A simple signaling device for increased mains voltage. Scheme, description

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A simple signaling device for increased mains voltage. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies

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This simple but reliable device, designed to sound an alarm about an emergency increase in mains voltage, can be assembled in just a couple of hours. Being constantly connected to the network, consuming less than one watt of power, it continuously monitors the good condition of the 220 V AC lighting network.

Many of us at least once in our lives have encountered such a situation when several electronic and / or electromechanical devices suddenly failed in the apartment at the same time, which can sometimes be especially disappointing if the repair costs reach 30% or more of the cost of a new device. This state of affairs with the cost of repairing damaged devices is typical if a refrigerator, washing machine, microwave oven and other similar expensive household appliances fail.

The schematic diagram of the device is shown in Fig.1.

Simple signaling device for increased mains voltage

AC mains voltage 220 V through the safety resistor R1 is supplied to the rectifier bridge VD1-VD4. From the output of the diode bridge, the rectified mains voltage is supplied to an overvoltage sensor made on a high-voltage varistor R3, a zener diode VD5, a current-limiting resistor R4 and R2, VD6-VD8. When the voltage in the network does not exceed 250 ... 270 V, the varistor R3 and the zener diode VD5 are closed, the oxide capacitor C1 is discharged, the transistor VT1 is closed. The signal circuit, implemented on a flashing LED and a piezoceramic sound emitter with a built-in generator, is de-energized.

As soon as the voltage in the network exceeds the set value, for example, reaching 380 ... 450 V (which can happen due to a natural disaster, negligence of personnel serving low-voltage power lines, for other reasons), then the amplitude of the rectified voltage will increase to 370 .. .630 V. The varistor and zener diode will open, the capacitor C1 will charge to a voltage of more than 1,2 V, the transistor VT1 will open. The flashing LED will start flashing, and in time with it, sound beeps with a frequency of 1 ... 1 kHz will be heard from HA4.

The supply voltage of the transistor node is limited to 12 V by a chain of VD11 zener diode and HL2 LED connected in series. At a nominal mains voltage of 220 V, the current through the LED is about 3 mA, and at a mains voltage of 380 V - about 6 mA. With a mains voltage that has reached 450 V, the total power dissipated by resistors R6-R8 is about 3,3 watts. The power constantly consumed by the device from the network at a supply voltage of 220 V does not exceed 0,75 W.

It is advisable to use this overvoltage detector in conjunction with other designs designed to automatically disconnect loads from the network in case of a dangerous supply voltage. It can also be built into a power surge protector, control units for refrigerator units, a washing machine, or manufactured as an independent device.

Resistor R1 is desirable to take a non-flammable safety type P1-7 or imported discontinuous. The remaining resistors are of the MLT, C1-4, C2-23, C2-33 type. Varistor R3 must be selected according to the opening voltage at a given AC input voltage. For example, for a maximum input voltage of 270 VAC, low power varistors .NR05K361, .NR-05K391, .NR-07K391 are suitable. If it is impossible to purchase such or a similar varistor, it can be replaced by several high-voltage zener diodes, for example, three KS630A. The zener diode VD5 is designed to accurately adjust the moment the alarm is turned on at a given input voltage.

Depending on the type and instance of the varistor used, this zener diode can have a stabilization voltage of 10 ... 50 V or be excluded from the circuit, and a jumper is installed in its place on the printed circuit board. The type of this zener diode can be any of the low-power ones, for example, KS515G 15 V, KS508D - 24 V, KS539G - 39 V, KS547V - 47 V. Diodes VD1-VD4 must be high-voltage and withstand a reverse voltage of at least 800 V. They can work in their place diodes RL106, RL107, 1N4006, 1N4007, BY133, EM513, KD247D, KD247E, KD257D, KD105G. Instead of four diodes, one diode rectifier bridge can also be used, for example, DB107, RS207. The remaining diodes are any of the series KD105, KD243, 1N4001-1N4007.

LED HL1 - flashing L56BHD, L56BGD, L56BSRD / B, L796BSRG / B, L796BGD or another similar one without a built-in current-limiting resistor. LED HL2 - any single-chip visible color of the glow, for example KIPD02A-1K, KIPD66V2, KIPD21G-K.

The HA sounder can be replaced by one of the listed ones with a built-in generator, for example EM-320BL, E.M472AL, EM-230, HPA17AX. Transistor VT1 must be with a base current transfer ratio of at least 100. Any of the KT342, KT3102, KT6114, SS9014, 2SC1222 series will do.

All parts of the device can be mounted on a printed circuit board with dimensions of 97x60 mm (Fig. 2).

Simple signaling device for increased mains voltage

Since the design has a galvanic connection with the mains voltage ~ 220 V, the safety rules must be observed when setting up and operating this signaling device.

Author: A.L. Butov

See other articles Section Protection of equipment from emergency operation of the network, uninterruptible power supplies.

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