Do-it-yourself semiautomatic device - detailed video

Created plan

Any scheme homemade device provides a separate sequence of work:

• At the initial level, it is necessary to provide a preparatory purge of the system. She will perceive the subsequent supply of gas;
• Then you need to start the arc power supply;
• Feed the wire;
• Only after all actions are completed, the inverter will start moving at a given speed.
• At the final stage, the seam should be protected and the crater should be filled;

Control board

To create an inverter, a special control board is required. On this device the units of the device must be mounted:

• Master oscillator, including a galvanic isolation transformer;
• The node by which the relay is controlled;
• Blocks feedback, responsible for the mains voltage and supply current;
• Thermal protection block;
• Block "antistic";

Enclosure selection

Before assembling the unit, you need to select the case. You can choose a box or box with suitable dimensions. It is recommended to choose plastic or thin sheet material. Transformers are mounted into the housing, which are connected to the secondary and primary reels.

Coil Matching

Primary windings are carried out in parallel. Secondary reels are connected in series. According to a similar scheme, the device is capable of accepting a current of up to 60 A. In this case, the output voltage will be 40 V. These characteristics are perfect for welding small structures at home.

Cooling system

During continuous operation, a homemade inverter can overheat greatly. Therefore, such a device requires a special cooling system. by the most simple method creating cooling is the installation of fans. These devices must be attached to the sides of the case. Fans must be installed opposite transformer device. Mechanisms are attached so that they can work on the hood.

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On sale you can see a lot of semi-automatic welding machines of domestic and foreign production, used in the repair of car bodies. If you wish, you can save on costs by assembling a semi-automatic welding machine in a garage.

Wire feed speed controller for semi-automatic welding

The set of the welding machine includes a housing, in the lower part of which a single-phase or three-phase power transformer is installed, a device for drawing a welding wire is located above.

The device includes a DC electric motor with a gear reduction mechanism, as a rule, an electric motor with a gearbox from a UAZ or Zhiguli windshield wiper is used here. The copper-plated steel wire from the feed drum, passing through the rotating rollers, enters the wire feed hose, at the exit the wire comes into contact with a grounded product, the resulting arc welds the metal. To isolate the wire from atmospheric oxygen, welding takes place in an inert gas environment. A solenoid valve is installed to turn on the gas. When using the prototype of the factory semiautomatic device, some shortcomings were revealed in them that prevent high-quality welding. This is a premature overload failure of the output transistor of the motor speed controller circuit and the absence of an automatic engine brake on the stop command in the budget circuit. The welding current disappears when it is turned off, and the engine continues to feed the wire for some time, which leads to excessive consumption of the wire, the risk of injury, and the need to remove excess wire with a special tool.

In the laboratory "Automation and Telemechanics" of the Irkutsk Regional CDTT, a more modern wire feed regulator circuit has been developed, the fundamental difference of which from the factory ones is the presence of a braking circuit and a double supply of the switching transistor in terms of starting current with electronic protection.

The circuit diagram of the wire feed controller includes a current amplifier on a powerful field-effect transistor. A stabilized speed setting circuit allows you to maintain power in the load regardless of the mains supply voltage, overload protection reduces the burning of the motor brushes during start-up or jamming in the wire feeder and the failure of the power transistor.

The braking circuit allows almost instantly stop the rotation of the motor.

The supply voltage is used from a power or separate transformer with a power consumption not lower than the maximum power of the wire pulling motor.

The circuit includes LEDs for indicating the supply voltage and the operation of the electric motor.

Device characteristic:

• supply voltage, V — 12…16;
• electric motor power, W - up to 100;
• braking time, sec - 0.2;
• start time, sec - 0.6;
• adjustment
• revolutions,% - 80;
• starting current, A - up to 20.

Step 1. Description of the semi-automatic welding regulator circuit

Electric scheme principle device shown in fig. 1. The voltage from the motor speed controller R3 through the limiting resistor R6 is supplied to the gate of a powerful field-effect transistor VT1. The speed controller is powered by an analog stabilizer DA1, through a current-limiting resistor R2. To eliminate interference possible from turning the slider of the resistor R3, a filter capacitor C1 is introduced into the circuit.
The HL1 LED indicates the on state of the welding wire feed regulator circuit.

