At 12 volts - essential tool modern radio electronics in household use. With it, you can quickly solder microcircuits, parts of an earpiece, electronic wristwatches, and repair your phone charger. Many radio amateurs prefer to make an electric soldering iron with their own hands. This work saves money and does not let you forget the school physics course.
Necessary materials and tools
You don’t need much material to make a soldering iron, and you can easily find it at home. These are copper wire for the manufacture of a directly soldering base, copper foil, a tin tube (for a casing) and nichrome wire, a handle (preferably plastic), an electrical cord in heat-resistant insulation, silicate glue, talc for electrical insulating mass.
Sometimes it's hard to find copper foil. You can use foil fiberglass. It is often used in the manufacture of printed circuits and circuit boards. If there are no such houses, you can go to the store and buy for 200 rubles necessary material. To get one sheet of copper foil, you need to heat the fiberglass with an ordinary iron and, dividing it into thin plates, pull the corner, wind it around a round stick.
The main element is a 220/12 volt transformer, through which the soldering iron will receive energy from the mains. TVK-11OL is often used. It can be found in old tube TVs.
Required following tools:
- tweezers;
- pliers;
- wire cutters;
- plates or boards for coating with adhesive mass;
- stove (electric or gas);
- rag.
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Soldering iron assembly steps
The copper wire you purchased will serve as the tip of the micro soldering iron. It will take only 50 mm. It must be sharpened in the form of a dihedral angle on one side and be sure to tin the edges. The finished sting will be inside the heating element.
The second stage in the manufacture of a microsoldering iron will be the preparation of a special electrical insulating mass. To do this, mix talc and liquid glass (silicate glue). Using a board or tweezers, apply insulation to the cylindrical surface, periodically sprinkling with talcum powder so that the mass does not stick to your hands.
Roll the copper foil into a tube about 35 mm long. This will be the base of the heating element. On one side, a soldering iron tip will be visible from under the tube. This tube must be covered with an insulating mass, as in the first case. The raw mass that you applied must be dried over the stove until completely solidified. Now you can wind the nichrome wire on the finished base by making a spiral. Its length should not exceed 350 mm. The turns must be laid carefully and very close to each other, while the upper and lower ends of the wire (from 30 to 60 mm) are left as conclusions. This structure is once again covered with a mixture of electrical insulation and dried over the stove.
Now the bar end of the wire must be bent back, pressed firmly against the surface of the tube and repeated applying the mass a third time. Only after that the heating element of the soldering iron can be considered completely ready for use.
The wire that protrudes from under the heating element must be covered with an electrical insulating mass. At the same time, you need to be patient and, each time applying a lot, do not forget to check the quality of the actions performed.
When the base is completely covered with insulation, you can start assembling the microsoldering iron. We connect the ends of the nichrome heater with a handle. To do this, we stretch an electric cord in heat-resistant insulation through the internal plastic cavity. Bare spots should be isolated with mass and dried. After that, we put a protective tin casing on the heater and connect it to the handle. The micro soldering iron is ready for use.
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Homemade resistor soldering iron
Radio amateurs often use the most unusual tools at hand to make various tools. Simplicity, reliability, ease of use - these are the technical characteristics of a do-it-yourself microsoldering iron.
As in the previous version, for the manufacture of a soldering iron, you will need copper and steel wires and double-sided textolite.
The new elements will be a ballpoint pen (for the manufacture of the case) and an MLT-0.5 resistor, which has a resistance of 5-10 ohms.
We begin work with the manufacture of the heating element. Use a scalpel or sandpaper to remove paint from the resistor. To do this, connect it to a regulated power source. After thorough cleaning of paint, remove one of the legs of the resistor, and use the other as a fastener and current lead. In the part of the resistor where the leg was removed, you need to drill a hole with a diameter of 1 mm to install the soldering tip. After that, countersink the hole with a larger diameter drill so that the soldering iron tip does not come into contact with the cup. With the help of a needle file, you need to make another cut in a round shape to fasten the current lead to a depth of 2/3 of the thickness.
The current lead can be made from a well-tinned spring, the rings of which should be tightly put on the cup.
The next stage of work is the manufacture of PCB boards. It has a wide part for soldering the current lead and dissipating heat, a middle part for the handle body, and a narrow part for attaching wires and cambric.
After these operations, you can start assembling. The current lead from the spring must be put on the front cup. The current leads are soldered to the PCB board. Install the tip of a microsoldering iron made of copper wire, after putting it in a piece of ceramic or mica, so that there is no current access. Now it remains to solder the wires to the board (preferably MGTF). As a battery, an adjustable BP1A, 0-15V is used. The micro soldering iron is ready for use.
The soldering technology with a homemade micro soldering iron is no different from the one you purchased in the store. With it, you can even perform miniature soldering. It is very convenient and does not require much skill to assemble.
