The light bulb used to illuminate the refrigerator chamber operates in a specific mode - in the cold. And as you know, the light bulb burns out constantly at the moment it is turned on, since its cold filament has low resistance. When turned on, an increased current flows through this thread, which destroys the light bulb filament. In the cell, the light bulb stays at a lower temperature than in the room. Therefore, the probability of failure of the light bulb is even greater. I propose to power the light bulb through a diode. And although the light bulb flashes at a frequency of 50 Hz, this does not interfere. I installed the same KD105 diode 2 years ago, and not a single light bulb failed. I used to have to change bulbs often. Zu for horse racing circuit Inserting a KD105 diode is very simple. In the refrigerator, the light bulb is in a Minion-type cartridge, inside which the KD105 diode fits perfectly, since it is small. We proceed as follows. We remove the cartridge "Mignon", having previously disconnected it from the network, and put a diode in it. At the diode, we first bite off the leads, leaving small tips for soldering wires to them. Having soldered the wires, we turn on the diode in the gap of one lead wire in series with the light bulb. Connect the lead wires. Next, put the cartridge in place and screw in the light bulb. Everything is ready. The diode KD 105 perfectly withstands the load, since the light bulb in the refrigerator with a power of only 15 W. V. O. Rashitov, a student of grade 11, Kyiv ....
For the "Temperature controller" scheme
To maintain a constant temperature in a given volume, you can use a simple device - a thermostat. The figure shows a basic electrical scheme simple thermostat. Its distinguishing features include the use of a transformerless power supply, which makes it possible to significantly reduce the dimensions of the device, the high accuracy of maintaining the set temperature (+0.12 ° C), as well as the management of a high-power heating element, which is necessary when heating large volumes. thermistor R3 type MMT-6. To ensure the necessary accuracy of maintaining the temperature, it is necessary to carry out forced air circulation through the thermistor using a small-sized fan. With good thermal insulation of the volume in which a constant temperature is maintained, the heating / waiting ratio is 1/3 ... 1/10. The set temperature is set using a variable resistor R5. Transistors VT1, VT2 must have a current transfer coefficient of more than 800. The indicator lamp HL1 serves to provide visual control over the heating mode. As a capacitor C1, you can use any paper with an operating voltage of at least that indicated in the diagram. The device is assembled on a small-sized, printed circuit board made of foil fiberglass. (Printed with abbreviation. Radio Television Electronics, 4/2002.) K. KLISARSKI...
For the scheme "Forced airflow for the refrigerator"
During the operation of refrigerators, their premature failure due to overheating of the compressor motor is often observed. The cramped operating conditions - insufficient distance from the cooler grate to the wall of the room and poor circulation of the cooling air - lead to a long compressor operation to reach the set cut-out temperature. Large refrigeration units use a fan to force-cool the refrigerant to keep the temperature in the cooling chambers in line with food storage requirements. The absence of forced cooling simplifies the design of a household refrigerator, but reduces its service life. The proposed device for additional cooling of the radiator and compressor consumes no more than 20 W from the mains. The principle of its operation is based on the automatic inclusion of forced airflow to the radiator after the compressor starts. Voltage regulator on kt 803a When the compressor is turned off, the device switches to standby mode with low power consumption. The device (Fig. 1) contains: - current sensor T1; - current sensor voltage stabilizer VD1, C1, VD4; - current sensor voltage amplifier on optocoupler VU1; - a waiting multivibrator on an analog timer DA2 with elements for setting the fan speed R4, R5, R6, NW. VD5; - output power amplifier on optocoupler VU2. On LEDs HL1. HL2 indicates the compressor is on and the power is on. The power supply is made on a power transformer T2, followed by voltage stabilization by an analog DA1 microcircuit. At the time of automatic start refrigerator from the internal temperature sensor (thermal relay) in the network, an almost fivefold current surge occurs, which creates voltage on the winding I tr ...
