That might be interesting. The ability to change the supply voltage of a soldering iron designed for 220 V, among other things, allows you to return an already burned out one to operation. And use it in the future, for example, with a switching power supply from an imported TV, which at the output gives exactly half of the network. Bringing these two products together results in an intermediate option between a soldering iron with a regulator and a full-fledged soldering station. This is within the power of any radio amateur. I will show how to do this using the example of changing the supply voltage of a Chinese-made soldering iron, which did not inspire confidence for use without modification.
We disassemble the soldering iron
To disassemble the soldering iron, it was necessary to completely unscrew the two screws connecting the protective casing to the heating element and holding the tip, and three self-tapping screws securing the working part to the handle. Move the insulation from the wires and unwind the connecting twists.
Mica with soldering iron spiral
Inside the protective casing is a heating element. They are to be dealt with. It is necessary to make a change in the amount of wound nichrome wire - change the resistance of the heating element. Now it is 1800 ohms, 400 ohms are needed. Why exactly so many? Currently working with a UPS, the soldering iron has a resistance of 347 Ohms, its power is from 19 to 28 W, the second there is a desire to make it less powerful, so Ohm was added.
Rewind soldering iron
Winding the tip of the soldering iron
The sting is inserted into the heater again, clamped with screws and into the drill chuck. If you disassemble and unwind excess nichrome while holding the heating element in your hands, then everything will be much more complicated. The binding wire is removed.
The released wrappers of fiberglass and mica are removed. There is a slot in the mica from the side of the sting, where the conductor is inserted, going from nichrome to the network wire - therefore, it does not unwind, but the weakened mica wrapper is removed from it. Mica is a very brittle material. The end of the nichrome wire attached to the conductor is disconnected. Its thickness is just over 4 microns.
Nichrome must be wound on something round, the ideal option is a spool of thread. Unscrewed - rewound and so on until the end. It is not necessary to disconnect the second end of the nichrome wire.
Soldering iron wire resistance
Now you need to wind a length of 400 ohms, and in centimeters it will be about 70 (the total length of a nichrome wire of 300 cm is 1800 ohms, hence 400 ohms will be 66.66 cm). A latch (clothespin) is placed on a length of 70 cm and in the hanging position of the coil, slightly guiding with your fingers, winding is performed with an interval that ensures its termination at the first conductor. The rate of attempts is not limited, the main thing is not to break the nichrome. At the end of the winding, a control measurement of the resistance is necessary.
As soon as it turned out to wind the required amount of nichrome, we cut off the wire with an allowance of 1 - 2 cm and attach it to the conductor. We put on the mica winding, passing the conductor into the slot in it and pressing it against it (of course, on top of it).
From above we install a winding made of fiberglass and seal it by pressing, we wind the tying wire. The heating element designed for power supply with a voltage of 85 - 106 V is assembled.
Soldering iron assembly
Since the working part was previously attached to the handle with unintelligibly clumsy and short self-tapping screws, they had to be replaced. To do this, holes for new self-tapping screws were deepened at the attachment points on the handle.
Before connecting the mains wire to the conductors going to the nichrome heater, a plastic clamp was installed and adjusted on it.
The casing of the heating element ends with a kind of cooling radiator, through the holes in it and is attached to the handle. Here, to increase the cooling effect, the gap between it and the handle was increased using metal washers.
Tests
Soldering iron current consumption 190 mA
The UPS with which the soldering iron will work at the output under load gives from 85 to 106 V. The current consumption is 190 mA, this is at a minimum voltage. Power 16 W.
Soldering iron current consumption 240 mA
At maximum voltage, the current consumption is 260 mA. Power 26 W. Wish received.
Heating rate
In conclusion, the test for the duration of heating. Up to 257 degrees in 2 minutes 20 seconds. An excellent result, if we take into account that from a network with a voltage of 225 V, it heated up to 250 degrees in 5 and a half minutes.