Sometimes there are situations when the owner simply cannot do without a simple soldering iron. For example, you need a multi-core cable for an outlet, or from a burned-out appliance. At such moments, one has to either borrow an instrument, or postpone the matter for an indefinite period. After all, not everyone wants to buy an expensive soldering iron or soldering station if he is not a repairman. However, there is a simple way out of this situation - to independently assemble a small soldering iron, it is just right for small work. The manufacturing process will not take much time and effort, but you can save some money and gain invaluable experience. Next, we will tell you how to make a soldering iron with your own hands at home. You will be offered several designs, and you can choose the one that suits you the most.
Idea #1 - Use a Resistor
First and most simple technology making an electric soldering iron with your own hands - using a powerful resistor. The device will be designed to operate at a voltage of 6 to 24 volts, which will allow it to be powered by various current sources, and even make a portable version powered by a car battery. In order to make your own tool, you will need the following materials:
To make a soldering iron from a resistor at home, you must follow these steps:
- At the end of a thick copper rod, you need to drill a hole and drive the thread under the screw with a tap. It is also necessary to cut a groove for the retainer, which in our case is the spring ring. This can be done with a triangular needle file or a hacksaw.
- From the second end, drill a hole with a diameter like a thin rod, which will act as a mini soldering iron tip.
- All elements of the rod must be assembled into one whole, as shown in the photo.
- The resistor is prepared for mounting the soldering iron tip, which must be inserted and fixed at the back with a screw with a washer.
- From a textolite or plywood plate, you need to make a comfortable handle with a seat for a resistor and a wire with your own hands. To do this, use a jigsaw to cut out two identical halves of the handle and make holes and recesses for screws and nuts.
- Connect the power cord to the heater terminals. It must be screwed onto the screws so that the contact is reliable.
- The finished homemade soldering iron is twisted and checked.
We draw your attention to the fact that with such a portable gun you can easily solder microcircuits and even with your own hands. It can work not only from the power supply, but also from the battery. On the forums, we met a lot of reviews, where this homemade version was connected from a 12 volt cigarette lighter, it is also very convenient!
Please note that when first turned on, all soldering irons may smoke and stink for a while. This is normal for any model, as some elements of the paintwork will burn out. This will stop later.
Video instructions for making a simple electrical appliance
Idea number 2 - The second life of a ballpoint pen
There is another unusual, but at the same time simple idea how to make a soldering iron with your own hands from improvised materials for soldering small parts or smd components. In this case, again, it will come in handy for us, but now it’s not PEV (as in the previous version), but MLT, with a power of 0.5 to 2 watts. 
So, first you need to prepare the following materials:
- Ballpoint pen of the simplest design.
- Resistor with characteristics: resistance 10 Ohm, power 0.5 W.
- Double-sided textolite.
- Copper wire with a diameter of 1 mm, it can be wound from an old choke or you can buy a single-core copper wire in insulation at an electrician's store and carefully remove it with a clerical knife
- Steel or copper wire with a diameter of not more than 0.8 mm.
- Wires for connecting to the network.
Making a soldering iron from a pen at home is quite simple, you just need to follow these steps:
- Remove a layer of paint from the surface of the resistor. This operation can be carried out with the help of a skin, a needle file or a file, in extreme cases, a knife. The main thing is not to overdo it, so as not to damage the resistor. If the paint is difficult to remove, connect the product to a regulated power supply and heat it up a little.
- 2 wires come out of the barrel, cut one of them and drill a hole for a copper wire in this place (diameter 1 mm). To prevent the wire from touching the cup (this must be avoided), countersink with a thicker drill, as shown in the photo below. In addition, you need to make a small cut for the wire right on the resistor cup. A triangular file will help you with this again.
- Bend the steel wire into the shape of a ring-shaped handle, with a diameter similar to that of a drank on a cup. If you have copper wire, then you need to clamp the cup in it and twist it with pliers so that the contact is reliable, but do not overdo it, otherwise you will wrinkle the body. Remember that the wire must be without varnish insulation.
- Carefully cut out the board from the double-sided PCB with your own hands, exactly the same as shown in the example in the photo. It is not necessary to buy a new sheet of textolite. You can use a jigsaw to cut a suitable piece from any unnecessary double-sided board. Or do without it altogether: twist the wire with wires, and attach them to the handle with superglue. The main thing to pay attention to is that the distance between the heating element and the handle is more than 5 cm, otherwise the plastic may melt.
- Next, you need to assemble a homemade soldering iron from the handle, which should not cause difficulties.
- It remains to install thin sting to the seat. To prevent the copper wire from burning through the resistor, you need to make a protective layer of a piece of mica or ceramic between the back wall and the sting.
- The last thing to do is to connect the homemade product to a 1 A power supply and a voltage of no more than 15 Volts using wires.
That's the whole technology of creating a homemade mini soldering iron at home. As you can see, there is nothing complicated in making this tool, and you can easily cope with it, and all the materials can be found at home by dismantling old equipment or looking for them in the bins.
How to make a more complex model of a mini soldering iron at home?
Video review of a device with nichrome wire, powered by 12 volts
Idea #3 - Powerful Impulse Pattern
This option is suitable for those who are already more or less familiar with radio engineering and can read the corresponding diagrams. A master class on making a homemade pulsed soldering iron will be provided following the example of this scheme: 
The advantage of this tool is that the tip heats up within 5 seconds after turning on the power, while the heated rod can easily melt the tin. At the same time, it can be made from a switching power supply from a fluorescent lamp, slightly improving the board at home.
