JPH1169648A - Method for charging secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably detects the full charging of secondary batteries, by controlling the charge of the secondary batteries if a charging condition calculated as the relation of the charging current of the voltage, charging period and halt period of the secondary batteries is equal to or lower than a given value after the secondary batteries were charged for a given period of time as charge per one pulse. SOLUTION: A control device 3 outputs an ON signal to a charge control switch Q1 to charge secondary batteries 2A, 2B for a given period of time as charge per one pulse. Then, it determines whether or not the voltages VH and VL of the secondary batteries 2A, 2B exceed 4.10 V. In a state in which the voltages VH and VL of the secondary batteries 2A, 2B are over 4.10 V, the control device 3 calculates a value with the equation of IA×Ton/(Ton+Toff based on a charging current IA detected by a detecting resistor R1, a charging period Ton and halt period Toff. When this value is equal to or lower than a given value of 0.05C, the secondary batteries 2A, 2B are judged to be fully charged so that the charge control switch Q1 is switched off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pulse charging a secondary battery by repeating charging and resting,
The present invention relates to a method for charging a secondary battery, which controls the charging by accurately detecting the full charge of the secondary battery.

[0002]

2. Description of the Related Art A lithium ion secondary battery, which is one of the secondary batteries, has a high capacity and can take out a high voltage. Therefore, the size and weight of a portable electric device using the lithium ion secondary battery as a power source can be reduced. Recently, it has received a lot of attention.

[0003] The lithium ion secondary battery is usually charged by a constant voltage and a constant current. The present applicant has proposed a pulse charging method as a charging method capable of quick charging with a simpler circuit ( JP-A-9-7641).

In such a pulse charging method, as a charge per pulse, the secondary battery is charged by a predetermined capacity (for example, by a predetermined charging current for a predetermined time), and then temporarily stopped. This pause is performed until the battery voltage of the secondary battery drops to a predetermined voltage. Then, when the battery voltage falls below the predetermined voltage, charging of the secondary battery is restarted. Thereafter, by repeating this, the secondary battery is pulse-charged. When the suspension period of the charging is equal to or longer than a predetermined time, it is determined that the secondary battery is fully charged, and the charging is controlled (ie, terminated).
Is what you do.

[0005] According to this charging method, the secondary battery can be rapidly charged with a simple circuit configuration, and the charge control accompanying the detection of the full charge of the secondary battery can be easily performed.

[0006]

However, in the above-mentioned method, there is a possibility that the full charge of the secondary battery cannot be accurately detected due to the setting of the voltage of the charging power supply or the voltage fluctuation.

FIG. 3 shows that the voltage of the charging power source is set sufficiently higher than the full charge voltage (4.10 V) of the secondary battery, and the pulse charging is performed as described above while supplying a constant current to the secondary battery. 5 shows changes in the battery voltage and the charging current in the case where the battery voltage is changed.
In this case, a constant charging current is always supplied to the secondary battery even when the charging of the secondary battery proceeds and the battery voltage increases. For this reason, the charging suspension period gradually becomes longer as the charging of the secondary battery proceeds, and the suspension period is longer than a predetermined time. By detecting this, charging can be terminated assuming that the secondary battery is fully charged.

By the way, if the voltage of the charging power supply is set high, if the full charge of the secondary battery cannot be detected accurately,
There is a possibility that the battery voltage of the secondary battery abnormally rises, causing a problem that the secondary battery is deteriorated. For this reason, it is preferable that the voltage of the charging power supply be suppressed to about 4.50 V, which is slightly higher than the full charging voltage.

FIG. 4 shows changes in the battery voltage and the charging current of the secondary battery in such a case. In this case, the charging current does not become a constant current but decreases from the initial stage of charging. This is for the following reason. That is, in the path from the charging power supply to the secondary battery, there are various resistance components such as wiring resistance and resistance of the charge control switch. This resistance component causes a voltage loss, and the voltage actually applied to the secondary battery becomes lower than the output voltage of the charging power supply. As a result, as the battery voltage of the secondary battery increases, the charging current decreases.

As described above, when the charging current gradually decreases without becoming a constant current, it takes a considerable time until the charging suspension period becomes longer than a predetermined time, or the suspension period does not reach the predetermined time or more. There is fear. As a result, there is a possibility that the charging time becomes abnormally long or that the full charge cannot be detected.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a step of charging a secondary battery for a predetermined time as charging per pulse, and, after the charging, a battery of the secondary battery. Repeating the step of suspending charging until the voltage becomes equal to or lower than a predetermined voltage, and in the method of pulse-charging the secondary battery, IA × Ton / (Ton + Toff) is used as the charging current IA, the charging period Ton, and the pause period Toff. When the value is equal to or less than a predetermined value, charging of the secondary battery is controlled.