Table. The dependence of the resistance of the heating element on the power and voltage of the soldering iron
And here is a table that will help you navigate the required resistance of the heating element, depending on the desired power and the available supply voltage. Author - Babay iz Barnaula.
As is known, the only available high-temperature insulating material with high thermal conductivity is mica. To solve the problem of attaching mica to the surface of the mandrel, I was "helped" by an ordinary collet pencil. So, all I had to do was choose the appropriate size of the pencil and remove the slotted tube from it.
In order not to wrinkle a thin-walled tube, when installing a drill in a chuck, I picked up a steel rod of a suitable diameter and drowned out the edge of the tube with it.
Now you can safely wind the coil of the heating element.
I think you have already guessed that if you insert the edge of the mica gasket into the slot of this tube, then, when winding, the turns of wire will securely fix the gasket. After winding, the heating element can be easily removed from the tube by moving along the slot.
This is how the finished heating element, made by hand, looks like. You can see all the subtleties of this technology in the attached video.
An electric soldering iron is a hand tool designed to fasten parts together using soft solders, by heating the solder to a liquid state and filling the gap between the soldered parts with it.
As you can see in the drawing, the electrical circuit of the soldering iron is very simple, and consists of only three elements: a plug, a flexible electrical wire and a nichrome spiral.
As can be seen from the diagram, the soldering iron does not have the ability to adjust the tip heating temperature. And even if the power of the soldering iron is chosen correctly, it is still not a fact that the temperature of the tip will be required for soldering, since the length of the tip decreases over time due to its constant refilling, solders also have different melting temperatures. Therefore, to maintain the optimum temperature of the soldering tip, it is necessary to connect it through thyristor power controllers with manual adjustment and automatic maintenance of the set temperature of the soldering tip.
Soldering iron device
The soldering iron is a red copper rod that is heated by a nichrome spiral to the melting temperature of the solder. The soldering iron rod is made of copper due to its high thermal conductivity. After all, when soldering, you need to quickly transfer heat to the soldering iron tip from the heating element. The end of the rod has a wedge shape, is the working part of the soldering iron and is called a sting. The rod is inserted into a steel tube wrapped in mica or fiberglass. Mica is wound with nichrome wire, which serves as a heating element.
A layer of mica or asbestos is wound over the nichrome, which serves to reduce heat loss and electrical insulation of the nichrome spiral from the metal body of the soldering iron.
The ends of the nichrome spiral are connected to the copper conductors of an electric cord with a plug at the end. To ensure the reliability of this connection, the ends of the nichrome spiral are bent and folded in half, which reduces heating at the junction with the copper wire. In addition, the connection is crimped with a metal plate, it is best to crimp with an aluminum plate, which has a high thermal conductivity and will more effectively remove heat from the junction. For electrical insulation, tubes made of heat-resistant insulating material, fiberglass or mica are put on the junction.
The copper rod and the nichrome spiral are closed by a metal case consisting of two halves or a solid tube, as in the photo. The body of the soldering iron on the tube is fixed with cap rings. To protect a person's hand from burns, a handle made of a material that does not see heat well, wood or heat-resistant plastic is mounted on the tube.
When the soldering iron plug is inserted into the socket, electric current flows to the nichrome heating element, which heats up and transfers heat to the copper rod. The soldering iron is ready for soldering.
Low-power transistors, diodes, resistors, capacitors, microcircuits and thin wires are soldered with a 12 W soldering iron. Soldering irons 40 and 60 W are used for soldering powerful and large radio components, thick wires and small parts. For soldering large parts, for example, gas column heat exchangers, you will need a soldering iron with a power of one hundred or more watts.
Soldering iron supply voltage
Electric soldering irons are available for 12, 24, 36, 42 and 220 V mains voltage, and there are reasons for this. The main thing is human safety, the second is the mains voltage in place soldering work is done. In production, where all equipment is grounded and there is high humidity, it is allowed to use soldering irons with a voltage of not more than 36 V, while the body of the soldering iron must be grounded. The on-board network of a motorcycle has a DC voltage of 6 V, a car - 12 V, a truck - 24 V. In aviation, a network with a frequency of 400 Hz and a voltage of 27 V is used.
