JPH05268732A - Charger of battery - Google Patents

Abstract

PURPOSE:To enable a secondary battery to be charged fully in ideal condition by arranging the constitution such that a temperature detecting means detects the temperature rise when a battery comes close to full charge and the temperature rises and that a DELTAV changeover means makes charge control DELTAV small. CONSTITUTION:A temperature detecting means is composed of a thermistor 5, an A/D converter 4, and an arithmetic circuit 3. The arithmetic circuit 3 operates the voltage signal and the temperature signal inputted from the A/D converter 4 by means of a microcomputer, and controls a switching means 2, and detects the terminal voltage of a battery in sampling cycles, and stores the maximum value in a memory. And, the stored voltage value is compared with the detected voltages being sampled one after another, and if the detected voltage is higher than the value stored in the memory, it is rewritten with the detected voltage, and when it is lower, it is left as it is. Furthermore, the arithmetic circuit 3 changes over the charge voltage DELTAV for changing over a switching means 2 from ON to OFF with the temperature signal being input from a thermistor 5, and when temperature of the battery gets over the set temperature, this lowers it.

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 detecting a full charge of a battery and controlling a charging current.

[0002]

2. Description of the Related Art Secondary batteries such as nickel-cadmium batteries gradually increase in voltage when charged. However,
When fully charged, the voltage rises to the peak value and then drops. Therefore, full charge can be achieved by detecting that the voltage has decreased from the peak value by ΔV and stopping charging, or by switching from quick charging to trickle charging. The value of ΔV for detecting full charge is adjusted so that the battery does not become overcharged and does not reach the full charge prematurely. However, it is actually very difficult to accurately design the value of the charge control ΔV that controls the charge in this state. If the charge control ΔV is reduced, the battery will not be overcharged, but due to the influence of noise during charging, it will be prematurely cut off and cannot be fully charged. On the contrary, if the charge control ΔV is increased, premature disconnection does not occur, but there is a drawback that overcharge occurs. In the actual charging device, if the charging control ΔV is designed so as not to cause overcharging, it is impossible to prevent premature disconnection due to noise.

A charging device developed to avoid this drawback is described in Japanese Patent Application Laid-Open No. 2-101934. The device described in this publication detects a full change by detecting both the gradient change of the voltage curve during charging and ΔV. The voltage rise curve when charging a nickel-cadmium battery is shown in FIG. As shown in this figure, the voltage rises in a gentle curve at the beginning of charging, the slope becomes steep on the way, and thereafter the slope becomes gentle again. At the end, it drops by ΔV from the peak value. In order to detect the slope of the voltage curve, the time Ti during which the voltage rises by Vd is detected, and when Ti satisfies the following conditions, it is detected that full charge is approaching. T _i-1 ≧ Ti ≦ T _{i + 1} ……………

[0004]

As described above, the device for detecting full charge based on both ΔV and the voltage rise curve has a feature of preventing premature disconnection as compared with a device for detecting only ΔV. This is because the voltage rise curve of the battery does not satisfy the above equation unless the battery is close to full charge.
However, the device of this structure has a drawback that it cannot accurately fully charge all the secondary batteries. For example, the capacity is 70 ~
When the secondary battery in a state close to 80% of full charge is recharged, the voltage does not rise in the curve shown in FIG. 1 but rises as shown in FIG. When the voltage rises along the curve shown in this figure, the above equation is not satisfied even when the full charge is near. The temperature rise curve is loose →
The reason is that the gradient does not change from steep to gentle. Therefore, this device can fully charge the fully discharged secondary battery so that the secondary battery does not expire early, but has a drawback that all the batteries cannot be fully charged in an ideal state.

The present invention was developed to solve this drawback, and an important object of the present invention is to fully charge a secondary battery in an ideal state without affecting the capacity of the battery. To provide a charging device.

[0006]

The charging device of the present invention was developed to improve the above-mentioned object and has the following constitution. That is, the present invention is an improved charging device that sequentially detects the battery voltage and detects that the battery voltage has decreased from the peak value by ΔV to control charging. The charging device of the present invention includes a temperature detecting means for detecting the temperature of the battery and a ΔV switching means controlled by the temperature detecting means to switch the charging control ΔV. When the temperature of the battery rises as the battery approaches full charge, the battery temperature is detected by the temperature detection means, and the temperature detection means causes the ΔV switching means to reduce the charge control ΔV.
That is, the charging device of the present invention is characterized in that the charging state is controlled by both the battery temperature and ΔV.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate a charging device for embodying the technical idea of the present invention,
The device of the present invention does not specify the material, shape, structure, and arrangement of the components as the following structures. The device of the present invention can be modified in various ways within the scope of the claims.

The battery charger shown in FIG. 3 includes a charging power source 1, a switching means 2, an arithmetic circuit 3, voltage dividing resistors R1 and R2, an A / D converter 4, a thermistor 5, and
And a display circuit 6.