For "Grounded GP for 14-28 MHz bands"
For the scheme "Simple power regulator"
For the circuit "TIMER FOR PERIODICAL LOAD ON"
Consumer Electronics It is unlikely that anyone will be satisfied with doing this manually. Yes, and sometimes it is necessary to manage the load in the absence of a person. The proposed machine will be able to perform such a task. When leaving on vacation, some apartment owners leave the machine at home, which every evening turns on the lighting in the apartment for several hours, creating the illusion of the presence of the owners. Often this serves as a kind of watchdog from uninvited guests. Another example is the failure of the thermostat of a compression refrigerator, as a result of which either there is no cold in the refrigerator compartment, or the motor runs continuously and soon burns out. The way out (temporary - before buying a thermostat, or permanent, if the refrigerator is of an old model) can be an automatic machine that periodically turns on the refrigerator. A distinctive feature of the proposed machine in comparison with the published one is a large range of exposure times, which can be made from a few minutes to several days by selecting the denominations of some parts. Relay rs 527 connection diagram This was achieved thanks to the use of a capacitor C2 with a double electric layer - an ionistor [З] in the time-setting circuit (Fig. 1). The device has two independent regulators that set the duration of "Work" (R5) and "Pause" (R6). The basis of the machine is a multivibrator on an operational amplifier (op-amp) DA1, which controls the operation of a short pulse generator made on a unijunction transistor VT1 - it, in turn, ensures the opening of the triac VS1. The generator is powered from the mains through a rectifier on diodes VD5, VD6 with a ballast capacitor C5. To power the multivibrator, a parametric stabilizer is installed, consisting of a ballast resistor R7 and zener diodes VD1, VD2. The multivibrator is assembled according to a well-known scheme with...
For the circuit "SINGLE PULSE INDICATOR"
Radio amateur designerSINGLE PULSE INDICATOR When checking the performance of devices on integrated circuits, it becomes necessary to indicate the passage of a single pulse. It is difficult, moreover, with the help of special oscilloscopes to register the appearance of a single pulse, sometimes very short, a few tens of nanoseconds. Figure 1 shows a basic indicator of the appearance of a single negative pulse. Fig.1 The elements D1.1 and D1.2 form a trigger, to one input of which the output of the device under test is connected, and to the other - through the SI button - a logic zero voltage is applied, which returns the trigger to its original state. Before starting work with the indicator, set it to its initial state by briefly pressing the button S1. If we now connect the indicator to the device under test, then the first pulse received at the input will switch the trigger to another stable state and the lighting of LED V1 will mark the appearance of the pulse. "Elektrotehnicar" (SFRY), 1976 N 7 Note. In the indicator of a single pulse, you can use the K155LA3 chip and the KL101B or KL101V LED ....
For "Antenna switch" scheme
Components of amateur radio equipment Antenna switch The rapid switching of the antenna from reception to transmission and vice versa, when it is necessary to provide half-duplex telegraph operation, is still a problem in amateur radio communications. UA3TCH offers antenna switches based on 2A520A diodes, which have a direct differential resistance of 3.5 ohms, a closed capacitance of less than 1 pF, and a reverse voltage of 800 V (Fig. 1). Fig.1 When the lamp of the final stage of the transmitter is closed, an active resistance of approximately 500 Ohms is connected to the antenna from the side of the P-circuit (if its quality factor is approximately 100). It practically does not shunt the input of the receiver, and therefore, during the reception, there is no need to turn off the P-loop. Moreover, it somewhat improves the selectivity of the receiver, since it has a series resonance below the receive frequency. For example, when operating on the 14 MHz band, it suppresses signals well near the frequency of 12.5 MHz. The switch diodes are switched with a voltage of -12V when receiving and +250V when transmitting using a node on a KT605 transistor (not shown in the diagram). Diodes 2A520A can be changed to 2A507A, which, however, have a lower reverse allowable voltage (500 V). In this case, instead of the V2 diode, two 2A507A diodes are connected in series ....
