JP3426616B2 - Battery charger - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charging device capable of preventing overcharge of a fully charged battery.

[0002]

2. Description of the Related Art Secondary batteries such as nickel-cadmium batteries have the property that the voltage increases as they are charged.
When fully charged, this battery has a characteristic that the voltage rises to a 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. ΔV to detect full charge
The value of is adjusted so that the battery does not become overcharged and does not expire prematurely. However, it is necessary to accurately design the value of the charge control ΔV that controls the charge in this state.
Actually very difficult. If the charge control ΔV is reduced,
The battery will not be overcharged, but due to noise during charging, it will prematurely expire and cannot be fully charged. On the contrary, charge control Δ
If V 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.

In order to avoid this drawback, JP-A-2-10
The charging device described in Japanese Patent No. 1934 has been developed. The device described in this publication detects full charge 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 gradient becomes steep on the way, and thereafter the gradient becomes gentle again. At the end, ΔV falls 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} ……………

Thus, both ΔV and the voltage rise curve are
The device that detects a full charge with is a device that detects only ΔV.
Compared with this, it has the feature of preventing premature cutting. It ’s full
If you do not approach charging, the battery voltage rise curve
This is because the expression of is not satisfied. However, this structure
The built-in device does not fully charge all secondary batteries.
There is a point. For example, for a full charge with a capacity of 70-80%
When the secondary battery in a close condition is recharged, the voltage is shown in Fig. 1.
The curve does not rise, but rises as shown in Figure 2.
It When the voltage rises in the curve shown in this figure, full charge
Even if it gets closer to the above Is never satisfied. It
Shows that the voltage rise curve changes from gentle → steep → gentle slope
The reason is not to do it.

The present inventor has, in order to solve this drawback,
When the battery temperature is detected and the battery temperature rises, charging control Δ
We have developed a charging device that reduces V to prevent overcharging (Japanese Patent Application No. 4-60643). This device utilizes the property that the temperature of the battery rises when approaching full charge, and when the temperature rises near the full charge of the battery, the charge control ΔV is switched to a small value to prevent overcharging.

[0006]

This device has a feature that it is possible to prevent overcharge of a fully charged battery, as compared with a device that detects the slope of a voltage rise curve. However, this device has a drawback that a fully charged battery having a low temperature is overcharged. This is because if the low temperature fully charged battery is recharged, it will be overcharged before the temperature rises. Therefore, this charging device has a drawback that it is not possible to normally determine the full charge in a state where the ambient temperature is low.

The present invention was developed with the object of solving this drawback, and an important object of the present invention is to prevent overcharging of a fully charged battery regardless of ambient temperature and to prevent rechargeable batteries. To provide a charging device that can be fully charged in an ideal state.

[0008]

The charging device of the present invention was developed to improve the above-mentioned object, and has the following configuration. 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 timer means and ΔV switching means. The timer means starts counting when charging is started. The ΔV switching means detects the battery voltage and stops the charging of the battery or reduces the charging current Δ
Switch V. That is, if the battery voltage rises above the set value while the timer means is counting, ΔV
The switching means reduces the charging control ΔV to prevent overcharging of the fully charged battery.

The setting time of the timer means is set to an optimum value in consideration of the charging current of the battery, etc., but is set to a range of several tens of seconds, for example.

[0010]

The charging device of the present invention performs the following operation to charge the battery. When a fully charged battery is recharged, the voltage of the battery close to full charge rises as shown by the curve A in FIG. That is, when charging is started, the voltage rapidly rises. Therefore, the battery voltage rises above the set voltage V _REF within the set time T _c of the timer means. The charging device detects that the battery voltage rises above the set value within the set time of the timer means, and switches the charging control ΔV to a small value. For example, the ΔV switching means switches the charge control ΔV from 20 mV to 10 mV, and stops the charging or switches to trickle charging when the battery voltage drops by 10 mV from the peak.

When the discharged battery is charged, the voltage of the fully discharged battery increases according to the curve B in FIG. Therefore, the battery voltage does not rise above the set voltage V _REF during the set time T _c of the timer means. Therefore, the charging device charges the battery according to a normal routine without switching the charging control ΔV to a small value in the initial stage of charging.

[0012]

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 charging device shown in FIG. 4 includes a charging power source 1, a switch means 2, an arithmetic circuit 3, and a voltage dividing resistor R.
1, R2, an A / D converter 4, a thermistor 5, 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 (not shown).

When the battery 7 is fully charged, the switch 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. A switching element such as a transistor, a FET, or a relay can be used as the switch unit 2.

