Often, urgent business on the farm requires the manufacture of a homemade welding machine. It is not so difficult to assemble such a device from scrap materials, and this kind of experience will be useful to any master. The issue of welding parts often arises in a variety of situations, and not everyone can afford to buy a welding machine. It is preferable to assemble it from a three-phase transformer, since in this case it will not require any rewinding.
Scheme of the device of the welding machine.
Materials and tools for the assembly will need the following:
- electrical steel;
- old transformer;
- wire studs;
- insulating tape;
- winding wire;
Scheme and technical characteristics of welding machines
Figure 1. The electrical circuit diagram of a bridge rectifier welding machine, with an indication of polarity when welding thin sheet metal.
The device, assembled at home, should have the following characteristics:
- dimensions and weight are small;
- 220 V power supply;
- the duration of the work, which will be at least 5-7 electrodes de = 3-4 mm.
The mass of the product and its dimensions can be adjusted by reducing its power, because they depend on it. The duration of its normal operation depends on the quality of the material from which the core is made and the degree of thermal resistance of the wire, which is wrapped. To maximize the welding time, use a core of steel with high magnetic permeability.Back to table of contents
What current to use for the welding machine
In homemade welding machines can be applied current constant or alternating. Those units that use low alternating currents can be used for welding roofing and automotive iron, as well as any other thin-sheet metal. Such self-made welding machines are distinguished by the stability of the welding arc, and the welding process itself with their help can be carried out with direct or reverse polarity under the condition that a constant voltage is applied.
Functional diagram of the power source of the welding machine.
When direct current is applied, it can be welded using electrode wire, without using a plaster, including electrodes, which were originally intended for welding metals with direct or alternating current. In order for the arc to light up when a small current is applied, it is desirable to impart an excessive voltage at idle to the insulating winding. In order to straighten the arc of alternating current, bridge rectifiers with high-power diodes and mandatory cooling radiators are used (Fig. 1).
This figure shows that to reduce the voltage spikes, one CA terminal is connected to the electrode holder, using a special T-shaped filter for this. The filter itself should consist of a choke L1, which is a coil wrapped with a copper busbar of 50-70 turns with a mandatory tap from the middle, with a capacitor C1.
Table of required specifications for the welding machine.
Copper bus winding on the core OCO-12, which can be taken from an unnecessary step-down transformer, or similar in characteristics of another, but with the condition that its power will be no less. In this case, the following pattern is observed: the greater the cross section of iron of the choke reducing throttle, the less likely its magnetic system to become saturated at work.
This is an important point in welding, because if at high currents the magnetic system enters the saturation, as happens when cutting, then the inductance of the choke decreases rapidly and quickly, which does not smooth the current. The welding arc in such conditions functions unstable. The capacitor C1 itself is a battery of lower capacity, at 350-400 UF, and a voltage of at least 220 V capacitors of the type MBM, MBG or others, having the same characteristics.Back to table of contents
General principles of manufacturing and maintenance
Figure 2. Falling external characteristic of the welding machine.
In order to straighten and adjust the welding current in a self-made welding machine, a circuit using high-power controlled thyristors is used, which should make it possible to change the voltage from 0.1 to 0.9 Uxx. In addition to welding, the same regulators are used to charge the batteries or to power the electric heating elements. Homemade AC welding machine is used for this special, designed exclusively for work with alternating current; take the appropriate electrodes.
In order for the welding machine to function efficiently, a whole set of certain rules is required. In order for arc ignition to be considered normal, it is necessary to obtain a sufficiently large value of the output voltage. If you make the device using the circuit yourself, the output voltage should not exceed Uxx = 60-65 V, since otherwise safe operation is not guaranteed, a higher no-load voltage can be dangerous. Welding machines made with the use of specialized industrial equipment may have Uxx = 70-75 V. At the same time, the value of I st, denoting the welding voltage, is required in order to ensure arc burning steadily, regardless of what the electrode diameter is. The value of the welding voltage Ucb can be equal to 18-24 V.
Rod type magnetic core.
