Need for customization temperature regime occurs when using different systems thermal or refrigeration equipment... There are many options, and they all require a control device, without which the systems can operate either at maximum power or at the full minimum of capabilities. Control and adjustment are carried out using a thermostat - a device capable of acting on the system through a temperature sensor and turning it on or off as needed. When using ready-made sets of equipment, control units are included in the delivery set, but for self-made systems you have to assemble the thermostat yourself. The task is not the easiest one, but it is quite solvable. Let's take a closer look at it.
A thermostat is a device that can respond to changes in temperature conditions. By the type of action, trigger-type thermostats are distinguished, which turn off or turn on heating when a predetermined limit is reached, or smooth-acting devices with the possibility of fine and precise adjustment, capable of controlling temperature changes in the range of fractions of a degree.
There are two types of thermostats:
Mechanical devices do not allow for high tuning accuracy. They are both a temperature sensor and an actuator combined into a single unit. The bimetallic plate used in heating devices is a thermocouple made of two metals with different coefficients of thermal expansion.
The main purpose of the thermostat is to automatically maintain the required temperature
When heated, one of them becomes larger than the other, which causes the plate to bend. The contacts installed on it open and stop heating. Upon cooling, the plate returns to its original shape, the contacts close again and heating resumes.
A chamber with a gas mixture is a sensitive element of a refrigerator thermostat or heating thermostat. With changes in temperature, the volume of gas changes, which causes a movement of the membrane surface connected to the lever of the contact group.
The thermostat for heating uses a chamber with a gas mixture that works according to the Gay-Lussac law - when the temperature changes, the volume of gas changes
Mechanical thermostats are reliable and provide stable operation, but the setting of the operating mode occurs with a large error, almost "by eye". Electronic circuits are used when fine tuning is required to provide an adjustment within a few degrees (or even finer). The temperature sensor for them is a thermistor that can distinguish the smallest changes in the heating mode in the system. For electronic circuits, the situation is the opposite - the sensitivity of the sensor is too high and it is artificially roughened, bringing it to the limits of reason. The principle of operation consists in changing the resistance of the sensor caused by fluctuations in the temperature of the controlled environment. The circuit reacts to changes in signal parameters and increases / decreases heating in the system until another signal is received. The capabilities of electronic control units are much higher and allow you to get the temperature setting of any accuracy. The sensitivity of such thermostats is even excessive, since heating and cooling are processes with high inertia, which slow down the response time to command changes.
Manufacturing mechanical thermostat at home, it is quite difficult and irrational, since the result will work in a too wide range and will not be able to provide the required tuning accuracy. Most often, self-made electronic thermostats are assembled, which allow you to maintain the optimal temperature of the warm floor, incubator, ensure the desired water temperature in the pool, heat the steam room in the sauna, etc. There can be as many options for using a homemade thermostat as there are systems in the house that need to be set up and temperature controlled. For rough adjustment using mechanical devices, it is easier to purchase ready-made elements, they are inexpensive and readily available.
A homemade thermostat has certain advantages and disadvantages. The advantages of the device are:
The disadvantages include:
The main problem is the need for training or, at least, the participation of a specialist in the process of creating the device.
The thermostat is manufactured in stages:
The stages of manufacturing the device have their own characteristics, so they should be considered in more detail.
Materials required for assembly include:
In the process, you may need other tools or materials, so this list should not be considered exhaustive and final.
The choice of the scheme is determined by the capabilities and level of training of the master. The more complex the circuit, the more nuances will arise when assembling and configuring the device. At the same time the most simple schemes allow you to get only the most primitive devices that work with a high error.
Let's consider one of the simple schemes.
In this circuit, a zener diode is used as a comparator
The figure on the left shows the circuit of the regulator, and on the right - the relay block that turns on the load. The temperature sensor is R4 and R1 is the variable resistor used to set the heating mode. The control element is the TL431 zener diode, which is open as long as there is a load on its control electrode above 2.5 V. Heating of the thermistor causes a decrease in resistance, which causes the voltage on the control electrode to drop, the zener diode closes, cutting off the load.
The other scheme is somewhat more complicated. It uses a comparator - an element that compares the readings of a temperature sensor and a reference voltage source.
