Thermostats are widely used in modern household appliances, automobiles, heating and air conditioning systems, in manufacturing, in refrigeration equipment and during the operation of ovens. The principle of operation of any thermostat is based on turning on or off various devices after reaching certain temperature values.
Modern digital thermostats are controlled using buttons: touch or conventional. Many models are also equipped with a digital panel that displays the set temperature. The group of programmable thermostats is the most expensive. With the help of the device, you can provide for a change in temperature by the hour or set the required mode for a week in advance. The device can be controlled remotely: via a smartphone or computer.
For a complex technological process, for example, a steel furnace, making a thermostat with your own hands is a rather difficult task that requires serious knowledge.But to assemble a small device for a cooler or incubator is within the power of any home craftsman.
In order to understand how the temperature regulator works, consider a simple device that is used to open and close the damper of a mine boiler and is triggered when the air heats up.
For the operation of the device, 2 aluminum pipes, 2 levers, a return spring, a chain that goes to the boiler, and an adjusting unit in the form of a crane-axle box were used. All components were installed on the boiler.
As you know, the coefficient of linear thermal expansion of aluminum is 22x10-6 0С. When an aluminum pipe is heated with a length of one and a half meters, a width of 0.02 m and a thickness of 0.01 m to 130 degrees Celsius, an elongation of 4.29 mm occurs. When heated, the pipes expand, due to this, the levers are displaced, and the damper closes. As the pipes cool down, they decrease in length, and the levers open the damper. The main problem when using this circuit is that it is very difficult to accurately determine the response threshold of the thermostat. Today, preference is given to devices based on electronic components.
Typically, relay-based circuits are used to maintain the set temperature. The main elements included in this equipment are:
Semiconductor elements, thermistors, resistance thermometers, thermocouples and bimetallic thermostats can be used as a sensor.
The thermostat circuit reacts to the excess of the parameter over the set level and turns on the executive device. The simplest version of such a device is a bipolar transistor element. The thermal relay is based on the Schmidt trigger. A thermistor acts as a temperature sensor - an element whose resistance changes depending on an increase or decrease in degrees.
R1 is a potentiometer that sets the initial offset on thermistor R2 and potentiometer R3. Due to the adjustment, the actuator is triggered and relay K1 is switched when the resistance of the thermistor changes. In this case, the operating voltage of the relay must correspond to the operating power supply of the equipment. To protect the output transistor from voltage surges, a semiconductor diode is connected in parallel. The load value of the connected element depends on the maximum current of the electromagnetic relay.
Before starting work, you should decide on the power of the future thermostat and the temperature range in which it will work. The refrigerator will require some elements, and the heating will require others.
One of the elementary devices, by the example of which you can assemble and understand the principle of operation, is a simple do-it-yourself thermostat designed for a fan in a PC. All work is done on a breadboard. If there are problems with the pallet, then you can take a solderless board.
The temperature sensor reacts to an increase in degrees, due to which the whole circuit is triggered, and the fan turns on.
Now let's move on to setting up. To do this, turn on the computer and adjust the potentiometer, setting the value for the off fan.At the moment when the temperature approaches the critical one, we reduce the resistance as much as possible before the blades rotate very slowly. It is better to make the adjustment several times to make sure that the equipment is working efficiently.
The modern electronic industry offers elements and microcircuits that differ significantly in appearance and technical characteristics. Each resistance or relay has several analogs. It is not necessary to use only those elements that are indicated in the diagram; you can take others that match the parameters with the samples.
When adjusting heating systems, it is important to accurately calibrate the device. This will require a voltage and current meter. To create a working system, you can use the following diagram.
Using this scheme, you can create outdoor equipment to control a solid fuel boiler. The role of the zener diode is performed by the K561LA7 microcircuit. The operation of the device is based on the ability of the thermistor to reduce resistance when heated. The resistor is connected to the electricity voltage divider network. The required temperature can be set using the variable resistor R2. The voltage is supplied to the 2I-NOT inverter. The resulting current is fed to the capacitor C1. A capacitor is connected to 2I-NOT, which controls the operation of one trigger. The latter is connected to the second trigger.
