JP2641328B2 - Ni-Cd battery charge / discharge control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge / discharge control circuit for a Ni-Cd battery used for a small electronic device, and more particularly to a charge / discharge control circuit for a Ni-Cd battery stored for a long time.

[0002]

2. Description of the Related Art FIG. 3 is a conceptual diagram of a conventional Ni-Cd battery charge / discharge control circuit. As a charge control method for a Ni-Cd battery,-[Delta] V control is generally and often used.

[0003] The terminal voltage of a Ni-Cd battery rises as it is charged, and the voltage drops when charging is continued after the completion of charging. The -ΔV control is a method of detecting this voltage drop to control charging.

[0004]

In general, Ni-Cd batteries have a large self-discharge, and many of them are discharged by long-term storage after charging. For example, storage at 45 ° C. for one month reduces the capacity storage rate from 100% to about 30%,
It is known that even at 5 ° C., it becomes about half in five months. After being stored for such a long time, the Ni-Cd battery may not recover to its original capacity unless it is charged and discharged several times. For example, after storage at 20 ° C. for 13 years, a single charge can only charge up to about 70% of the capacity.
Recovers to nearly%. However, even in this case, if the temperature is high, the charged capacity decreases. For example, at 42 ° C., about 8
It can only be 0% capacity ratio. Further, if shallow charging / discharging is repeated for a Ni-Cd battery stored for a long period of time, when a deep discharge is performed with a heavy load, a phenomenon called a memory effect reduction may occur. In other words, a normal Ni-Cd battery has a characteristic that a relatively stable voltage is maintained during the use period, and the voltage drops when the remaining capacity is almost exhausted. The voltage drops once, and when the remaining capacity is almost exhausted, the voltage drops again. Many N
Since voltage is monitored in an electronic device using an i-Cd battery, if this memory effect phenomenon occurs, it is determined that there is no capacity even though the remaining capacity is sufficient, and an alarm is generated or operation stops. Problem.

[0005] That is, if the temperature around the Ni-Cd battery is high during charging, or if the temperature of the Ni-Cd battery is high during repeated charging and discharging, sufficient capacity recovery cannot be performed. Has a problem of causing a memory effect phenomenon.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem by repeating charge and discharge by controlling temperature.
An object of the present invention is to provide a charge / discharge control circuit capable of restoring the capacity of a battery to the maximum.

[0007]

SUMMARY OF THE INVENTION The present invention provides Ni-Cd
A constant current charging circuit and a discharging control circuit for the battery;
a cooling element provided close to the surface of the i-Cd battery;
A temperature sensor provided in close proximity to the surface of the Ni-Cd battery, means for repeating charging and discharging of the Ni-Cd battery,
Means for controlling the cooling element such that the output of the temperature sensor becomes substantially constant during charging of the Cd battery.

[0008]

When the charging cycle of the Ni-Cd battery is started, its surface temperature is detected and the cooling element is driven to a predetermined temperature. Thereby, charging and discharging can be repeatedly performed at a temperature optimal for charging.

[0009]

FIG. 1 is a block diagram of a Ni-Cd battery charge / discharge control circuit according to an embodiment of the present invention.

The Ni-Cd battery 1 is set in a battery housing (not shown). N set around the battery storage
A temperature sensor 2 and a Peltier element 3 as a cooling element are provided so as to be in contact with the surface of the i-Cd battery. Ni-
The Cd battery 1 has a constant current charge control circuit 4 and a discharge control circuit 5
And an A / D converter 6 for digitizing the battery output. The constant current charge control circuit 4 and the discharge control circuit 5 are controlled by the CPU 7, and the output of the A / D converter 6 is input to the CPU 7. The output of the temperature sensor 2 is amplified to a predetermined level by an amplifier 8, and the output signal is A
It is digitized by the / D converter 9 and input to the CPU 7. The CPU 7 is connected to a display unit 10 for displaying the capacity calculated after charging and an input device 11 for inputting a specified voltage and a specified capacity of the Ni-Cd battery.

The discharge control circuit 5 includes a plurality of switch elements (transistors) for switching a discharge current.
One of the switches is selected by the CPU 7.

Next, the operation of the above control circuit will be described with reference to the flowchart of FIG.

FIG. 2 shows a schematic operation of the CPU 7.

The Ni-C stored for a long time in the battery housing
When the battery 1 is stored, the operation is started. First, a specified voltage and a specified capacity of the Ni-Cd battery are input from the input device 11 by the operator. The CPU 7 stores the input data in a memory, and further determines a charging time required for charging the input specified capacity.

Since the capacity of the Ni-Cd battery 1 is unknown in the initial state, the Ni-Cd battery 1 is first discharged (n2).
The selection of the switch at this time is determined from the data input at n1.

Subsequently, temperature control is started at n3. The temperature control method is as follows.
The Peltier element 3 is driven via the switching means 12 so that the surface temperature of the Cd battery 1 is maintained at about 20 to 30 ° C.

At n4, a counter N for counting the number of times of charging during charging / discharging is set to 0, and charging is started (n5).
Charging is performed by -ΔV control. That is, −ΔV is monitored at every unit time from the output of the A / D converter 6, and when the magnitude becomes equal to or less than the fixed value K1, it is determined to be the charging end point, and the process goes to n7 to stop charging. Then, the charging time at that time is stored in the memory as t _N. Thereafter, discharge is performed (n9).

Next, at n10, it is determined whether or not the difference between the previous charging time and the current charging time is equal to or less than a fixed value K2. Since the charging time for obtaining the specified capacity is calculated in advance when the specified capacity is input in n1, sufficient capacity recovery is performed when the charging time is very close to the calculated charging time. You can judge that it was done. Here, the determination is made by monitoring the difference in charging time. That is, when the difference between the charging times becomes equal to or less than the predetermined value, the process goes to n11, the capacity at that time is calculated and displayed on the display unit 10, and the processing is ended. On the other hand, if the difference between the charging times is larger than the predetermined value at n10, the process returns to n5 and the charge / discharge cycle is executed again. The charge / discharge cycle is repeated a certain number of times while controlling the temperature in this manner.

[0019]

During charging and discharging, the temperature of the Ni-Cd battery is maintained at a substantially constant value, so that a sufficiently deep charging and discharging cycle can be repeated. For this reason, Ni
Even with a -Cd battery, its original capacity can be recovered to the maximum.

[Brief description of the drawings]

FIG. 1 is a block diagram of a Ni-Cd battery charge / discharge control circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation of a CPU in the charge / discharge control circuit.

FIG. 3 is an external view of a conventional Ni-Cd battery charge / discharge control circuit.

[Explanation of symbols]

 1-Ni-Cd battery 2-temperature sensor 3-Peltier element 4-constant current charge control circuit 5-discharge control circuit

Claims (1)

(57) [Claims] 1. A constant current charging circuit and a discharging control circuit for a Ni-Cd battery, a cooling element provided near a surface of the Ni-Cd battery, and a temperature sensor provided near a surface of the Ni-Cd battery. Means for repeating charging and discharging of the Ni-Cd battery; and means for controlling the cooling element such that the temperature sensor output becomes substantially constant during charging of the Ni-Cd battery. Battery charge / discharge control circuit