Resistor soldering iron. Scheme, description

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Resistor soldering iron. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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I recommend to the readers of the magazine an easily calculated, easy to manufacture and very reliable electric soldering iron. For example, I have several of these at home: from a "tiny machine" for working with microelectronics to a powerful "cleaver" with which I patch leaky metal tanks, repair well filters and other large-sized parts. Moreover, the heating element for each electrical appliance is ... a resistor of the appropriate power (type PE or PEV), powered by a household electrical network with a voltage of 220 V. Extinguishing resistances, if you cannot do without them, are reactive, more precisely, capacitive, allowing you to solve rather complex electrical problems with the minimum dimensions of the devices themselves.

As practice has shown, in order to carry out calculations in the manufacture of soldering irons with resistor heaters, it is enough to know Ohm's law (I \uXNUMXd U / R), the elementary power formula (P \uXNUMXd IU) and tolerably use four arithmetic steps.

Suppose that, having a PEV30 vitrified resistor with a nominal value of 100 ohms, you decided to make a soldering iron based on it for operation from a 220 V power supply. Referring to the above ratios, it is easy to determine the required data: current 2,2 A, power consumption 484 W. But...

The 30-watt parameter appearing in the name of the resistor used is the dissipation power at which the PEVZO can maintain its nominal value for a long time (thousands of hours!) without noticeably heating up. Mounted as a heater in a soldering iron (of course, with an inserted copper heat sink rod), this resistor must and can dissipate power many times greater than the nameplate one.

True, 484 W will also be unbearable for him - it will melt. Taking this into account, we will lower (for example, four times) the power per 100-ohm PEV30 by connecting a special damping resistance in series with it. Then the current that will flow through such a circuit will also decrease and become equal, according to calculations, to 0,55 A. This means that the voltage drop across the heater resistor will now be only 55 V.

But the network is 220 V. Therefore, 165 V is the proportion of damping resistance, the value of which, according to the law of electrical engineering known from the school bench, should be equal to 300 Ohms. As such a circuit element, a capacitor (for example, of the MBGCH type), designed for an operating voltage of 250-300 V, is the best fit.

We know from theory that the equivalent resistance of a 1 microfarad capacitor at a frequency of 50 Hz is approximately 3 kΩ. We need 300 ohms. Given this, we select the capacitance of the quenching capacitor 10 times larger, that is, equal to 10 microfarads.

So, the necessary data is received. Now you can proceed directly to the manufacture of the soldering iron itself.

The rod is machined (or purchased with subsequent refinement); material - red copper, diameter - with a minimum (in relation to the inner hole of the selected resistor) gap, which is recommended to be filled with silicate office glue during assembly (not shown in the figure). Although the glue worsens the heat transfer from the heater, it dampens the "copper rod - nichrome spiral" system, protecting the fragile ceramic base of the vitrified resistor from cracking. In addition, the crystallized adhesive layer virtually eliminates the occurrence of backlash in the main assembly of the soldering iron.

Resistor soldering iron
Soldering iron based on a resistor: 1 - tip (copper rod), 2 - resistor, 3 - asbestos filaments, 4 - electric cord, 5 - ceramic bushing, 6 - handle (plastic based on thermosetting resins), 7 - rubber bushing, 8 - housing - metal tube, 9 - M4 bolt (3 pcs.), 10 - insulation (lacquered fabric), 11 - metal casing

As for the conductive wires welded to the resistor terminals, it would seem that they can simply be brought out through a hole in the tube-case. But with a high power soldering iron, it is difficult to avoid melting and burning the insulation at the cord (and there it is not far from a short circuit). Therefore, it is better to play it safe by reinforcing the insulation at the point of connection of the wires to the resistor with a heat-resistant asbestos thread (followed by impregnation with silicate glue) and installing a ceramic sleeve on the tube body. It will not be superfluous to use an additional elastic (rubber) sleeve at the input of the power cord into the soldering iron handle.

last tip. The power of the soldering iron can be quickly changed by adding or reducing the capacitance of the capacitors in the battery. For example, in order to quickly heat up the working rod, it is enough to connect two more of the same in parallel instead of the 10 microfarads used. The total electric capacity of the battery will then triple. As the required temperature is reached, the power can be reduced, leaving, say, 20 microfarads connected (with prolonged operation, they are limited even to the previous 10 microfarads). Moreover, if the mass of the heated rod is solid, then it happens that preference is given to a soldering iron with a quenching capacity, the real value of which is less than necessary, and only occasionally (and not for long) is a reserve connected - the entire battery of capacitors.

Perhaps the above details of the manufacture and calculation of resistor soldering irons will not seem very relevant to anyone, but I think they will be useful not only for beginner DIYers.

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