There are also design limitations, for example, it is difficult to make a 12 W soldering iron for a supply voltage of 220 V, since the spiral will need to be wound from a very thin wire and therefore many layers will be wound, the soldering iron will turn out to be large, not convenient for small work. Since the winding of the soldering iron is wound from nichrome wire, it can be powered by both alternating and constant voltage. The main thing is that the supply voltage matches the voltage for which the soldering iron is designed.
Heating power of soldering irons
Power electric soldering irons are 12, 20, 40, 60, 100 W and more. And this is not accidental either. In order for the solder to spread well over the surfaces of the soldered parts during soldering, they need to be heated to a temperature slightly higher than the melting point of the solder. Upon contact with the part, heat is transferred from the tip to the part and the temperature of the tip drops. If the diameter of the soldering iron tip is not sufficient or the power of the heating element is low, then having given off heat, the tip will not be able to heat up to the set temperature, and it will be impossible to solder. At best, you get a loose and not strong solder.
A more powerful soldering iron can solder small parts, but there is a problem of inaccessibility to the soldering point. How, for example, to solder a microcircuit with a leg pitch of 1.25 mm into a printed circuit board with a 5 mm soldering iron tip? True, there is a way out, several turns of copper wire with a diameter of 1 mm are wound onto such a sting and soldered with the end of this wire. But the bulkiness of the soldering iron makes the job almost impossible. There is one more limitation. With high power, the soldering iron will quickly warm up the element, and many radio components do not allow heating above 70 ° C, and therefore, the allowable soldering time is no more than 3 seconds. These are diodes, transistors, microcircuits.
Do-it-yourself soldering iron repair
The soldering iron stops heating for one of two reasons. This is due to rubbing of the power cord or burnout of the heating coil. Most often the cord frays.
Checking the health of the power cord and soldering iron spiral
When soldering, the power cord of the soldering iron is constantly bent, especially strongly at the exit from it and the plug. Usually in these places, especially if the power cord is hard, it frays. First, such a malfunction manifests itself by insufficient heating of the soldering iron or its periodic cooling. Eventually, the soldering iron stops heating up.
Therefore, before repairing the soldering iron, you need to check the presence of supply voltage in the outlet. If there is power at the outlet, check the power cord. Sometimes a cord malfunction can be determined by gently bending it at the exit from the plug and soldering iron. If the soldering iron at the same time became a little warmer, then the cord is definitely faulty.
You can check the serviceability of the cord by connecting the probes of a multimeter to the pins of the plug, which is included in the resistance measurement mode. If the reading changes when the cord is bent, the cord has frayed.
If it is found that the cord break is located at the exit point of the plug, then to repair the soldering iron it will be enough to cut off part of the cord along with the plug and install a collapsible cord on the cord.
If the cord is frayed at the point of exit from the soldering iron handle or the multimeter connected to the pins of the plug does not show resistance when the cord is bent, then you will have to disassemble the soldering iron. To gain access to the place of attachment of the spiral to the wires of the cord, it will be enough to remove only the handle. Next, sequentially touch the probes of the multimeter to the contacts and pins of the plug. If the resistance is zero, then the spiral is broken or it has poor contact with the wires of the cord.
Calculation and repair of the heating winding of the soldering iron
When repairing or when making an electric soldering iron or any other heating device on your own, you have to wind the heating winding from nichrome wire. The initial data for the calculation and selection of wire is the resistance of the winding of the soldering iron or heater, which is determined based on its power and supply voltage. You can calculate what the resistance of the winding of a soldering iron or heater should be using the table.
