Refrigerator turn-on delay timer. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Refrigerator turn-on delay timer. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

Comments on the article

The author talks about one of the common causes of failure of domestic refrigerators and offers two options for the device to protect them.

The operating instructions for some household refrigerators, for example, STINOL, say that they can be reconnected to the network no earlier than 4 ... 5 minutes after being turned off. This time is necessary for the condensation and pressure drop of the refrigerant. Otherwise, the starting load on the compressor motor is too high, causing its windings to overheat. It is in this situation that engine failure is most likely.

It is impossible to fulfill this requirement without the use of additional protection devices. The household refrigerator is included around the clock. To put it out of action, even a short-term power outage, which is normal for our electrical networks, is enough, especially at night or when the owners are absent. In such cases, it is necessary to automatically delay turning on the refrigerator for approximately 5 minutes after the restoration of the mains voltage. It is this function that can be performed by the timer, the circuit of which is shown in Fig. 1.

Refrigerator turn-on delay timer

It works like this. At the first moment after the mains voltage is applied, the capacitor C3 is discharged and it starts charging through the resistor R3. Logic element DD1.1 serves as a threshold device. While the voltage at its inputs is below the switching threshold, its output is high, and the output of the element DD1.2 is a low logic level. Transistor VT1 is closed, there is no current in its emitter circuit. Therefore, the thyristors of optocouplers U1 and U2, and with them the triac VS1 are closed. Refrigerator power circuit is open.

After about 5 minutes, the voltage across the capacitor C3 will reach a level at which the state of the elements DD1.1, DD1.2 will begin to change and the transistor VT1 will open. Due to the positive feedback through the resistors R4 and R5, this process develops like an avalanche, the current through the LEDs of the optocouplers U1, U2 increases abruptly. As a result, the photothyristors of the optocouplers open in turn at the beginning of each half-cycle of the mains voltage, and the current flowing through them and the resistor R6 opens the triac VS1. The refrigerator is connected to the network.

If the mains voltage disappears for more than 1 ... 2 s, the capacitors C2 and C3 will have time to discharge (the latter through the diode VD6). Resistor R2 serves to speed up the discharge process. With the appearance of voltage, the process described above will be repeated and the refrigerator will be turned on only after 5 minutes.

The timer power unit is assembled according to a transformerless circuit with a quenching capacitor C1. Resistor R1 limits the inrush current when turned on. The voltage rectified by the VD1-VD4 diode bridge is stabilized using the HL1 LED and the VD5 zener diode connected in series. The glow of the LED is a sign of the presence of voltage in the network.

The timer is assembled in a case from the power supply unit BP2-3 (the so-called network adapter), which was equipped with some calculators. The socket for connecting the refrigerator is fixed on the block body from the side opposite to the mains plug, and inside the case - a printed circuit board made of foil fiberglass, shown in fig. 2.

Refrigerator turn-on delay timer

The K561LE5 microcircuit can be replaced with the K561LA7 without any adjustment of the circuit. Transistor VT1 - series KT312, KT315 with any letter indexes. Suitable low-power diodes with a permissible rectified current of at least 1 mA are suitable as VD4-VD30, and a replacement for VD6 should be selected with a low reverse current, for example, KD102B, KD104A. LED HL1 - any color of glow with a maximum current of 30 mA. The direct voltage drop across different types of LEDs can vary by 1 ... 2 V, which should be taken into account when choosing a VD5 zener diode. The total voltage on the zener diode and the LED should not go beyond 10 ... 15 V.

Capacitor C1 - K73-17, C2 - any oxide, C3 - oxide with a low leakage current, for example, the K52 series. All resistors are MLT or C2-33 of the power indicated on the diagram. Triac VS1 (its voltage class must be at least 4) is equipped with an aluminum heat sink with an area of several square centimeters and is attached to the board, for example, with epoxy glue.

