JPS6233817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery charging device that includes a detection control circuit that detects a predetermined state of charge of a battery to be charged and controls charging of the battery.

This type of device is widely used because it can rapidly charge a battery to be charged with a large charging current.

However, some of the batteries to be charged are internally short-circuited for some reason, and when such a short-circuited battery is charged, a short-circuited large current flows through the charging circuit, which may cause the charging device to burn out. For this reason, it is desirable to provide a detection circuit in the detection control circuit that detects an internal short-circuit state of the battery to be charged and stops charging the battery.

On the other hand, some of the batteries to be charged are in an overdischarged state (hereinafter referred to as overdischarged batteries). Here, the overdischarge state refers to a state in which the remaining electricity of the battery is completely discharged to the load, and the battery voltage at the time of the load is zero volts. When the battery to be charged is a nickel-cadmium battery, the anode is made of nickel oxide, the cathode is made of a cadmium compound, and caustic potassium is used as the electrolyte. The reaction during discharge is expressed at the anode as NiOOH+H ₂ O+e ^- →Ni(OH) ₂ +OH-.If the overdischarge condition is short, this chemical reaction will proceed only on the anode surface and will penetrate deep into the anode. NiOOH remains, and this NiOOH becomes the nucleus during the next charging, and a charging chemical reaction occurs quickly.

However, if the overdischarge condition becomes long-term, NiOOH
The change from Ni(OH) ₂ to Ni(OH)2 extends deep down, and the amount of NiOOH that should form the core during charging decreases, making the battery inactive.

In addition, in the case of forced discharge, for example, if two batteries with different residual amounts of electricity are connected in series and discharged, one battery with a small amount of remaining electricity will be discharged after the remaining amount of electricity becomes zero, and then the remaining amount of electricity will be reduced to zero. It is charged in the opposite direction with the discharge current. In one of the batteries, after the amount of remaining electricity becomes zero, gas is generated by electrolysis of water, and the reaction from NiOOH to Ni(OH) ₂ does not proceed deep into the anode. Therefore, a battery in a reverse charging state (hereinafter referred to as a reverse charging battery) is not inactivated.

The above-mentioned over-discharged batteries and reverse-charged batteries recover their voltage when placed under no load, just like normal batteries, but over-discharged batteries have a voltage below the normal battery voltage, and reverse-charged batteries have a negative voltage. . If charging current is supplied to these over-discharged batteries and reverse-charged batteries, the voltage will be restored and the battery will return to normal.

Therefore, if the detection circuit that detects the internal short-circuit state of the battery is activated immediately after charging starts, the voltage of over-discharged batteries or reverse-charged batteries at the start of charging is low, so these batteries will be treated in the same way as short-circuited batteries. Charging becomes impossible.

The present invention has been devised in view of this point, and is designed to prevent charging of over-discharged batteries, reverse-charged batteries, etc. that are in other states, except for batteries that are in an internal short-circuit state even after a predetermined short period of time has elapsed from the start of charging. An embodiment thereof will be described below with reference to the drawings.

FIG. 1 is a block diagram of the charging device. In this drawing, 1 is a charging power source and a switch circuit 2
The battery 4 to be charged is charged via the charging path 3 with the . Reference numeral 5 denotes a detection control circuit which detects a predetermined state of charge of the battery 4 and controls charging of the battery 4. The detection control circuit 5 includes a control circuit 6 that opens the switch circuit 2 by detecting a predetermined state of charge of the battery 4, and a detection circuit 7 that opens the switch circuit 2 by detecting an internal short circuit state of the battery 4. is provided. Further, a delay circuit 8 is provided within the detection circuit 7 so as to detect an internal short-circuit state of the battery 4 after a predetermined short-circuit time has elapsed from the start of charging.

FIG. 2 is a detailed diagram of the detection circuit 7. In this drawing, 9 is a comparator, to which the voltage at the voltage dividing point 14 of a series circuit of resistors 12 and 13 provided between the battery connection terminals 10 and 11 of the charging path 3 is applied to one input, and to the other input. A voltage at a reference voltage point 17 obtained by dividing the constant voltage Vcc by resistors 5 and 16 is applied to the input. A capacitor 18 is connected in parallel to the resistor 13, forming a delay circuit 8.

In the embodiment, the battery 4 is connected to the connection terminals 10 and 1.
In the case of no load with no connection between 1 and 1, connection terminal 10 is
2.4 volts, voltage dividing point 14 is 1.2 volts, reference voltage point 17 is 0.54 volts, and the delay time (time constant) of delay circuit 8 is 1.2 seconds.

