Network outage sensor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network
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Constant mains voltage is not only convenient in terms of, for example, artificial lighting, but also vital if it is the only source of energy that ensures the heating of the greenhouse, maintaining the temperature of the refrigerator or freezer. In addition, the absence of voltage in the network for a long time makes the security system vulnerable. It is enough for a cunning burglar to burn the electric meter and plugs and calmly empty your house, since all the batteries will be discharged. A miniature low-voltage relay is permanently connected to the 220 V network. It has electrical contacts that can be included in the monitoring circuit of a console or telephone transmitter. This relay controls the low-voltage electrical circuit by means of a break contact (rest contact).
Figure 1 shows a simple sensor circuit. AC voltage 220 V is rectified by a diode bridge D1-D4. R1 limits the inrush current at turn-on if C1 is discharged. C1 limits the average steady state current to approximately 15 mA. R2 is a protective resistor that discharges C1 while working with the circuit.
Ris.1
With reverse bias, the zener diode D6 limits the voltage applied to the relay, and with forward bias, it neutralizes the self-induction of the relay winding. As long as there is voltage in the network, diode D5 glows. It goes out as soon as the relay is powered off.
Figure 2 shows the PCB layout, which you can adapt to any relay model.
Ris.2
If necessary, make sure that the winding resistance is 1000 ohms for a 12V relay and 2000 ohms for a 24V relay. The advantage of a 24V relay is that it requires less winding current, which is important for most of these contacts.
Before applying voltage to the circuit, very carefully check the correct installation of the elements, especially the diodes.
Publication: N. Bolshakov, rf.atnn.ru
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