JPH03284131A - Quick charging circuit - Google Patents

Abstract

PURPOSE:To do charge without excess and deficiency in a short time by lowering the charge voltage when the charge current has decreased to the specified value so that it may be charged slowly. CONSTITUTION:At the start of charge, it is charged with large currents, and the charge currents decrease with the passage of time. When the storage battery nears complete charge, the charge currents fall to the specified current value. At this time (t), the charge currents are dropped to the trickle charge voltage, Hereby, the charge currents become smaller, and the trickle charge is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention performs rapid charging with a large current at the initial stage of charging, and continues charging to a certain extent even when charging is nearing completion, until almost completely charged. The present invention relates to a charging circuit that switches to a charging state using a weak current or a charging stop state after charging.

[Prior Art] Conventionally, as shown in FIG. 8, a charging control circuit for a storage battery of this type connects a storage battery 3 from a DC power source 1 via a control circuit 20.
The terminal voltage of the storage battery 3 is detected by the voltage detection circuit 50 and the control circuit 20
A signal is sent to control the charging current, the current value is monitored by the current detection circuit 60, and the signal is supplied to the control circuit 20, which supplies a predetermined charging current to the storage battery 3. It looks like this.

For example, in the constant voltage constant current method that has been commonly used, as shown in Figure 9, charging is carried out at a constant charging current, and when the terminal voltage reaches the set value, the voltage rise is suppressed and the voltage rise is suppressed. In this method, overcharging is prevented by reducing the current value.Also, as shown in FIG. There is a control method that sends a charge current and reduces the charging current in stages. In the charging methods described above, there are two methods: one is to set the charging voltage low from the beginning and continue charging without detecting the end of charging, and the other is to set the charging current relatively high initially and then reach a constant voltage state. A method is used to stop charging or switch to trickle charging after a certain period of time or when the temperature of the storage battery rises.

[Problems to be Solved by the Invention] In order to rapidly charge a storage battery, it is necessary to apply as high a voltage as possible and to flow as much current as possible. However, when applying a high voltage to the storage battery,
A storage battery will not be damaged if used for a short period of time, but if high voltage is continuously applied for a long period of time, it will overcharge, and much of the charging current will be spent on water electrolysis, which will shorten the battery's lifespan. there were.

Therefore, in order to charge in a short time, it is desirable to charge with a high voltage and large current at the beginning of charging, and to charge with a low voltage and minute current at the end of charging. However, the conventional charging method has the following problems at the initial stage of charging.

In other words, in the conventional constant voltage constant current method, the storage battery voltage is used to detect the end of charging, but since the terminal voltage of the storage battery increases when water electrolysis occurs at the end of charging, it is difficult to detect the end of charging. In order to detect this, the battery must be charged at a sufficiently lower voltage at the beginning of charging.

Also, since the charging current increases in proportion to the charging voltage, if the charging current is too large, the terminal voltage will rise before it is fully charged, and the charging stop voltage will be reached immediately. It is not possible to distinguish whether the voltage is rising due to the current or not, and charging ends before being fully charged. Therefore, a large current cannot flow during constant current charging.

Furthermore, since the charging voltage changes depending on the temperature, it is necessary to install a complicated correction circuit or lower the set voltage to provide some margin.

That is, in the conventional charging method, the voltage setting value must always be set lower than the upper limit voltage that does not affect the life of the storage battery. Moreover, since it is necessary to suppress the current at the initial stage of charging in order to detect a rise in voltage, only a lower voltage can be applied at the beginning of charging. Therefore, it is not suitable for rapid charging.

As described above, with the method of detecting the end of charging based on the storage battery voltage, the voltage and current at the initial stage of charging cannot be increased very much, and there is a limit to the shortening of charging time.

Next, problems at the end of charging will be explained. The fluctuation range of battery terminal voltage is 2.3 to 2 for lead-acid batteries.
．． The voltage is within a small range of 6V/eeel, and changes in a complicated manner depending on current, temperature, state of charge, etc., so it is difficult to determine whether the battery is fully charged or not based only on the terminal voltage of the storage battery.

For example, in the case of a storage battery, during constant current charging, the storage battery terminal voltage starts to rise rapidly at the end of charging when the state of charge is about 80%, and when the storage battery is charged to about 90%, the storage battery terminal voltage rises to almost the maximum value. Because of this,
In order to detect 100% charge, it is necessary to make a determination using a parameter different from the terminal voltage. Therefore, conventionally, charging has been stopped by detecting charging stoppage based on time, temperature, etc.

