A soldering iron is a tool without which home handyman can’t be avoided, but you’re not always satisfied with the device. The fact is that an ordinary soldering iron, which does not have a thermostat and therefore heats up to a certain temperature, has a number of disadvantages.
Soldering iron circuit diagram.
If during short-term work it is quite possible to do without a temperature regulator, then with a regular soldering iron, long time included in the network, its shortcomings are fully manifested:
- solder rolls off an excessively heated tip, resulting in weak soldering;
- scale forms on the tip, which has to be cleaned frequently;
- the working surface becomes covered with craters, and they must be removed with a file;
- it is uneconomical - in the intervals between soldering sessions, sometimes quite long, it continues to consume rated power from the network.
The temperature regulator for a soldering iron allows you to optimize its operation:
Figure 1. Diagram of a simple thermostat.
- the soldering iron does not overheat;
- it becomes possible to select the soldering iron temperature value that is optimal for a specific job;
- during breaks, it is enough to use the temperature regulator to reduce the heating of the tip, and then right time quickly restore the required degree of heating.
Of course, you can use LATR as a thermostat for a 220 V soldering iron, and for a 42 V soldering iron you can use a KEF-8 power supply, but not everyone has them. Another way out is to use an industrial dimmer as a temperature regulator, but they are not always commercially available.
DIY temperature regulator for a soldering iron
Return to contents
The simplest thermostat
This device consists of only two parts (Fig. 1):
- Push-button switch SA with normally open contacts and latching.
- Semiconductor diode VD, designed for a forward current of about 0.2 A and a reverse voltage of at least 300 V.
Figure 2. Diagram of a thermostat operating on capacitors.
This temperature controller works as follows: in the initial state, the SA switch contacts are closed and current flows through a heating element soldering iron during both positive and negative half-cycles (Fig. 1a). When you press the SA button, its contacts open, but the semiconductor diode VD passes current only during positive half-cycles (Fig. 1b). As a result, the power consumed by the heater is halved.
In the first mode, the soldering iron quickly warms up, in the second – its temperature decreases slightly, overheating does not occur. As a result, you can solder in quite comfortable conditions. The switch together with the diode is connected to the break in the supply wire.
Sometimes the SA switch is mounted on a stand and is triggered when the soldering iron is placed on it. During breaks between soldering, the switch contacts are open and the heater power is reduced. When the soldering iron is lifted, the power consumption increases and it quickly heats up to operating temperature.
Capacitors can be used as ballast resistance, which can be used to reduce the power consumed by the heater. The smaller their capacity, the greater the resistance to flow alternating current. Scheme simple thermostat, working on this principle, is shown in Fig. 2. It is designed to connect a 40W soldering iron.
When all switches are open, there is no current in the circuit. By combining the position of the switches, you can get three levels of heating:
Figure 3. Circuits of triac thermostats.
- The lowest degree of heating corresponds to the closure of the contacts of switch SA1. In this case, capacitor C1 is switched on in series with the heater. Its resistance is quite high, so the voltage drop across the heater is about 150 V.
- The average degree of heating corresponds to the closed contacts of switches SA1 and SA2. Capacitors C1 and C2 are connected in parallel, the total capacity is doubled. The voltage drop across the heater increases to 200 V.
- When switch SA3 is closed, regardless of the state of SA1 and SA2, the heater is supplied with full mains voltage.
Capacitors C1 and C2 are non-polar, designed for a voltage of at least 400 V. To achieve the required capacitance, several capacitors can be connected in parallel. Through resistors R1 and R2, the capacitors are discharged after the regulator is disconnected from the network.
There is another option for a simple regulator, which is not inferior to electronic ones in reliability and quality of work. To do this, a variable wirewound resistor SP5-30 or some other one with suitable power is connected in series with the heater. For example, for a 40-watt soldering iron, a resistor rated at 25 W and having a resistance of about 1 kOhm is suitable.
Return to contents
Thyristor and triac thermostat
Operation of the circuit shown in Fig. 3a, the operation of the previously disassembled circuit in Fig. is very similar. 1. Semiconductor diode VD1 passes negative half-cycles, and during positive half-cycles, current passes through thyristor VS1. The proportion of the positive half-cycle during which the thyristor VS1 is open ultimately depends on the position of the variable resistor R1 motor, which regulates the control electrode current and, consequently, the firing angle.
Figure 4. Triac thermostat circuit diagram.
