging, and it is determined that the battery is fully charged when the temperature differential reaches a predetermined value, for example, 1 ° C / min. It is a method to do.

By the way, in this temperature differential detection type quick charger, it is usual not to determine the full charge by temperature differential detection for a fixed time (for example, 3 minutes) from the start of the rapid charge. For example, when a battery used outdoors (eg, 0 ° C.) is brought indoors (eg, 25 ° C.) for quick charging in a cold area such as a ski resort, the battery temperature and the ambient temperature are initially different from each other. Because the temperature difference is large, the amount of temperature rise per minute exceeds 1 ° C. even immediately after the start of charging, and it may be determined that the battery is fully charged even though it is not fully charged. In such a case, the battery is naturally insufficiently charged.

Therefore, for example, a time of 3 minutes is set as the time for the temperature rise of the battery to settle due to the ambient temperature,
During this period, full charge determination is not performed by temperature differential detection, and 3
A method of performing temperature differential detection after a lapse of minutes has been considered. In this way, the temperature rise due to charging can be reliably captured, and full charge can be correctly determined.

However, in this method, when the battery is brought in from a low temperature outdoors to be charged indoors, a full charge will not be erroneously determined, but a fully charged battery which has already been charged can be recharged. If it does, the full charge is not judged for a time of 3 minutes after the start of charging. Therefore, even if the battery is fully charged, recharging is performed for 3 minutes + 1 minute = 4 minutes. It may be charged. Also, the temperature differential detection is not 1 ° C./min, but is 4 ° C./min.
In the case of 4 minutes, the rapid charging is stopped after 3 minutes of the temperature differential non-detection time + 7 minutes of 4 minutes of the unit time of the temperature differential detection, and therefore overcharge is performed for 7 minutes. The battery temperature rises by 15 ° C or more, and the deterioration of the battery progresses.

[0006]

As described above, in the conventional quick differential charger using the temperature differential detection method, when the battery is brought from a low ambient temperature environment to a high ambient temperature for quick charging, the battery is fully charged immediately after the start of charging. The battery may be insufficiently charged due to the detection of the battery charge.To avoid this problem, if the full charge determination is not performed by the temperature differential detection for a certain period of time after the start of charging, the already charged battery will be When recharged, there is a problem that overcharge occurs and the battery deteriorates.

The present invention has been made in order to solve the above-mentioned problems of the quick charger by the conventional temperature differential detection method, and there is no shortage of charge due to erroneous determination of full charge, and the state of full charge. It is an object of the present invention to provide a charging device for a secondary battery, which is free from the risk of being overcharged by rapidly charging the battery.

[0008]

A charging device for a secondary battery according to the present invention comprises a temperature detecting means for detecting the temperature of the secondary battery, and a temperature rise per unit time of the temperature detected by the temperature detecting means. Temperature differential detecting means for obtaining a temperature differential value which is an amount, charge control means for terminating the rapid charging when the temperature differential value obtained by the temperature differential detecting means reaches a reference temperature differential value, and the reference temperature differential It is characterized in that it further comprises a reference temperature differential value control means for sequentially and stepwisely changing the value at least once or more with the lapse of time after the start of charging (thus, the reference temperature differential value becomes two or more types).

Here, the reference temperature differential value control means specifically includes, for example, a table storing the relationship between the elapsed time after the start of charging and the reference temperature differential value, and a timer for measuring the elapsed time after the start of charging. And reading the reference temperature differential value corresponding to the elapsed time measured by the timer from the table.

Further, the charge control means, when the temperature differential value obtained by the temperature differential detecting means gradually increases at the time of starting charging or after a certain time elapses from this, or when it becomes larger than at the time of the previous charging, the rapid charging is performed. May be stopped, and when the temperature differential value gradually decreases after the start of charging or after a certain period of time elapses from this, or when it becomes smaller than the previous charging, control may be performed to continue rapid charging.