The charging device shown in FIG. 4 detects ΔV switching means for turning off the switch means 2 by detecting that the battery voltage has dropped from the peak, and the voltage dividing resistors R1 and R2 and the A / D converter 4. , And the arithmetic circuit 3. Voltage dividing resistor R
1 and R2 divide the battery voltage into a predetermined voltage and input it to the A / D converter 4. The A / D converter 4 converts the divided voltage from an analog signal to a digital signal,
Input to the arithmetic circuit 3. Further, the A / D converter 4 is
The signal from the thermistor 5 is also converted into a digital signal and input to the arithmetic circuit 3.

The arithmetic circuit 3 is a microcomputer (hereinafter referred to as a microcomputer) having timer means built therein.
The voltage signal input from the / D converter 4 is calculated to control the switch unit 2. 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 is left 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 detection voltage decreases by ΔV from the peak voltage stored in the memory. The arithmetic circuit 3 calculates the charging control ΔV (for example, 20 mV, or 1 from the peak voltage in which the compared sampling voltage is the stored value of the memory).
It is determined whether the voltage drops below 0 mV.

Further, the arithmetic circuit 3 has a set voltage V _REF.
And the set time T _c is stored as timer means. The set time _Tc of the timer means is, for example, 10-6.
The time is set to 0 second, preferably 10 to 35 seconds. The timer means starts counting when charging of the battery is started. When the battery voltage rises above the set voltage V _REF while the timer means is counting, the arithmetic circuit 3 switches the charging control ΔV to a small value. Therefore, the arithmetic circuit 3, when the timer means is counting,
It is detected whether the battery voltage is equal to or higher than the set voltage V _REF , and when the battery voltage is lower than the set voltage V _REF ,
The charging control ΔV for turning off the switch means 2 is set to 20 mV, and when the battery voltage becomes higher than the set voltage V _REF , the charging control ΔV is switched to 10 mV. When the battery voltage 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 battery for switching the charging control ΔV 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 set voltage V _REF is
In the case of nickel-cadmium battery, 1.4V per cell
It is adjusted to 1.7V, preferably 1.45V to 1.65V.

The arithmetic circuit 3 controls the charge control ΔV at the beginning of charging.
FIG. 5 shows a flowchart for switching between the two.
Start charging. At this time, the timer means starts counting. The timer means determines whether or not the set time _Tc has elapsed. When the set time T _c has passed,
Sample the battery voltage. It is determined whether the sampled voltage is higher than the set voltage V _REF . When the sampling voltage is higher than the set voltage V _REF , the charging control ΔV is switched to a small value. For example, in this process, the charge control ΔV is switched from 20 mV to 10 mV. In this process, the sampling voltage is the set voltage V
_What is higher than _REF is a battery that is close to full charge.
For a battery close to full charge, the charge control ΔV is switched to a small value in this process. Therefore, overcharging is prevented, full charge is detected with high sensitivity, and charging is stopped. When it is determined that the sampling voltage is lower than the set voltage V _REF , the charging control ΔV is not switched. A battery whose sampling voltage is lower than the set voltage V _REF is not a battery close to full charge. Therefore, this battery is charged in a normal charging routine.

FIG. 3 is a graph showing a state in which the voltage of a nickel-cadmium battery to be charged rises. A curve B in FIG. 5 shows the characteristics of a deeply discharged battery, and a curve A shows the charging characteristics of a shallowly discharged battery, for example, a battery having 70 to 80% or more of its capacity remaining. As shown by the curve B, in the deeply discharged nickel-cadmium battery, the voltage rises first and then the voltage rises slowly, and when the battery is fully charged, the voltage rises and then decreases from the peak value by ΔV. As shown by the curve A, the voltage of the nickel-cadmium battery, which is close to full charge, rises with a steep gradient from the beginning of charging, and the voltage is set to the set voltage V at the set time T _c of the timer means.
_It will be higher than _REF .

The charging device shown in FIG. 4 detects the battery voltage when the set time _Tc set by the timer means has elapsed, and the battery to be charged is a battery close to full charge, or
It is determined whether the battery is fully discharged. When charging a battery that is close to full charge, the ΔV switching means controls the charging Δ
V is switched to a low level to detect full charge with high sensitivity. The fully discharged battery is charged in a normal routine without the ΔV switching unit switching the charging control ΔV to a small value in order to prevent premature battery termination.

