Automatic discharge and charger for batteries. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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The proposed device, after connecting the battery, first discharges it, then charges it, and then goes into standby mode. I pre-set the discharge and charge voltages in the range of 1 ... 12 V, and the discharge and charging currents - in the range of 0 ... 0,25 A.

The scheme of the device is shown in fig. 1. It contains a power supply, discharge and charge current stabilizers, as well as a control and indication unit. The power supply is assembled on a step-down transformer T1, a rectifier on a diode bridge VD1 with a smoothing capacitor C1 and an integrated voltage regulator DA2. The output voltage of the stabilizer, in addition to powering microcircuits and other elements, is used as a model for monitoring the voltage of the battery.

Rice. 1 (click to enlarge)

The output current of the stabilizer does not exceed 15 mA and practically does not affect the change in its output voltage.

The control and indication unit contains two OU DA 1.1, DA1.2, which are used as comparators, two triggers DD1.1 and DD1.2, electronic switches on transistors VT1, VT2, VT4, VT5 and a current stabilizer on the transistor VT3 OU DA1.2 monitors the voltage on the battery when it is discharged. The variable resistor R1 sets the voltage to which it must be discharged. As long as the voltage on it exceeds the set value, at the output of the op-amp DA1.2 it corresponds to a low logic level of the op-amp DA1.1 controls the voltage of the battery when it is charging. The variable resistor R3 sets the voltage to which it must be charged. As long as the voltage on it is less than the set value, there is a low level at the output of the op-amp DA1.1.

The discharge current stabilizer is a voltage controlled current source (ITUN). It is assembled on the op-amp DA3.1, transistor VT6 and resistor R23 - current sensor. Capacitors C7 and SE ensure stable operation of ITUN. The discharge current is set by a variable resistor R17.

Its value can be determined by the formula I_cut = U_R17 / R₂₃, where U_R17  - voltage on the engine resistor R17.

The charging current stabilizer is assembled on a VT7 transistor, the exemplary voltage source is on a VD2 zener diode, the current through which is stabilized by the VT3 transistor, and the resistor R26 acts as a current sensor. The variable resistor R25 sets the charging current. The VD3 diode prevents the battery from discharging through the VT7 transistor when the device is disconnected from the mains. In the same situation, resistors R7 and R8 limit the input currents of the op amp DA1.1 and OA1.2.

The device works as follows. After connecting the battery, variable resistors R1 and R3 set the voltage values ​​to which it is necessary to discharge and charge the battery, and turn on the device in the network. By briefly pressing the button SB1 "Start" triggers DD1.1 and DD1.2 will be set to zero - low level on the direct outputs (pins 1 and 13 DD1) and high on the inverse (pins 2 and 12). The supply voltage will go to the resistor R15, and the control voltage of the discharge current stabilizer will appear on the engine of the resistor RI7, so it will start working. This mode is indicated by the glowing LED HL2 "Discharging", since it will receive the supply voltage through the open transistor VT2.

As the battery discharges, the voltage on the battery will begin to decrease, and when it becomes less than the voltage on the engine of the resistor R1, the comparator DA1. 2 will switch. A high level will appear at its output, which will set the trigger DD1.2 to a single state. A low level will be set at the inverse output, so the discharge current will become close to zero, the HL2 LED will go out, and the VT5 transistor will open. Since the transistor VT4 is open at the same time due to the high level at the inverse output of the trigger DD1.1, current will flow through the zener diode VD2 and the charging current stabilizer will start working. This mode is induced by the burning LED HL3 "Charging".

As charging increases, the voltage on the battery increases, and when the cut-off voltage, which is set by resistor R3, is reached, the op-amp DA2.1 will switch, changing to a high-low output level. The trigger DD1 1 will be set to a single state, which will lead to the opening of the transistor VT1 and the closing of the transistor VT4. Charging will stop, the HL3 LED will turn off, and the HL1 LED "End of charging" will light up.

Most of the parts are installed on a printed circuit board made of one-sided foil fiberglass, the drawing of which is shown in Fig. 2. Capacitors C5, C6 and C8 are mounted on the side of the printed conductors on the terminals of the microcircuits DD1, DA1 and DA3. Transistors VT6, VT7, after being installed on the board, are attached to a plate with dimensions of 99x25x10 mm and a thickness of 1,5 mm made of aluminum alloy, which serves as a heat sink. Moreover, the transistor VT6 is fixed through a heat-conducting insulating gasket. The board is installed on the bottom of a plastic case of a suitable size, and a step-down transformer T1 is also fixed there. Variable resistors, LEDs and a button are installed on the housing cover, and a fuse holder is installed on the side wall.

Fig. 2

Fixed resistors MLT C2-23 are used, variables are SPZ-4AM of group A, but it is possible to replace them with variable resistors of a different type with a linear dependence of resistance on the angle of rotation of the engine. Oxide capacitors - K50-35 or imported, the rest - K10-17. Transistors KT3102A are interchangeable transistors. KT3102, KT342, KT315 with any letter indices, KT3I07 - for transistors. KT3107? KT361 also with any letter index. Transistor. KT303V can be replaced with KP303G, KPZS3D, transistor, KT973A - with KT973B OU LM358M, we will replace it with analogues KR1040UD1, KR1464UD1R, an analogue of the LM7B12CV chip - KR142EN8B. Button SB1 - any with self-return, for example, P2K without fixation. Step-down transformer - TS-10-ZM or another one that provides an alternating voltage of 15 ... 18 V on the secondary winding with an output current of up to 0,3 A. We can replace the RB152 diode bridge with any one with a permissible reverse voltage of at least 50 V and a direct current of at least 0,5 A or separate diodes with the same parameters.

If the installation is done correctly and the moments are correct, the adjustment comes down to grading the scales of the resistors R1 and R3, R17 and R2S and adjusting the discharge and charging current stabilizers. First, the scales of the resistors R1 and R3 are calibrated - for this, the power is turned on, and a voltmeter is connected in turn to their engines. changing the position of the resistor sliders, set the required voltage and make the appropriate marks on the scale. The scale of the resistor R1 is graduated through 1 V at the rate of 1 V per battery), the scale of the resistor R3 is through 1,45 V. For example, the scale of the resistor R1 is 1, 2, 3, 4, 5, 6, 7 and 8 V, and the scale resistor R3 - 1,45; 2,9; 4,35: 5,8; 7,25; 8,7; 10,15 and 11,6 V.

To calibrate the scale of resistors R17 and R25, their sliders are set to the lower (R17) and right (R25) positions according to the diagram, and an ammeter is turned on in series with a charged battery and connected to the device. The engines of the resistors R1 and R3 are set to the upper position according to the diagram, the device is connected to the network and the "Start" button SB1 is briefly pressed. The device will start in discharging mode. The engine of the resistor R17 is set to the upper position according to the scheme and the maximum discharge current is controlled. If necessary, it is changed by selecting the resistor R15. Then calibrate the scale of the resistor R17, making marks on it in accordance with the readings of the ammeter.

To calibrate the scale of the resistor R25, its engine is set to the leftmost position according to the diagram and the supply voltage (12 V) is briefly applied to the S input (pin 8) of the DD1.2 trigger - the device will go into charging mode. If necessary, the maximum value of the charging current is set by selecting the resistor R22. Next, calibrate the scale of the resistor R25, making marks on it corresponding to the readings of the ammeter.

Author: Mazepa N.

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