A similar circuit with a comparator is applicable to regulate the temperature of the warm floor
Any change in voltage caused by an increase or decrease in the resistance of the thermistor creates a difference between the reference and the working line of the circuit, as a result of which a signal is generated at the output of the device that causes the heating to be turned on or off. Such schemes, in particular, are used to adjust the operating mode of the warm floor.
The assembly order of each device has its own characteristics, but some general steps can be highlighted. Consider the build progress:
To configure the device, you must either have a reference device, or know the voltage rating corresponding to a particular temperature of the controlled environment. For individual devices, there are own formulas showing the dependence of the voltage on the comparator on temperature. For example, for the LM335 sensor, this formula looks like:
V = (273 + T) 0.01,
where T is the required temperature in Celsius.
In other schemes, adjustment is made by selecting the values of the adjusting resistors when creating a certain, known temperature. In each case, you can use your own methods, which are optimal for the existing conditions or used equipment. The requirements for the accuracy of the device also differ from each other, therefore, there is no single adjustment technology in principle.
The most common malfunction of homemade thermostats is the instability of the thermistor readings, caused by poor quality parts. In addition, there are often difficulties with setting the modes, caused by a mismatch in ratings or a change in the composition of parts required for correct work devices. Majority possible problems directly depend on the level of training of the master who assembles and configures the device, since skills and experience in this matter mean a lot. Nevertheless, experts say that making a thermostat with your own hands is a useful practical task that gives you good experience in creating electronic devices.
If you are not confident in your abilities, it is better to use a ready-made device, of which there are enough on sale. It should be borne in mind that a failure of a regulator at the most inopportune moment can cause serious troubles, which will take effort, time and money to fix. Therefore, when deciding on self-assembly, you should approach the issue as responsibly as possible and carefully weigh your capabilities.
For automatic maintenance temperature regime, you can create a thermostat with your own hands. A high-quality homemade product will perform its functions no worse than a factory counterpart. After a thorough study of the assembly process, upgrades and repairs will not be difficult.
From the examples given, the basic requirements for the accuracy that a suitable thermostat circuit must provide is clear. In some situations, it is necessary to maintain a given level not lower than ± 1C °. To control the operating parameters, an on-line display is needed. Load capacity is essential.
The listed features explain the purpose of typical functional units:
For your information. In addition to the parts considered, the thermal relay circuit may contain additional components to supply power to the electric heater, another powerful load.
Any thermostat circuit operates on the same principles. The temperature information is compared with the set value. The crossing of a certain level activates the executive device to correct the monitored parameter as required.
In its simplest form (refrigerator relay), a mechanical switch is used. For a more accurate adjustment (engine speed), not only microelectronics are used, but also specialized software.
To make a simple do-it-yourself thermostat, a circuit for a personal computer power supply is better than other options.
The thermistor is used to measure the temperature at the reference point. The potentiometer is set optimal value to turn on the fan. This scheme is not capable of changing the speed. Connects the inductive load of the MOSFET transistor. An analogue with suitable power characteristics can be used.
A do-it-yourself temperature controller can be made as part of an old boiler modernization project. The type of fuel does not matter, although it is easier to ensure a good result using gas equipment.
In this example, the developers created a temperature control device in a fruit / vegetable storage. To analyze the incoming data, a microcircuit with the following blocks was selected:
If the switches are in the appropriate position, the LED matrix shows the current temperature value or the reference level. Use the buttons in step-by-step mode to set the desired response threshold.
Creating a functional thermostat with your own hands is not too difficult. Nevertheless, you need to realistically assess your own capabilities. The following instructions will help you make the right decision.
To eliminate unnecessary difficulties, a circuit with a power supply unit without a transformer is used. A conventional diode bridge is used to rectify the supply voltage. The required level of the constant component is maintained by a zener diode. The surge is eliminated by the capacitor.
A typical divider is suitable for voltage control. A resistor is installed in one arm, which reacts to temperature changes. A relay is suitable for controlling the actuator.
This device can be used to maintain the temperature in a mini greenhouse, another limited space. The main element is an operational amplifier microcircuit, which is turned on in the voltage comparison mode. Fine and coarse adjustment of the threshold is performed using resistors R5 and R4, respectively.