It is better to solder on a mole rat. As a battery, you can take any device operating within 3-15 V.
In order to create a fully functioning thermostat with accurate calibration, you cannot do without digital elements. Consider a temperature control device for a small vegetable store.
The main element here is the PIC16F628A microcontroller. This microcircuit provides control of various electronic devices. The PIC16F628A microcontroller contains 2 analog comparators, an internal oscillator, 3 timers, CCP comparison modules and USART data exchange.
When the thermostat is operating, the value of the existing and set temperature is fed to the MT30361 - a three-digit indicator with a common cathode. In order to set the required temperature, use the buttons: SB1 - to decrease and SB2 - to increase. If you carry out the setting while simultaneously pressing the SB3 button, you can set the hysteresis values. The minimum hysteresis value for this circuit is 1 degree. A detailed drawing can be seen on the plan.
When creating any of the devices, it is important not only to properly solder the circuit itself, but also to think about how best to place the equipment. It is necessary that the board itself be protected from moisture and dust, otherwise a short circuit and failure of individual elements cannot be avoided. Also, care should be taken to isolate all contacts.
VIDEO
The thermostat for a water heater works on the principle of a thermometer - it measures the temperature. Why is this necessary and what is the risk of element failure, read in our publication.
How does the device work? On the control panel, you set the heating values. As soon as the water reaches the set parameters, the temperature sensor is triggered, sending a signal to the control module. The latter gives the command to turn off the heating element.
In storage boilers, the water is constantly warm thanks to the temperature regulator.As soon as the indicators decrease, the heating element starts up again and continues heating. Therefore, you can get hot water at any time, without long waiting.
In modern models, the thermal relay is equipped with a shutdown button - thermal protection. When the heating element overheats or heats the contents above the specified rate, the protection is triggered and the work stops. Otherwise, the heating element burns out.
There are several types of thermostat:
Rod - obsolete type, no longer used. It is based on a tube that expands when the water is heated. From the expansion, the heating element shutdown key is triggered. Capillary ... The design is the same, but in this case the tube contains liquid, which expands and activates the heating element relay. The error is 3-4 degrees.Electronic ... The most accurate of all sensors. Equipped with protection against switching on without water.Regulators have been developed for the electric water heater:
Mechanical and electronic (invoice and built-in, respectively). Mechanical ones are triggered when the bimetallic plates expand, electronic ones when the sensor signal.
Programmable and mechanical. The first requires setting the necessary indicators, the second are triggered by boiling or when the maximum manually set temperature is reached.
Does the boiler stop heating or, on the contrary, is overheating the water? The thermostat is checked first.
If possible, the item can be repaired or a new one installed.
Disconnect the equipment from the network.
Shut off the water supply.
Drain the contents of the tank. For this, a special valve can be used. What is a safety valve for? Read in a separate article.
Dismantle the heating element. To do this, unscrew the nuts and bolts of the flange, remove it from the body.
The thermostat is usually located at or near the base of the heater.
Disconnect the wiring and remove the sensor from the base.
In the case of a mechanical model, you can clean bimetallic plates from oxidation ... To do this, moisten a piece of cloth with alcohol, wipe the plates. If oxidation is widespread, then sand it with fine sandpaper.
You need to do this carefully so as not to touch the sensor contacts.
Due to power surges, the NC contact could stick. To adjust, carefully detach it from the body, clean up the problem area. Normally, the contact should fit into the socket automatically.
How to repair a contact if it does not work:
Remove the part completely from the body.
Clean its surface, as well as the seat.
If after cleaning the contact does not turn on, place insulating tape underneath.
Reinstall the stem.
Assemble the case.
It makes no sense to carry out repairs if:
But how to make sure in practice that the thermostat is faulty? This can be checked with a multimeter.
Set the multimeter to the resistance measurement mode as shown in the picture:
Apply the test leads to the pins of the part.
Look at the scoreboard. With infinite resistance, the thermostat cannot be restored; replacement is needed.
Shows resistance? Do this: set the multimeter to the minimum value. Use a lighter to warm up the thermostat tube. If it is OK, the resistance will increase and the protective relay will trip.