The welding rated current, as the diagram shows, should be I st = KK1 * de. In this formula, I bc denotes the amount of welding current supplied, A; K1 = 30-40 - that coefficient, which depends on the type and size of electrode used for welding, de, mm. In this case, the short circuit current nominal welding current should not exceed in its values by more than 30-35%. The arc, as noted, is stable only if the welding machine itself has a falling external characteristic. It is this one that determines the magnitude of the dependence arising between the amperage and the operating voltage passing at the time of work on the welding circuit of the circuit (Fig. 2).
Making the apparatus for welding at home from improvised materials, it should be remembered that it will be difficult to assemble a universal, covering currents from 15-20 to 150-180 A. For the initial stage, it would be more rational to restrict ourselves to an aggregate working with electrodes with a diameter of 2–4 mm. If it is nevertheless necessary to work on low-current welding, the same apparatus can be supplied with a separately designed device-rectifier, which will smoothly adjust the welding current.Back to table of contents
How to choose the right core
Toroidal type magnetic core: 1 - autotransformer core before rewinding; 2- core after rewinding.
If a toroidal (round) core is used at the same time, the tool assembled by such components will have technical characteristics exceeding the core cores by 4-5 times, and the electric losses in it will be small. This will depend on the layering and placement of the windings on the ring. For the manufacture of such a core is used a strip of transformer tape iron, laid in a special way in the torus. The characteristics of this transformer will be better than those of "P" and "W" - shaped analogs. Often for the manufacture of a toroid can not find iron, but you can use the plates from the old welding transformer or from the transformer from the TV of the old model. To do this, you need to break the "P" - shaped core into separate plates and straighten them then on the anvil.
To assemble their own welding machines, most often they use rod-type magnne-conductors, since they are more technological in production. You can type this core yourself, using electrical steel plates in arbitrary configurations. The thickness of the plates should be 0.35-0.55 mm, and they can be pulled together with the help of studs, which must be pre-insulated from the core. It should be considered that the windings of the welding machine must fit in the configuration of the core. The total area of the transverse core itself is calculated by the formula S = a * b in cm².
Ways of winding the windings of the welding machine on the core core type.
After receiving the plates, of them rivet hoop, the outer diameter of which will be 260 mm. The first plate, inserting the hoop inside, is held by the hand from unwinding, and the second plate is placed against it so that the inner diameter is 120 mm. The edges of the resulting toroid are filed. Then, 2 circles are cut out from the electrical cardboard, with an outer diameter of 270 mm and an inner diameter of 110 mm; from the same cardboard, a strip of 90 mm is required to be cut. Blanks are placed on 2 sides of the ring, wrapped with insulation.
To perform on the welding machine the first layer of the insulating winding, it is best to use a winding wire made of special-purpose copper and at the same time necessarily heat-resistant. The type of insulation on it should be fiberglass or cotton. The wires in an insulating sheath made of rubber or rubber fabric also have good heat resistance characteristics.
Ways of winding the windings of the welding machine on the toroidal core: 1. uniform; 2. sectional; a - network winding; b - power winding
It is not recommended to use wires in PVC insulation, since this type of insulation does not withstand the increased temperature and begins to melt. In this case, the risk of a short circuit is very large. You can use such wires if you replace the insulation yourself. You can also not remove it, and wind the wires directly on top of the second layer. So there is less risk of damaging the wire than when removed.
When choosing values for this formula, you should not put on the minimum, since at such values the unit will not receive the necessary power reserve, and therefore good welding in all quality parameters will not be possible. Such a design will overheat after a short time. This can be avoided by setting the cross section of the core in the welding machine to a value of from 45 to 55 cm, but using this option, you need to remember that the design will add weight to it.Back to table of contents
How to choose wires for winding
Usually, the primary winding is done using the PEV-2 copper wire, the diameter of this wire is 2 mm, while for the 220 V network, the total number of coils applied will be at least 170. This is largely due to the density of plate assembly.
To check the exact number of turns, an experiment should be conducted and then, if the current at idle is more than 1-2 A, the number of turns winds, and if it is less, then some are unwound.
The secondary winding is 30 turns, for her take wire PVZ, the cross section of which is 15-20 mm. The third winding also consists of 30 turns, but for it is used wire MGTF section of 0.35 mm. Between the layers of the winding must be laid insulation from the tape. It is easiest to work on the winding together, when one holds the free end and protects it from twisting, and the second carefully puts coils. In this case, it is desirable not to damage the insulation and therefore not touch the adjacent turns.