A soldering iron is a tool that a home wizard cannot do without, but the device is not always suitable. The fact is that an ordinary soldering iron, which does not have a thermostat and, therefore, heats up to a certain temperature, has several disadvantages.
Scheme of the soldering iron.
If during short work it is quite possible to do without a temperature controller, then a regular soldering iron, which is included in the network for a long time, has its drawbacks in full:
- solder rolls off an overheated tip, resulting in unstable soldering;
- scale is formed on the sting, which often has to be cleaned;
- the working surface is 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 nominal power from the network.
The thermostat for a soldering iron allows you to optimize its work:
Figure 1. Diagram of the simplest thermostat.
- the soldering iron does not overheat;
- it is possible to choose the temperature value of the soldering iron that is optimal for a particular job;
- during breaks, it is sufficient to reduce the tip heat using a temperature controller, and then at the right time to quickly restore the required degree of heating.
Of course, LATP can be used as a thermostat for a 220 V voltage soldering iron, and a KEF-8 power supply unit for a 42 V soldering iron, but not all have them. Another way out is to use an industrial dimmer as a temperature controller, but they are not always commercially available.
Temperature controller for soldering iron do it yourself
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The simplest thermostat
This device consists of only two parts (Fig. 1):
- SA pushbutton switch with break contacts and latching.
- Semiconductor diode VD, designed for direct current of about 0.2 A and reverse voltage not lower than 300 V.
Figure 2. Diagram of a thermostat operating on capacitors.
This temperature controller works as follows: in the initial state, the switches of the SA switch are closed and the current flows through the heating element of the soldering iron during both positive and negative half-periods (Fig. 1a). When the SA button is pressed, its contacts open, but the semiconductor diode VD transmits current only during positive half-periods (Fig. 1b). As a result, the power consumed by the heater is halved.
In the first mode, the soldering iron heats up quickly, in the second - its temperature decreases slightly, it does not overheat. As a result, you can solder in quite comfortable conditions. The switch together with the diode is included in the break of the supply wire.
Sometimes the SA switch is mounted on a stand and is triggered when a soldering iron is placed on it. In the intervals between soldering, the switch contacts are open, the power of the heater is reduced. When the soldering iron is raised, the power consumption increases and it quickly heats up to operating temperature.
As a ballast, with which you can reduce the power consumed by the heater, you can use capacitors. The smaller their capacity, the greater the resistance to the flow of alternating current. A diagram of a simple thermostat operating on this principle is shown in fig. 2. It is designed to connect a 40-watt soldering iron.
When all the switches are open, there is no current in the circuit. By combining the position of the switches, you can get three degrees of heating:
Figure 3. Schemes of triac thermostats.
- The lowest degree of heating corresponds to the closure of the contacts of the switch SA1. In this case, the capacitor C1 is switched on in series with the heater. Its resistance is quite large, so the voltage drop on the heater is about 150 V.
- The average degree of heating corresponds to the closed contacts of the 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 the switch SA3 is closed, regardless of the state of SA1 and SA2, the full supply voltage is applied to the heater.
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 disconnecting the regulator from the network.
There is another version of a simple regulator, which in terms of reliability and quality of work is not inferior to electronic ones. To do this, alternately with the heater includes a variable wire resistor SP5-30 or some other, having a suitable power. For example, for a 40-watt soldering iron, a resistor designed for a power of 25 W and having a resistance of the order of 1 kΩ will do.Back to table of contents
Thyristor and triac thermostat
The operation of the circuit shown in Fig. 3a, the operation of the previously disassembled scheme in fig. 1. Semiconductor diode VD1 transmits negative half-periods, and during positive half-periods the current passes through the VS1 thyristor. The fraction of the positive half-cycle during which the thyristor VS1 is open ultimately depends on the position of the slider of the variable resistor R1, which controls the current of the control electrode and, therefore, the firing angle.
Figure 4. Diagram of a simistor thermostat.
In one extreme position, the thyristor is open during the entire positive half period, in the second - it is completely closed. Accordingly, the power dissipated on the heater varies from 100% to 50%. If you turn off the diode VD1, then the power will change from 50% to 0.
In the diagram in fig. 3b, a thyristor with an adjustable unlocking angle of VS1 is included in the diagonal of the diode bridge VD1-VD4. As a consequence, the voltage adjustment at which the thyristor is unlocked occurs both during the positive and during the negative half period. The power dissipated on the heater changes when the slider of the variable resistor R1 rotates from 100% to 0. You can do without a diode bridge, if you use a triac instead of a thyristor as a regulating element (Fig. 4a).
With all the attractiveness of the thermostat with a thyristor or triac as a regulating element has the following disadvantages:
- during an abrupt increase in the current in the load, strong impulse noise appears, then penetrating into the lighting network and the ether;
- distortion of the form of the mains voltage due to the introduction of nonlinear distortion into the network;
- reduction of power factor (cos ϕ) due to the introduction of the reactive component.
The scheme of the ferrite ring.
To minimize impulse noise and non-linear distortion, the installation of surge protectors is desirable. The simplest solution is a ferrite filter, which is a few turns of wire wound on a ferrite ring. Such filters are used in most pulsed power supplies for electronic devices.
The ferrite ring can be taken from the wires connecting the computer system unit with peripheral devices (for example, with a monitor). Usually they have a cylindrical thickening, inside which is a ferrite filter. The filter device is shown in Fig. 4b. The more turns, the higher the quality of the filter. Place the ferrite filter should be as close as possible to the source of interference - thyristor or triac.
In devices with a smooth change in power, the regulator slider should be calibrated and its position marker should be noted. When setting up and installing, disconnect the device from the network.
The diagrams of all the above devices are quite simple and a person with minimal skills in assembling electronic devices is able to repeat them.