[0011]

According to the present invention, when the secondary battery is set in the charging device and the rapid charging is started, the reference temperature differential value is set to a relatively large value for a certain time after the start of charging, and then,
The reference temperature differential value is set to a value smaller than this. Therefore, if the reference temperature differential value initially set is set to a relatively large appropriate value, it is possible to prevent a battery that is not in a fully charged state from being erroneously determined to be fully charged, thus preventing insufficient charging. Also, if the reference temperature differential value after a lapse of a certain time from the start of charging is set to an appropriate value that is smaller than the initially set reference temperature differential value, when a fully charged battery is set, rapid charging will stop immediately. As a result, overcharging is prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a secondary battery charging device showing an embodiment according to the present invention. In FIG. 1, a battery pack 1 includes a secondary battery (hereinafter, simply referred to as a battery) 2 such as an alkaline secondary battery and a thermistor 3 for temperature measurement arranged near the battery 2 in a housing. is there. Figure 1
Shows a state in which the battery pack 1 is set in the charging device 4. A mobile phone or other device in which the battery pack 1 is incorporated may be set in the charging device 4.

The charging device 4 is constructed as follows. The charging device 4 has a commercial AC power source 5 (for example, 100V)
Power from is input and filter 6 for noise removal
After being converted into a direct current by the rectifying / smoothing circuit 7 via, the signal is supplied to the primary side of the transformer 8. On the primary side of the transformer 8,
A switching transistor 9 composed of a power MOS transistor is connected via a resistor 10. The switching transistor 9 is a PWM (pulse width modulation) circuit 1
It is switched by the output of 1. As a result, a pulse current flows in the primary side of the transformer 8 and energy is transmitted to the secondary side of the transformer 8. The output generated on the secondary side of the transformer 8 is converted into a direct current by the rectifying and smoothing circuit 12,
It is supplied as a charging current to the battery 2 through the quick charging transistor 13 or the series circuit of the trickle charging transistor 14 and the resistor 15 and further through the backflow prevention diode 16. The output of the rectifying / smoothing circuit 12 is also supplied to the light emitting element 18 of the photocoupler 17, and the output of the light receiving element 19 of the photocoupler 17 is input to the PWM circuit 11.

The microcontroller 20 is mainly composed of a microcomputer and controls the rapid charging transistor 13, the trickle charging transistor 14, the photocoupler 17 and the LED 31. This microcontroller 20 has a voltage at the connection point between the resistor 21 and the thermistor 3 (hereinafter referred to as the thermistor voltage).
Vt and a voltage Vb obtained by dividing the voltage VB of the battery 2 by the resistors 22 and 23 (hereinafter, referred to as a battery voltage division value) Vb are input.

The resistors 24-29 and the operational amplifier 30 are
It is provided for controlling the charging current to be constant. The inverting input terminal of the operational amplifier 30 receives the terminal voltage of the resistor 24 that is inserted in series in the charging path and detects the charging current via the resistor 27, and the non-inverting input terminal of + 5V.
A voltage (reference voltage) obtained by dividing the power supply voltage of 2 by the resistors 25 and 26 is input via the resistor 28. Operational amplifier 30
A resistor 29 is connected between the inverting input terminal and the output terminal, and the gain of the operational amplifier 30 is determined by the resistors 27 and 29. The output terminal of the operational amplifier 30 is connected to the side of the light emitting element 18 of the photocoupler 17 opposite to the side connected to the output terminal of the rectifying / smoothing circuit 12. With such a configuration, feedback control is performed so that the inverting input terminal and the non-inverting input terminal of the operational amplifier 30 have the same potential.

For example, when the charging current of the battery 2 is large and the terminal voltage of the current detecting resistor 24 is large, the inverting input terminal of the operational amplifier 30 has a higher potential than the non-inverting input terminal thereof, and therefore the operational amplifier 30 has a higher potential. Output voltage decreases, and the current flowing through the light emitting element 18 increases. As a result, the output pulse width of the PWM circuit 11, that is, the on-time width of the switching transistor 9 is shortened, the energy transmitted to the secondary side of the transformer 8 is reduced, and the charging current is reduced.

On the contrary, when the charging current of the battery 2 is small,
Since the inverting input terminal of the operational amplifier 30 has a lower potential than the non-inverting input terminal thereof, the output voltage of the operational amplifier 30 increases and the current flowing through the light emitting element 18 decreases, so that the PWM
The output pulse width of the circuit 11, that is, the on-time width of the switching transistor 9 increases, and the energy transmitted to the secondary side of the transformer 8 increases, so that the charging current increases.