This option is designed to connect electric underfloor heating and other powerful loads. Attention should be paid to the increased reliability of the product, which is ensured by the galvanic isolation of circuits with weak and strong currents.
In some situations, you will need the skills of making a complex printed circuit board... The simplest circuits are assembled in a few minutes using a soldering iron and hinged mounting technology. Before performing work operations, you must purchase:
The shopping list is based on the selected electrical diagram. To protect the device from adverse external influences and improve appearance create an appropriate body.
The pros and cons of individual schemes are assessed taking into account actual operating conditions. Sometimes it is profitable to spend time and money at the stage of implementation of an idea in order to extend the life of the finished product. It makes no sense to create a homemade product if a factory analogue with official guarantees is cheaper.
To extend the life of the thermostat, use the following recommendations:
It is not difficult to restore a homemade thermal sensor with your own hands, since the verification technology (settings) is known. Factory repair instructions can be found on the manufacturer's official website.
In rainy, snowy or slushy weather, it is always required to dry your shoes after the street. In order not to wear wet shoes to the radiator every time, it was decided to make a low-power heated floor for drying shoes in the hallway, near front door... As you know, to control the temperature of underfloor heating, you need a thermostat, you can buy it, but it is much more pleasant to assemble the device yourself.
Specifications:
Thermostat operation
At the moment the device is turned on, the mains alternating voltage through the transformerless power supply (R1, R2, C1, C3, C5, VD1, VD2) is rectified and stabilized to 15V, the green LED indicates the presence of voltage. The divider consisting of R4, R5 and R9 sets the threshold for turning on / off the thermostat, and since the floor is cold, R9 (thermistor) has a maximum resistance of about 10 kΩ, while a voltage higher than 2.5V is supplied to the regulating input of the TL431 zener diode through R4, R5, Zener diode is open. The current flows through the chain VD3, R6, HL2, U1, the optosimistor is open, the red diode indicates this. An open optosimistor U1 forms a divider R7, R8, C2, the VS1 triac turns on, the floor heats up. At the moment when the floor temperature increases, the resistance of the R9 sensor (thermistor) decreases and, as a result, there comes a moment when the voltage at the regulating input of the zener diode becomes lower than the reference 2.5V, TL431 is closed, followed by the optosimistor and triac closes, the red LED goes out, heating section is disabled. As the floor cools down by several degrees, the process is repeated, the device maintains the set temperature.
Setting up and installing
R4 sets the maximum temperature, the lower the resistance R4, the higher the maximum heating temperature of the heating section. R5 sets the minimum temperature, the higher the R5 resistance rating, the wider the temperature control range. R9 (thermistor) is a temperature sensor, it decreases its resistance as the temperature rises, so it controls the on / off of the thermostat depending on the floor temperature. With the help of R7 it is possible to regulate the power at the output of the thermostat.
The thermostat on / off threshold should be set after installing the R9 sensor. The sensor leads should be insulated with, for example, heat shrink tubing.
The sensor should be installed close to the heating section, for example between the turns of the heating cable.
All cables and the sensor must be putty, and the ends lead into the junction box. In the future, tiles will lay on this floor.
In my case, the thermostat housing is made of an unnecessary RJ-45 socket
The board is divorced and adjusted for a specific case. And yes, I advise using angle screw terminals with straight terminals will be very inconvenient.
The power of the heating section is 300W, the triac must be installed through a mica gasket on a radiator of a suitable size with an area of 50 cm2. If the power of the heating section does not exceed 150W, then you can do without a radiator.
Good luck to all! Take care of your health!
Attention! The thermostat circuit has no protection against overheating of the heating section!