As in the previous examples, we will first consider the materials from which you can make a soldering iron with your own hands at home. Before assembly, you must prepare the following improvised means:
All you need is to connect the tip to the secondary winding, which, in fact, is already part of it. After that, one of the ballast leads must be connected to the primary winding of the transformer and all the elements of the circuit must be fixed in a reliable case that will protect you from accidental electric shock, since the circuit contains a life-threatening voltage of 220 volts!
The principle of operation of this design is that the ballast from the lamp creates an alternating voltage that is applied to the primary winding of the transformer and is reduced to low values, while the current increases many times over. One turn, which is, in fact, the tip of the soldering iron, acts as a resistor, on which heat is dissipated. When the button is pressed, current is supplied to the circuit, and rapid heating occurs, after the button is released, the tip cools quickly, which is very convenient, since you do not have to wait long for the tool to heat up and cool down.
Idea #4 - Simple Wire Option
There is another option for making a miniature soldering iron - using nichrome wire. For this you will need:
Manufacturing process:
- Drill a hole in the bar for the copper wire 3 times larger than its diameter.
- Put a piece of copper wire in it so that it protrudes about 5 cm and fix it there with thick plaster putty, let it dry.
- Put on a copper bar, which is a sting, insulation and wind the required amount of nichrome wire, leaving a distance between the turns. Also put insulation on the ends and bring them closer to the handle. Then connect to twists with wires. Tape them to the handle with electrical tape.
That's all, you have another simple and reliable DIY soldering iron design.
We still recommend using either the first or the second option, which is more understandable and easier to manufacture. As for the transformer version, although it is more powerful, it is still not so convenient to use. We hope that these photo instructions were useful for you and finally we recommend that you definitely watch all the video examples in which the assembly process is considered in more detail!
Also read:
For soldering electronic circuits, special care must often be taken when heating the leads of semiconductor elements. They are very sensitive to temperature.
In addition, sometimes when debugging a circuit, you have to solder with the power connected. In this case, using a conventional soldering iron powered by a 220 volt network is dangerous. For such cases, it is better to use an electric soldering iron that operates on a voltage of 12 volts.
A 12 volt soldering iron can operate on both AC and DC.
A soldering iron operating on direct current can even be connected to the vehicle's on-board network, provided that its power does not exceed the calculated power of the car's electrical wiring.
There are many designs of soldering irons on the market that use low voltage. You can distinguish them by the obligatory inscription on the case, on the packaging.
This voltage must also be indicated in the technical specifications of the tool. If you have an unnecessary soldering iron for 220 volts, you can make a 12 volt one yourself.
Alteration of an old soldering iron
In order to remake a standard soldering iron, you need to disassemble it, remove the heating element. Instead, a nichrome thread with a thickness of 0.02-0.20 mm should be wound on a mica substrate. The thread can be removed from any used electrical appliance, such as a hair dryer.
The length of the thread is selected experimentally depending on the thickness and the required degree of heating of the soldering iron. When winding the thread, it is necessary to ensure that the turns do not touch each other.
The sequence of work is as follows:
- after selecting the length of the wire, the turns are fixed with some heat-resistant glue;
- the thread at both ends is connected by wires to a power source. It can be a 12 volt converter, a power tool battery, or a car battery;
- the case of a new 12 volt soldering iron must be assembled and it will not differ in any way from the previous one.
In order not to accidentally turn on the tool in a 220 volt network, it is recommended to make a catchy, clearly visible inscription on the handle - “12v”.
From a resistor
You can make a miniature homemade 12 volt soldering iron using fixed metal film resistors, for example, a 2 W MLT-2.
They work even with an overload up to 6-10 times, so it is easy to get power from them up to 12-20 watts. But a significant part of it will be wasted on heat exchange with air due to the relatively large surface area of the resistor. For manufacturing, you need a resistor with a nominal value of 24-27 ohms.
One of its fairly thick leads will serve as a soldering iron tip, the second as a contact for the power wire.
The resistor case near the contact-sting must be cleaned of paint and tightly wrapped with a second supply wire. The working scheme of the soldering iron is ready.
It remains only to place it in a case that will be convenient to use. To do this, the resistor is wrapped with a heat-resistant heat-insulating material, for example, fiberglass, and placed in a plastic tube of a suitable diameter.
Use in the car
In modern cars, there are few such components and parts that can be repaired independently, outside the garage or workshop. Most likely, it can be damaged wire harnesses at the folds.
Such malfunctions are easy to fix right on the road. It is enough to remove excess insulation and twist the wires, then protecting the twist with insulating tape.
But the wiring of the car works in very difficult conditions. It is subject to vibrations, frequent changes in temperature and humidity, especially in winter.
Under such conditions, contact in the twist can be lost, and when using a conventional single-wire electrical circuit, the loss of contact can unpredictably affect the behavior of the car.
To prevent this undesirable phenomenon, it is recommended to solder the twist. To do this, you will need a car soldering iron powered by a cigarette lighter.