For the scheme "AUTOMATIC FOR WATERING PLANTS"
Consumer ElectronicsWATERING MACHINEBasic scheme simple automatic machine, which includes the supply of water to a controlled area of soil (for example, in a greenhouse) when its moisture content decreases below a certain level, is shown in the figure. The device consists of an emitter follower on transistor V1 and a Schmitt trigger (transistors V2 and V4). The actuator is controlled by the electromagnetic relay K1. Humidity sensors are two metal or carbon electrodes. immersed in the ground. With fairly wet soil, the resistance between the electrodes is small, so the transistor V2 will be open, the transistor V4 will be closed, and the relay K1 will be de-energized. As the soil dries out, the soil resistance between the electrodes increases, the bias voltage based on transistors V1 and V3 decreases, Finally, at a certain voltage at the base of transistor V1, transistor V4 opens and relay K1 is activated. Its contacts (not shown in the figure) close the circuit for turning on a damper or an electric pump that supplies water for irrigating a controlled area of soil. With an increase in humidity, the resistance of the soil between the electrodes decreases, after reaching the required level, the transistor V2 opens, the transistor V4 closes and the relay is de-energized. Watering stops. The variable resistor R2 sets the threshold for the operation of the device, which ultimately determines the soil moisture in the controlled area. Transistor V4 is protected from voltage surges of negative polarity when relay K1 is turned off by diode V3. "Elecnronique pratique" (France), N 1461 Note. The device can use transistors KT316G (V1, V2), KT602A (V4) and diodes D226 (V3) ....
Modern refrigerators are considered reliable household appliances. There are practically no complex electronics in them, therefore, there are a minimum of parts that fail. The most common failure of the refrigerator is the failure of the thermostat. In the scheme of mechanical control of the operation of the refrigerator, it participates in the operation of the engine-compressor. The thermostat is mounted in the chamber or on the front panel of the unit.
In the latest generation of refrigeration devices, the thermostat has replaced the device more accurately copes with its duties. In this article we will try to figure out how to check the refrigerator thermostat.
General scheme of operation of the refrigeration unit
As you know, refrigeration and work on freon. So far, this is the only gas that is not dangerous and, due to its special properties, is able to change its state of aggregation. It moves through the cooling system with the help of a motor-compressor. First, an increased pressure is created on the rear wall of the unit, while a reduced pressure is formed on the evaporator. As a result, the freon located on the back of the cooler liquefies, and evaporation begins on the evaporator, which is confirmed by the refrigerator diagram attached to the instructions.
Temperature control device
The thermostat is a fairly simple device. Even in modern refrigerators and refrigerators, this is a simple contact group. It is controlled by a manometric device with a capillary tube, the end of which is in the chamber and measures the temperature. Today there are two types of temperature controllers in refrigerators: mechanical and electronic.
A modern thermostat has two main elements. This is a box in which there are control and actuators, and a capillary extended into a tube. The box is a bellows (hermetically packed tubular spring). The accuracy of the determined indicators depends on its tightness. The compression and expansion of the bellows is regulated by a spring, optimizing it with pressure indicators. Modern ones may have several springs. It depends on the destination: refrigerator or freezer.
More reliable and allows you to smoothly regulate the operation of the entire refrigeration system - an electronic thermostat for the refrigerator. The price of this device is much higher than mechanical ones and ranges from two thousand rubles (while a mechanical one costs up to a thousand). In an electronic thermal relay, a thyristor, sometimes a resistor, is responsible for sensitivity.
In refrigerators with high energy consumption, such thermostats quickly fail. In Class A+ refrigeration units with linear compressors, electronic temperature controllers need to be replaced much less frequently. Therefore, most of the manufacturers of such equipment today are switching to linear compressors with electronic temperature controllers.
The principle of operation of the device
The direct purpose of the thermostat in the refrigeration unit is to maintain the temperature regime set by the consumer. In compression refrigeration devices, the thermostat turns the compressor motor on and off, and in absorption refrigeration devices, the heater. The device that regulates the temperature in the cooling chambers is classified as a manometric design. This means that the operation of the unit depends on the instability of the pressure of its filler (usually gas) with temperature fluctuations.
A mechanical thermostat is a lever device that has a power lever and a contact circuit. The elastic element (tubular bellows) of the thermostatic system and the spring act on the power lever. The electrical part of the device is separated from the mechanical part by an electrically insulating gasket.