If you are convinced of a malfunction, it is important to select the correct product for replacement. How to do it? It is best to take an old regulator and go to the store with it to purchase an analogue. Or write down the serial number that is on each product.
Fastening method.
The size.
Voltage.
Additional functions.
The parameters must match those indicated in the passport for the boiler.
If you are not good at repairing, then you can call a repairman for a replacement.
Remember the safety precautions and watch the video on the topic:
The LLC LOKI company offers underfloor heating repair at the prices indicated below. We search for the place of breakage or damage without opening the floor using special devices. In the place of damage, we will install a special repair sleeve on the cable. Soldering and electrical tape in the case of a heating cable are not applicable in principle. We will replace the thermostat and thermosensor.
Causes failure of the warm floor:
Mechanical damage such as cuts, crushing (deformation) of the heating cable. The heating cable may not be completely cut, but only cut or cut to the heating core - this is quite enough for the system to stop working. How long will she survive with such injuries? This is individual and depends on many factors, as a rule, the critical life of underfloor heating is the first three years.
Heating cable operation in air. This happens when air voids remain under the tiles. After all, as we all know from school physics lessons, air and tile glue heat up at different speeds, it is in the places of air voids that the heating core of the underfloor heating burns out.
Damage to the thermostat or temperature sensor,
For all work on the repair of a warm floor we provide a guarantee ... Repair parts are always available.
Ask your question to our consultants by phone in St. Petersburg:
Photos of damage to the warm floor:
It's no secret that sometimes thermostats fail, and at the most inopportune moment. There are several reasons for this sad event. The most common is incorrect installation: an error in the wiring diagram (such as: mixing up wires and terminals, too much load), painting the installed thermostat with paint, installing the thermostat in a damp room. With such errors, the thermostat either immediately fails, or its service life is significantly reduced. Have the thermostat installed by a professional electrician.
The second reason is related to the design features of thermostats. The fact is that basically their power supplies are built according to a transformerless circuit with a ballast capacitor (almost all regulators from such companies as: OJ Electronics, Eberle, Raychem, some DEVI), or according to a key stabilizer circuit such as Devireg D530, Devireg D535 , Veria B45, Veria T45.
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Such thermostats are sensitive to impulse noise on the power supply, which occurs when devices such as a welding transformer, a hammer drill or an electric lawn mower are turned on next to the regulator, which is often the case in country houses. In such conditions, it is better to use regulators with transformer power supplies that do not allow impulse noise (for example, NTC100 Busch Jaeger regulator).
If your regulator is out of order, do not rush to throw it away. In most cases, the regulator can be repaired.
Our company carries out warranty repairs of thermostats purchased through our network of stores or through our dealers, as well as non-warranty repairs of any regulators.
The cost of such repairs is fixed - 1000 rubles.
Your the warm floor suddenly stopped heating or did it not turn on immediately after laying the tiles?
Floor heating thermostat
There can be only two reasons for underfloor heating malfunctions: thermostat ... for some reason does not supply voltage to the heating cable and / or open circuit of the heating cable. In this article, we will cover the first one - thermostat does not work .
What is a thermostat and how it works read here Thermostat malfunction is easy to diagnose ... This can usually be done by any technically competent person who knows how to use a multimeter.
To diagnose the thermostat, it must be dismantled .
Dismantling the underfloor heating thermostat
IMPORTANT! Before starting work, be sure to disconnect the power supply to the thermostat ... if it is powered through a separate machine or de-energize the entire apartment by turning off the input switch or unscrewing the plugs.
The thermostat does not turn on ... the control lamp on the front panel does not light up or the display does not turn on.In this case, first you need to check if there is power at the supply terminals. To do this, with the power off, dismantle the thermostat from the mounting box without disconnecting the wires. Then, turning on the power, you need to check the presence of voltage at the supply terminals of the thermostat. The lead terminals are marked with the letters N (zero) and L (line / phase). The voltage is checked either with a multimeter (tester) - between the supply terminals or with a probe screwdriver - at terminal L and, just in case, at terminal N. According to the rules, a blue wire (wire with a blue stripe) must be connected to terminal N, and to terminal L - white or red (brown) wire. If there is no voltage on the supply wires, the problem is not in the underfloor heating system, but in the wiring or in the switchboard. If your diagnostics revealed that the phase wire is suitable for terminal N of the thermostat, the so-called "re-phasing" - it is necessary to reverse the supply wires, having previously disconnected the voltage. "Re-phasing" can lead to failure of the thermostat.