Knowing the supply voltage and measuring the resistance of any heating appliance, such as a soldering iron, electric kettle, electric heater or electric iron, you can find out the power consumed by this household appliance. For example, the resistance of a 1.5 kW electric kettle will be 32.2 ohms.
| Table for determining the resistance of a nichrome spiral depending on the power and supply voltage of electrical appliances, Ohm | ||||||
|---|---|---|---|---|---|---|
| Power consumption soldering iron, W | Soldering iron supply voltage, V | |||||
| 12 | 24 | 36 | 127 | 220 | ||
| 12 | 12 | 48,0 | 108 | 1344 | 4033 | |
| 24 | 6,0 | 24,0 | 54 | 672 | 2016 | |
| 36 | 4,0 | 16,0 | 36 | 448 | 1344 | |
| 42 | 3,4 | 13,7 | 31 | 384 | 1152 | |
| 60 | 2,4 | 9,6 | 22 | 269 | 806 | |
| 75 | 1.9 | 7.7 | 17 | 215 | 645 | |
| 100 | 1,4 | 5,7 | 13 | 161 | 484 | |
| 150 | 0,96 | 3,84 | 8,6 | 107 | 332 | |
| 200 | 0,72 | 2,88 | 6,5 | 80,6 | 242 | |
| 300 | 0,48 | 1,92 | 4,3 | 53,8 | 161 | |
| 400 | 0,36 | 1,44 | 3,2 | 40,3 | 121 | |
| 500 | 0,29 | 1,15 | 2,6 | 32,3 | 96,8 | |
| 700 | 0,21 | 0,83 | 1,85 | 23,0 | 69,1 | |
| 900 | 0,16 | 0,64 | 1,44 | 17,9 | 53,8 | |
| 1000 | 0,14 | 0,57 | 1,30 | 16,1 | 48,4 | |
| 1500 | 0,10 | 0,38 | 0,86 | 10,8 | 32,3 | |
| 2000 | 0,07 | 0,29 | 0,65 | 8,06 | 24,2 | |
| 2500 | 0,06 | 0,23 | 0,52 | 6,45 | 19,4 | |
| 3000 | 0,05 | 0,19 | 0,43 | 5,38 | 16,1 | |
Let's look at an example of how to use the table. Let's say you need to rewind a 60 W soldering iron designed for a supply voltage of 220 V. Select 60 W from the leftmost column of the table. On the upper horizontal line, select 220 V. As a result of the calculation, it turns out that the resistance of the soldering iron winding, regardless of the material of the winding, should be equal to 806 ohms.
If you needed to make a soldering iron with a power of 60 W, designed for a voltage of 220 V, a soldering iron for power from a 36 V network, then the resistance of the new winding should already be 22 ohms. You can independently calculate the winding resistance of any electric heater using an online calculator.
After determining the required resistance value of the soldering iron winding, from the table below, the appropriate diameter of the nichrome wire is selected based on the geometric dimensions of the winding. Nichrome wire is a chromium-nickel alloy that can withstand heating temperatures up to 1000 ° C and is marked Kh20N80. This means that the alloy contains 20% chromium and 80% nickel.
To wind a soldering iron spiral with a resistance of 806 ohms from the example above, you will need 5.75 meters of nichrome wire with a diameter of 0.1 mm (you need to divide 806 by 140), or 25.4 m of wire with a diameter of 0.2 mm, and so on.
I note that when heated for every 100 °, the resistance of nichrome increases by 2%. Therefore, the resistance of the 806 ohm spiral from the above example, when heated to 320˚С, will increase to 854 ohms, which will practically not affect the operation of the soldering iron.
When winding the soldering iron spiral, the turns are stacked close to each other. When heated, the red-hot surface of the nichrome wire oxidizes and forms an insulating surface. If the entire length of the wire does not fit on the sleeve in one layer, then the wound layer is covered with mica and the second one is wound.
For electrical and thermal insulation of the heating element winding, the best materials are mica, fiberglass cloth and asbestos. Asbestos has an interesting property, it can be soaked with water and it becomes soft, allows you to give it any shape, and after drying it has sufficient mechanical strength. When insulating the winding of the soldering iron with wet asbestos, it should be taken into account that wet asbestos conducts eclectic current well and it will be possible to turn on the soldering iron in the mains only after the asbestos has completely dried.