In this way, the resistance 2 depending on the charging current
Feedback control is performed so that the terminal voltage of No. 4 and the reference voltage obtained by the resistors 25 and 26 become equal to each other, and the charging current is subjected to constant current control.

The microcontroller 20 controls by software processing using a microcomputer. FIG. 2 shows a functional block diagram of the microcontroller 20.

In FIG. 2, the thermistor voltage Vt and the battery voltage division value Vb are converted into digital values by the A / D converters 41 and 42, respectively, and then the battery temperature calculation unit 4
3 and the battery voltage detector 44, respectively, to obtain the battery temperature TB and the battery voltage VB. The output of the battery temperature calculation unit 43 is input to the battery temperature determination unit 45 and the temperature differential calculation unit 46. The battery temperature determination unit 45 determines in what temperature range the battery voltage is.
The temperature differential calculation unit 46 calculates the temperature differential of the battery, that is, the amount of temperature rise per unit time.

The output of the temperature differential calculation section 46 is input to the temperature differential value determination section 54. The temperature differential value determination unit 54 compares the temperature differential value obtained by the temperature differential calculation unit 46 with the reference temperature differential value read from the reference temperature differential value table 55 to determine the magnitude. Reference temperature differential value table 55
Shows the relationship between the elapsed time after the start of rapid charging and the reference temperature differential value stored in a memory such as a ROM, an example of which is shown in FIG.

On the other hand, the output of the battery voltage detection unit 44 is input to the battery state determination unit 47. The battery state determination unit 47
It is determined from the battery voltage whether or not the battery 2 is normal. The output of the A / D converter 41 is also input to the battery pack set detection unit 48. Battery pack set detector 48
Is for detecting whether or not the battery pack 1 is set in the charging device 4.

A / D converter 41, battery temperature determination unit 45,
The outputs of the battery state determination unit 47, the battery pack set detection unit 48, and the temperature differential value determination unit 54 are input to the charging control unit 50, and the charging control unit 50 uses the outputs to rapidly charge the rapid charging transistor 13. A charge control signal 51, a trickle charge control signal 52 for the trickle charging transistor 14, and a charge start signal 53 are generated. The charge start signal 53 is supplied to one end of the resistor 28 in FIG.

Further, the charge control unit 50 obtains the reference temperature differential value corresponding to the elapsed time from the reference temperature differential value table 55 based on the output (timer value) of the timer 49 which measures the elapsed time from the start of the rapid charging. It also controls to read out and give this to the temperature differential value determination unit 54.

Next, the operation of this embodiment will be described with reference to the flow chart shown in FIG. First, the thermistor voltage V
t is read via the A / D converter 41 (step 101). When the battery pack 1 is set in the charging device 4, the thermistor voltage Vt decreases from + 5V until then due to the partial pressure of the thermistor 3 and the resistor 21. here,
When the thermistor voltage Vt becomes equal to or lower than a predetermined value (for example, 4.8 V), the battery pack set detection unit 48 detects that the battery pack 1 is set in the charging device 4 (step 102).

When the set of the battery pack 1 is detected in step 102, the battery temperature calculation unit 43 converts the thermistor voltage Vt into temperature data to calculate the battery temperature TB (step 103), and then the battery temperature determination unit 4
According to 5, it is determined whether the battery temperature TB is in the range of 0 ° C. or higher and 40 ° C. or lower (step 104). When the battery temperature TB falls within the range of 0 ° C. ≦ TB ≦ 40 ° C., the trickle charge control signal 52 output from the charge control unit 50 subsequently becomes “L” level, and the trickle charge transistor 14 is turned on. Then, trickle charging is performed (step 105). Thereafter, the battery voltage division value Vb is read via the A / D converter 42 (step 106), the battery voltage VB is obtained by the battery voltage detection unit 44, and the battery voltage VB is further obtained by the battery state determination unit 47.
It is determined from B that the battery 2 is normal (step 1
07). Specifically, the battery voltage VB per unit cell is 1.
When 0V ≦ VB ≦ 1.7V, the battery 2 is judged to be normal. Here, if the battery 2 is not normal, the process ends and rapid charging is not performed.