In this case, the time and temperature rise from transition to a constant voltage state to completion of charging vary significantly depending on the discharge state of the storage battery and the temperature of the environment, so overcharging or undercharging is likely to occur.

For example, when recharging a battery that is almost fully charged, charging should be terminated immediately after charging begins. In such a case, the charging voltage immediately rises to a constant voltage state, but if the charging time is specified by a timer, charging will continue until the predetermined time elapses. Also, considering that the end of charging is determined by the temperature on the surface of the storage battery, storage batteries have a large heat capacity and are made of plastic cases with poor thermal conductivity, so even if the temperature of the electrodes rises, the surface of the storage battery Since the temperature does not rise quickly, there is a problem that overcharging is likely to occur.

Therefore, the main object of the present invention is to provide a quick charging circuit that can charge a storage battery in a short period of time and without excess or deficiency.

[Means for Solving the Problems] A quick charging circuit according to the present invention includes a DC power source for charging a storage battery, and a charging current detection means for detecting that the charging current to the storage battery has decreased to a predetermined current value. and charging voltage control means for lowering the charging voltage to the storage battery in response to the detection output of the detection means.

[Operation] In the present invention, the charging voltage of the storage battery is set from the beginning to an upper limit voltage that does not affect the lifespan for a short time. This allows the maximum charging current to flow through the storage battery, allowing it to be fully charged in the shortest possible time. In the present invention, furthermore, by detecting a decrease in the charging current, lowering the voltage when the battery is nearly fully charged, and then slowly charging the battery, it is possible to quickly and reliably charge the battery.

As a result, charging can be performed with high voltage and large current at the beginning, and charging can be performed with low voltage and minute current at the end of charging.

In the case of constant voltage charging, the charging current changes significantly depending on the charging state, so it is extremely easy to detect the end of charging. In other words, the fact that the charging current has decreased sufficiently means that no more charging is possible, which proves that the battery is almost fully charged.

Therefore, detection of the storage battery temperature for detecting the end of charging and a control circuit such as a timer are not required.

[Embodiments of the Invention] Embodiment 1 FIG. 1 is a schematic block diagram showing the electrical configuration of an embodiment of the invention. As shown in FIG. 1, a charging current is supplied from a DC power supply 1 to a storage battery 3 via a control circuit 2. The detection circuit 5 detects a decrease in the charging current and sends a signal to the control circuit 2 to control the set voltage. The DC power supply 1 is a DC power supply for charging the storage battery 3, and the control circuit 2 controls the charging voltage to be maintained at a predetermined voltage, and also controls the charging voltage according to a signal based on the predetermined charging current value detected by the current detection circuit 5. This circuit lowers the set voltage value.

Preferably, a resistor or accelerator is inserted to limit the maximum current so that the charger does not become overloaded in the early stages of charging, the set voltage is controlled in multiple stages, or the charging voltage is inversely proportional to the charging current. and lower it.

FIG. 2 is a graph showing the charging characteristics of an embodiment of the present invention. As shown in FIG. 2, at the start of charging, the battery is charged with a large current by constant voltage charging, and the charging current decreases as time passes. When the storage battery is nearly fully charged, the charging current decreases to a predetermined current value. Current detection circuit 5 detects this decrease in current and supplies a signal indicating completion of charging to control circuit 2.

The current detection circuit 5 may be one that outputs a charging completion signal in response to the rate of change of the charging current reaching a predetermined value. When the control circuit 2 receives this signal at time t1, it reduces the charging voltage to a trickle charging voltage. As a result, the charging current becomes smaller, and the weak trickle charging current performs charging sufficient to replenish the self-discharge.

In addition, the broken line in FIG. 2 is a charging characteristic curve when the charger control voltage at the initial stage of charging is lowered a little, and the dashed-dotted line is a charging characteristic curve when it is further lowered. Thus, lowering the charging voltage reduces the initial charging current and increases the charging time.

FIG. 3 is a block diagram in the case where the control circuit is constituted by a microcomputer, a transistor for controlling the charging voltage so that the voltage corresponds to the voltage setting value outputted by the microcomputer, and a drive circuit for the transistor. The current is detected by a shunt resistor 5a, and the voltage across it is digitized by an A/D converter 2d and input to the microcomputer 2c. The microcomputer 2C calculates the voltage setting value according to the flowchart in FIG. 4, converts it into an analog voltage through the D/A converter 2b, and applies the voltage to the base of the voltage control transistor 2a. If the battery voltage (which is equal to the emitter voltage of transistor 2a) is lower than the potential difference between the base voltage and the pace emitter saturation voltage (approximately IV), a base current flows through the transistor, and the collector current of the transistor (battery charging current) flows. Therefore, the charging voltage is always controlled by the potential difference between the base voltage and the pace emitter saturation voltage.