Almost all car cigarette lighters are powered by a wire line rated for up to 15 A. This is quite enough to connect a soldering iron with a power of up to 100 watts. And more is unlikely to be needed. They also remake the cigarette lighter itself into a palnik. It turns out a miniature infrared hair dryer.
In older cars, soldering may be needed to repair relay and fuse mounting blocks, to solder terminals to wires broken during use.
The variety of modern soldering stations is amazing. Silicon, impulse, gas ... And you can make a traditional soldering iron (with a heating thread) with your own hands. This will be discussed in the material presented.
For any radio amateur, a soldering iron is the number one tool. Of course, in stores you can pick up an electrical appliance for every taste. However, it costs a certain amount of money, and it is interesting for any master to have a hand in making such useful device. In addition, if you need a specific tool, only a home-made device can help out.
First, let's look at how the soldering iron works.
The basis is the body, which mechanically protects the heating element. A two-piece handle is put on the body. Its task is to protect hands from high temperatures. Power wire runs through it.
The heating element (usually nichrome wire) is wound around an insulator, such as mica. Inside is a sting, which is fixed in the body with a screw.
There are also pulse devices, their principle of operation differs from the considered option.
How to make a simple soldering iron at home
First of all, you need to define the functions. The selected project will depend on this. You need a soldering iron for SMD elements, or for car maintenance. You can choose from several options.
Soldering iron for garage made of ceramic resistor C5-35V
Such resistors withstand high temperatures, have a power dissipation from 3 W to 150 W. The body of the element is made of heat-resistant ceramics, the working element is a nichrome thread.
We make a typical car soldering iron for emergency repair of wiring in the garage. Of course, the power will be from a 12 volt battery.
A C5-35V resistor with a resistance of 20 ohms and a power of 7 watts is suitable.
The handle is most convenient to make a pistol type. The material is textolite or ebonite, the main thing is good heat resistance and poor thermal conductivity.
We have a heating element (actually a resistor), now we will make a working sting and a conductor for heat transfer. It is necessary to pick up two copper rods. One is installed inside the C5-35V case and will serve as a thermal energy accumulator. The second bar, thinner, will be a working sting.
IMPORTANT! A thick bar must be fitted as tightly as possible to the inner diameter of the resistor, to reduce heat loss.
You can take the rod a little thicker, and grind it with sandpaper, rotating the drill in the chuck.
To assemble a soldering iron with your own hands, home (and not only) craftsmen are primarily driven by economic considerations. A simple 220 V soldering iron for ordinary small soldering work is better, of course, to buy. However, it is also possible to modify it without disassembling it in order to extend the life of the sting. But here's an "ax" for 150-200 W, which can be used to solder metal water pipes, costs not 4.25, but ten times more. And not Soviet rubles, but evergreen conventional units. The same problem arises if you need to solder outside the reach of the mains from a 12 V car or a pocket lithium-ion battery. How to independently make a soldering iron for such cases, and not only for such cases, is discussed in today's publication.
What is smd
Sub Micro Devices, subminiature devices. You can clearly see smd by opening a mobile phone, smartphone, tablet or computer. Using smd technology, tiny (perhaps smaller than a match cut) components without wire leads are mounted by soldering onto pads, called polygons in smd terminology. The polygon can be with a thermal barrier that prevents heat from spreading along the tracks of the printed circuit board. Here the danger is not only and not so much in the possibility of delamination of the tracks - the piston connecting the mounting layers can break from heating, which will make the device completely unusable.
A soldering iron for smd must be not only micro-powerful, up to 10 watts. The heat reserve in its tip should not exceed that which the soldered part can withstand. But long soldering with a soldering iron that is too cold is even more dangerous: the solder still does not melt, but the part warms up. And the soldering mode is significantly affected by the outside temperature, and the more, the lower the power of the soldering iron. Therefore, soldering irons for smd are made either with a time limit and / or the amount of heat transfer during soldering, or in the operational, during the current technological operation, temperature adjustment of the tip. Moreover, you need to keep it 30-40 degrees higher than the melting point of the solder with an accuracy of literally up to 5-10 degrees; this is the so-called. permissible temperature hysteresis of the tip. This is greatly hindered by the thermal inertia of the soldering iron itself, and the main task in designing one is to achieve its lowest possible time constant for heat, see below.
It is possible to make a soldering iron at home for any of these purposes. Incl. and powerful for soldering steel or copper plumbing, and accurate enough mini for smd.
Note: in fact, in a soldering iron, the tip is the working (tinned) part of its rod. But, since there are other different rods, for clarity, we will consider the entire rod as a sting. If the working part of the soldering iron is mounted on the rod, it is called a tip. Let's assume that the tip with the rod is also a sting.
Simplest
For now, let's not get into the complexity. Let's say we need a regular 220V soldering iron without any fuss. We go to choose and see the difference in prices reaches 10 or more times. We understand why. First: a heater, nichrome or ceramic. The latter (not "alternative"!) Is practically eternal, but if the soldering iron is dropped on a hard floor, it can crack. The tip of soldering irons on ceramics is necessarily non-replaceable - which means you need to buy a new one. And the nichrome heater, if the soldering iron is not forgotten turned on at night, lasts more than 10 years; with occasional use - over 20. And in extreme cases, it can be rewound.