Resistor R3 sets the feed rate of the welding wire to the place of arc welding.

Trimmer resistor R5 allows you to choose the best option for controlling the engine speed, depending on its power modification and power supply voltage.

Diode VD1 in the voltage regulator circuit DA1 protects the chip from breakdown if the polarity of the supply voltage is reversed.
The field-effect transistor VT1 is equipped with protection circuits: a resistor R9 is installed in the source circuit, the voltage drop across which is used to control the voltage at the gate of the transistor, using the comparator DA2. At a critical current in the source circuit, the voltage through the tuning resistor R8 is supplied to the control electrode 1 of the comparator DA2, the anode-cathode circuit of the microcircuit opens and reduces the voltage at the gate of the transistor VT1, the speed of the motor M1 will automatically decrease.

To eliminate the operation of protection against impulse currents that occur when the brushes of the electric motor spark, capacitor C2 is introduced into the circuit.
A wire feed motor is connected to the drain circuit of transistor VT1 with collector spark reduction circuits C3, C4, C5. A circuit consisting of a VD2 diode with a load resistor R7 eliminates the reverse current pulses of the motor.

The two-color LED HL2 allows you to control the state of the electric motor: with a green glow - rotation, with a red glow - braking.

The braking circuit is made on the electromagnetic relay K1. The capacitance of the filter capacitor C6 is chosen small - only to reduce the vibration of the armature of the relay K1, a large value will create inertia when braking the motor. Resistor R9 limits the current through the relay winding when the power supply voltage is increased.

The principle of operation of braking forces, without the use of reverse rotation, is to load the reverse current of the electric motor during rotation by inertia, when the supply voltage is turned off, to a constant resistor R11. Recovery mode - transferring energy back to the network allows you to stop the motor in a short time. At a complete stop, the speed and reverse current will be set to zero, this happens almost instantly and depends on the value of the resistor R11 and capacitor C5. The second purpose of the capacitor C5 is to eliminate the burning of contacts K1.1 of relay K1. After applying mains voltage to the control circuit of the regulator, relay K1 will close the circuit K1.1 of the electric motor power supply, the drawing of the welding wire will resume.

The power supply consists of a network transformer T1 with a voltage of 12 ... 15 V and a current of 8 ... 12 A, the diode bridge VD4 is selected for a double current. If there is a semi-automatic secondary winding of the corresponding voltage on the welding transformer, power is supplied from it.

Step 2. Details of the semi-automatic welding regulator circuit

The wire feed regulator circuit is made on a printed circuit board made of single-sided fiberglass with a size of 136 * 40 mm (Fig. 2), except for the transformer and motor, all parts are installed with recommendations for possible replacement. The field effect transistor is mounted on a radiator with dimensions of 100 * 50 * 20 mm.

Field-effect transistor analogue of IRFP250 with a current of 20 ... 30 A and a voltage above 200 V. Resistors of the MLT type 0.125; resistors R9, R11, R12 - wire. Resistors R3, R5 set type SP-ZB. The type of relay K1 is indicated on the diagram or No. 711.3747-02 for a current of 70 A and a voltage of 12 V, they have the same dimensions and are used in VAZ vehicles.

Comparator DA2, with a decrease in speed stabilization and transistor protection, can be removed from the circuit or replaced with a KS156A zener diode. The VD3 diode bridge can be assembled on Russian diodes of the D243-246 type, without radiators.

The DA2 comparator has a complete analogue of foreign-made TL431CLP.

Solenoid valve for inert gas supply Em.1 - regular, for a supply voltage of 12 V.

Step 3. Adjustment of the semi-automatic welding regulator circuit

The adjustment of the wire feed regulator circuit of the semi-automatic welding machine begins with checking the supply voltage. Relay K1, when voltage appears, should operate, having a characteristic click of the armature.

By increasing the voltage at the gate of the field-effect transistor VT1 with the speed controller R3, check that the speed starts to grow at the minimum position of the resistor R3 slider; if this does not happen, correct the minimum speed with the resistor R5 - first set the engine of the resistor R3 to the lower position, with a smooth increase in the value of the resistor R5, the engine should gain minimum speed.