Working conditions for freon - concentrated steam, the pressure of which depends on temperature conditions. Liquid gas accumulates at the end of the tube. The segment of the tube, in which the separation of vaporous freon and liquid freon takes place, reacts to temperature fluctuations. It is this segment that is in the cooling zone.
Location of thermostat
The mode is always associated with a knob that switches temperature modes. In models of previous generations, the thermostat is located under a plastic cover inside the refrigerator compartment. To replace it, you need to pick up the mode switch with a flat screwdriver, remove it, then dismantle the plastic cover.
In models of recent years, from the attached instructions (refrigerator diagram), you can find out where the thermostat is located in the refrigerator. Most often it is placed above the door. To get to it, you need to dismantle the mode switch and the plastic structure that covers the thermal relay.
Possible problems
Several breakdowns can be associated with the thermostat. For example, the refrigerator freezes, but very weakly. In this case, you need to try to adjust the temperature controller or replace it. Before checking the refrigerator thermostat, you need to make sure that the door closes tightly enough and the compressor is running at the set power.
It happens that the device began to leak or the compressor works without stopping. It is not necessary that in each of these cases it is the thermostat that fails. It is likely that the cause may be different, but the temperature controller needs to be checked first.
Possible damage to the temperature controller
The most common cause of thermostat failure is wear and tear. Why it happens? Refrigerator thermostat malfunctions can be associated with loss of tightness, swelling or oxidation. Cases of defective devices are known, but this is rare. Therefore, repairing such a system does not make sense. It will be cheaper to replace the thermostat in the refrigerator.
How to test the thermostat yourself
There are several ways to check the refrigerator thermostat:
- The most reliable, experts say, is to check with a tester. It will show if there is resistance. To do this, the thermostat is dismantled (after turning off the refrigerator from the network). Its location can be found in the instructions that came with the refrigerator. But almost always it is under the temperature switch. If the tester is analog, it must be switched to the resistance-measuring mode and the starting point must be set. Then calibrate (connect the probes and at the same time set the arrow to "zero"). The digital tester must be switched to the "200" or "chain ringing" position. Before measuring, you must first soak the thermostat in ice water. This way the readings will be accurate.
- How to check the refrigerator thermostat using an easier way? You need to turn off the unit. It is necessary to remove the terminals from the thermostat and directly close the wires with a small piece of wire. Next, turn on the refrigerator and listen to see if the compressor starts. Then everything is simple: if the compressor is silent, then you need to continue troubleshooting. Perhaps these are problems with the starting mechanism or the compressor itself. If the latter works, then the thermostat in the refrigerator needs to be replaced.
Faulty thermostat in the refrigerator "Stinol"
This brand of refrigerators is very popular in our country. Almost the only disadvantage of such units is that the thermostat becomes faulty very quickly (after 5-6 years of operation). The reason for the breakdown is the short working life of this device, supplied by the German company RANCO (5 years). The tightness of the bellows, which is sensitive to temperature fluctuations, is broken in the thermostat.
Defects indicating that it is the refrigerator thermostat that is faulty:
- "Stinol" does not start when the switch is turned to the "off" label (no click).
- above the norm even when the regulator is set to “maximum”.
- The compressor of the device works without stopping, even when the regulator knob is in the “off” position.
At home, it is impossible to accurately determine the malfunction of the Stinol refrigerator thermostat. But if the compressor turns on with the jumper closed, it means that there is a high probability that the temperature controller is faulty, and therefore it is necessary to contact a company that performs urgent repairs of refrigerators.
Urgent troubleshooting
Breakdown of the refrigerator due to the failure of the thermostat, especially in the hot season, looks like the end of the world. Food disappears, there is no way to cool drinks, a leak may occur that will damage the flooring. Naturally, it is necessary to call the master.
It should be noted that urgent repairs of refrigerators are always carried out at home. But a professional master with extensive experience will easily determine the malfunction by the symptoms mentioned and will come to the call with the necessary set of spare parts.
You can adjust the operation of the thermostat yourself
After replacing the temperature controller or after a long period of use, the operation of the refrigerator may change slightly. There may be several reasons, but most often it is not fully adjusted thermostat. How to fix it?