When the battery 2 is normal, the timer 49 is started (step 108), the elapsed time from the charging start time is measured, and the timer value of this timer 49 (the elapsed time from the charging start time) is used. The reference temperature differential value is set based on the reference temperature differential value table 55 (step 109). Then, when the quick charge control signal 51 output from the charge control unit 50 becomes “L” level, the quick charge transistor 13 is turned on, and
When the charging start signal 53 becomes "L" level, rapid charging is performed (step 110). During this time,
The LED 31 is controlled by the microcontroller 20 and lights up to indicate that the quick charge is being performed. Also,
During this rapid charging, the charging current is kept constant by the above-mentioned feedback control.

Further, during the rapid charging, the temperature differential calculating unit 46 calculates the temperature differential of the battery temperature TB, that is, the temperature increase rate per unit time (for example, 1 minute), and the temperature differential value is judged as the temperature differential value. Step 1 in part 54
When it becomes equal to or higher than the reference temperature differential value set in 09, it is determined that the battery 2 is fully charged (step 111). When the battery 2 is determined to be fully charged, both the quick charge control signal 51 and the charge start signal 53 become “H” level,
The quick charge ends.

Next, a method of setting the reference temperature differential value will be specifically described. FIG. 4 shows the rapid charging characteristics when the ambient temperature is 25 ° C. and the battery temperature is 25 ° C. As shown in the figure, when 1.0 C is supplied as the charging current I, the battery voltage VB gradually rises, and the battery temperature TB also rises accordingly. The temperature increase rate of the battery temperature TB is relatively large immediately after the start of charging 401, then gradually increases, and becomes large again at 402 when the battery is near full charge. Here, in the conventional case, the temperature differential detection is performed immediately after the start of the rapid charge, and when it reaches the reference temperature differential value of 1 ° C./min, it is regarded as full charge and the rapid charge is stopped.

A characteristic 501 of FIG. 5 is a temperature rise characteristic of the battery temperature due to charging when both the ambient temperature and the battery temperature are 25 ° C. On the other hand, for example, when the ambient temperature is 25 ° C. and the battery temperature is 0 ° C.
This corresponds to the case where the battery pack 1 is brought in and charged in a room at ℃), and the battery temperature TB rises as shown by the characteristic 502 in FIG. According to this characteristic 502, the battery temperature rises to 3.3 ° C. after 3 minutes from 0 ° C., so that the temperature rises by 1.1 ° C. or more in 1 minute without charging. If the temperature rise due to charging is added to this temperature rise, the characteristic 503 of FIG.
Since the temperature rises from 0 ° C. to 5 ° C. after 3 minutes, the temperature differential detection immediately after the start of the rapid charging causes a false determination as a full charge. In order to avoid this erroneous determination, conventionally, the determination of full charge by temperature differential detection is not performed for 3 minutes immediately after the start of rapid charging.

On the other hand, in this embodiment, according to the contents of the reference temperature differential value table 55 shown in FIG. 6, the reference temperature differential value is gradually reduced, for example, every minute with the lapse of time from the start of charging. . According to the reference temperature differential value table 55, the reference temperature differential value is 2.7 ° C./minute for 1 minute from the start of charging and 1.8 ° C./minute for 1 minute to 2 minutes.
1.5 ° C./min between 2 and 3 minutes, and 1. between 3 and 4 minutes.
The setting is variably set to 1 ° C./minute and 4 ° C./minute to 1.0 ° C./minute.

