Miniature low voltage soldering iron. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Miniature low voltage 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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The soldering iron was and still remains the main assembly tool for a radio amateur. Both the course of work and its result largely depend on the functionality, convenience, and appearance of the tool. For the installation of miniature radio components and microcircuits, including components sensitive to interference and static electricity, I have developed a cheap design of a miniature low-voltage soldering iron. Its operating voltage is 6 V, power is 12 ... 15 watts. The outer diameter of the heating unit is 5,5 mm.

Miniature Low Voltage Soldering Iron

The features include small dimensions and weight, ease of manufacture, ease of changing the soldering rod, neat appearance. The design is made taking into account the capabilities of the home workshop and consists of a small number of parts that do not require a lathe for their manufacture. The basis of the soldering iron is the heating unit. Its casing 3 (see figure) is a thin-walled metal tube, inside which there is a sleeve 2 with a locking screw for fixing the soldering rod 1, a ceramic tube 4 with a wire heating element 5 wound around it. The heating element is separated from the casing by a mica tube 6.

The outputs of the heating element are passed through insulating ceramic tubes 7 of small diameter and electrically connected to the wires of the power cable by 12 screws with washers, which are fixed on the end of the front plug 11 of the soldering iron handle using threaded bushings 10. The bushings are glued into the holes drilled in the plug 11. assembly is also screwed to the front stopper of the handle. To do this, the end of the casing tube is cut with side cutters along the generatrices to a length of 2 ... 3 mm from the edge and the petals are bent at an angle of 90 degrees with tweezers, so that a “chamomile flower” is obtained with petals about 1 mm wide. The petals of the casing 3 are clamped between the flanges 8, two bushings 9 are placed under the flange package, and the entire assembly is attached to the end of the front plug of the handle with two long M2 screws.

Ground wire 14 is connected to one of the screws. Another pair of threaded bushings 10, glued into the end of the plug, is provided for fastening the flanges. The threaded bushings must be positioned so that the flanges do not cover the screws securing the power conductors. The casing 3 is made of a metal large-volume ballpoint pen, which has a cut off conical part with a writing unit. A suitable element from an old telescopic radio antenna is suitable as a casing blank. Sleeve 2 can be made of steel or brass. The outer diameter must be such that the sleeve enters the casing with force, and the inner diameter must be 3 mm. The thread for the lock screw is M2. The axial length of the sleeve is about 6 mm.

It is important that the misalignment of the inner and outer diameters of the sleeve does not exceed 0,05 ... 0,1 mm. Tubular constant capacitors (KTK series, etc.) are used as ceramic elements of the heater. - They solder the wire leads, remove the paint with a solvent, and remove the external metal coating with fine sandpaper. For the heating element, you will need a piece of a household electric stove spiral with a resistance of 2,5 ... 3 Ohms (it is advisable to provide a technological allowance of 30 ... 40 mm). The wire is carefully aligned and bent in half with a radius of about 0,5 mm at the bend. Then the resulting pair of wires is wound in increments of 0,5 ... 0,7 mm, starting from the fold, onto the drill shank with a diameter approximately 0,5 mm smaller than the diameter of the ceramic tube used.

The winding should be shorter than the tube by about 3 mm. The conclusions of the spiral are bent so that they are diametrically opposed to one another. The ceramic tube, rotating, is introduced into the spiral. The distance between the edges of the spiral and the ends of the tube should be 1 ... 1,5 mm. A thin screwdriver or a knife blade evens out the gap between the individual turns of the spiral. Flanges 8 are cut out of sheet steel with a thickness of 0,7 ... 1 mm. Soldering iron handle - team. The front and back plugs are made from a wooden spool of thread. An empty coil is cut in half. Holes are drilled in the flange of the front plug 11, into which bushings 10 with an M2 internal thread are installed on synthetic glue under the screws for fastening the heater housing and the conductor.

If the plug (or handle) is made of dense wood (for example, beech), threaded bushings can be dispensed with and the heater leads and flange package can be fastened with screws. The tubular body 13 of the pen, 90 ... 100 mm long, is glued from thick paper on a mandrel of a suitable diameter. The rear plug (not shown in the drawing) is made from the second half of the coil, cutting off excess wood with a knife. Both plugs are glued into the body with synthetic glue. If there were no ready-made bushings 9 (outer diameter - 5 ... 6 mm, inner - 2.1 ... 3 mm, length - 4,4 ... 7 mm), they can be replaced with elongated nuts with M2,5 thread or MZ. In extreme cases, it is permissible to replace each bushing with a column of three or four MOH nuts.

First, the heater is assembled. A mica plate from a worn-out factory electric soldering iron EPSN-40/220 is rolled into a tube 2 ... 3 mm longer than the ceramic tube of the heating element. Mica will be more flexible if it is carefully ignited in a flame. This mica tube 6 is inserted into the casing and the sleeve 2 is shifted deeper into the working position. The gap in the casing 3 assembled with the mica tube 6 must be such that the heating element not only enters without effort, but the gap does not exceed a few tenths of a millimeter. The casing is threaded into the central hole of one of the flanges 8, the second flange 8 is pressed from the other end and pre-compressed with two screws and nuts. Insulating ceramic tubes 7 are put on the leads of the heating element and the leads are bent in opposite directions. The heating element is inserted into the casing from the side of the flanges.

A sleeve 2 is inserted into the casing from the front side. It is advisable to provide a mica washer 6 ... 0,2 mm thick between it and the mica tube 0,3, which will prevent accidental shorting of the end of the spiral on the sleeve. The sleeve is fixed with a locking screw. With two long M2 screws, the flange package 8 is fixed to the handle by placing bushings 9. The power cable 12 is passed through the axial hole in the handle and the ends of its conductors are screwed together with the heater leads, while the excess length of the leads is cut off. It remains to insert the soldering rod 2 into the sleeve 1, fix it with a screw - and the tool is ready. The rod is made of rigid copper wire with a diameter of 3 mm. The rod blank is slightly flattened with a hammer approximately in the middle. This thickening will serve as a stop, preventing the rod shank from sinking too deep into the soldering iron heater channel - the end of the shank should not reach the edge of the heating element tube by 1,5 ... 2 mm. It must be borne in mind that the very small thickness, and hence the low strength of the ceramic tube of the heating element, require precise adjustment of the shape and dimensions of the soldering rod shank. The shank must enter the heater without jamming and with minimal play.

For the same reason, the soldering iron should be protected from impacts and heavy mechanical loads on the soldering rod. Forming the tip of the soldering rod is best done with a hammer (rather than a file) - this will increase its resistance to dissolution in solder. The "departure" of the rod from the soldering iron (the length of the working part of the rod) should not be more than half the length of the shank, otherwise the tip will quickly cool during soldering, which will immediately negatively affect the quality of the connection. It is advisable to have a set of soldering rods with different tip shapes. Changing the rod takes only a few seconds. If there is no need to change it often, then even in this case, with intensive use of the soldering iron, it is useful to remove the rod at least once a week, pour out the dark powder of copper oxide from the channel and put it in place.

This measure will prevent the rod from jamming in the heater and the inevitable breakage of the ceramic tube. It is necessary to power the soldering iron from the secondary winding of an isolating step-down transformer with good winding insulation. It is desirable to provide for the possibility of regulating the voltage supplying the soldering iron.

In the description of the proposed design, only reference dimensions are indicated. They can be varied over a wide range, depending on the parts and materials available to the radio amateur.

Publication: rp.butovonet.ru

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