In one extreme position the thyristor is open during the entire positive half-cycle, in the second it is completely closed. Accordingly, the power dissipated by the heater varies from 100% to 50%. If you turn off the VD1 diode, the power will change from 50% to 0.
In the diagram shown in Fig. 3b, a thyristor with an adjustable firing angle VS1 is included in the diagonal of the diode bridge VD1-VD4. As a result, the voltage at which the thyristor is unlocked is adjusted during both the positive and negative half-cycles. The power dissipated by the heater changes when the variable resistor R1 is turned from 100% to 0. You can do without a diode bridge if you use a triac rather than a thyristor as a control element (Fig. 4a).
Despite all its attractiveness, a thermostat with a thyristor or triac as a control element has the following disadvantages:
- When the current increases abruptly in the load, strong impulse noise occurs, which then penetrates into lighting network and ether;
- distortion of the mains voltage waveform due to the introduction of nonlinear distortions into the network;
- reduction of power factor (cos ϕ) due to the introduction of a reactive component.
To minimize impulse noise and nonlinear distortion, it is desirable to install network filters. The simplest solution is a ferrite filter, which consists of several turns of wire wound around a ferrite ring. Such filters are used in most switching power supplies for electronic devices.
A ferrite ring can be taken from the wires connecting the computer system unit with peripheral devices (for example, a monitor). Usually they have a cylindrical thickening, inside of which there is a ferrite filter. The filter device is shown in Fig. 4b. The more turns, the higher the quality of the filter. The ferrite filter should be placed as close as possible to the source of interference - a thyristor or triac.
In devices with a smooth change in power, the regulator slider should be calibrated and its position marked with a marker. When setting up and installing, you should disconnect the device from the network.
The circuits of all the above devices are quite simple and can be repeated by a person with minimal skills in assembling electronic devices.
There are many models of soldering irons in stores - from cheap Chinese ones to expensive ones, with a built-in temperature controller; they even sell soldering stations.
Another thing is whether the same station is needed if similar works Should it be done once a year, or even less often? It's easier to buy an inexpensive soldering iron. And some people still have simple but reliable Soviet instruments at home. A soldering iron that is not equipped with additional functionality heats up as long as the plug is plugged in. And when turned off, it cools down quickly. An overheated soldering iron can ruin the work: it becomes impossible to solder anything firmly, the flux quickly evaporates, the tip oxidizes and the solder rolls off it. An insufficiently heated tool can completely ruin the parts - due to the fact that the solder does not melt well, the soldering iron can be held close to the parts.
To make your work more comfortable, you can assemble a power regulator with your own hands, which will limit the voltage and thereby prevent the soldering iron tip from overheating.
DIY soldering iron regulators. Overview of installation methods
Depending on the type and set of radio components, power regulators for a soldering iron can be different sizes, with different functionality. You can assemble either a small simple device, in which heating is stopped and resumed by pressing a button, or a large one, with a digital indicator and program control.
Possible types of installation in the housing: plug, socket, station
Depending on the power and tasks, the regulator can be placed in several types of housing. The simplest and most convenient one is a fork. For this you can use Charger for a cell phone or any adapter housing. All that remains is to find the handle and place it in the wall of the case. If the soldering iron body allows it (there is enough space), you can place the board with the parts in it.
Another type of housing for simple regulators is a socket. It can be either single or a tee-extension. In the latter you can very conveniently place a handle with a scale.
There may also be several options for installing a regulator with a voltage indicator. It all depends on the radio amateur’s intelligence and imagination. This can be either the obvious option - an extension cord with an indicator built into it, or original solutions.
You can even assemble something like a soldering station and install a soldering iron stand on it (it can be purchased separately). When installing, we must not forget about safety rules. The parts need to be insulated - for example, with heat shrink tubing.
Circuit options depending on the power limiter
The power regulator can be assembled according to different schemes. The main differences lie in the semiconductor part, the device that will regulate the flow of current. This could be a thyristor or triac. For more precise control of the operation of a thyristor or triac, you can add a microcontroller to the circuit.
You can make a simple regulator with a diode and a switch - in order to leave the soldering iron in working condition for some (possibly long) time, without allowing it to cool down or overheat. The remaining controls make it possible to set the temperature of the soldering iron tip more smoothly - under different needs. Assembling the device according to any of the schemes is done in a similar way. The photographs and videos provide examples of how you can assemble a power regulator for a soldering iron with your own hands. Based on them, you can make a device with the variations you personally need and according to your own design.
