Electronic charging control relay. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers

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Every car enthusiast wants to more fully control the state of the power supply system in the car. Both overcharging and undercharging the battery negatively affect its "health", reducing the already short life of the energy storage device. The proposed article is devoted to the issues of ensuring optimal operating conditions for the battery.

The battery-generator-relay-regulator (on-board voltage stabilizer), as a rule, is a charging control relay as an element for monitoring the health of the battery-generator-relay-regulator system. The operating experience of the classic Zhiguli shows that it is possible to improve the information content of the control lamp by replacing their standard PC702 relay with its electronic version.

An analysis of the control devices published in the pages of the Radio magazine over the past 75 years has not revealed an option that is suitable in all respects. Still, it seems optimal that in which the signal lamp on the instrument panel, in addition to the lack of charging, would also indicate excess voltage in the power supply system

The device offered to the attention of readers differs from the known ones by its complete structural and electrical interchangeability with the PC702 relay, quick assembly and dismantling. It implements a mixed principle of monitoring the state of the vehicle's on-board network. The absence or presence of a battery charge is determined not by the voltage level, but by the absence or presence of a charging current. This is how the PC702 relay works.

This principle provides certain advantages: it ensures the simplicity and reliability of the device, the absence of the need to determine and set the response threshold, and practically independence from temperature, which is important for measuring units. Overvoltage monitoring - traditional, by means of a maximum voltage sensor (PMS).

The charge control relay can be functionally divided into the following components (see schematic diagram): charging current sensor with voltage amplifier - R1-R3, VT1; DMN - R5-R7, DA1; pulse generator - C2, R8, DD1.1; current amplifier - VT2; buffer inverter - DD1.2-DD1.4.

When the contacts of the switch SA1 "Ignition" are closed (the engine is not started or is running at low speed), the transistor VT1 remains closed, since a slight reverse current of the diodes VD2, VD4, VD6 of the generator unit flows in its base circuit. Therefore, the voltage on the capacitor C1 and the lower input of the Schmitt trigger DD1.1 according to the circuit is practically zero.

DMN is a voltage comparator made on a controlled zener diode DA1 (TL431ILP, domestic analogue of KR142EN19 [1]). The zener diode is closed, since at its control output the voltage taken from the R5R6 divider is less than the internal reference one (it is equal to 2,5 V).

Therefore, the capacitor C2 through the blocking diode VD1 of the device is charged almost to the supply voltage. The pulse generator is inhibited and its output is high. The output of the buffer DD1.2-DD1.4 is low, the transistor VT2 is open and saturated. The control lamp HL1 is on, indicating the absence of the battery charging current.

As the engine speed increases, the voltage generated by the vehicle's generator G1 increases. As soon as it exceeds the voltage on the battery, the diodes of the three-phase bridge VD1-VD6 of the generator unit open. A pulsating current appears in the base circuit of the transistor VT1. As a result, a pulse sequence with a variable duty cycle is formed on its collector. Integrating capacitor C1 separates the DC component. As soon as its value exceeds approximately two-thirds of the supply voltage of the microcircuit, the Schmitt trigger DD1.1 will switch to the opposite state. As a result, the transistor VT2 closes and the lamp HL1 turns off.

Note that according to the logic of operation in both described modes, the device does not differ from the PC702 relay.

Operation in the third mode depends on the voltage level in the on-board network. If a temperature-compensated stabilizer similar to [2, 3] is installed on the car, then the upper control limit can be taken equal to 15,5 ... 16 V. When using a conventional relay-regulator (stabilizer) 121.3702, this threshold can be reduced to 14,5 .. .15 V.

Upon reaching the selected threshold, the DMN is activated and the voltage at the anode of the blocking diode VD1 decreases to approximately 2 V. The charged capacitor C2 closes the diode VD1, removing the blocking from the pulse generator.

Capacitor C2 starts to discharge through the resistor R8 and the output of the Schmitt trigger DD1.1. As soon as the capacitor voltage, decreasing, reaches a third of the supply voltage of the microcircuit, the DD1.1 trigger will switch and a high level will appear at its output. The capacitor will again begin to charge through the resistor R8 from the trigger output - the generator will begin to produce rectangular pulses.

As a result, the transistor VT2 will periodically open and close, the HL1 lamp will flash, signaling a malfunction in the electrical equipment, leading to an excess voltage of the on-board network. The use of a microcircuit with Schmitt triggers is due to their good noise immunity due to the "hysteresis" characteristic.

Elements HL2, R11 form a duplicate indicator. It is not required, but will help out if the HL1 lamp burns out.

In the relay, instead of KT502A, any silicon p-n-p transistor can work, and instead of KT973A, any composite silicon pn-p structure with a permissible collector current of at least 2A can work. It is advisable not to change the KR1561TL1 microcircuit to others due to its greater load capacity. When choosing a DA1 chip, it should be borne in mind that the operating temperature range of the TL431ILP zener diode (and its varieties related to the industrial standard) is from -40 to +80 ° С; for the domestic analogue KR142EN19 - from -10 to +70 ° С.

The relay is assembled on a 47x29 mm circuit board made of textolite or getinaks 1 mm thick. Connections are made with MGTF wire with a cross section of 0,07 mm2, and the most high-current ones are 0,35 mm2. The board is attached to the getinax board of the PC702 relay through two plastic bushings.

To install an electronic analog, it is necessary to expand the metal casing of the relay, remove the executive electromagnetic relay from the board, shorten terminal 3 to 5 ... 87 mm. Solder flexible conductors to terminals 30/51, 85 and 87. Connect the common wire of the electronic analogue of the relay to the metal casing to ensure contact during installation with the car body. After installing the board in the casing, roll it around the perimeter again.

To test the relay's performance, an adjustable DC voltage source from 10 to 16 V with an output current of up to 1,5 A is required. The positive output of the source is connected to terminal 87, and the negative output is connected to a common wire. An indicator automobile lamp AA30-51 is connected to terminal 12/3.

By changing the supply voltage from 10 to 14 V, the lamp is turned on. Connect terminal 85 through a resistor with a resistance of 51 ... 100 Ohms to a common wire - the lamp should turn off. Then the supply voltage is gradually increased and the pulsed switching on and off of the lamp is observed. The "hysteresis" of the threshold voltage usually does not exceed 20 mV.

As described, check the performance of the relay on the car. Turn on the ignition - the indicator lamp on the side panel turns on and shines continuously. The engine is started, and in the idle mode, the lamp is turned off.

Close the conductors to each other, suitable for terminals 15 and 67 of the relay-regulator, having previously removed them from the pins. Carefully increase the engine speed, and, depending on the load of the on-board network, control the pulsed operation of the lamp with a frequency of several hertz (it depends on the ratings of the elements R8, C2).

Literature

1. Integrated circuits. Microcircuits for linear power supplies and their application (reference book). - M.: Dodeka, 2001.
2. Biryukov S. A simple thermally compensated voltage regulator. - Radio, 1994, No. 1, p. 34, 35.
3. Lomanovich V. Thermally compensated voltage regulator. - Radio, 1985, No. 5, p. 24-27.

Author: V. Khromov, Krasnoyarsk

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