Setting the refrigerator thermostat is a laborious and lengthy process. The elapsed time depends on the duration of the cycles between turning on and off this device. If time is limited, you can debug the thermostat by measuring the temperature in the freezer or refrigerator. In this case, there is no necessary correction for ambient temperature.
Fundamental basics of debugging a thermostat
Adjustment consists in tensioning or weakening the power spring. To do this, you need to find out where the screw of the power spring is located, in which direction the turn will weaken the temperature, and in which it will increase for a particular refrigerator model. Typically, turning the screw on the spring clockwise increases the temperature, and counterclockwise decreases the temperature (one turn is approximately 5-6 ° C).
Before starting work, you need to pull out the gasket between the bellows and the chamber wall (after the adjustment is completed, the gasket should return exactly to its place). Then the temperature on the evaporator shelf is measured with the motor-compressor running and the average temperature regime. After 3-3.5 hours, the temperature is measured again. After comparing the initial and final temperatures, it is necessary to relax or tighten the power spring (after disconnecting the refrigerator from the mains).
The described electrical circuit of the electronic thermostat for the refrigerator changes the duration of the pause in the operation of the compressor, which depends on the internal temperature.
Description of the operation of the thermostat for the refrigerator
The electrical circuit (Fig. 1.35) contains a generator on the DD1 chip, keys on the radio elements DD2.2, DD2.3 and an inverter on the DD2.1 element.
The generator on the K176IE5 chip has switchable RC circuits (Rl, R3, Cl and R2, R4, C2). modification of timing circuits is performed by keys on the K561KT3 chip. Key management begins with signals from the output of the fifteenth bit (pin 5) of the signal divider DD1.
At a high voltage at the output 5 to the internal log. one RC circuit (R2, R4, C2) is connected to the elements of the DD1 chip. At low voltage, the electrical signal is reversed by the inverter on the element DD2.1 and, through the key DD2.2, another electrical circuit is connected (Rl, R3, Cl). To change the refrigerator thermostat, the resistance R4 can have a value of 100 kilo-ohms or more.
When the temperature in the refrigerator drops to 0 degrees, the MMT4 brand thermistor with a resistance of 220 kilo-ohms had a resistance of 400 kOhm. Since the thermistor is connected in the circuit that determines the duration of the pause, the lower the temperature in the refrigerator compartment, the greater the moment of pause in the operation of the refrigerator compressor.
Therefore, the temperature is adjusted by changing the duration of the pause in the operation of the refrigerator compressor by the resistance R3. The control impulse, through the key on the transistor VT1, turns on the intermediate electric relay Kl, which turns on a more powerful relay. Intermediate electric relay brand RES6, RES49.
The K561KT3 chip can be changed to K176KT1. Switch SA1 is needed to enable the continuous operation of the compressor after defrosting the refrigerator. The printed circuit board of the electric relay is shown in Figure 1.36, and from the side of the installation of radio components, Figure 1.37.
The dimensions of the board are limited by the size of the electric relay for 220 V. Rectifier diodes and filter capacitances are located on the board. Thermistor R3 is soldered to a thin wire of the MGTF brand and placed in a freezer.
Resistance R4 and switch SA1 are placed close to the plastic side cover of the relay. The alternating voltage going to the electrical circuit must be such that the rectified voltage is not more than 9 V. At a lower voltage. the K176IE5 chip can still work, however, at voltage. more than 9V, it may not work.
If you need an extremely low frequency generator with separate adjustment of the duration of high and low levels, then the resistance R3 can be replaced by a potentiometer up to 3 MΩ. The frequency is approximately calculated by the formula F = 0.7/RC.
When calculating the duration, it should be remembered that the moment of work or pause will be equal to half the calculated one, since only a part of the period is taken - either a high level or a low one.
The electronic thermostat for refrigerator will help in cases where your own (factory) thermostat is faulty or its accuracy is no longer sufficient. Older refrigerators use a mechanical temperature thermostat using a liquid or gas filled capillary.
When the temperature changes, the pressure inside the capillary also changes, which is transferred to the membrane (bellows). As a result, the thermostat turns the refrigerator compressor on and off. Of course, such a temperature control system has low accuracy, and its parts wear out over time.
