JPS6325868Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery charging device having a function of preventing overcharging of a battery to be charged.

In order to prevent overcharging of a battery, it is necessary to detect a predetermined state of charge of the battery. Conventional methods for this detection include methods of detecting the charging voltage of the battery and methods of detecting the temperature rise of the battery due to charging. It has been known. However, the charging voltage detection method generally has a complicated circuit configuration and has the disadvantage that the battery cannot be sufficiently charged. On the other hand, the temperature detection method does not have this drawback, but once a predetermined battery temperature is detected,
When the charging current is cut off or reduced, the battery temperature decreases and a large charging current flows again, causing repeated charging, which may lead to overcharging of the battery. Further, when a thermostat is used as a battery temperature detection element and the thermostat is inserted into a battery charging path, there is a risk that the contacts of the thermostat may be welded if the battery charging current is large.

The present invention is directed to solving the drawbacks of the conventional temperature detection method, and one embodiment of the present invention will be described below with reference to the drawings. In the figure, A is a charger and B is a battery pack. Charger A has two input terminals 2, 2' connected to AC power supply 1 and three output terminals 3 to 5, and the output terminals are connected to and detached from corresponding terminals 6 to 8 of battery pack B. Can be combined freely. Primary coil 10 of step-down transformer 9 of charger A
are connected to the input terminals 2, 2', and both ends of the secondary coil 11 are connected to the anodes of rectifier diodes 12, 12', respectively. The cathodes of both diodes are commonly connected, and a smoothing capacitor 13 is interposed between the cathodes and an intermediate tap 11' of the secondary coil 11. Between the common connection cathode end and the output terminal 3, the emitter-collector of a PNP transistor 14 is inserted as a charging control switch element, and a resistor 15 is connected between the emitter and base. A resistor 16 and an SCR 17 are inserted in series between the base of the transistor 14 and the output terminal 4, and this series circuit forms a signal current path 18 of the transistor 14 together with a thermostat to be described later. Reference numeral 19 is the gate circuit of the SCR 17, and a series circuit consisting of a resistor 20, a starting switch 21 that is closed only during starting, and a resistor 22 is connected in parallel to the smoothing capacitor 13, and the connection point between the starting switch 21 and the resistor 22 is connected to the SCR 17. Configured by connecting to a gate. The intermediate tap 11' is connected directly to the output terminal 5.

Battery pack B includes a charged battery 23 inserted between terminals 6 and 8, and a thermostat 24 that is attached closely to the battery and inserted between terminals 7 and 8 so as to be affected by the heat of the battery. It consists of.

In the above configuration, each terminal 6 of battery pack B
~8 to the corresponding output terminals 3 to 5 of charger A,
Connect the AC power supply 1 to the input terminals 2 and 2. In this state, when the start switch 21 is temporarily closed only when charging is started, the gate current of the SCR 17 flows between the gate and cathode of the SCR via the start switch and the thermostat 24. For this reason, SCR1
Resistors 15 and 16 are connected between the anode and cathode of 7.
A main current flows through the thermostat 24 and
SCR17 becomes conductive. Since this main current is a current smoothed by the smoothing capacitor 13, SCR1
7 remains conductive until the main current disappears when the thermostat 24 is opened. Due to the conduction of SCR17,
A voltage drop occurs across resistor 15, and correspondingly, a base current flows through transistor 14, making it conductive. The collector current of the transistor becomes a charging current for the battery 23, and charges the battery. As battery charging progresses and the battery approaches a fully charged state, the battery temperature begins to rise, and when it reaches a predetermined temperature, for example 45°C, the thermostat 24 opens. Therefore, SCR17 is no longer conductive,
Transistor 14 is cut off, and battery 2
3 charging is completed.

After charging is completed, even if the thermostat 24 is closed due to a drop in battery temperature, the SCR 17 remains cut off, and the battery will not be charged again unless the start switch 21 is closed again.

As described above, according to the present invention, the thermostat, which is activated by the thermal influence from the battery to be charged, is inserted in the signal current path of the control signal that conducts the charging control switch element of the battery, together with the anode and cathode of the SCR. Therefore, since the charging current of the battery does not flow through the thermostat, there is no welding between the contact pieces of the thermostat as in the conventional case. In addition, the SCR keeps the signal current flowing through the switch element unless the thermostat is opened, so even if there is a temporary drop in the power supply voltage, the conduction state of the switch element can be maintained. Battery charging can be stabilized. Furthermore, after charging is completed, both the switch element and the SCR are in a cut-off state, which has great practical effects such as almost no power loss.

[Brief explanation of drawings]

The drawing is an electrical circuit diagram showing an embodiment of the device according to the present invention. 14...Switch element, 23...Battery to be charged,
18...Signal current path, 17...SCR, 24...
Thermostat, 19... Gate circuit, 21...
Start switch.

Claims (1)

[Scope of utility model registration request] A series circuit of a switch element and a battery to be charged is provided at the rectified and smoothed output end of the AC power source, and the anode/cathode of the SCR and the battery are connected to the signal current path of the control signal that makes the element conductive. A battery charging device comprising: a thermostat that opens due to the influence of heat from the SCR; and a starting switch inserted between the rectified and smoothed output terminal and the gate of the SCR to turn on the SCR.