ZY: See the comments to the article.
| Designation | Type of | Denomination | Quantity | Note | Shop | My notebook | |
|---|---|---|---|---|---|---|---|
| Semiconductor elements | |||||||
| VS1 | Triac | BT136-600E | 1 | BT139-600 | Into notepad | ||
| U1 | Optocoupler | MOC3061M | 1 | MOC3041 | Into notepad | ||
| VD1 | Diode bridge | DB104 | 1 | Into notepad | |||
| VD2 | Zener diode | 1N4744A | 1 | Into notepad | |||
| VD3 | Voltage reference IC | TL431 | 1 | Into notepad | |||
| HL1 | Light-emitting diode | L-132XGD | 1 | green | Into notepad | ||
| HL2 | Light-emitting diode | L-132XID | 1 | Red | Into notepad | ||
| Resistors | |||||||
| R1 | Resistor | 1 mΩ | 1 | Into notepad | |||
| R2 | Resistor | 51 Ohm 1W | 1 | Into notepad | |||
| R3 | Resistor | 2.2 k Ohm | 1 | Into notepad | |||
| R4 | Resistor | 18 kΩ | 1 | * | Into notepad | ||
| R5 | Variable resistor | 20 kΩ | 1 | * | Into notepad | ||
| R6 | Resistor | 1.1 k Ohm | 1 | Into notepad | |||
| R7 | Resistor | 270 Ohm | 1 | * | Into notepad | ||
| R8 | Resistor | 30 kΩ | 1 | ||||
The electronic thermostat for refrigerator will help in cases when your own (factory) thermostat is faulty or its accuracy is no longer sufficient. Older refrigerators use mechanical thermostat temperature using liquid or gas, with which the capillary is filled.
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 thermostating system has low accuracy, and its parts wear out over time.
As you know, the storage temperature of food in refrigerator compartment should be + 2 ... 8 degrees Celsius. The working temperature of the refrigerator is +5 degrees.
An electronic thermostat for a refrigerator is characterized by two parameters: start and stop temperature (or average temperature plus hysteresis value) of the compressor. Hysteresis is necessary to prevent the refrigerator compressor from turning on too often.
This circuit provides a hysteresis of 2 degrees at average temperature 5 degrees. Thus, the refrigerator compressor turns on when the temperature reaches + 6 degrees and turns off when it drops to + 4 degrees.
This temperature range is sufficient to maintain optimal temperature storage of food, and at the same time it ensures comfortable operation of the compressor, preventing excessive wear. This is especially important for older refrigerators that use thermal relays to start the engine.
The electronic thermostat is a suitable replacement for the original thermostat. The thermostat reads the temperature using a sensor whose resistance changes depending on the temperature change. For these purposes, a thermistor (NTC) is often used, but the problem is its low accuracy and the need for calibration.
To ensure accurate temperature control and avoid hours of calibration, the this option thermostat for the refrigerator was selected. 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 sensor output can be monitored 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 resistor R1 and therefore the current across it changes in proportion to the temperature. This current causes a drop across the resistor R2. The voltage drop controls the operation of the transistor VT1. If the voltage drop exceeds the threshold voltage of the base-emitter transition, transistors VT1 and VT2 open, relay K1 turns on, whose contacts are connected instead of the contacts of the old thermostat.
Resistor R3 provides positive feedback. This adds a small current to R2, which shifts the threshold and thus provides hysteresis. The coil 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 suitable place... Resistor R1 is soldered directly to the temperature sensor, which in turn allows the LM35 to be connected to the circuit board with just two wires.
The wires connecting the sensor can introduce noise into the circuit, so capacitor C2 is added to suppress the noise. 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 mains.
The big advantage of this circuit is that it starts working immediately upon first startup and does not need to be calibrated or 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.
Portable USB oscilloscope, 2 channels, 40 MHz ....
The operation of a gas or electric boiler can be optimized by using the external control of the unit. Remote thermostats available on the market are intended for this purpose. This article will help you understand what these devices are and understand their varieties. It will also consider the question of how to assemble a thermostat with your own hands.
Any electric or gas boiler is equipped with a set of automation that monitors the heating of the coolant at the outlet of the unit and turns off the main burner when the set temperature is reached. Equipped with similar facilities and solid fuel boilers... They allow you to maintain the temperature of the water within certain limits, but nothing more.
In this case, climatic conditions indoors or outdoors are not taken into account. This is not very convenient, the homeowner has to constantly select the appropriate boiler operating mode on his own. The weather can change during the day, then it becomes hot or cool in the rooms. It would be much more convenient if the boiler automation was guided by the indoor air temperature.
To control the operation of the boilers depending on the actual temperature, various thermostats for heating are used. Being connected to the boiler electronics, such a relay turns off and starts heating, maintaining the required air temperature, and not the coolant.
