Electric heating boiler control. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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The proposed microcontroller control unit is designed and manufactured to replace the regular control unit for the electric heating boiler "EVAN EPO-7,5/220 V", which does not provide sufficient ease of operation. It can also be used to control other electric heaters.

After the purchase and installation of the boiler "EVAN EPO-7,5 / 220 V", the shortcomings of the control unit with which it was equipped were revealed. The main one is the simultaneous switching on and off of the three electric heaters installed in the boiler. The resulting current surges and voltage drops in the network are so great that they cause malfunctions of some electronic devices powered by it. There were even failures of them. In addition, a powerful contactor, which periodically turned on and off the heaters to maintain the set temperature, rumbled throughout the house, and the block hanging on the wall in which it was installed “jumped” until it fell and broke. It was decided not to repair this block, but to develop and manufacture a new one, eliminating the shortcomings if possible and expanding the functions performed.

The new control unit was made four-channel with electronic switching. Three channels control the heaters in a timed manner, which greatly reduces the inrush current drawn from the mains. The contactor is used only for emergency shutdown of heaters in case of boiler overheating. The fourth channel controls the water pump of the heating system. There is a mode of rapid heating of the boiler to a predetermined temperature with the pump turned off and then turning it on to supply hot water to the heating system.

The new system, like the old one, stabilizes the water temperature at the outlet of the boiler, although it is possible to switch to its stabilization at the inlet. If you connect a room temperature sensor to the control unit, the system automatically switches to the stabilization mode for this parameter.

A diagram of the new control unit, together with temperature sensors and actuators (heaters and a water pump), is shown in fig. 1. The heating system is switched on and off by switch SA1, which supplies mains voltage to the power module. After that, all other modules of the control unit start working. The EK1-EK3 heaters are supplied with 220 V voltage through the KM1 contactor, SA3-SA5 circuit breakers and a module of triac switches controlled by signals generated in the microcontroller module. Contactor type - NC1 -25. When the boiler is operating normally, its contacts are closed.

Rice. 1 (click to enlarge)

The M2 motor control circuit, which drives the water pump, which includes the SA2 machine and one of the channels of the triac module, differs only in that it cannot be opened by the KM1 contactor. This is necessary so that in the event of an emergency shutdown of the heaters, the pump continues to work, providing water circulation in the heating system and its accelerated cooling. The heat sinks of the triacs that switch the heaters and the pump are blown by a two-speed computer fan M1, size 80x80x20 mm, with a supply voltage of 12 V.

Two-color LEDs HL1-HL4 are connected to the module of triac switches. Their red glow crystals turn on when mains voltage is applied to the inputs of the corresponding triac switches, and green - when their triacs are opened. In the latter case, the color of the LED turns yellow, which indicates that the mains voltage is applied to the heater or pump. Diodes VD1-VD8 protect the LEDs from reverse voltage.

The water temperature sensors at the outlet of the boiler (BK1), at its inlet (BK2), as well as the air temperature in the heated room (BK3) are connected to the microcontroller module through the power supply module and intermodule connections. On the outputs of sensors BK1 - BK3, filter parts are mounted (respectively R1C1, R2C2, R3C3). According to the diagram, wires of short lengths of standard USB cables with plugs of USB-A connectors are soldered to the terminals 1, 2 of the sensors and the free terminals of the resistors.

Standard automotive coolant temperature sensors 1-2 are used as housings for VK19 and VK3828 sensors, from which all "insides" have been removed. The DS18B20 sensors, together with the parts soldered to them and the ends of the cables, are inserted into the formed cavities and filled with automotive sealant.

After the sealant has hardened, the VK1 sensor is screwed into place of the previously existing water temperature sensor at the outlet of the boiler. Diameter and thread pitch are suitable. To install the VK2 sensor, it is necessary to make an insert with a threaded hole in the pipeline supplying water to the boiler.

A piece of heat-shrinkable tube is put on the VKZ sensor and the end of the cable leading to it for protection from external influences. This sensor is placed in a heated room away from heat sources and protected from drafts.

The VK5-VKZ sensors are connected to the X1 connector of the power supply module and intermodule connections by cables made of USB extension cords with USB-A cable sockets. as a thermal switch SF1, signaling an unacceptable overheating of water, TM108 is used - a standard car engine cooling fan switch. There is a place for its installation in the boiler, the thread pitch and diameter are suitable. The contacts of this switch are closed when the water temperature in the boiler reaches 92 ^оC, which leads to the immediate release of the armature by the contactor KM1 and turning off all heaters. The contacts of the SF1 switch open when the water temperature drops to 87 ^оC.