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If power is present and correctly connected in phases, and the control lamp or display on the thermostat does not turn on, then the thermostat is out of order. Such a malfunction in "field" conditions is not corrected; it is easier to replace the entire thermostat. If the warranty period for the thermostat has not yet expired, you must change it under warranty.
The thermostat turns on, but does not go into operation ... on the front panel only the green light is on or the display turns on but the floor heating icon is not displayed.In this case, the initial check consists in setting a higher temperature by unscrewing the thermostat wheel in the direction of increase or setting on the display a temperature that is obviously higher than the current temperature in the room (30-350). If, in this case, the thermostat does not go into operating mode, the thermostat will most likely need to be replaced.
When the thermostat is turned on, the red light on the panel immediately changes color to green or blinks red, the display shows an inscription about the temperature sensor malfunction.
The temperature sensor is out of order. It is quite possible to replace it on your own, provided that the temperature sensor is initially correctly installed in the corrugated tube that goes into the junction box. To do this, after turning off the power, dismantle the thermostat, disconnect the wires of the temperature sensor (as a rule, these are the thinnest wires) connected to the corresponding terminals on the rear panel. Terminals are identified by the word "sensor" or "sensor" and can be located separately from the main terminal block. After disconnecting the sensor, you can check its resistance. The resistance of thermal sensors from different manufacturers is different and is in the range of 5-15 KOhm (Kiloohm). The electrical resistance of your sensor is indicated in the certificate for the thermostat. It should be borne in mind that some household testers cannot measure electrical resistance more than 2KΩ.
If the resistance of the temperature sensor matches the nameplate, poor contact in the terminals is possible. To check, you can carefully reconnect the sensor wires to the appropriate terminals. The thermostat should work ... If this does not happen, the thermostat must be checked at the service center.
Read the length of the floor plinth
If, for some reason, you were unable to replace the failed thermal sensor on your own, our wizard will do it quickly and accurately or suggest other ways to solve the problem.
The thermostat goes into operation ... a red light on the front panel or the heating icon on the display is on, but the floor is not heating up.In this case, most likely, there was breakage of the heating core underfloor heating cable. The article Why the warm floor does not work will help you understand the reasons?
You can diagnose a break in the following way. The wires leading to the underfloor heating system are disconnected from the previously de-energized thermostat, and the electrical resistance between them is measured. The resistance must correspond to the value indicated in the passport for your warm floor. If the resistance tends to infinity and / or is measured by MegaOhms, unfortunately, your warm floor really happened breakage of the heating core ... Our foreman will repair the breakage using special tools and fixtures.
If you do not have the time or opportunity to study the causes of the malfunction, just call 958-81-66 - underfloor heating repair technician, Yuri Igorevich (St. Petersburg)
Not every consumer knows that the repair of any home appliances, including the refrigerator, can be done independently without contacting a service center. Even a novice master can deal with simple breakdowns. Today we will try to figure out how to replace the refrigerator thermostat with our own hands. And also let's talk about what kind of device it is and what are its characteristics and purpose?
First, let's figure out what it actually is. A thermostat is a device that monitors the t˚C in your refrigerator and gives signals to the compressor, causing it to turn on and off depending on the degree of cooling in the compartment. It works very simply. The thermostat is a relay. On one side of it there is a special hermetically sealed tube filled with freon. On the other hand, the contacts of the electrical circuit, with their help, the compressor is controlled.
See also - How to adjust the thermostat (thermostat) in the refrigerator
Everything works very simply. The end of the capillary tube is attached to the evaporator. Since it is filled with a refrigerant, for example freon, then with an increase in t˚C inside the refrigerating chamber, the pressure in it increases. This closes the corresponding relay contacts and turns on the compressor. After a while, t˚C in the refrigerator compartment decreases, the pressure in the bellows tube drops and the contacts open. The compressor turns off.