Overload protection is set by resistor R8 during forced braking of the motor. When the field-effect transistor is closed by the comparator DA2 during overload, the HL2 LED will go out. Resistor R12 at a power supply voltage of 12 ... 13 V can be excluded from the circuit.
The scheme has been tested on different types of electric motors, with similar power, the braking time mainly depends on the mass of the armature, due to the inertia of the mass. Heating of the transistor and diode bridge does not exceed 60°C.

The printed circuit board is fixed inside the body of the semi-automatic welding machine, the engine speed control knob - R3 is displayed on the control panel along with indicators: HL1 on and a two-color engine operation indicator HL2. Power is supplied to the diode bridge from a separate winding of the welding transformer with a voltage of 12 ... 16 V. The inert gas supply valve can be connected to capacitor C6, it will also turn on after the mains voltage is applied. The power supply of power networks and electric motor circuits is to be carried out with a stranded wire in vinyl insulation with a cross section of 2.5 ... 4 mm2.

Starting circuit of the welding semiautomatic device

Characteristics of the semi-automatic welding machine:

• supply voltage, V - 3 phases * 380;
• primary phase current, A - 8 ... 12;
• secondary voltage idle move, V - 36…42;
• no-load current, A - 2 ... 3;
• open circuit voltage of the arc, V - 56;
• welding current, A - 40 ... 120;
• voltage regulation, % — ±20;
• switching on duration, % - 0.

The wire is fed into the welding zone in the semi-automatic welding machine using a mechanism consisting of two steel rollers rotating in opposite directions by an electric motor. To reduce the speed, the electric motor is equipped with a gearbox. From the conditions of smooth adjustment of the wire feed speed, the rotation speed of the DC electric motor is additionally changed by the semiconductor wire feed speed controller of the semi-automatic welding machine. An inert gas, argon, is also supplied to the welding zone to eliminate the effect of atmospheric oxygen on the welding process. The mains supply of the semi-automatic welding machine is made from a single-phase or three-phase mains, a three-phase transformer is used in this design, recommendations for power supply from single-phase network indicated in the article.

Three-phase power allows the use of a smaller cross-section winding wire than when using a single-phase transformer. During operation, the transformer heats up less, the voltage ripple at the output of the rectifier bridge decreases, and the power line is not overloaded.

Step 1. Operation of the semi-automatic welding start circuit

The connection of the power transformer T2 to the mains is switched by triac switches VS1 ... VS3 (Fig. 3). The choice of triacs instead of a mechanical starter eliminates emergencies in case of breakage of contacts and eliminates the sound from the "clapping" of the magnetic system.
Switch SA1 allows you to disconnect the welding transformer from the network during maintenance work.

The use of triacs without radiators leads to their overheating and arbitrary switching on of the semi-automatic welding machine, so the triacs must be equipped with budget radiators 50 * 50 mm.

It is recommended to equip the semi-automatic welding machine with a 220 V fan, its connection is parallel to the mains winding of the T1 transformer.
A three-phase transformer T2 can be used ready-made, for a power of 2 ... 2.5 kW, or you can buy three transformers 220 * 36 V 600 VA, used for lighting basements and metal-cutting machines, connect them according to the star-star scheme. In the manufacture of a home-made transformer, the primary windings must have 240 turns of PEV wire with a diameter of 1.5 ... 1.8 mm, with three taps 20 turns from the end of the winding. The secondary windings are wound with a copper or aluminum bus with a cross section of 8 ... 10 mm2, the amount of PVZ wire is 30 turns.

Taps on the primary winding allow you to adjust the welding current depending on the mains voltage from 160 to 230 V.
The use of a single-phase welding transformer in the circuit allows the use of an internal electrical network used to power home electric furnaces with an installed power of up to 4.5 kW - the wire suitable for the outlet can withstand currents up to 25 A, there is grounding. The cross section of the primary and secondary windings of a single-phase welding transformer in comparison with a three-phase version should be increased by 2 ... 2.5 times. A separate ground wire is required.

