JPH04248334A - Charge/discharge control circuit for ni-cd battery - Google Patents

Abstract

PURPOSE:To realize maximum recovery of Ni-Cd battery by repeating charge/ discharge operation through temperature control. CONSTITUTION:Temperature control is carried out by receiving an output from a temperature sensor 2 and driving a Peltier element 3 through a switching means 12 so that the surface temperature of an Ni-Cd battery 1 is maintained in the range of 20-30 deg.C. - V is monitored every unit time based on an output from an A/D converter and when the magnitude thereof drops below a contant value K1, a decision is made that the end of charging operation has reached and the charging operation is stopped. The charging time is stored in a memory and then discharging operation is carried out. According to the invention, even an Ni-Cd battery preserved for a long term can be recovered to the maximum.

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 Ni--Cd batteries used in small electronic devices, and more particularly to a charge-discharge control circuit for Ni--Cd batteries that have been stored for a long period of time.

0002

2. Description of the Related Art FIG. 3 shows a conceptual diagram of a conventional Ni--Cd battery charge/discharge control circuit. -ΔV control is commonly used as a charging control method for Ni--Cd batteries.

[0003] As the Ni--Cd battery is charged, the terminal voltage increases, and when charging is continued after charging is complete, the voltage decreases. -ΔV control is a method of detecting this voltage drop and controlling charging.

0004

Generally, Ni--Cd batteries have a large self-discharge rate, and a large amount of the battery is discharged during long-term storage after charging. For example, after one month of storage at 45°C, the capacity storage rate decreases from 100% to approximately 30%, and 20%
It is known that the temperature decreases by about half in five months at ℃. After a Ni-Cd battery has been stored for such a long period of time, it may not recover to its original capacity unless it is charged and discharged several times. For example, after being stored at 20℃ for 13 years, a single charge will only reach about 70% of the capacity, but after repeated discharging and charging, the capacity will reach about 100% after 7 charges.
Recovers to nearly %. However, even in this case, if the temperature is high, the capacity to be charged will decrease. For example, at 42℃, about 8
The capacity ratio is only 0%. Furthermore, if a Ni--Cd battery that has been stored for a long period of time is repeatedly subjected to shallow charging and discharging, a phenomenon called memory effect reduction may occur when deep discharging is subsequently performed under a heavy load. In other words, a normal Ni-Cd battery maintains a relatively stable voltage during the period of use, and the voltage drops when the remaining capacity is exhausted, but this memory effect phenomenon occurs when the remaining capacity is sufficient. The voltage drops once, and when the remaining capacity is about to run out, the voltage drops again. many N
Electronic equipment using i-Cd batteries monitors voltage, so if this memory effect phenomenon occurs, it will be determined that there is no capacity even though there is sufficient remaining capacity, causing an alarm or stopping operation. There is a problem with processing.

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 achieved. had the problem of causing a memory effect phenomenon.

The purpose of the present invention is to solve the above problems by repeating charging and discharging through temperature control, and to
It is an object of the present invention to provide a charge/discharge control circuit that can recover the capacity of a battery to the maximum extent.

[0007]

[Means for Solving the Problems] This invention provides Ni-Cd
A constant current charging circuit and a discharge control circuit for a battery, and
a cooling element provided close to the surface of the i-Cd battery;
A temperature sensor provided close to the surface of the Ni-Cd battery, a means for repeatedly charging and discharging the Ni-Cd battery, and a temperature sensor provided close to the surface of the Ni-Cd battery;
- Means for controlling the cooling element so that the output of the temperature sensor becomes substantially constant during charging of the Cd battery.

[0008]

[Operation] When the Ni--Cd battery enters a charging cycle, its surface temperature is detected and the cooling element is driven to maintain a predetermined temperature. Thereby, charging and discharging can be repeatedly performed at the optimum temperature for charging.

[0009]

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

[0010] The Ni-Cd battery 1 is set in a battery storage section (not shown). There is a set N around this battery compartment.
A temperature sensor 2 and a Peltier element 3, which is 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 charging control circuit 4 and a discharge control circuit 5.
and an A/D converter 6 that digitizes 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.
The signal is digitized by the /D converter 9 and input to the CPU 7. Also connected to the CPU 7 are a display section 10 that displays the capacity calculated after charging, and an input device 11 for inputting the specified voltage and capacity of the Ni-Cd battery.

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

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

FIG. 2 schematically shows the operation of the CPU 7.

[0014] Ni-C stored in the battery compartment for a long time
When the battery 1 is stored, operation starts. First, the operator inputs the specified voltage and capacity of the Ni-Cd battery from the input device 11. The CPU 7 stores the input data in the memory, and further calculates the charging time required to charge the battery to the specified input capacity.

Since the capacity of the Ni--Cd battery 1 is unknown in its initial state, it 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 based on the output from the temperature sensor 2.
- 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 and discharging is set to 0, and charging is started (n5). Charging is performed by -ΔV control. That is, -ΔV from the output of the A/D converter 6 is monitored every unit time, and when the magnitude becomes less than a certain value K1, it is determined that the charging end point is reached, and the charging is stopped at step n7. Then, the charging time at that time is stored in the memory as tN. After that, discharge is performed (n9).

Next, at n10, it is determined whether the difference between the previous charging time and the current charging time is less than or equal to a certain value K2. Since the charging time to obtain the specified capacity is calculated in advance when the specified capacity is input in n1, sufficient capacity recovery will occur when the charging time becomes very close to the calculated charging time. It can be determined that the Here, this determination is made by monitoring the difference in charging time. That is, when the difference in charging time becomes less than a certain value, the process goes to n11, calculates the capacity at that time, displays it on the display unit 10, and ends the process. On the other hand, if the difference in charging time is larger than a certain value at n10, the process returns to n5 and the charging/discharging cycle is executed again. In this way, charging and discharging cycles are repeated a certain number of times while controlling the temperature.

[0019]

[Effects of the Invention] During charging and discharging, the temperature of the Ni--Cd battery is maintained at a substantially constant value, so that sufficiently deep charging and discharging cycles can be repeated. For this reason, Ni stored for a long time
Even a -Cd battery can recover its original capacity to its fullest extent.

[Brief explanation of the drawing]

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 the 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 charging control circuit 5-Discharge control circuit

Claims (1)

[Claims] 1. A constant current charging circuit and a discharge control circuit for a Ni-Cd battery, a cooling element provided close to the surface of the Ni-Cd battery, and a temperature sensor provided close to the surface of the Ni-Cd battery. an Ni-Cd battery comprising: means for repeating charging and discharging of the Ni-Cd battery; and means for controlling the cooling element so that the temperature sensor output remains approximately constant during charging of the Ni-Cd battery. Battery charge/discharge control circuit