To analyze the sensor signals and generate control signals for heaters and other system devices, a universal microcontroller module described in [1] with a specially developed program was used. In order to connect LED indicators instead of a graphic LCD, the module has undergone a slight modification. The tuning resistor R15 that regulated the LCD contrast was removed (the numbering of the module elements is according to the diagram in Fig. 1 in [1]). As a result of this, two contacts of the X4 connector, released as a result, are used to transmit additional control signals for LED indicators. For this, pin 2 is connected to the PC7 output (pin 28), and pin 18 is connected to the PD7 output (pin 30) of the microcontroller DD1.

The diagram of the LED indication and control module connected to the microcontroller module instead of the LCD is shown in fig. 2. Three-digit seven-element LED indicators HG1 - HG3 with a common cathode are installed in it, which display information about the operation of the boiler. They depend on the selected operating mode of the heating system.

Rice. 2 (click to enlarge)

The microcontroller generates information for displaying on indicators HG1-HG3 in the form of a serial 24-bit code, which is converted by three eight-bit shift registers connected in series into a parallel code supplied to the anodes of the indicator elements. The first of these registers is located in the microcontroller module (DD2 according to its scheme). It serves the HG1 indicator. The other two (DD1 and DD2 in the display module under consideration) serve respectively the indicators HG2 and HG3. The value of the high-order bit of register DD24 is loaded first into the 2-bit register, and the value of the low-order bit of register DD2 of the microcontroller module is loaded last.

The LEDs HL1-HL3 of the display module display the heater control signals generated by the microcontroller module, respectively EK1, EK2 and EKZ. LED HL4 turns on when the water temperature in the boiler drops, and HL5 - when it rises. Using the SB1-SB4 buttons, they switch the operating modes of the system and change their parameters.

The diagram of the module of triac switches is shown in fig. 3. It has four identical channels. The positional designations of the elements of each of them are provided with prefixes that match the channel numbers. The control signals generated by the microcontroller module are fed through the X1 connector to the emitting diodes of the triac optocouplers 1U1-4U1, which provide galvanic isolation between the control and executive circuits.

Rice. 3 (click to enlarge)

The applied optocouplers MOC3063 [2] have nodes for binding the moments of opening of the phototriacs to the moments when the voltage applied to them passes through zero. This significantly reduces the level of switching interference. The executive elements of the switches are powerful triacs 1VS1-4VS1 installed on heat sinks, which are blown by the M1 fan (see Fig. 1).

The control unit for this fan, connected to connector X3, is assembled on a transistor VT1. The signal to turn on the fan comes from the microcontroller to connector X2 simultaneously with the appearance of a signal on X1 that turns on any of the heaters, and is removed after a set time after the last of the heaters is turned off. This ensures rapid cooling of heated triacs.

All power inputs (through resistors 1R5-4R5) and outputs (through resistors 1R6-4R6) of the switching channels are connected to the XP4 connector, to which LEDs are connected to indicate the mains voltage supply to the inputs (XT1-XT4 contacts) of the switches and its appearance on the connector contacts X5 to which the heaters and the pump are connected.

On fig. 4 shows a diagram of the module for inter-module connections and power supply for low-power nodes. Transformer T1 lowers the mains voltage of 220 V to 15 V, which then rectifies the diode bridge VD1. After smoothing the ripples with capacitors C2 and C3, the rectified voltage is stabilized by the integral stabilizers DA1 and DA2. The first outputs a voltage of 12 V to power relay K1 and fan M1 (see Fig. 1), the second - 5 V to power the microcontroller module. The power supply module also contains a control unit for the heater emergency shutdown contactor, consisting of a VT1 transistor and a K1 relay.

Rice. 4 (click to enlarge)

Connector X3 is connected to the microcontroller module, and X4 - to temperature sensors. Connector X5 outputs heater and pump control signals, as well as supply voltages for the switching module.

The details of each module of the boiler control unit are mounted on a separate printed circuit board made of foil fiberglass with a thickness of 1,5 mm. A drawing of the board of the microcontroller module is available in [1]. Trimmer resistor R15 is not installed on it, and pins 2 and 18 of connector X4 are connected to the previously indicated microcontroller outputs with jumpers from an insulated wire. No other modifications are required.

The printed circuit board of the display and control module is double-sided. The drawing of its printed conductors is shown in fig. 5, and the location of parts - in Fig. 6. If this board will be manufactured using technology without sides, short lengths of bare wire. The conclusions of the parts are also soldered on both sides.

Fig. 5

Fig. 6

The remaining printed circuit boards are single-sided. A drawing of the triac switch module board is shown in fig. 7. Connections of electrodes 1 of triacs with contact pads on the printed circuit board are made with insulated wires with a cross section of at least 2,5 mm². Fan M1 is fixed on U-shaped heat sinks of triacs 1VS1 - 1VS4 (Fig. 8). To do this, threaded holes are made in the upper shelves of the heat sinks. A drawing of the power module board and intermodule connections is shown in fig. 9.