The charging power source 1 lowers the household voltage of 100 V to the charging voltage of the secondary battery to rectify it, and includes a transformer, a diode and a smoothing capacitor, which are not shown.

When the battery 7 is fully charged, the switching means 2 is controlled by the arithmetic circuit 3 to switch from the ON state to the OFF state and the charging of the battery 7 is stopped. For the switching means 2, switching elements such as transistors, FETs and relays can be used.

The charging device shown in FIG. 3 detects ΔV switching means for turning off the switching means 2 when it detects that the battery voltage has dropped from the peak, and is provided with voltage dividing resistors R1 and R2 and an A / D converter.
It is composed of a converter 4 and an arithmetic circuit 3. The voltage dividing resistors R1 and R2 divide the battery voltage into a predetermined voltage, and A / D
Input to the converter 4. The A / D converter 4 converts the divided voltage from an analog signal into a digital signal and inputs the digital signal into the arithmetic circuit 3. In addition, the A / D converter 4
Also converts the signal from the thermistor 5 into a digital signal and inputs it to the arithmetic circuit 3.

The temperature detecting means for detecting that the battery is close to full charge and controlling the ΔV switching means to switch the charge control ΔV to a low level is the thermistor 5, the A / D converter 4, and the arithmetic circuit 3. It consists of. The thermistor 5
It is arranged inside the battery pack to detect the battery temperature.

The arithmetic circuit 3 is a microcomputer (hereinafter referred to as a microcomputer), which controls the switching means 2 by calculating a voltage signal input from the A / D converter 4 and a temperature signal. The arithmetic circuit 3 detects the terminal voltage of the battery at a sampling cycle of, for example, 1 second. The detected battery voltage is stored in the memory. The memory stores the maximum value of the detected voltage. In order to store the maximum voltage in the memory, the voltage value stored in the memory is compared with the detected voltage which is sampled one after another. When the detected voltage is higher than the stored value of the memory, the stored value of the memory is rewritten with the detected voltage. When the detected voltage is lower than the stored value in the memory, the stored value in the memory remains unchanged. When the battery voltage is increasing, the detection voltage gradually increases. Therefore, in this state, the stored value of the memory is rewritten to the detection voltage. When the battery becomes close to full charge and the terminal voltage of the battery drops, the detected voltage drops by ΔV from the peak voltage stored in the memory. The arithmetic circuit 3 determines whether the compared sampling voltage has dropped to 20 mV or 10 mV or less from the peak voltage stored in the memory.

Further, the arithmetic circuit 3 switches the charging control ΔV for turning the switching means 2 from ON to OFF by the temperature signal input from the thermistor 5 via the A / D converter 4. Therefore, the arithmetic circuit 3 detects the battery temperature by the thermistor 5 together with the battery voltage at a constant sampling cycle. The charge control ΔV is switched by detecting whether the battery temperature is below or above the set value. When the battery temperature is lower than the set value, the charge control ΔV for turning off the switching means 2 is set to 20 mV, and when the battery temperature is higher than the set temperature, the charge control ΔV is set to 10.
Switch low to mV. When the battery temperature is low and the battery is not charged, the charge control ΔV is increased to prevent premature disconnection due to the influence of noise or the like. When the battery is near full charge, the charge control ΔV is lowered to prevent overcharging. The temperature at which the charging control ΔV is switched is adjusted to an optimum value in consideration of the charging current of the battery, the capacity of the battery and the like. For example, the charge control ΔV is adjusted in the range of 40 ° C to 90 ° C, preferably 45 ° C to 70 ° C.

FIG. 4 shows a flow chart in which the arithmetic circuit 3 detects the battery temperature and ΔV and controls the switching means 2. As shown in this figure, the switching means 2 is controlled by the following operation of the arithmetic circuit 3. The battery voltage and the battery temperature are sampled at regular intervals. It is determined whether the battery temperature is higher than the set temperature T. If the battery temperature is lower than the set temperature T, charge control ΔV
Is A (for example, 20 mV). If the battery temperature is higher than the set temperature T, charge control ΔV
Is B (for example, 10 mV). It is detected whether the battery voltage has dropped below the charge control ΔV. If the battery voltage is lower than the charge control ΔV,
The switching means 2 is turned off and the charging is completed. When the battery voltage is not lower than the charge control ΔV, the operation from is repeated.