[0012]

FIG. 1 is a block circuit diagram showing an embodiment of a battery pack charged using the charging method of the present invention. 1A and 1B are a pair of charging terminals connected to a charging power supply (not shown), 2A and 2B are two lithium ion secondary batteries (hereinafter simply referred to as secondary batteries) connected in series,
Q1 is a charge control switch composed of a MOSFET connected in series between the charging terminal 1A and the secondary battery 2A, and R1 is a detection resistor for detecting a charging current connected in series between the charging terminal 1A and the secondary battery 2A. It is.

Reference numeral 3 denotes a control unit for controlling charging of the secondary batteries 2A and 2B based on the battery voltages of the secondary batteries 2A and 2B and the charging current detected by the detection resistor R1. The control unit 3 detects the individual battery voltages VH and VL of the secondary batteries 2A and 2B, and continuously detects the charging current IA. Further, an ON / OFF signal is output to the charge control switch Q1 to control charging of the secondary batteries 2A and 2B.

Hereinafter, the operation of the present embodiment will be described with reference to the operation flowchart of FIG. 2 and the waveform diagram of FIG.

In step S1, the control section 3 outputs an ON signal to the charge control switch Q1, and the secondary battery 2A,
2B charging is started. For example, when the secondary batteries 2A and 2B are both lithium ion secondary batteries having a capacity of 1000 mAh, such charging is continuously performed under the conditions of a charging voltage of 4.5 V and a charging current of 1A (that is, a 1C current). Will be

In step S2, the control unit 3 controls the battery voltage VH or VL of one of the secondary batteries 2A and 2B.
Is higher than 4.10V. If both battery voltages VH and VL are equal to or lower than 4.10 V, the charging in step S1 is continued, and if any of the battery voltages VH or VL exceeds 4.10 V, the process proceeds to step S3.

In step S3, the control section 3 performs charging under the above conditions for a predetermined time (for example, 200 msec). Subsequently, in step S4, the control unit 3
An OFF signal is output to the charge control switch Q1 to suspend charging of the secondary batteries 2A and 2B. At the same time, the control unit 3 controls the battery voltages VH and VL of the rechargeable batteries 2A and 2B during the charging suspension.
, And measurement of the charging suspension period is started.

In step S5, the control unit 3 sets the battery voltages VH and VL of the secondary batteries 2A and 2B to 4.
It is determined whether the voltage has become 10 V or less. When any of the battery voltages VH and VL has dropped to 4.10 V or less, the control unit 3 determines in step S6 that the charge control switch Q1
Is output to restart charging of the secondary batteries 2A and 2B, and the process returns to step S3.

Thus, steps S3 to S6
Is repeated, the charging during the charging period Ton and the suspension of charging until the battery voltages VH and VL drop to 4.10 V are repeated, and the secondary batteries 2A and 2B are pulse-charged.

Meanwhile, in a state where the battery voltages VH and VL of the secondary batteries 2A and 2B do not fall below 4.10 V, the control unit 3 determines in step S7 the charging current IA detected by the detection resistor R1 and the charging period Ton. And pause period To
IA × Ton / (Ton + Toff) is calculated based on ff, and it is determined whether or not this value is equal to or less than a predetermined value 0.05C. If the value is not equal to or less than the predetermined value 0.05C, it is determined that the secondary batteries 2A and 2B are not yet fully charged, and the process returns to step S5. On the other hand, if the predetermined value is 0.05C or less, it is determined that the secondary batteries 2A and 2B are fully charged, and in step S8, the control unit 3 outputs an OFF signal to the charge control switch Q1 and ends the charging. .

The above-mentioned predetermined value is not limited to 0.05 C, but may be set to an appropriate value of 0.3 C or less, preferably an appropriate value of 0.1 C or less.

[0022]

According to the present invention, there is provided a step of charging a secondary battery for a predetermined time as charging per pulse, and a step of stopping charging until the battery voltage of the secondary battery becomes equal to or lower than a predetermined voltage after the charging. Is repeated to control charging of the secondary battery when IA × Ton / (Ton + Toff) is equal to or less than a predetermined value as the charging current IA, the charging period Ton, and the pause period Toff. Therefore, it is possible to reliably detect the full charge of the secondary battery and perform accurate charge control.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing one embodiment of the present invention.

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

FIG. 3 is a waveform diagram showing changes in battery voltage and charging current.

FIG. 4 is a waveform diagram showing changes in battery voltage and charging current.

[Explanation of symbols]

 2A, 2B secondary battery 3 control unit Q1 charge control switch R1 detection resistor

Claims (1)

[Claims] 1. A step of charging a secondary battery for a predetermined time as charging per pulse, and a step of suspending charging after the charging until the battery voltage of the secondary battery becomes equal to or lower than a predetermined voltage. In the method for pulse charging the secondary battery, the charging of the secondary battery is controlled when IA × Ton / (Ton + Toff) is equal to or less than a predetermined value as a charging current IA, a charging period Ton, and a pause period Toff. A method for charging a secondary battery.