The difference in price has now been reduced to 3-4 times, what else is the matter? In pity. Nickel-plated copper with special additives dissolves little with solder and burns very slowly in the soldering iron holder, but it is expensive. Brass or bronze heats up worse, and it is impossible to solder smd with them - the temperature hysteresis cannot be brought back to normal due to the much worse thermal conductivity of the material than that of copper. The red-copper sting is also eaten by solder, and swells quite quickly from copper oxide, but it is cheaper.
Note: a sting made of electrical copper (a piece of winding wire) for conventional soldering iron unsuitable - quickly dissolves and burns. However, for smd, such a sting is the very thing, its thermal conductivity is the maximum possible, and thermal inertia and hysteresis are minimal. True, you will have to change it often, but the sting is the size of a match or less.
Burning and swelling of the red-copper tip can be dealt with simply by being careful: after finishing the work and letting the soldering iron cool, the tip is removed, beaten off the oxide, tapping on the edge of the table, and the soldering iron clip channel is blown through. With the dissolution of solder, it is worse: it is often inconvenient to grind the sting and it quickly works.
You can make a soldering iron tip made of ordinary red copper many times more resistant to the action of molten solder without sharpening its working end, but forging it to the desired shape. Cold copper is perfectly forged with an ordinary metalworker's hammer on the anvil of a desktop vise. The author of this article has had a forged tip in the ancient Soviet EPTsN-25 for more than 20 years, although this soldering iron is at work, if not every day, then certainly every week.
simple resistor
Calculation
The simplest soldering iron can be made from a wire resistor; this is a ready-made nichrome heater. It is also easy to calculate: when dissipating the rated power in free space, the wire resistors heat up to 210-250 degrees. With a heat sink in the form of a sting, the “wiremaker” keeps a long-term power overload by 1.5-2 times; the temperature of the sting will not be lower than 300 degrees. It can be increased to 400, giving a power overload of 2.5-3 times, but then after 1-1.5 hours of operation, the soldering iron will need to be allowed to cool.
Calculate the required resistance of the resistor according to the formula: R = (U ^ 2) / (kP), where:
R is the desired resistance;
U - operating voltage;
P is the required power;
k is the above power overload factor.
For example, you need a 220V 100W soldering iron to solder copper pipes. The heat transfer is large, so we take k = 3. 220 ^ 2 = 48400. kP = 3 * 100 = 300. R = 48400/300 = 161.3 ... Ohm. We take a 100 W 150 or 180 Ohm resistor, because There are no 160 Ohm "wire wires", this value is from a range of 5% tolerance, and "wire wires" are not more accurate than 10%.
The opposite case: there is a resistor with a power p, what power can a soldering iron be made of it? What voltage should it be powered from? Remember: P = U^2/R. We take P = 2p. U^2 = PR. We take the square root of this value, we get the operating voltage. For example, there is a 15 W 10 ohm resistor. The power of the soldering iron goes up to 30 watts. We take the square root of 300 (30 W * 10 Ohm), we get 17 V. From 12 V, such a soldering iron will develop 14.4 W, you can solder a trifle with fusible solder. From 24 V. From 24 V - 57.6 W. The power overload is almost 6 times, but occasionally and for a short time it is possible to solder something big with this soldering iron.
Manufacturing
How to make a soldering iron from a resistor is shown in fig. above:
- We select a suitable resistor (pos. 1, see also below).
- We prepare the details of the sting and fasteners for it. A groove on the rod is selected under the annular spring with a needle file. Threaded blind holes are made under the bolt (screw) and the tip, pos. 2.
- We collect the rod with a tip in the sting, pos.3.
- We fix the tip in the heater resistor with a bolt (screw) with a wide washer, pos. four.
- We fasten the heater with a sting to a suitable handle in any convenient way, pos. 5-7. One condition: the heat resistance of the handle is not lower than 140 degrees, the resistor leads can heat up to such a temperature.
Subtleties and nuances
The soldering iron described above from 5-20 W resistors was made by many (including the author in the days of his pioneering youth) and, having tried it, they were convinced that they could not seriously work. It heats up for an unbearably long time, and only solders a trifle with a poke - a layer of ceramics interferes with heat transfer from the nichrome spiral to the sting. That is why the heaters of factory soldering irons are wound on mica mandrels - the thermal conductivity of mica is orders of magnitude higher. Unfortunately, it is impossible to roll mica into a tube at home, and winding 0.02-0.2 mm nichrome is also not for everyone.
But with soldering irons from 100 W (resistors from 35-50 W), the matter is different. The thermal barrier made of ceramics in them is relatively thinner, on the left in the figure, and the heat reserve in a massive sting is an order of magnitude greater, because its volume grows with the cube of its dimensions. It is quite possible to qualitatively solder the joint of copper pipes 1/2 ″ 200 W with a soldering iron from a resistor. Especially if the sting is not prefabricated, but one-piece forged.