Description of the operation of the thermostat for the refrigerator
As you know, the temperature of food storage in the refrigerator should be + 2 ... 8 degrees Celsius. The operating temperature of the refrigerator is +5 degrees.
The electronic thermostat for the refrigerator is characterized by two parameters: the start and stop temperature (or the average temperature plus the hysteresis value) of the compressor. The hysteresis is necessary to prevent the refrigerator compressor from turning on too often.
This circuit provides a hysteresis of 2 degrees at an average temperature of 5 degrees. Thus, the refrigerator compressor turns on when the temperature reaches + 6 degrees and turns off when it drops to + 4 degrees.
Material: ABS + metal + acrylic lenses. LED lights...
This temperature range is sufficient to maintain the optimal storage temperature of the food, and at the same time it ensures comfortable operation of the compressor, preventing its excessive wear. This is especially important for already old refrigerators that use a thermal relay to start the engine.
The electronic thermostat is a suitable replacement for the original thermostat. The thermostat reads the temperature using a sensor, the resistance of which changes depending on the change in temperature. The thermistor (NTC) is often used for these purposes, but the problem lies in its low accuracy and the need for calibration.
To ensure an accurate setting of the controlled temperature and get rid of many hours of calibration, in this version of the thermostat for the refrigerator was chosen. It is an integrated circuit, linearly calibrated in degrees Celsius, with a factor of 10 mV per degree Celsius. Due to the fact that the threshold temperature is close to zero, the relative change in the output voltage is large. Therefore, the signal from the output of the sensor can be controlled using a simple circuit consisting of only two transistors.
Since the output voltage is too low to open the transistor VT1, the LM35 sensor is turned on as a current source. Its output is loaded with a resistor R1 and therefore the current on it changes in proportion to the temperature. This current causes a drop across resistor R2. The voltage drop controls the operation of the transistor VT1. If the voltage drop exceeds the threshold voltage of the base-emitter junction, transistors VT1 and VT2 open, relay K1 turns on, whose contacts are connected instead of the contacts of the old thermostat.
Resistor R3 creates positive feedback. This adds a small current to R2, which shifts the threshold and thus provides hysteresis. The winding of the electromagnetic relay must be rated for 5 ... 6 volts. The contact pair of the relay must withstand the required current and voltage.
The LM35 sensor is located inside the refrigerator in a suitable location. The resistance R1 is soldered directly to the temperature sensor, which in turn allows you to connect the LM35 to the circuit board with just two wires.
The wires connecting the sensor can introduce interference into the circuit, so capacitor C2 is added to suppress interference. The circuit is powered by a built-in 5 volt power supply. The current consumption mainly depends on the type of relay used. must be securely isolated from the network.
The big advantage of this circuit is that it starts working immediately at the first start and does not need to be calibrated and adjusted. If it becomes necessary to slightly change the temperature level, then this can be done by selecting the resistances R1 or R2. Resistance R3 determines the amount of hysteresis.
Do-it-yourself refrigerator thermostat
It all started with the fact that after returning from work and opening the refrigerator found it warm. Turning the thermostat knob did not help - the cold did not appear. Therefore, I decided not to buy a new unit, which is also rare, but to make an electronic thermostat on the ATtiny85 myself. With the original thermostat, the difference is that the temperature sensor is on the shelf, and not hidden in the wall. In addition, 2 LEDs appeared - they signal that the unit is on or the temperature is above the upper threshold.
Device Diagram:
To connect, it was necessary to conduct a second 220 V wire (taken from a lighting lamp) to power the transformer.
The connector to which the potentiometer is connected is also the ISP programming connector.
The board is protected from moisture with a special varnish for printed circuit boards.
The transformer here is 6 V. This was chosen to minimize losses on the 7805 chip.
The relay here can also be put on 12 V. If you take the voltage to it to the stabilizer. To reduce costs, it would be possible to create a transformerless power supply, although there are supporters and opponents of such a solution (electrical safety). Another cost cut is the elimination of the AVR microcontroller. There are Dallas thermometers that can also work in thermostat mode.
