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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Dual mode charger. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells It is known that preventive work with batteries takes a lot of time from motorists and requires constant attention during their charging, especially at the final stage. The device proposed by the author will help car owners to solve a number of problems that arise in this case. Conducting a control-training cycle involves the process of discharging the battery with its subsequent charging to the nominal voltage. Recently, alternating current charging has become popular, in which the charging component in energy significantly exceeds the discharge one. This makes it possible to effectively deal with the sulfation of the battery plates and reduce the time spent on a complete control and training cycle. In order to improve operational convenience in the charger, it is desirable to have a node that allows you to stop charging the battery when it reaches the final voltage, which will help to avoid the danger of overcharging the battery. The chargers described in [1,2] undoubtedly have a number of positive properties and provide a large charging current. The only, in my opinion, their drawback is the bulky power supply transformer, which is necessary to deliver high power to the load. However, as practice shows, for preventive work with batteries up to 55 Ah, it is quite enough to have a charger that provides an output current of up to 4 A. A slightly lower charging current, in comparison with the rated ten-hour charging current, can easily be compensated by an increase in charging time. This mode is even more preferable when carrying out preventive work. The proposed dual-mode charger (see diagram) largely meets the above requirements. It differs from those described in "Radio" earlier by the presence of only one secondary winding in the network transformer, which simplifies its manufacture. The use of a smaller size transformer made it possible to reduce the weight and dimensions of the structure.
Main technical characteristics of the device
In order to simplify the power supply of the charger, it uses a half-wave rectifier, the function of which is performed by the diode VD1. The HL1 LED serves as an indicator that the device is connected to the network. A generator is assembled on a unijunction transistor VT1, which generates pulses of the switching node of the trinistor VS1. The shift of the control pulse relative to the beginning of the working half-cycle of the mains voltage is set by resistors R3 - R5, changing the charging time of the capacitor C1 to the opening voltage of the emitter junction of the transistor VT1. Resistor R4 regulates the charging current, and resistor R3 sets the upper limit of adjustment during the tuning process. The lower the resistance of the resistor R4, the faster the capacitor C1 is charged to the threshold voltage and the earlier the trinistor VS1 opens, the greater the charging current of the battery connected to the terminals X1 and X2. At a threshold voltage on the capacitor C1, the pn junction emitter-base 1 of the transistor VT1 opens and the capacitor is discharged through it. There is a sharp decrease in resistance between the base terminals of the transistor, and a pulse is formed on the primary winding of the transformer T2, which triggers the switching node of the trinistor VS1. The open state of the trinistor is maintained due to the holding current until the end of the working half-cycle. In the next working half-cycle, the process is repeated. A characteristic feature of the control unit is that it is powered by a battery connected to the output terminals of the charger. If the battery is not connected, then the trinistor is closed and does not allow the generated pulses to control the transistors VT3, VT4, as a result of which the charger is protected from a short circuit in the output when there is no load. If the battery is connected in the wrong polarity, the control unit is protected from reverse voltage by the VD11 diode, and the closed trinistor does not allow a short circuit current to occur in the circuit. With such a circuit solution, it was possible to achieve, without the introduction of special additional measures, the protection of the device from short circuits and the connection of a rechargeable battery in reverse polarity. The shaper of charge-discharge cycles of the battery with a time ratio of 3:1 (45 s - charging, 15 s - discharging), made on the integral timer KR1006VI1 (DA1), is borrowed from the device described in [3]. Only the parameters of the time-setting circuits of the shaper were changed. When setting the SA2 switch to the "Imp." at the output of the timer (pin 3), alternating high and low voltage levels are formed, starting from the discharge cycle. A high level opens transistors VT2 and VT6. Opening, the transistor VT2 blocks the operation of the shaper, and the transistor VT6 connects the discharge resistor R24 to the battery. The discharge mode is indicated by the HL3 LED. When a low-level voltage appears at the output of the timer, transistors VT2 and VT6 close and the battery charging cycle begins. To continuously charge the battery, switch SA2 is set to the "Continuous" position. The shaper is turned off. The continuous charging mode is indicated by the HL2 LED. The device for automatically turning off the charging current is assembled on an operational amplifier (op-amp) DA2, turned on by a comparator. The exemplary voltage at its inverting input forms the VD9 zener diode, and a part of the output voltage taken from the resistor R27 engine is supplied to the non-inverting input. When the final voltage of 14,4 V is reached at the terminals of the battery, a high voltage is set at the output of the DA2 microcircuit, which opens the transistors VT2 and VT5, thereby blocking the operation of the DA1 timer and the VS1 trinistor turn-on pulse shaper. In addition, a high level through the VD10 diode enters the non-inverting input, thereby maintaining a high level at the output of the op-amp. This state of the OS is indicated by the HL4 LED. Control the charging current of the battery in the process of charging on the ammeter RA1. The described charger is made in a metal perforated case with dimensions of 150x150x80 mm. The transformer is made on a steel magnetic circuit ШЛ20х32. Winding I contains 1070 turns of PETV-2 0,4 wire, and winding II - 126 turns of wire with a diameter of 1,18 mm. You can, of course, use a transformer of a larger size, while increasing the size of the case. For transformer T2, a magnetic circuit of size K10x6x4,5 made of M2000NM ferrite was used. Each of the transformer windings contains 45 turns of PETV-2 0,25 wire. They are wound simultaneously with two wires. The VD1 diode and the VS1 trinistor are installed (through mica spacers) on one common heat sink - a 60x60 mm aluminum plate 3 ... 4 mm thick. The heat sink function of the VT6 transistor can be performed by the metal base of the case. A printed circuit board for mounting other elements of the charger was not developed. It was replaced by a breadboard panel measuring 75X70 mm with a vertical installation of radio elements. The main parameters of the resistors and capacitors used in the charger are shown in the diagram. We can replace the KD206 diode with any of the same type or from the KD202 series. Instead of OU KR140UD708, K140UD7 is suitable. Diodes VD3 - VD7 and VD10 - any low-power. KT503B transistors are interchangeable with KT3117B, KT502B - with KT209B or KT501B, and KT827B - with any of the KT827, KT829, KT972 series. The adjustment of the device is carried out with a fully charged battery with a voltage of 12 V connected to the output terminals. The SA27 switch is set to the "Non" position. Then, by connecting the charger to the network, the variable resistor R3 slider is moved to the lower (according to the diagram) position and the charging current is set to 2 A with the resistor R4. resistance. Next, the SA3 switch is switched to the "Imp." and, using a voltmeter or oscilloscope, check the duration of the charge-discharge cycles. In this case, it should be taken into account that when the power is turned on, the discharge cycle occurs first and its duration is somewhat longer than in the steady state. This is explained by the fact that at the moment the power is turned on, the capacitor C4 is completely discharged. To establish a circuit breaker, you will need an adjustable DC source with an output voltage of 15 V and a class 1 DC voltmeter. A voltage of 2 V is supplied to the output terminals X2, X1 from an external DC source and its value is monitored with a voltmeter. The engine of the resistor R2 is shifted in the direction of increasing the voltage at the non-inverting input of the op-amp until the LED HL14,4 "End of charging" lights up. On this, the establishment of the proposed device can be considered complete. Literature
Author: L.Lyaskovsky, Kiev
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