Note: wirewound resistors are available for power dissipation up to 160 watts.
Only for a soldering iron, you need to look for old-type resistors PE or PEV (in the center in the figure, still in production). Their insulation is vitrified, withstands repeated heating to light red without loss of properties, it only darkens when it cools. The ceramics inside are clean. But the C5-35V resistors (on the right in the figure) are painted, inside too. It is completely impossible to remove the paint in the channel - the ceramics are porous. When heated, the paint chars and the sting sticks tightly.
Soldering iron regulator
An example with a low-voltage soldering iron from a resistor is given above for good reason. The PE resistor (PEV) from the trash or from the iron market most often turns out to be of the wrong value for the available voltage. In this case, you need to make a power regulator for the soldering iron. These days, it's much easier, even for people who don't know much about electronics. The ideal option is to buy from the Chinese (well, Ali Express, otherwise) a ready-made universal voltage and current regulator TC43200, see fig. on right; it is inexpensive. Permissible input voltage 5-36 V; output - 3-27 V at current up to 5 A. Voltage and current are set separately. Therefore, you can not only set the desired voltage, but also adjust the power of the soldering iron. There is, for example, a tool for 12 V 60 W, but now you need 25 W. We set the current to 2.1 A, 25.2 W will go to the soldering iron and not a milliwatt more.
Note: for use with a soldering iron, the stock TC43200 multi-turn regulators are best replaced with conventional potentiometers with graduated scales.
Pulse
Many people prefer pulse soldering irons: they are better suited for microcircuits and other small electronics (except smd, but see below). In standby mode, the tip of an impulse soldering iron is either cold or slightly warmed up. Solder by pressing the start button. At the same time, the sting quickly, for fractions of a unit, heats up to operating temperature. It is very convenient to control the soldering: the solder spread, squeezed the flux out of the drop - released the button, the sting cooled down just as quickly. You just need to have time to remove it so that it does not solder there. The danger of burning a component with some experience is minimal.
Types and schemes
Impulse heating of the soldering iron tip is possible in several ways, depending on the type of work and the requirements for the ergonomics of the workplace. In amateur conditions, or for a small individual IP, a pulsed soldering iron is more convenient and more affordable to do one of the following. schemes:
- With a current-carrying sting under the current of industrial frequency;
- With an isolated sting and its forced heating;
- With current-carrying tip under high frequency current.
Electrical circuit diagrams of pulsed soldering irons of these types are shown in Fig: pos. 1 - with a current-carrying sting of industrial frequency; pos. 2 - with forced heating of the insulated tip; pos. 3 and 4 - with a high-frequency current-carrying tip. Next, we will analyze their features, advantages, disadvantages and ways to implement at home.
50/60 Hz
The scheme of a pulse soldering iron with a tip under the current of industrial frequency is the simplest, but this is not its only advantage, and not the main thing. The potential at the tip of such a soldering iron does not exceed a fraction of a volt, so it is safe for the most delicate microcircuits. Until the induction soldering irons of the METCAL system appeared (see below), a significant part of the installers in the electronics production worked precisely with industrial frequency impulses. Disadvantages - bulkiness, significant weight and, as a result, poor ergonomics: on a shift longer than 4 hours. workers got tired and started making mistakes. But there are still a lot of industrial-frequency pulsed soldering irons in amateur use: Bison, Sigma (Sigma), Svetozar, etc.
The device of a pulsed soldering iron at 50/60 Hz is shown in pos. 1 and 2 fig. Apparently, in order to save on production costs, manufacturers most often use transformers on cores (magnetic cores) of type P (pos 2), but this is far from the best option: in order for the soldering iron to solder like an EPTsN-25, transformer power is needed 60-65 watts. Due to the large stray field, the transformer on the P-core in the short-circuit mode is very hot, and the heating time of the sting reaches 2-4 s.
If the P-core is replaced with a SL from 40 W with a secondary winding from a copper bus (pos. 3 and 4), then the soldering iron can withstand hourly work at an intensity of 7-8 solders per minute without unacceptable overheating. For operation in the mode of periodic short-term short-circuits, the number of turns of the primary winding is increased by 10-15% against the calculated one. This design is also advantageous in that the tip (copper wire with a diameter of 1.2-2 mm) can be attached directly to the terminals of the secondary winding (pos. 5). Since its voltage is a fraction of a volt, this further increases the efficiency of the soldering iron and lengthens its operating time before overheating.
With forced heating
The scheme of a soldering iron with forced heating does not require special explanation. In standby mode, the heater operates at a quarter of the rated power, and when you press the start button, the energy accumulated in the capacitor bank is released into it. By disconnecting / connecting to the battery capacity, you can rather roughly, but within acceptable limits, dose the amount of heat generated by the sting. Dignity - the complete absence of induced potential on the sting, if it is grounded. The disadvantage is that on commercially available capacitors, the circuit is only feasible for resistor mini-soldering irons, see below. It is mainly used for episodic work on hybrid assembly boards not saturated with components, smd + ordinary printed wiring in through caps.