Establishing a timer comes down to setting the required response delay by selecting resistor R3. It should be taken into account that an excessive increase in the resistance of this resistor leads to delay inconsistency caused by the influence of leakage currents of the capacitor C3 and between the PCB conductors. The leakage current of an oxide capacitor that has not been energized for a long time is usually increased. Therefore, be sure to check the delay after the timer has been running continuously for at least a day, and if necessary, set it again.

A timer similar in purpose and principle of operation can be assembled according to the scheme shown in Fig. 3.

Refrigerator turn-on delay timer

Its main difference is that the load (refrigerator) is switched not with a triac, but with the help of relay K1. The trigger, which switches when the voltage on the capacitor C2 reaches the threshold level, is formed in this case by the elements DD1.1 and DD1.4. Parallel connected elements DD1.2, DD1.3 - a buffer stage that controls an electronic key on a transistor VT1, in the collector circuit of which the relay winding K1 is connected. Resistor R5 is needed to accelerate the discharge of capacitors after turning off the mains voltage. The current flowing through it is not enough to keep relay K1 in the triggered state. Transformer T1, diode bridge VD1 and capacitor C1 - the power supply unit of the timer.

LEDs HL1 and HL2 serve to indicate the presence of voltage in the network and the status of the timer. If none of them is lit, there is no mains voltage. From the moment the voltage appears until the refrigerator is turned on, the HL1 LED is on. Then it goes out and the HL2 LED lights up.

When choosing a relay, it should be borne in mind that its contacts must be designed for switching a current of several amperes consumed by the refrigerator in starting mode. In the author's version of the timer, the REN-18 relay is used, passport РХ4.564.706. Transformer T1 - with a voltage on the secondary winding of 6 V at a load current of 300 mA. The rectified voltage on the capacitor C1 was 7 ... 8 V. If there is a relay with a high response voltage, the voltage on the secondary winding of the transformer should be increased accordingly. However, with an increase in the rectified voltage in excess of 15 V, the DD1 microcircuit should be powered through a simple stabilizer with an output voltage of no more than the specified one. Be sure to shunt the output of the stabilizer with a 1 kΩ resistor, which creates a discharge circuit for capacitor C2.

The timer is assembled on a board made of one-sided foil fiberglass. Almost all of the circuits are mounted by printed circuits, with printed conductors located near one of the edges of the 80 mm wide board (Fig. 4). The foil was removed from the rest of its surface, relay K1 and transformer T1 were installed there.

Refrigerator turn-on delay timer

The board is covered with a cover made of insulating material with holes for LEDs and a socket for connecting a refrigerator. Establishing a timer comes down to setting the required shutter speed by selecting the resistance of the resistor R1.

Author: I. Nechaev, Kursk

See other articles Section Clocks, timers, relays, load switches.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

Spiders, feeding on graphene, weave the strongest web 11.09.2017

The web is already strong enough to hold small insects that have fallen into it, but thanks to the discovery of scientists in the future, it may be able to withstand the weight of a person.

Nicola Pugno and other scientists from Trent University (Italy) conducted a study during which graphene and carbon nanotubes were added to the drinking water of spiders.

When the test spiders weaved the web, as they always did, it turned out to be five times stronger than normal - and can be compared with carbon fiber and Kevlar, the strongest materials on Earth.

Punyo noted that scientists already knew about the biominerals present in the protein matrices and hard tissues of insects, which provide great strength and durability to their mandibles (upper jaws) and teeth; thus, researchers were more interested in whether it is possible to artificially improve the quality of spider silk by introducing various nanomaterials into its protein structures.

So far, these are only the first steps in the study of webs woven by spiders using graphene and nanotubes, and Punyo's results should be rechecked. It is noted that if they are confirmed, such an improved web can be used, for example, for the manufacture of ropes, cables, etc.

Other interesting news:

▪ Biodegradable stent for children with respiratory diseases

▪ Mach Xtreme Express SSDs

▪ Purity of speech affects memory

▪ wine allergy

▪ Poison web

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Car. Article selection

▪ Del's article? Very simply: it is the money of others. Popular expression

▪ article What are sunspots? Detailed answer

▪ article Machinist (fireman) of the boiler room. Job description