The present invention does not specify the state of charge after the set time has elapsed. For batteries that are not fully charged within the set time,
It can be recharged in all conditions that are or will be adopted. For example, as shown in the flowchart in FIG. 6, charging can be performed while detecting the battery temperature with the thermistor. The A / D converter samples the battery voltage and the battery temperature at regular intervals. It is determined whether the battery temperature is higher than the set temperature T.
When the battery temperature is lower than the set temperature T, the charging control ΔV for stopping the charging of the battery is set to 20 mV, for example.
When the battery temperature is higher than the set temperature T, charge control Δ
V is switched to, for example, 10 mV. It is detected whether the battery voltage has dropped below the charge control ΔV. When 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.

In the above embodiment, when the battery is fully charged,
It is configured to stop charging. However, in the present invention, it is not always necessary to stop the charging by setting the charging current of the battery to 0 when the full charging of the battery is detected. 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.

Furthermore, in the above embodiment, the set time T
_{When c} has elapsed, the battery voltage is detected, and at this time, it is determined whether the battery voltage is higher than the set voltage VREF, and the battery charge state is detected. However, the apparatus of the present invention, until the elapse of the set time T _c, the voltage of the battery at a constant period is measured a plurality of times, than the setting voltage V _REF before the elapse of the set time T _c It is also possible to judge whether it has become higher. For example, the set time T _c is set to 20 seconds, the voltage of the battery is sampled at a cycle of 1 second, it is judged whether the sampled voltage is higher than the set voltage VREF every time, and the sampling voltage becomes equal to or higher than the set voltage VREF. , ΔV switching means for charging control Δ
It is also possible to switch V to a small value.

[0025]

The battery charging device of the present invention detects whether the voltage of the battery rises above the set voltage during the fixed time when the charging is started, detects the state of charge of the battery to be charged, and charges the battery. The value of the charge control ΔV for detecting full charge is changed according to the charging state of the battery. Therefore, the device of the present invention has a feature that a battery close to full charge can be recharged without being overcharged. For a battery close to full charge, the battery voltage rises rapidly at the beginning of recharging, and becomes higher than the set voltage during the set time of the timer means. The device of the present invention, when the voltage of the battery exceeds the set voltage during the set time, switches the charging control ΔV to a small value to detect the full charge with high sensitivity, in other words, detects the full charge early and stops the charging, Alternatively, switching to trickle charging can effectively prevent overcharging of a fully charged battery. The conventional device that detects the battery temperature and switches the charge control ΔV to high sensitivity is also
Although it is possible to prevent overcharging of a battery close to full charge,
This device has the drawback of overcharging when the ambient temperature is low. This is because when the ambient temperature is low, the battery is overcharged before the battery temperature rises. On the other hand, the device of the present invention has a feature that it is possible to prevent overcharge of a battery which is close to full charge, regardless of the ambient temperature. Particularly preferably, when the battery is close to full charge when the ambient temperature is low, the voltage of the battery rises quickly, so that the battery can be reliably prevented from being overcharged at this time.

[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 a voltage and a temperature change of a battery close to full charge.

FIG. 3 is a graph showing voltage changes of a battery that is close to full charge and a battery that is deeply discharged.

FIG. 4 is a block diagram of a battery charging device showing an embodiment of the present invention.

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

FIG. 6 is a flowchart showing a battery charging method after a set time has elapsed.

[Explanation of symbols]

1 ... Power supply for charging 2 ... switch means 3 ... Arithmetic circuit 4 ... A / D converter 5 ... Thermistor 6 ... Display circuit 7 ... Battery R1, R2 ... Dividing resistance

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Claims (3)

(57) [Claims] 1. A battery voltage is sequentially detected to detect that the battery voltage has decreased by ΔV from a peak value and to stop charging,
Alternatively, in a battery charging device configured to reduce the charging current, the battery voltage is set to be equal to or higher than a set voltage within a set time of the timer means that includes timer means and ΔV switching means and starts counting when charging is started. A battery charger, wherein the ΔV switching means is configured to switch to a smaller charging control ΔV for reducing the charging current when the battery voltage rises. 2. The battery voltage is detected sequentially to detect the battery voltage.
Detection of a decrease in ΔV from the peak value and stopping charging,
Or charging a battery configured to reduce charging current.
In electrical equipment, A timer means and a ΔV switching means are provided to start charging.
And at the set time of the timer means to start counting, the battery
If the voltage rises above the set voltage, the ΔV switching means
Change charging control ΔV to decrease charging current
A battery charging device having the above-mentioned configuration. 3. The set time of the timer means is 10 to 60 seconds.
The battery charger according to claim 1 or 2.