At high frequency
Pulse soldering irons at an increased or high frequency (tens or hundreds of kHz) are very economical: the thermal power at the tip is almost equal to the nameplate electric inverter (see below). They are also compact and lightweight, and their inverters are suitable for powering constant heating resistor mini-soldering irons with an insulated tip, see below. Heating the tip to operating temperature - in a fraction of a second. Any thyristor voltage regulator 220 V can be used as a power regulator without modifications. They can be powered by a constant voltage of 220 V.
Note: for power over approx. 50 W RF impulse soldering iron is not worth doing. Although, for example. computer IPBs come with a power of up to 350 W or more, but it is almost impossible to make a sting for such power - either it will not warm up to operating temperature, or it will melt itself.
A serious drawback is that the influence of the own inductance of the sting and the secondary winding affects the operating frequencies. Because of this, an induced potential of more than 50 V may occur on the tip for more than 1 ms, which is dangerous for the CMOS component (CMOS, CMOS). Also a significant drawback - the operator is irradiated by the power flow of the electromagnetic field (EMF). You can work with a pulsed HF soldering iron with a power of 25-50 W for no more than an hour a day, and up to 25 W - no more than 4 hours, but no more than 1.5 hours in a row.
The easiest way to circuit the inverter of a 25-30 W pulsed RF soldering iron for ordinary soldering work is based on a 12 volt halogen lamp power adapter, see pos. 3 fig. with diagrams. The transformer can be wound on a core of 2 K24x12x6 ferrite rings stacked together with a magnetic permeability μ of at least 2000, or on a W-shaped magnetic core of the same ferrite with a cross section of at least 0.7 square meters. see Winding 1 - 250-260 turns of enameled wire with a diameter of 0.35-0.5 mm, windings 2 and 3 - 5-6 turns of the same wire each. Winding 4 - 2 turns in parallel of a wire with a diameter of 2 mm or more (on a ring) or a braid from a television coaxial cable (pos. 3a), also parallel.
Note: if the soldering iron is more than 15 W, then it is better to replace the MJE13003 transistors with MJE130nn, where nn> 03, and put them on radiators with an area of 20 sq. cm.
The inverter option for a soldering iron up to 16 W can be made on the basis of a pulse starting device (IPU) for LDS or the filling of a burned-out economy light bulb, respectively. power (do not hit the flask, there are mercury vapors!) Refinement is illustrated by pos. 4 in fig. with diagrams. What is highlighted in green may be different in the IPU of different models, but we do not care. We need to remove the starting elements of the lamp (highlighted in red in pos. 4a) and short-circuit points A-A. We get the diagram of pos. 4b. In it, in parallel with the phase-shifting inductor L5, a transformer is connected on the same ring as in the previous one. case or on W-shaped ferrite from 0.5 sq. cm (pos. 4c). Primary winding - 120 turns of wire with a diameter of 0.4-0.7; secondary - 2 turns of wire D> 2 mm. Sting (pos. 4d) from the same wire. The finished device is compact (pos. 4e) and can be placed in a convenient case.
Mini and micro on resistors
A soldering iron with a heating element based on a metal-film resistor MLT is structurally similar to a soldering iron made of a wire resistor, but it is performed at a power of up to 10-12 watts. The resistor operates with a power overload of 6-12 times, because, firstly, the heat sink through a relatively thick (but absolutely thinner) tip is larger. Secondly, MLT resistors are physically several times smaller than PE and PEV. The ratio of their surface to volume resp. increases and heat transfer to the environment increases relatively. Therefore, soldering irons on MLT resistors are made only in mini and micro versions: when you try to increase the power, the small resistor burns out. Although MLTs for special applications are produced for power up to 10 W, it is really possible to make only a soldering iron on MLT-2 for small discrete components (placers) and small microcircuits on your own, see for example. video below:
Video: micro-soldering iron on resistors
Note: the chain of MLT resistors can also be used as a heater for an autonomous battery soldering iron for ordinary soldering work, see next. video clip:
Video: rechargeable mini soldering iron
It is much more interesting to make a mini soldering iron from an MLT-0.5 resistor for smd. The ceramic tube - the MLT-0.5 body - is very thin and almost does not interfere with heat transfer to the tip, but it will not let a thermal impulse pass at the moment it touches the polygon, which is why the smd components often burn out. Having picked up a sting (which requires quite considerable experience), you can slowly solder smd with such a soldering iron, continuously monitoring the process under a microscope.
The manufacturing process of such a soldering iron is shown in Fig. Power - 6 watts. Heating is either continuous from an inverter from those described above, or (better) with forced heating by direct current from a 12 V power supply.
Note: how to make an improved version of such a soldering iron with a wider range of applications is described in detail here - oldoctober.com/en/soldering_iron/
induction
The induction soldering iron is by far the pinnacle of technical achievements in the field of soldering metals with eutectic solders. Basically, a soldering iron induction heating this is a miniature induction furnace: the HF EMF of the inductor coil is absorbed by the metal of the tip, which is heated by the Foucault eddy currents. Making an induction soldering iron with your own hands is not so difficult if you have a source of RF currents, for example. computer impulse block power, see e.g. plot
Video: induction soldering iron
However, the qualitative and economic indicators of induction soldering irons for ordinary soldering work are low, which cannot be said about their harmful effects on health. In fact, their only advantage is that the sting that has become attached to the clip in the case can be torn out, for fear of breaking the heater.