FIG. 4 is a flowchart for controlling the charging voltage in multiple stages. When charging starts, the microcomputer calls the program shown in FIG. 4 and executes charging control.

That is, the microcomputer first performs initial settings such as setting the charging voltage to a voltage setting value (step SL). Next, a set voltage is supplied to the D/A converter to start charging (step S2). Next, the charging current is measured (step S3). The charging current is obtained by dividing the voltage across the shunt resistor 5a by its resistance value. Next, the charging current is compared with the current setting value, and if the charging current is large, the process returns to step S2 (step 84). If the charging current is smaller, it is checked whether the current setting value is the minimum value (step S5), and if it is less than the minimum value, the charging control is ended (
Step S7). On the other hand, if it is larger than the minimum value, the voltage setting value and current setting value are lowered by 1 (step S6) and the process returns to step S2.

In this way, charging can be performed with high voltage and large current at the beginning, and charging can be performed with constant voltage and minute current at the end of charging.

Example 2 FIG. 5 shows an example in which a resistor is used to control the voltage.

The DC power supply does not necessarily have to have a completely constant voltage, and it is desirable to have a high internal impedance in order to prevent overloading of the charger.

When controlling the charging voltage analogously with a transistor,
As the capacity of the storage battery increases, the charging current also increases.
This is disadvantageous because the control section generates a large amount of heat. In such cases, similar control can be achieved by turning the resistor on and off.

- As an example, a case will be explained in which control is performed in three stages: quick charging, normal charging, and triple charging. This operating situation is shown in FIG.

Initially, charging is performed with a large current through the quick charging current limiting resistor 6, and when the charging current becomes less than the first set value, the resistor is switched and normal charging is performed through the normal charging current limiting resistor 7. Furthermore, charging progresses and the current increases to the second level.
When the voltage decreases to the set value, the resistance is switched again and charging is performed through the trickle charging resistor 8.

In this way, a large current initially flows through the resistor 6, and rapid charging is performed. As the charging progresses, the charging current decreases, and when the current detection circuit 5 detects this, it generates a control signal indicating the completion of rapid charging. switch 9
In response to this signal, switches the connection to a larger resistor 7 and performs normal charging. At this time, the rapid charging amount is set to stop at about 70 to 80% of the storage battery capacity.

At the end of charging, when the current further decreases, the current detection circuit 5 detects this again and outputs a control signal to terminate normal charging. Switch 9 responds to this signal by switching to a larger resistor 8 for trickle charging.

When using a resistor to control the voltage, as shown in Figure 7,
Current limiting resistors may be connected in series to increase the number of stages to enable rapid charging.

According to the first and second embodiments described above, compared to the conventional constant voltage 3 voltage constant current charging method, there is no need to detect the storage battery voltage, so the circuit becomes simpler.

[Effects of the Invention] As described above, according to the present invention, by detecting a drop in the charging current and controlling the charging voltage, charging can be performed at a high current in a short time with a simple configuration. ,
It is possible to obtain a state of charge with no excess or deficiency. Therefore, rapid charging can be performed reliably and inexpensively.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the electrical configuration of a first embodiment of the present invention. FIG. 2 is a graph showing the charging characteristics of the first embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the detection circuit and control circuit of the first embodiment of the present invention. FIG. 4 is a diagram for explaining the operation of the control circuit shown in FIG. 3. FIG. 5 is a block diagram showing the electrical configuration of a second embodiment of the invention. FIG. 6 is a block diagram showing charging characteristics of a second embodiment of the present invention. FIG. 7 is a four block diagram showing a modification of the second embodiment. FIG. 8 is a block diagram showing the configuration of a conventional charger. FIG. 9 is a graph showing charging characteristics during conventional constant voltage constant current charging. FIG. 10 is a graph showing charging characteristics when the conventional current value is changed in multiple stages. In the figure, 1 is a DC power supply, 2 is a control circuit, 3 is a storage battery, 5 is a current detection circuit, 6.7 and 8 are resistors, 9, 10
and 11 indicate a switch.

Claims (1)

[Scope of Claims] A DC power supply for charging a storage battery; a charging current detection means for detecting that the charging current to the storage battery has decreased to a predetermined current value; and a charging current detection means responsive to a detection output of the detection means. and a charging current control means for reducing the charging current to the storage battery.