Thyristor- a kind of electronic key. Passes current in only one direction. Unlike a diode, a thyristor has 3 outputs - a control electrode, an anode and a cathode. The thyristor opens by applying a pulse to the electrode. It closes when the direction changes or the current flowing through it stops.
Or a triac is a type of thyristor, but unlike this device, it is double-sided and conducts current in both directions. It is essentially two thyristors connected together.
Triac or triac. Main parts, principle of operation and method of display in diagrams. A1 and A2 - power electrodes, G - control gate
The power regulator circuit for a soldering iron, depending on its capabilities, includes the following radio components.
Resistor- serves to convert voltage into current and vice versa. Capacitor- the main role of this device is that it stops conducting current as soon as it is discharged. And it begins to conduct again - as the charge reaches the required value. In regulator circuits, the capacitor is used to turn off the thyristor. Diode- semiconductor, an element that passes current in the forward direction and does not pass in the reverse direction. Subtype of diode - zener diode- used in devices for voltage stabilization. Microcontroller- a microcircuit that provides electronic control of the device. There are varying degrees of difficulty.
Circuit with switch and diode
This type of regulator is the easiest to assemble, with the fewest parts. It can be collected without payment, by weight. The switch (button) closes the circuit - all voltage is supplied to the soldering iron, opens it - the voltage drops, and so does the temperature of the tip. The soldering iron remains heated - this method is good for standby mode. A rectifier diode rated for a current of 1 Ampere is suitable.
Assembling a two-stage regulator on weight
- Prepare parts and tools: diode (1N4007), switch with button, cable with plug (this can be a soldering iron cable or an extension cord - if you are afraid of ruining the soldering iron), wires, flux, solder, soldering iron, knife.
- Strip and then tin the wires.
- Tin the diode. Solder the wires to the diode. Remove excess ends of the diode. Put on heat shrink tubing, process with heat. You can also use an electrically insulating tube - cambric. Prepare a cable with a plug in the place where it will be more convenient to mount the switch. Cut the insulation, cut one of the wires inside. Leave part of the insulation and the second wire intact. Strip the ends of the cut wire.
- Place the diode inside the switch: the minus of the diode is towards the plug, the plus is towards the switch.
- Twist the ends of the cut wire and the wires connected to the diode. The diode must be inside the gap. The wires can be soldered. Connect to terminals, tighten screws. Assemble the switch.
Regulator with switch and diode - step by step and clearly
Thyristor regulator
Regulator with power limiter - thyristor - allows you to smoothly set the soldering iron temperature from 50 to 100%. In order to expand this scale (from zero to 100%), you need to add a diode bridge to the circuit. The assembly of regulators on both a thyristor and a triac is done in a similar way. The method can be applied to any device of this type.
Assembling a thyristor (triac) regulator on a printed circuit board
- Make a wiring diagram - outline the convenient location of all the parts on the board. If the board is purchased, the wiring diagram is included in the kit.
- Prepare parts and tools: printed circuit board(it must be done in advance according to the diagram or purchased), radio components - see the specification for the diagram, wire cutters, knife, wires, flux, solder, soldering iron.
- Place the parts on the board according to the wiring diagram.
- Use wire cutters to cut off the excess ends of the parts.
- Lubricate with flux and solder each part - first resistors with capacitors, then diodes, transistors, thyristor (triac), dinistor.
- Prepare the housing for assembly.
- Strip and tin the wires, solder them to the board according to the wiring diagram, and install the board into the case. Insulate the connection points of the wires.
- Check the regulator - connect it to an incandescent lamp.
- Assemble the device.
Circuit with low-power thyristor
A low-power thyristor is inexpensive and takes up little space. Its peculiarity is hypersensitivity. To control it, a variable resistor and capacitor are used. Suitable for devices with a power of no more than 40 W.
Specification
Circuit with a powerful thyristor
The thyristor is controlled by two transistors. The power level is controlled by resistor R2. The regulator assembled according to this scheme is designed for a load of up to 100 W.