Much more interesting are the induction mini-soldering irons of the METCAL system. Their introduction in the production of electronics made it possible to reduce the percentage of defects due to the mistakes of installers by 10,000 times (!) And lengthen the work shift to a normal one, and the workers dispersed after it vigorous and capable in all other respects.
The device of the METCAL type soldering iron is shown at the top left in fig. The highlight is in the ferronickel coating of the tip. The soldering iron is powered by high-frequency precisely sustained frequency of 470 kHz. The thickness of the coating is chosen such that at a given frequency, due to the surface effect (skin effect), Foucault currents are concentrated only in the coating, which is very hot and transfers heat to the sting. The sting itself turns out to be shielded from EMF and induced potentials do not arise on it.
When the coating warms up to the Curie point, above which the ferromagnetic properties of the coating disappear in terms of temperature, it absorbs EMF energy much weaker, but it still does not let HF into copper, because. maintains electrical conductivity. Having cooled below the Curie point by itself or due to the outflow of heat to the solder, the coating again begins to intensively absorb EMF and heats up the tip. Thus, the sting keeps the temperature equal to the Curie point of the coating with an accuracy of literally up to a degree. The thermal hysteresis of the tip is negligible, because determined by the thermal inertia of the thin coating.
In order to avoid harmful effects on people, soldering irons are produced with non-replaceable tips, tightly fixed in a coaxial cartridge, through which it is supplied to the RF coil. The cartridge is inserted into the soldering iron handle - a holder with a coaxial connector. Cartridges are available in 500, 600 and 700 types, corresponding to the Curie point of the coating in degrees Fahrenheit (260, 315 and 370 degrees Celsius). Main working cartridge - 600; 500th solder especially small smd, and 700th large smd and scattering.
Note: to convert degrees Fahrenheit to Celsius, you need to subtract 32 from Fahrenheit, multiply the remainder by 5 and divide by 9. If it is necessary the other way around, add 32 to Celsius, multiply the result by 9 and divide by 5.
Everything is great about METCAL soldering irons, except for the price of the cartridge: for “(company name) new, good” - from $40. "Alternative" ones are one and a half times cheaper, but are produced twice as fast. Making your own METCAL tip is unrealistic: the coating is applied by spraying in a vacuum; galvanic at the Curie temperature instantly exfoliates. A thin-walled tube mounted on copper will not provide absolute thermal contact, without which METCAL simply turns into a poor soldering iron. Nevertheless, to make yourself an almost complete analogue of the METCAL soldering iron, and with a replaceable tip, although difficult, but possible.
induction for smd
The device of a home-made induction soldering iron for microcircuits and smd, similar in performance to METCAL, is shown on the right in fig. Once similar soldering irons were used in special production, but METCAL completely replaced them due to better manufacturability and greater profitability. However, you can make such a soldering iron for yourself.
Its secret is in the ratio of the shoulders of the outer part of the sting and the shank protruding from the coil into the inside. If it is as shown in Fig. (approximately) and the shank is covered with thermal insulation, the thermal focus of the tip will not go beyond the winding. The shank will, of course, be hotter than the tip, but their temperatures will change synchronously (theoretically, the thermal hysteresis is zero). Once you have set up the automation with the help of an additional thermocouple that measures the temperature of the tip of the tip, you can continue to solder safely.
The role of the Curie point is played by a timer. It is reset by a signal from the temperature controller for heating, for example, by opening the key that shunts the storage tank. The timer is started by a signal indicating the actual start of the inverter operation: the voltage from the additional winding of the transformer of 1-2 turns is rectified and unlocks the timer. If the soldering iron is not soldered for a long time, the timer will turn off the inverter after 7 seconds until the tip cools down and the thermostat gives a new heating signal. The bottom line here is that the thermal hysteresis of the tip is proportional to the ratio of the times of the turned off and on heating of the tip O / I, and the average power on the tip is the reverse I / O. Up to a degree, such a system does not hold the temperature of the sting, but +/-25 Celsius with a working sting of 330 provides.
Finally
So what kind of soldering iron to do? A powerful one made of a wire resistor is definitely worth it: there is nothing at all, it doesn’t ask for food, but it can help out thoroughly.
It is also worth making a simple soldering iron for smd from an MLT resistor on the farm. Silicon electronics is exhausted, it is at an impasse. Quantum is already on its way, and graphene clearly loomed in the distance. Both do not directly interface with us, like a computer through a screen, mouse and keyboard, or a smart phone / tablet through a screen and sensors. Therefore, the silicon framing will remain in the devices of the future, but only smd, and the current scattering will seem like something like radio tubes. And do not think that this is fiction: only 30-40 years ago, not a single science fiction writer thought of a smartphone. Although the first samples of mobile phones were already there. And an iron or a vacuum cleaner "with brains" to the then dreamers and in bad dream would not come to mind.
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