A common thermostat is a small electronic unit mounted on a wall in a suitable location and connected to a heat source with wires. There is only a temperature regulator on the front panel, this is the cheapest type of device.
In addition to her, there are other types of thermal relays:
Note. The model, where the sensor is located outside the building, provides weather-dependent regulation of the boiler plant operation. The method is considered the most effective, since the heat source reacts to a change weather conditions even before they affect the temperature inside the building.
Multifunctional thermostats, which can be programmed, significantly save energy. In those hours of the day when no one is at home, support high fever there is no sense in the rooms. Knowing the work schedule of his family, the homeowner can always program the temperature switch so that at certain hours the air temperature drops, and the heating is turned on an hour before the arrival of people.
Household thermostats equipped with a GSM module are capable of providing remote control of the boiler plant via cellular communication. A budget option- sending notifications and commands in the form of SMS messages from a mobile phone. Advanced versions of the devices have their own applications installed on the smartphone.
Commercially available heating control devices are reliable enough and do not cause any complaints. But at the same time, they cost money, and this does not suit those homeowners who are at least a little versed in electrical engineering or electronics. After all, understanding how such a thermal relay should function, you can assemble and connect it to the heat generator with your own hands.
Of course, not everyone can make a complex programmable device. In addition, to assemble such a model, you need to purchase components, the same microcontroller, digital display and other parts. If you are a new person in this business and understand the issue superficially, then you should start with some simple scheme, assemble and put it into operation. Having achieved a positive result, you can aim at something more serious.
First you need to have an idea of what elements a thermostat with temperature control should consist of. The answer to the question is given by the schematic diagram presented above and reflecting the algorithm of the device's operation. According to the scheme, any thermostat must have an element that measures the temperature and sends an electrical impulse to the processing unit. The task of the latter is to amplify or transform this signal in such a way that it serves as a command to the executive element - the relay. Further, we will present 2 simple schemes and explain their work in accordance with this algorithm, without resorting to specific terms.
A zener diode is the same semiconductor diode that passes current in only one direction. The difference from a diode is that the zener diode has a control contact. While the set voltage is applied to it, the element is open and the current flows through the circuit. When its value falls below the limit, the chain is broken. The first option is a thermal relay circuit, where a zener diode plays the role of a logical control unit:
As you can see, the diagram is divided into two parts. On the left side, the part preceding the control contacts of the relay is shown (designation K1). Here, the measuring unit is a thermal resistor (R4), its resistance decreases with increasing ambient temperature. The manual temperature controller is a variable resistor R1, the circuit is powered by a voltage of 12 V. In normal mode, a voltage of more than 2.5 V is present on the control contact of the zener diode, the circuit is closed, the relay is on.
Advice. Any inexpensive commercially available device can serve as a 12 V power supply. Relay - reed switch brand RES55A or RES47, thermal resistor - KMT, MMT or the like.
As soon as the temperature rises above the set limit, the resistance of R4 drops, the voltage becomes less than 2.5 V, the zener diode will break the circuit. Next, the relay will do the same, turning off the power section, whose diagram is shown on the right. Here, a simple thermostat for the boiler is equipped with a D2 triac, which, together with the closing contacts of the relay, serves as an executive unit. The boiler supply voltage of 220 V passes through it.
This circuit differs from the previous one in that instead of a zener diode, it uses a K561LA7 logic microcircuit. The temperature sensor is still a thermistor (designation - VDR1), only now the decision to close the circuit is made by the logic block of the microcircuit. By the way, the K561LA7 brand has been produced since Soviet times and costs mere pennies.
For the intermediate amplification of the pulses, the KT315 transistor is involved, for the same purpose, a second transistor, KT815, is installed in the final stage. This diagram corresponds to the left side of the previous one, the power unit is not shown here. As you might guess, it can be similar - with the KU208G triac. The operation of such a homemade thermostat has been tested for boilers ARISTON, BAXI, Don.
It is not difficult to independently connect the thermostat to the boiler; there are a lot of materials on this topic on the Internet. But making it with your own hands from scratch is not so easy, in addition, you need a voltage and current meter to make the adjustment. Buying a finished product or taking on its manufacture yourself - the decision is up to you.