When the variable reference temperature differential value shown in the reference temperature differential value table of FIG. 6 is used, the temperature differential detection operation for the battery temperature rise characteristics 502 and 503 of FIG. 5 is as follows. FIG. 7 is an enlarged view showing changes in the characteristics 502 and 503 of FIG. 5 immediately after the start of charging. In the characteristic 503 of FIG. 7, the battery temperature 1 minute after the start of charging is 2.3 ° C., and the reference temperature differential value during this period is 2.7 ° C. /
Since it is less than a minute, it is not judged to be fully charged. The battery temperature 2 minutes after the start of charging is 3.8 ° C, and the temperature rise between 1 minute and 2 minutes is 1.5 ° C, which is smaller than the reference temperature differential value of 1.8 ° C / minute during this period. After all, it is not judged to be fully charged. Similarly, the temperature rise during 2 to 3 minutes is 1.
2 ° C, which is smaller than the standard temperature differential value of 1.5 ° C / min,
In addition, the temperature rise between 3 minutes and 4 minutes is 0.9 ° C., which is smaller than the reference temperature differential value of 1.1 ° C./minute, and the temperature rise per minute after 4 minutes is the reference temperature differential value of 1. Since it is smaller than 0, it is not determined to be fully charged.

In this way, when the reference temperature differential value is set to a large value immediately after the start of charging, when the battery pack 1 is brought into a room at a temperature of 25 ° C. from a low temperature place of 0 ° C. and the battery 2 is rapidly charged, the battery 2 is charged. It is possible to avoid insufficient charging without erroneously determining that the battery is fully charged even though it is not fully charged.

Next, consider the case where the battery temperature TB is 0 ° C. and the fully charged battery is rapidly charged. The battery temperature rise characteristic in this case is shown by the characteristic 504 in FIG. 7. According to this characteristic 504, the battery temperature after 1 minute from the start of charging is 2.6 ° C., which is smaller than the reference temperature differential value 2.7 ° C., so it is not determined that the battery is fully charged. The battery temperature after 2 minutes from the start of charging was 4.7 ° C, and the temperature rise between 1 minute and 2 minutes was 2.1 ° C, and the reference temperature differential value during this period was 1.8 ° C /
Since it is larger than the minute, it is determined that the battery is fully charged and the charging is stopped.

After a certain period of time has elapsed after the start of charging, the reference temperature differential value is set to a small value to set a fully charged battery. Since the determination is made and the rapid charging is immediately stopped, overcharging of the battery 2 can be prevented.

Next, consider the case where the battery temperature TB is 25 ° C. and the fully charged battery is rapidly charged. The battery temperature rise characteristic in this case is a characteristic obtained by subtracting the characteristic 502 from the characteristic 503 because the characteristic 502 of FIG. 4 is not added. According to this characteristic, the temperature rise 1 minute after the start of charging is 2.6 ° C.-1.6 ° C. = 1.0 ° C., which is smaller than the reference temperature differential value 2.7 ° C./min. Not judged, the battery temperature after 2 minutes was 4.7 ° C-2.7 ° C, which was a temperature increase of 1.0 ° C with respect to the battery temperature of 1.0 ° C after 1 minute, and the reference temperature differential value was 1 Since it is less than 0.8 ° C / min, full charge is not detected. After 3 minutes, the battery temperature was 7.3 ° C-3.
At 6 ° C, the temperature rises by 1.7 ° C after 2.0 minutes after the battery temperature reaches 2.0 ° C. Since it is smaller than the reference temperature differential value of 1.5 ° C / min, it is determined that the battery is fully charged and the rapid charging is stopped. To be done.

That is, in such a case, in the conventional case, the battery temperature was raised by about 15 ° C. because the full charge was determined 4 minutes after the start of charging and the rapid charging was stopped, but in the present embodiment, charging was performed. Since the rapid charging is stopped 3 minutes after the start time, the temperature rise of the battery can be suppressed to about 7.3 ° C. For this reason, overcharging of the battery is further suppressed, and the cycle life is extended accordingly.

For batteries that are not fully charged, the standard temperature differential value is a normal value (for example, 1 ° C.) after 4 minutes.
/ Min), the full charge will be correctly detected as before.

The present invention is not limited to the above embodiments, but can be implemented with various modifications. For example, in the above-described embodiment, the battery temperature is measured every 1 minute, and the temperature rise amount per minute is determined for the reference temperature differential value, but the battery temperature measurement time interval is longer or shorter than this.
For example, the value may be 30 seconds.