FIG. 5 and FIG. 2 are graphs showing the state where the voltage and temperature of the nickel-cadmium battery to be charged rise. FIG. 5 shows the characteristics of the deeply discharged battery, and FIG. 2 shows the charging characteristics of the shallowly discharged battery, for example, a battery in which 70 to 80% of the capacity remains. As shown in FIG.
For deeply discharged nickel-cadmium batteries, the battery voltage rises as charging progresses. When the battery voltage is close to the full charge, the voltage rise becomes slow, and when the battery is fully charged, the voltage decreases from the peak value by ΔV. On the other hand, the temperature of the battery also rises as the charging progresses, especially when the input energy is not consumed by the battery reaction and is consumed as thermal energy near the full charge,
The temperature rises sharply. In addition, nickel that has been shallowly discharged
As the cadmium battery becomes fully charged,
As shown in FIG. 2, both the battery voltage and the battery temperature rise. However, the rising curve of the battery voltage of this battery is slightly different from the curve shown in FIG. That is, the voltage rises with a steep gradient from the beginning of charging.

The charging device shown in FIG. 3 has a circuit configuration that detects both the battery temperature and ΔV and terminates charging. That is, as indicated by the chain line in the figure, when the temperature of the battery is lower than the set temperature T, the charge control ΔV is set to A (for example, 20
mV) and becomes higher than the set temperature T, the charge control ΔV is adjusted to B (for example, 10 mV) as low as possible. Therefore, the charging control ΔV for switching the switching means 2 by the arithmetic circuit 3 is switched between B and A above and below the set temperature T.

The above battery charging device is constructed so as to detect the absolute value of the battery temperature and switch the charging control ΔV. This charging device has a feature that the secondary battery can be fully charged easily and reliably. However, the charging device according to the present invention does not necessarily detect the absolute value of the battery temperature and switches the charging control ΔV, and for example, detects the rate of change of the battery temperature per unit time to detect the charging control ΔV. It is also possible to switch. It is because the rising curve of battery temperature is
This can be realized by utilizing the steepness as the battery is fully charged.

Furthermore, the battery charger of the present invention does not necessarily specify the battery charging current to 0 even if the battery temperature and ΔV are detected to detect that the battery is fully charged. .. For example, it is possible to perform rapid charging with a large current until the battery is fully charged, and then switch to trickle charging with a small charging current after the battery is fully charged. As described above, the device in which the trickle charge is performed after the full charge has a feature that the full charge can be performed more completely.

[0020]

According to the battery charging apparatus of the present invention, the temperature of the battery is detected by the temperature detecting means. The temperature detection means is
When the battery becomes higher than the set value by controlling the V switching means, the charge control ΔV is decreased. That is, when the battery is near full charge, the charge control ΔV is reduced to prevent overcharging, and when the battery does not reach full charge, the charge control ΔV is increased and the battery is prematurely cut off due to the influence of noise or the like and is not fully charged. Are prevented. In particular, in the present invention, whether or not the battery is approaching full charge is detected by the battery temperature and the charging control ΔV is switched. Therefore, a battery having a remaining capacity of 70 to 80% can be recharged and fully charged without being overcharged, which cannot be realized by the conventional device that detects the voltage rise curve and switches the charge control ΔV. It has the feature that it can be charged in exactly the ideal state. In particular, when the battery is close to full charge, the input power of the battery is reduced in the proportion used for charging the battery and is consumed as thermal energy. This is because when the battery is close to full charge, the charging reaction of the battery gradually decreases, and the rate of energy consumption as a chemical reaction decreases. Therefore, the secondary battery has a property that the temperature rise curve becomes steep when the battery is near full charge.
That is, by detecting the temperature, it is possible to reliably detect that the battery is near full charge. Further, the fact that the amount of heat generated increases near the full charge is also effective in reducing the error due to the influence of the initial temperature of the battery. Therefore, there is a feature that the secondary battery can be surely fully charged in the winter or the summer without measuring the temperature at the initial stage of charging. However, it goes without saying that more ideal charging can be performed by detecting the temperature at the beginning of charging and controlling the temperature at which the charging control ΔV is switched according to the initial temperature.

[Brief description of drawings]

FIG. 1 is a graph showing a voltage rise curve of a deeply discharged battery.

FIG. 2 is a graph showing voltage and temperature change of a shallowly discharged battery.

FIG. 3 is a block diagram of a battery charging device showing an embodiment of the present invention.

4 is a calculation flowchart of a calculation circuit of the charging device shown in FIG.

FIG. 5 is a graph showing changes in voltage and temperature of a deeply discharged battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Charging power supply 2 ... Switching means 3 ... Arithmetic circuit 4 ... A / D converter 5 ... Thermistor 6 ... Display circuit 7 ... Battery R1, R2 ... Dividing resistance

Claims (1)

[Claims] 1. A battery charger configured to detect battery voltage successively, detect that the battery voltage has decreased from a peak value by ΔV, and control charging, to detect temperature of the battery. Means and a ΔV switching means controlled by the temperature detecting means to switch the charging control ΔV, and when the temperature of the battery rises near full charge, the battery temperature is detected by the temperature detecting means and the ΔV switching means. Is configured to reduce the charge control ΔV.