JPH06133467A - Charger - Google Patents

Abstract

PURPOSE:To perform the optimum display of full charge regardless of ambient temperature. CONSTITUTION:This charger has a current detecting means 5, which detects a charging current for a secondary battery 2, and computing means 1 and 6, which compute the time until the full charge is displayed in response to the required time until the charging current detected by the current detecting means 5 is decreased from the first current value to the second current value that is lower than the first current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charger for charging a secondary battery, especially a non-aqueous secondary battery such as a lithium ion secondary battery, with a constant voltage.

[0002]

2. Description of the Related Art Among rechargeable batteries that can be used over and over by being repeatedly charged, a lithium-ion rechargeable battery, in particular, has a voltage about three times higher than that of a nickel-cadmium battery and a high capacity. Has recently been attracting attention.

By the way, the performance of such a secondary battery is deteriorated when it is overcharged beyond a predetermined voltage. Therefore, in the lithium ion secondary battery, constant current / constant voltage charging is usually performed so that the lithium ion secondary battery is not charged above a predetermined voltage. That is, constant current charging is performed at the initial stage of charging, and when the battery voltage is close to the set value, switching to constant voltage charging is performed (see, for example, JP-A-4-183232). Then, when the charging current becomes almost 0 or when a predetermined time elapses, the full charge is displayed and the charging is finished.

[0004]

By the way, the charging characteristics of the secondary battery are affected by the ambient temperature during charging. FIG. 3 shows that the ambient temperature is zero in a lithium ion secondary battery.
The characteristics of charging current-charging time in the case of C, 25 C and 60 C are shown.

As can be seen from the figure, the time required for the charging current to reach full charge and to converge to almost zero depends on the ambient temperature during charging. Especially at low temperatures (eg 0
If the battery is charged in the (.degree. C.) state, the time until the charging current converges to almost 0 becomes very long. As a result, even though the battery is almost fully charged, the display of the fully charged battery is not displayed for a long period of time, which is not very convenient.

Further, when the full charge display is performed after a lapse of a predetermined time, the charge amount at the full charge display time varies because the charge characteristics at ambient temperature during charging are different.

Therefore, an object of the present invention is to properly perform full-charge display regardless of the ambient temperature during charging.

[0008]

According to the present invention, in a charger for charging a secondary battery with a constant voltage, a current detecting means for detecting a charging current of the secondary battery and a charging current detected by the current detecting means. And a calculating means for calculating a time until a full-charge display is performed according to a time required to decrease from a first current value to a second current value lower than the first current value. Is characterized by.

[0009]

According to the present invention, by recognizing the time required for the charging current to decrease from the first current value to the second current value lower than the first current value, it is possible to indirectly charge the battery. The ambient temperature of the secondary battery or the capacity of the secondary battery is indirectly measured. Then, according to the required time, the time until the full-charge display is performed is calculated, and the appropriate full-charge display is performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block circuit diagram showing an embodiment of the present invention, in which 1 is a control unit having a RAM, a ROM for storing a charging control program and various charging conditions, a microcomputer and other peripheral circuits. Reference numeral 2 denotes a lithium ion secondary battery (hereinafter, simply referred to as a secondary battery), 3 receives alternating current from a commercial power source (not shown), and supplies the secondary battery 2 with constant-current / constant-voltage charging power. The power source unit 4 receives the power from the power source unit 3, and the secondary battery 2 receives 1C to 2C until the voltage of the secondary battery 2 reaches a predetermined voltage (for example, 4.1V).
3. The constant current is supplied to the secondary battery 2 after reaching a predetermined voltage.
A charge control unit that supplies a constant voltage of 1 V, 5 a current detection unit that detects a charging current I of the secondary battery 2, 6 a timer circuit that starts counting time from the start of charging, and 7 an LED
And its drive circuit, when full charge display time,
It is a charge display unit that displays a full charge.

FIG. 2 is a flow chart showing the operation of one embodiment of the present invention. In step S1, charging is started. At the same time, in step S2, the timer circuit 6 starts counting. With the start of charging, the charge control unit 4 first performs constant-current charging of the secondary battery 2, and then the secondary battery 2
Reaches a predetermined voltage, constant voltage charging is performed.

In step S3, it is determined whether the charging current I detected by the current detector 5 has dropped to the first current value I1. Now, when it is determined that the first current value I1 is reached, in step S4, the first count value t1 of the timer circuit 6 at that time is read out,
It is temporarily stored in the control unit 1.

Then, in step S5, the charging current I detected by the current detector 5 is the first current value I1.
To the second current value I2 is determined. When it is determined that the second current value I2 has been reached, the second count value t2 of the timer circuit 6 at that time is read out and temporarily stored in the control unit 1 in step S6.

When the count value t2 is read, in step S7, the control unit 1 calculates the time t3 for displaying the full charge by the calculation formula of t3 = t2 + a (t2-t1). In addition, a is an arbitrary constant (for example, 3).

Here, (t2-t1) is the time required for the charging current I to drop from the first current value I1 to the second current value I2, and this time is the ambient time as described. The higher the temperature, the shorter it becomes. As a result, the full-charge display time t3 calculated by the above-described calculation formula becomes shorter as the ambient temperature becomes higher, in other words, the time to reach full charge becomes shorter as the ambient temperature becomes higher. The time is set appropriately according to the characteristics.

Then, in step S8, it is determined whether or not the count value of the timer circuit 6 has reached t3 calculated above. If it is determined that t3 has been reached, the charge display section 7 is displayed in step S9. It will be displayed that the battery is fully charged.

[0017]

According to the present invention, in the charger for charging the secondary battery with a constant voltage, the current detecting means for detecting the charging current of the secondary battery and the charging current detected by the current detecting means are Since there is provided a calculating means for calculating the time until the full-charge display is performed according to the time required from the current value of 1 to the second current value lower than the first current value, Even though the ambient temperature is not measured, an appropriate full-charge display can be displayed without being affected by the ambient temperature.

[Brief description of drawings]

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

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

FIG. 3 is a characteristic diagram showing charging characteristics of a secondary battery.

[Explanation of symbols]

 1 control unit 2 secondary battery 5 current detection unit 6 timer circuit 7 charging display unit

Claims (1)

[Claims] 1. In a charger for charging a secondary battery with a constant voltage, a current detecting means for detecting a charging current of the secondary battery and a charging current detected by the current detecting means are first
And a calculation unit that calculates a time until a full charge display is performed according to a time required from the current value of 1 to a second current value lower than the first current value. Charger to do.