In the table of FIG. 6, the reference temperature differential value is variable from 0 to 4 minutes, but it may be variable from 0 to 10 minutes. On the contrary, in the table of FIG. 6, the reference temperature differential value is changed five times, but may be changed twice. For example,
From 0 to 4 minutes, with a differential value of 2.7 ° C, 1.0 minutes after 4 minutes
It is the differential value of ° C.

The full charge determination algorithm based on the temperature differential detection described in the above embodiment is merely an example, and may be different from the above. For example, in FIG. 7, when the temperature differential value gradually decreases, the full charge determination may not be performed, and the full charge determination may be performed when the temperature differential value exceeds the temperature differential value up to that point. A specific example of this full charge determination method is shown below. In the claim 3, in the expression "when the temperature differential value gradually decreases after the start of charging or after a certain period of time elapses", the reason for "when the temperature gradually decreases after a certain period of time" is as follows. (1) When charging starts, a small charging current may flow for a certain period of time, which is inconsistent with charging start time, and (2) when temperature differential value is measured every 30 seconds after starting rapid charging. Depending on the battery pack, the temperature may not change during the first minute. In this case, the fixed time may be set to 1 minute and the temperature differential value may be checked after the fixed time has passed. This is because.

(Condition 1) Battery temperature 0 ° C., ambient temperature 25 ° C.
When a quick charge of a battery that is not fully charged is started. In this case, at the time point 402 approaching full charge in FIG. 4, the temperature rise per minute of the battery is as follows.

1 minute later ... 2.3 ° C. (2.3 ° C.-0 ° C. = 2.3.
3 ° C 2 minutes later ... 1.5 ° C (3.8 ° C-2.3 ° C = 1.5 ° C) 3 minutes later 1.2 ° C (5.0 ° C-3.8 ° C = 1.2 ° C) ) 4 minutes later ... 0.9 ° C. (5.9 ° C.-5.0 ° C. = 0.9 ° C.) In this example, the amount of temperature rise per minute gradually decreases, so full charge based on temperature differential detection is performed. The quick charge is continued without making the determination.

(Condition 2) Battery temperature 0 ° C., ambient temperature 25 ° C.
When the quick charge of a fully charged battery is started. in this case,
The temperature rise per minute of the battery is as follows, for example. 1 minute later ... 2.6 ° C (2.6 ° C-0 ° C = 2.6 ° C) 2 minutes later ... 2.1 ° C (4.7 ° C-2.6 ° C = 2.1 ° C) 3 minutes later ... 2.6 [deg.] C. (5.3 [deg.] C.-4.7 [deg.] C. = 2.6 [deg.] C.) In this example, the temperature rise of the battery is large 3 minutes after 2 minutes, so the temperature differential detection is performed 3 minutes later. The full charge state is determined based on the above, and the quick charge is stopped.

(Condition 3) Battery temperature 25 ° C., ambient temperature 25
When quick charging of a battery that is not fully charged at ℃ is started. In this case, the temperature rise of the battery every minute is as follows, for example. After 1 minute ... 2.3 ° C. (2.3 ° C.-1.6 ° C. = 0.7 ° C.) After 2 minutes ... 1.5 ° C. ((3.8 ° C.-2.7 ° C.)-0.7 ° C.
= 0.4 ° C.) 3 minutes later ... 1.2 ° C. ((5.0 ° C.-3.6 ° C.)-1.1 ° C.
= 0.3 ° C.) In this example, since the temperature rise of the battery every minute is gradually reduced, rapid charging is continued without determining the full charge state.

(Condition 4) Battery temperature 25 ° C., ambient temperature 25
When quick charging of a fully charged battery at ℃ is started. In this case, the temperature rise of the battery every minute is as follows, for example. 1 minute later ... 1.0 ° C. (battery temperature: 2.6 ° C.-1.6 ° C. =
1.0 ° C, temperature rise: 1.0 ° C-0 ° C = 1.0 ° C) 2 minutes later ... 1.0 ° C (battery temperature: 4.7 ° C-2.7 ° C =
2.0 ° C., temperature rise: 2.0 ° C.-1.0 ° C. = 1.0 ° C. 3 minutes later ... 1.7 ° C. (battery temperature: 7.3 ° C.-3.6 ° C. =)
3.7 ° C., temperature rise: 3.7 ° C.−2.0 ° C. = 1.7 ° C.) In this example, the temperature rise of the battery is large after 3 minutes and after 2 minutes, so it takes 3 minutes to reach full temperature. The state of charge is determined and the quick charge is stopped.

