How to make a power control for a soldering iron

The power regulator for a soldering iron is a device that allows you to control the process of soldering. The quality of this process can be significantly increased if you take control of the basic parameters. A soldering iron is a necessary tool in the household for a person who loves to do everything with his own hands.

The power regulator on the triac.

The main characteristic of soldering is the maximum temperature at the soldering tip. The power regulator for a soldering iron provides its change in the necessary mode. This allows not only to improve the quality of metal compounds, but also to increase the service life of the apparatus itself.

What is the regulator for?

Scheme of the simplest thyristor power control.

Soldering of metals is due to the fact that the molten solder fills the space between the joined workpieces and partially penetrates into their material. The strength of the connecting seam largely depends on the quality of the melt, i.e. from the temperature of its heating. If the soldering iron tip has an insufficient temperature, then it is necessary to increase the heating time, which can destroy the material of the parts and lead to premature failure of the device itself. Excessive heating of the filler metal leads to the formation of products of thermal decomposition, which significantly reduces the quality of the weld.

The temperature of the working area of ​​the soldering tip and the time it takes to set depends on the power of the heating element. Smooth change of voltage allows you to choose the optimal mode of operation of the heater. Consequently, the main task that the power regulator for a soldering iron has to solve is the installation of the required amount of electrical voltage and its maintenance during the soldering process.

Simplest schemes

Figure 1. Diagram of a two-stage power controller for a soldering iron.

The simplest power control circuit for a soldering iron is shown in Figure 1. Such a scheme has been known for more than 30 years and has performed well at home. It allows you to solder parts with power control in the range of 50-100%.

Such an elementary circuit is assembled at the output ends of the variable resistor R1 and is combined with four soldering points. The positive terminal of the capacitor C1, the leg of the resistor R2 and the control electrode of the thyristor VD2 are soldered together. The thyristor case plays the role of the anode, so it should be isolated. The whole circuit is small and fits into the case from an unnecessary power supply of any device.

A hole with a diameter of 10 mm is drilled on the wall of the case, in which the variable resistor with its threaded leg is fixed. As a load, you can use any light bulb with a capacity of 20-40 watts. A cartridge with a light bulb is fixed in the housing, and the top of the light bulb is output in the hole, so that the device can be controlled by its luminescence.

Details that should be used in the recommended scheme: 1N4007 diode (any similar for current 1 A and voltage up to 600 V can be used); thyristor KU101G; electrolytic capacitor with a capacity of 4.7 microfarads at a voltage of 100 V; 27-33 kΩ resistor with power up to 0.5 W; variable resistor SP-1 resistance up to 47 kOhm. The power controller of a soldering iron with such a scheme proved to be reliably with EPSN-type soldering irons.

A simple, but more modern scheme can be based on the replacement of a thyristor and a diode by a triac, and a neon light bulb like МН3 or МН4 can also be used as a load. The following parts are recommended: triac KU208G; 0.1 μF electrolytic capacitor; variable resistor up to 220 kOhm; two resistors of 1 kΩ and 300 ohms.

Design improvement

Miniature power regulator.

The power regulator, assembled on the basis of the simplest scheme, makes it possible to maintain the soldering mode, but does not guarantee the complete stability of the process. There are a number of fairly simple designs that allow for stable maintenance and temperature control on the soldering iron tip.

The electrical part of the device can be divided into the power section and control circuit. The power function is determined by the thyristor VS1. Voltage from the electrical network (220 V) is supplied to the control circuit from the anode of this thyristor.

The operation of the power thyristor is controlled on the basis of transistors VT1 and VT2. The power supply to the control system is provided by a parametric stabilizer, which includes the resistance R5 (to eliminate excess voltage) and the zener diode VD1 (to limit the increase in voltage). Variable resistor R2 provides manual regulation of the voltage at the output of the device.

Circuits of thyristor power regulators.

The assembly of the regulator with the installation of the power section of the circuit occurs as follows. To the terminals of the thyristor solder the legs of the diode VD2. The legs of resistance R6 are connected to the control electrode and the cathode of the thyristor, and one leg of resistance R5 to the anode of the thyristor, the second leg to the cathode of the Zener diode VD1. The control electrode is connected to the control unit by connecting the transistor VT1 to the emitter.

The basis of the control unit is silicon transistors KT315 and KT361. With their help, the voltage generated on the control electrode of the thyristor is set. The thyristor transmits current only if an unlocking voltage is applied to its control electrode, and its value determines the strength of the transmitted current.

The entire regulator circuit has a small-sized design and fits easily into the body of the invoice outlet. A plastic housing should be selected to simplify drilling. The power unit and the control unit should be assembled on different sockets, and then connected with three wires. The best option is to assemble panels on a PCB with foil coating, but in practice all the connections can be made with thin wires and assemble the panels on any insulating plate (even on thick cardboard).

Build a power regulator with your own hands

The device is assembled inside the outlet housing. Outlet ends are connected to the outlet so that it will be possible to connect the soldering iron by simply inserting its plug into the socket of the outlet. In the case, first, you should fix the variable resistor, and bring its threaded part out through the drilled hole. Then it should be placed in the case of a thyristor with a hung power unit. Finally, the control panel is installed in any free space. Below the socket is covered with a lid. The power cord is connected to the input of the power cord with a plug, which is removed from the socket housing for connection to the electrical network.

Before connecting the soldering iron, the power regulator should be checked. For this purpose, a voltmeter or multimeter is connected to the terminals of the device (into the socket). A voltage of 220 V is applied to the input of the device. Gently rotating the variable resistor knob, observe the change in the instrument reading. If the voltage at the output of the regulator smoothly increases, then the device is assembled correctly. The practice of using the device shows that the optimal value of the output voltage is 150 V. This value should be fixed with a red mark indicating the position of the variable resistor knob. It is advisable to note several values ​​of voltage.

Visual control

The power regulator mounted according to the recommended method allows you to change the temperature of the tip within the required limits. For the convenience of monitoring installation performance, you should consider the possibility of visual monitoring of voltage. At the input of the device, the supplied electrical signal is best observed using an LED. For this, parallel to the power supply input, an LED is connected through a resistor of about 60-100 kΩ.

To control the output voltage, use a small-sized voltmeter with a scale up to 250 V. The voltmeter is installed parallel to the output of the device.

The device must be placed in a plastic case and installed on the same base as the power regulator itself, which also plays the role of a socket for a soldering iron.

Necessary tool

Tools necessary for work: screwdriver, pliers, nippers, handsaw, ruler, electric drill.

In the manufacture of the regulator will need the following tool:

• soldering iron 25-40 W;
• electric drill;
• knife;
• scissors;
• awl;
• screwdriver;
• pliers;
• side cutters;
• clippers;
• hacksaw;
• emery sandpaper;
• ruler;
• calipers.

The quality of the joining of metals by the soldering method significantly depends on the temperature in the heat-affected zone. A self-made power regulator for a soldering iron, assembled even under a simplified scheme, allows stabilizing the process and establishing control over the temperature at the work site.