Another important component of the thermostat is the spring, which compresses and expands its contacts. It depends on her how and when they will work. For example, in order to open the contacts at a low pressure in the system (low t˚C), less effort is needed, for a large one - more. The tension of the spring is adjusted using the thermostat switch knob. This is how the temperature regime changes in the Atlant refrigerator and other models with mechanical control.
Some models of refrigerators are equipped with an electronic thermostat. It consists of a temperature sensor and a control module. In modern models, several sensors can be installed for each cooling zone. If your refrigerator has an electronic temperature control mode, it may require specialized knowledge to repair it.
See also - 5 models of refrigerators that we do not advise you to buy
Well, we have disassembled the device and characteristics of the device, we move on to the next question. In order to repair the thermostat with your own hands, you first need to find it.
inside the refrigerating chamber;
outside the refrigerator.
This arrangement is typical for earlier models of Atlant refrigerators and others. If you open the refrigerator, you can see a small plastic box placed on one of the panels. This is the thermostat. To get to it, you just need to remove the temperature selector knob and unscrew the protective case.
Modern refrigeration units are arranged a little differently. In them, the device we need is located outside the refrigerator chamber. It is usually located at the top of the refrigerator, above the door. But it may be in another place.
See also - Why does a refrigerator need a voltage regulator
Do we really need a temperature controller? Maybe the cause of the breakdown is completely different? Most often, the signs of a breakdown of a thermostat are obvious: (See also: Why the refrigerator does not freeze - what to do?)
the refrigerator works without stopping and does not turn off on its own;
the unit begins to freeze strongly in the refrigerator compartment, where, in normal mode, there should be, albeit a low, but still positive temperature;
the refrigerator shuts down spontaneously and no longer makes any sounds.
Each of these faults can be caused by the temperature controller. In order not to spend money on calling a specialist, we will try to fix the breakdown with our own hands.
disconnect the refrigerator from the power supply;
remove all food from it and defrost it well;
move the thermostat knob to the “Max” position or turn on the freeze, if any;
place a thermometer on the middle shelf of the refrigerator compartment (not in the freezer), it is best if it also has a negative measurement scale;
turn on the refrigeration unit (empty, no food);
wait 2 hours, then quickly remove the thermometer and evaluate its reading.
broken thermostat;
burned out motor start relay;
the engine of the refrigeration unit burned out.
The last two reasons are, of course, very serious. But we are now interested in the first one. To make sure that you need to replace the thermal relay, you need to check it:
disconnect the refrigerator from the mains;
find the location of the thermostat and remove the protective covers;
inspect the device carefully.
Most often, the temperature controller has three to four colored wires. One of them is usually yellow with a longitudinal green stripe. This is grounding. We won't need it, so set it aside to avoid accidentally snagging it.All wires that fit the body of the thermal relay, short-circuit each other directly. If, after turning on the refrigerator, you hear a steady hum of the engine, it means that the temperature regulator is out of order and you will have to replace it with a new one.
orange, red or black - connects the thermostat to the motor;
brown - zero, the wire leading to the outlet;
white, yellow or green - leads to a light indicating that the refrigerator is on;
striped yellow-green - ground.
If you find such a nuisance, several factors may be the reason. So first you need to do all the steps described in the first paragraph. If the thermometer readings were + 6 ° C or less, quickly turn the thermostat adjustment knob until the refrigerator is turned off.
remove the cover of the upper hinge and unscrew the bolts under it;
remove the refrigerator compartment door;
further, remove the plug in the refrigerator roof and unscrew one screw (most often it has a built-in hexagon);
we unscrew the screws holding the roof (located at the back) and remove it;
remove the temperature control knob;
take out the temperature regulator by unscrewing 2 self-tapping screws that secure the bracket;
change the node to a new one and perform all actions in the reverse order.
get to the detail;
disconnect the capillary tube from the evaporator body;
carefully pull it out of the case;
disconnect the relay itself;
carefully insert the new bellows tube and secure it to the evaporator;
connect all the necessary wires and attach the relay in place.
If this is your first time doing this kind of work, take pictures of your every step with your phone or camera. The photos will help a lot when assembling, if you forget what and where was connected.
Video (click to play).
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