When a short-circuited battery with an internal short-circuit is connected between the connecting terminals 10 and 11 in this state, the battery voltage is 0.4 volt or less as shown in the voltage characteristic diagram of FIG. 3a. For this reason, the voltage at the voltage dividing point 14 decreases from 1.2 volts to 0.2 volts or less, as shown in the voltage characteristic diagram of FIG. 4a, and after the delay time of the delay circuit 8, the voltage at the voltage dividing point 14 becomes smaller than the voltage at reference voltage point 17 of 0.54 volts. Therefore, the comparator 9 detects this state and the comparator output switches from high to low, opening the switch circuit 2 of the charging path 3 and stopping charging of the shorted battery.

Next, when an over-discharged battery is connected between the connection terminals 10 and 11, the voltage of the battery rises immediately at the start of charging, and exceeds 1.2 volts after the delay time, as shown by the solid line in the voltage characteristic diagram in Figure 3b. becomes. The voltage at the voltage dividing point 14 decreases from 1.2 volts, as shown in the voltage characteristic diagram in FIG. The over-discharged battery continues to be charged normally, and when a predetermined state of charge is reached, the control circuit 6 detects this state and opens the switch circuit 2, ending battery charging. When charging a reverse charge battery, the battery voltage is different from that of an overdischarged battery in that it rises from a negative voltage, as shown by the broken line in Figure 3b, but the voltage after the delay time is different from that of an overdischarged battery. They are almost the same and can be charged in the same way as over-discharged batteries.

A dendrite shot battery is a short-circuited battery before charging starts, but when a large charging current is applied, the dendrite portion (dendrite crystal) is destroyed, and the battery returns to normal after the delay time of the delay circuit 8. For this reason, it is also possible to charge the battery of the dendrite shot. In the case of a nickel-cadmium battery, dendrite shoots tend to occur during trickle charging in a high temperature atmosphere, for example.

The charging reaction at the cathode is expressed as Cd(OH) ₂ +2e ^- →Cd+2OH ^- , and the cadmium crystals on the cathode extend like branches and reach the anode, causing a short circuit between the cathode and the anode. This condition is called dendrite shoot.

As described above, according to the present invention, a detection circuit is provided that detects an internal short-circuit condition of a battery to be charged and stops charging the battery, and the detection circuit detects the internal short-circuit condition after a predetermined short period of time has elapsed from the start of charging. Therefore, even over-discharged batteries and reverse-charged batteries, which exhibit a low voltage at the start of charging as well as internally short-circuited batteries, will recover their battery voltage after the predetermined time has elapsed, so these over-discharged batteries, etc., can be can also be charged. Therefore, when the detection circuit is activated immediately after the start of charging, an over-discharged battery or the like that is often determined to be a defective battery can be charged in the same manner as a normal battery, and erroneous determination can be eliminated. Also, one input of the comparator that makes up the detection circuit is connected to a capacitor, and if the connection terminals of the battery are short-circuited due to some accident, this capacitor will instantly discharge and activate the comparator, so safety is high. Furthermore, since the method does not detect the voltage of a resistor connected in series with the battery, it has the effect of suppressing the amount of heat generated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the device according to the present invention, FIG. 2 is a detailed diagram of the detection circuit, FIGS. 3 a and b are voltage characteristic diagrams of a short-circuit battery and an over-discharged battery,
FIGS. 4a and 4b are input voltage characteristic diagrams of the detection circuit during charging of a short-circuited battery and an over-discharged battery. 5...Detection control circuit, 7...Detection circuit, 4...
Battery, 12, 13...Resistance that constitutes a voltage divider circuit,
Vcc...Reference voltage, 9...Comparator, 18...Capacitor, 8...Delay circuit.

Claims (1)

[Claims] 1. A detection control circuit that detects a predetermined state of charge of the battery to be charged and controls charging of the battery is provided, and a detection circuit that detects an internal short-circuit state of the battery and stops charging the battery is provided in the circuit. established,
In the charging device, the detection circuit detects the internal short-circuit condition after a predetermined period of time has elapsed from the start of charging, and the detection circuit includes a comparator that compares a voltage dividing point of a voltage dividing circuit connected in parallel with the battery with a reference voltage. has
A battery charging device characterized in that a delay circuit for determining the predetermined short time is configured by one resistor of the voltage dividing circuit and the capacitor via a capacitor in parallel with the voltage dividing circuit.