Even with the above logic, it is possible to detect the fully charged state 3 minutes after the start of the rapid charge of the fully charged battery, and basically, a constant battery temperature rise is detected within a fixed time. It can be judged that it was done.

Further, for 5 minutes after the start of the rapid charge, the full-charge state is judged by the above-mentioned logic, and thereafter, the original 1 ° C. /
It is also possible to use a logic for determining the fully charged state by detecting the temperature differential for more than a minute.

[0049]

As described above, according to the present invention, in the charging device of the type in which the full charge is judged by the temperature differential detection of the secondary battery to stop the rapid charging, after the reference temperature differential value is started to be charged. When the battery pack is brought into the room from a low temperature environment for quick charging, the battery will be insufficiently charged due to erroneous determination that the battery is not fully charged when it is fully charged. In addition, it is possible to prevent overcharging due to accidentally rapidly charging a fully charged battery.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a secondary battery charging device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of the microcontroller in FIG.

FIG. 3 is a flowchart for explaining the operation of the embodiment.

FIG. 4 is a diagram showing changes with time in battery voltage, battery temperature, and charging current during rapid charging for explaining the operation of the embodiment.

FIG. 5 is a diagram showing temperature rise characteristics of a battery under various conditions.

FIG. 6 is a diagram showing a configuration example of a reference temperature differential value table in the figure.

FIG. 7 is an enlarged view showing a part of the battery temperature rise characteristic of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery pack 2 ... Secondary battery 3 ... Thermistor 4 ... Charging device 5 ... Commercial AC power supply 6 ... Filter 7 ... Rectification smoothing circuit 8 ... Transformer 9 ... Switching transistor 11 ... Pulse width modulation circuit 12 ... Rectification smoothing circuit 13 ... Rapid Charge transistor 14 ... Trickle charge transistor 16 ... Backflow prevention diode 17 ... Photocoupler 20 ... Microcontroller 30 ... Operational amplifier 32 ... Discharge transistor 41 ... A / D converter 42 ... A / D converter 43 ... Battery temperature Calculation unit 44 ... Battery voltage detection unit 45 ... Battery temperature determination unit 46 ... Temperature differential calculation unit 47 ... Battery state determination unit 48 ... Battery pack set detection unit 49 ... Timer 50 ... Charge control unit 51 ... Rapid charge control signal 52 ... Trickle Charge control signal 53 ... Charge start signal 54 ... Temperature differential value determination unit 55 ... Reference temperature Minute value table

Claims (3)

[Claims] 1. A charging device having a function of rapidly charging a secondary battery, comprising temperature detecting means for detecting the temperature of the secondary battery, and a temperature rise per unit time of the temperature detected by the temperature detecting means. Temperature differential detecting means for obtaining a temperature differential value which is an amount, charge control means for terminating the rapid charging when the temperature differential value obtained by the temperature differential detecting means reaches a reference temperature differential value, and the reference temperature differential A charging device for a secondary battery, comprising: a reference temperature differential value control unit that sequentially and stepwise changes the value at least once or more with the lapse of time after the start of charging. 2. The reference temperature differential value control means has a table storing the relationship between the elapsed time after the start of charging and the reference temperature differential value, and a timer for measuring the elapsed time after the start of charging. The secondary battery charging device according to claim 1, wherein a reference temperature differential value corresponding to the elapsed time measured by the timer is read from the table. 3. The charge control means, when the temperature differential value obtained by the temperature differential detecting means gradually increases at the start of charging or after a certain period of time elapses from this, or when it becomes larger than that at the previous charging, rapid 2. The charging is stopped, and the rapid charging is continued when the temperature differential value gradually decreases at the start of charging or after a certain period of time elapses thereafter, or becomes smaller than the previous charging, the rapid charging is continued. Rechargeable battery charger.