Fig. 7

Fig. 8

Fig. 9

The device uses fixed resistors MLT, S2-33, oxide capacitors K50-35 or imported, the rest of the capacitors are K73-17. All microcircuits and indicators HG1-HG3 are installed in the panel.

The heating boiler control unit is assembled in a housing from the music center "LG" (Fig. 10). On the lower metal panel of the case, which became the rear panel of the unit, all modules, a contactor, circuit breakers and other large parts are fixed. The top plastic panel has turned into a front one. It has holes for indicators and control buttons, as well as for access to the SA1 switch and SA2-SA5 circuit breakers. The side walls of the case are cut to the desired dimensions. In its lower part there are connectors for connecting temperature sensors and external power circuits. The power circuits of the block are made with an insulated mounting wire with a cross section of at least 2,5 mm².

Fig. 10

The boiler is controlled using four buttons installed in the display and control unit. You can change the stabilization temperature at any time using the SB4 "+" and SB3 "-" buttons. If the sensor measuring the room air temperature is not connected, the water temperature in the boiler will stabilize. With the connection of this sensor, its readings are displayed on the indicator and the temperature in the room stabilizes.

The indicator HG1 of the indication and control module in the operating mode displays the set air temperature in the room if the BK3 sensor is present, and without it, the set water temperature in the boiler (at the outlet or at the inlet, depending on the set mode). The indicator HG2 displays the measured temperature of the air in the room or the water leaving the boiler. When the air temperature sensor is connected, the measured water temperature at the boiler outlet will be displayed on the HG3 indicator, and at the boiler inlet when it is disconnected.

By pressing the button SB1 "Mode" enter the service mode and select the parameter to be changed. Button SB3 "-" decrease, SB4 "+" increase the value of the selected parameter. By pressing the SB2 "Memory" button, the values ​​​​of the changed parameters are written to the EEPROM of the microcontroller. To restore the default settings, i.e. return to their values ​​that were in effect when the system was first turned on, it is necessary to hold the SB2 "Memory" button pressed for more than 5 s. When a continuous beep sounds, the button can be released.

In the service mode, the letter П with the number of the adjustable parameter is displayed on the HG2 indicator, and its value is displayed on the HG1 indicator. All adjustable parameters, their limits and default values ​​are shown in the table. It also includes parameters that are set in the operating mode, and therefore do not have symbols on the indicator. These are the values ​​of the water temperature in the boiler or the air in the room maintained by the heating system. All parameters can only take integer values. It should be remembered that the microcontroller program does not check their correctness. For this reason, common sense and caution should be exercised when changing parameters.

There are three ways to exit the service mode. Firstly, this happens after pressing the "Memory" button and writing information to the EEPROM. Secondly, automatically one minute after the last pressing of any button. Thirdly, as a result of enumeration of all parameters before entering the operating mode. All button presses are accompanied by confirmation beeps. Changed parameter values ​​that are not written to the EEPROM are only valid until the device is turned off.

When the microcontroller module is turned on for the first time with the program just loaded from it, the default parameter values ​​are overwritten in the EEPROM of the microcontroller. But for this, the EEPROM must be clean (contain 0FFH in all cells), otherwise the information will not be overwritten, all parameters will have to be set manually.

After the initialization of the temperature sensors and the indication system, the program checks the state of the SF1 thermal switch and, if the water temperature is below the permissible level, gives a short beep signal of readiness and turns on the contactor. Having determined which sensors are connected, the program controls the heaters, maintaining the set temperature of the water in the boiler or the air in the room. The readings of a missing or faulty sensor are replaced on the indicator by three dashes.

At a temperature below the set one, the pump, the triac cooling fan and, in turn, at specified intervals, the heating elements are turned on. When the set temperature is reached, the heating elements turn off one by one. By default, the pump continues to work without turning off, but with parameter P_2 you can set it to turn off after a period of time specified by parameter P_3 or when the water temperature drops to the value specified by parameter P_4. The fan for blowing triacs is turned off after the time set by parameter P_10 after the last heater is turned off.

When the temperature decreases by the number of degrees set by parameter P_1, the heaters will be turned on again and the temperature control cycle will be repeated. The higher the value of this parameter, the less often the heaters turn on, but the longer they work.

PCB files in Sprint Layout 5.0 format and the microcontroller program can be downloaded from ftp://ftp.radio.ru/pub/2014/03/epo_evan.zip.

Literature

1. Kiba V. Universal microcontroller module with graphic LCD. - Radio, 2010, No. 3, p. 28-30.
2. 6-pin DIP zero-cross phototriac driver optocoupler. - mkpochtoi.narod.ru/MOC3061_MOC3062_MOC3063_zerocross_ds.pdf.

Author: V. Kiba

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