Specification
| Name | Designation | Type/Denomination |
| Capacitor | C1 | 0.1 µF |
| Transistor | VT1 | KT315B |
| Transistor | VT2 | KT361B |
| Resistor | R1 | 3.3 kOhm |
| Variable resistor | R2 | 100 kOhm |
| Resistor | R3 | 2.2 kOhm |
| Resistor | R4 | 2.2 kOhm |
| Resistor | R5 | 30 kOhm |
| Resistor | R6 | 100 kOhm |
| Thyristor | VS1 | KU202N |
| Zener diode | VD1 | D814V |
| Rectifier diode | VD2 | 1N4004 or KD105V |
Assembling a thyristor regulator according to the above diagram into a housing - visually
Assembly and testing of a thyristor regulator (review of parts, installation features)
Circuit with thyristor and diode bridge
Such a device makes it possible to adjust power from zero to 100%. The circuit uses a minimum of parts.
Specification
Triac regulator
Triac-based regulator circuit with a small number of radio components. Allows you to adjust power from zero to 100%. The capacitor and resistor will ensure the smooth operation of the triac - it will open even at low power.
Assembling a triac regulator according to the given diagram step by step
Triac regulator with diode bridge
The circuit of such a regulator is not very complicated. At the same time, the load power can be varied over a fairly wide range. With a power of more than 60 W, it is better to place a triac on a radiator. At lower power, cooling is not needed. The assembly method is the same as with a conventional triac regulator.
Before installation, the assembled regulator can be checked with a multimeter. You only need to check with a soldering iron connected., that is, under load. We rotate the resistor knob - the voltage changes smoothly.
Regulators assembled according to some of the diagrams given here will already have indicator lights. They can be used to determine whether the device is working. For others, the simplest test is to connect an incandescent light bulb to the power regulator. The change in brightness will clearly reflect the level of the supplied voltage.
Regulators where the LED is in series with a resistor (as in the circuit with a low-power thyristor) can be adjusted. If the indicator does not light, you need to select the resistor value - take one with lower resistance until the brightness is acceptable. You cannot achieve too much brightness - the indicator will burn out.
As a rule, adjustment when correctly assembled circuit not required. With the power of a conventional soldering iron (up to 100 W, average power - 40 W), none of the regulators assembled according to the above diagrams require additional cooling. If the soldering iron is very powerful (from 100 W), then a thyristor or triac must be installed on the radiator to avoid overheating.
You can assemble a power regulator for a soldering iron with your own hands, focusing on your own capabilities and needs. There are many options for regulator circuits with various power limiters and by different means management. Here are some of the simplest ones. A short overview of the housings in which parts can be mounted will help you choose the device format.
IN Lately I had to repair a lot of small things. However, doing this with the available EPSN-25 soldering iron was not always convenient.
I ordered and received an inexpensive Chinese soldering iron with temperature control from 200 to 450 degrees.
The soldering iron comes with a set of five tips to perform various types works (replicas of Hakko 900 series).
The declared power of the soldering iron is 60 watts. I was a little disappointed by the length of the wire - 1.38 meters. As for me, the wire is a little short, but everything is individual and depends on the organization of the workplace and the location of the sockets.
Before turning it on, I disassembled the soldering iron and inspected it. inner world. The soldering is decent, the triac regulator circuit is (a regular dimmer), there is an indicator LED (it only reports the supply of mains voltage).
There is no thermal sensor, but its presence was not expected for such money. The heating element is stated to be ceramic - there is a characteristic step. However, there is a photo of such a broken heater online. And despite the step, inside there was nichrome wire. So, I can’t say that here ceramic heater. Its resistance is 592 Ohms. 
It would seem that everything is not bad, but the very first results were very puzzling. The first acquaintance of the soldering iron with rosin led to the Hollywood appearance of a cloud of smoke and cracking of the rosin throughout its entire depth. The adjustment didn't help much. The soldering iron was put aside until the wattmeter and thermometer arrived. At first I tried to take temperature measurements with an immersion kitchen thermometer, but its measurement limit of 300 degrees and its inertia forced me to refuse its services. 
For the entire review procedure appearance and inner peace, switching on, calling magic smoke, getting out of the stupor took about 20 minutes. The sting (replica 900M-K), the most massive of the set, after that acquired a very pale appearance and refused to make friends with tin. IT'S BURNED!!!
Since the parcels arrived three weeks apart, as they arrived, measurements were taken first of power consumption and then of temperature. The photos were taken both at home and in a “house in the village”, so the surrounding background in the photo, although different, was taken with my own hands and the same soldering iron appears in them.
SO:
Upon arrival of the wattmeter, I decided to measure the power consumed by the soldering iron and it turned out that it consumes the declared 60 W only at the moment it is turned on (very difficult to capture with a camera). In this case, the temperature regulator is set to the maximum position. I didn’t install the tip – although there are a lot of them in the set, but still.
The wattmeter reading quickly drops to 40 watts and then drops to 30.1 watts.
Then, after letting the soldering iron cool down, I turned the regulator to minimum and again measured consumption.
At the minimum, the start of consumption also starts from the area of 60 watts, but sharply decreases to 25.2 and finally stabilizes at 20.6 watts. 
Please note that heating occurs in the second half of the heater, where the tip is located.
But we solder not by power consumption, but by a tip with a certain temperature, and before the thermometer arrived, the soldering iron went back to the bench.
Upon arrival of the thermometer, I took measurements in the same positions of the regulator - maximum and minimum.
At maximum the temperature reached 587 degrees!!! (They slipped me a burner???) 
At a minimum - 276 degrees.
I modified the adjustment circuit by adding another capacitor in parallel to the existing capacitor with a total capacity of 47 nanoFarads * 400 Volts.
So with power consumption everything is already clear, i.e. it is not critical, so I only took temperature measurements at maximum and minimum and already at assembled form- with a sting:
At maximum it turned out: 
At minimum: 
Which borders on the heating level of my usual soldering iron EPSN-25. 
There is information on the Internet that the heating element can be unsoldered from the board and pushed forward slightly - this should supposedly increase the heat transfer to the soldering iron tip. 
I tried it, but didn’t notice a significant difference - the soldering iron didn’t suffer from underheating anyway. In addition, we must not forget about the linear expansion of materials as a result of heating and with such a modification, when assembled, the heater rests against the cold tip, and when heated, due to linear expansion, the heater may collapse. This is indirectly indicated by the fact that after these tests the nut securing the tip turned out to be quite loose. Therefore, I abandoned this modification and returned the heater to its original state.
For practical testing of the tips, I chose the most massive tip (replica 900M-K). Why him? Mass determines heat capacity, and therefore it will cool more slowly. By the way, all the tips are tinned from the factory and are not magnetic. Those. It’s hard to even call it a replica – it’s a pitiful semblance. Later, the most massive tip used at the beginning of testing was put under a needle file and it can be assumed that the tips are made of copper. However, their weight is confusing; for those made of copper they are quite light, although this is my subjective opinion not based on chemical analysis)). 
I didn’t experiment with all the tips, but out of habit I chose a replica 900M-T-3S (round with a bevel). I got used to this tip shape using EPSN-25.
But even here a fiasco awaited - even after modifying the soldering iron, the tip was burned at minimum power. I didn’t even bother installing the rest - they would get burned. The price of the entire set speaks for itself.
Since there was nothing left to lose, I remembered the needle file and mercilessly sharpened the T3S tip using the usual technology. I thought it was all in the bucket, but it turned out that in this form the tip is very friendly with tin and soldering took on a new meaning)). I can’t say how long it will last, but so far I’m happy with the result.
EVENTUALLY:
1. A thing for enthusiasts - it’s unlikely to be used without modification;
2. The tips from the set are garbage;
3. Buying new stings is a lottery) because there are a lot of fakes;
4. The tactile sensations from using the soldering iron are the most positive - it fits like a glove in your hand, thanks to the rubber lining, the grip is firmly fixed and there is no slipping of the hand, heating of the upper part of the handle after an hour of use at a temperature of around 250 degrees (soldered donors) is in the “absent” range to “not significant”;
5. Not a big takeaway work surface the tips from the soldering iron handle are a definite plus;
6. Fast heating, low solder consumption, undoubted convenience of soldering SMD components, the ability to change tips for different types works
Yes, this is not a professional tool for working every day for 8 hours, but for most radio amateurs who are getting their hands on it, it’s just the thing (taking into account the above).
Another quality that I cannot classify as a disadvantage, but thanks to which it differs from using a conventional low-power soldering iron with a conventional tip - rosin does not linger on the tips of the new soldering iron. Those. By the time you bring it to the board, the tip is already dry. This is due to the small size of the tips included in the kit and, as a consequence, small area surfaces.
I got out of the situation using Amtech RMA-223 flux. The soldering turns out perfect. The worst results were shown by the alcohol-rosin mixture.
Considering that you need to get used to each tool, I can say that after the experience gained and the adjustments made, I am generally satisfied with the soldering iron. Let everyone decide for themselves.