Additional regulation of the welding current is carried out by changing the angle of the triac turn-on delay. The use of a semi-automatic welding machine in garages and summer cottages does not require special network filters to reduce impulse noise. When using a semi-automatic welding machine in living conditions it should be equipped with an external noise filter.

Smooth regulation of the welding current is carried out using an electronic unit on a silicon transistor VT1 with the button SA2 "Start" pressed - by adjusting the resistor R5 "Current".

The connection of the welding transformer T2 to the mains is carried out by the SA2 "Start" button located on the welding wire supply hose. The electronic circuit through the optocouplers opens the power triacs, and the mains voltage is supplied to the mains windings of the welding transformer. After the voltage appears on the welding transformer, a separate wire feed unit is turned on, the inert gas supply valve opens, and when the wire coming out of the hose touches the workpiece to be welded, electric arc, the welding process starts.

Transformer T1 is used to power the electronic starting circuit of the welding transformer.

When the mains voltage is applied to the anodes of the triacs through the automatic three-phase machine SA1, the transformer T1 for supplying the electronic start-up circuit is connected to the line, the triacs are in the closed state at this time. The voltage of the secondary winding of the transformer T1, rectified by the diode bridge VD1, is stabilized by the analog stabilizer DA1, for stable operation of the control circuit.

Capacitors C2, C3 smooth out the ripple of the rectified supply voltage of the starting circuit. The triacs are turned on using the key transistor VT1 and triac optocouplers U1.1 ... U1.3.

The transistor opens with a positive polarity voltage from the DA1 analog stabilizer through the "Start" button. The use of low voltage on the button reduces the likelihood of an operator being struck by high voltage from the mains in the event of a wire insulation failure. The current regulator R5 regulates the welding current within 20 V. Resistor R6 does not allow reducing the voltage on the mains windings of the welding transformer by more than 20 V, at which the level of interference in the mains increases sharply due to the distortion of the voltage sine wave by triacs.

Triac optocouplers U1.1 ... U1.3 perform galvanic isolation of the mains from the electronic control circuit, allow a simple method to adjust the opening angle of the triac: the greater the current in the optocoupler LED circuit, the smaller the cutoff angle and the greater the current of the welding circuit.
The voltage to the control electrodes of the triacs is supplied from the anode circuit through the triac of the optocoupler, the limiting resistor and the diode bridge, synchronously with the mains phase voltage. Resistors in optocoupler LED circuits protect them from overload at maximum current. The measurements showed that when starting at the maximum welding current, the voltage drop across the triacs did not exceed 2.5 V.

With a large spread in the turn-on slope of triacs, it is useful to shunt their control circuits to the cathode through a resistance of 3 ... 5 kOhm.
An additional winding is wound on one of the rods of the power transformer to power the wire feed unit with an alternating current of 12 V, the voltage to which should be supplied after the welding transformer is turned on.

The secondary circuit of the welding transformer is connected to a three-phase DC rectifier on diodes VD3…VD8. Installation of powerful radiators is not required. The circuits for connecting the diode bridge with the capacitor C5 should be made with a copper bus with a cross section of 7 * 3 mm. The inductor L1 is made on iron from the power transformer of tube TVs of the TS-270 type, the windings are previously removed, and in their place a winding with a cross section of at least 2 times the secondary one is wound, until full. Between the halves of the transformer iron of the throttle, lay a gasket made of electrical cardboard.

Step 2. Installation of the semi-automatic welding start circuit

The starting circuit (Fig. 3) is mounted on a circuit board (Fig. 4) with a size of 156 * 55 mm, except for the elements: VD3 ... VD8, T2, C5, SA1, R5, SA2 and L1. These elements are fixed on the body of the semi-automatic welding machine. The circuit does not contain display elements, they are included in the wire feed unit: the on indicator and the wire feed indicator.

Power circuits are made with an insulated wire with a cross section of 4 ... 6 mm2, welding circuits - with a copper or aluminum bus, the rest - with a wire in vinyl insulation with a diameter of 2 mm.

The polarity of the holder connection should be selected based on the conditions of welding or surfacing when working with metal with a thickness of 0.3 ... 0.8 mm.

Step 3. Adjustment of the start-up circuit of the semi-automatic welding machine

The adjustment of the starting circuit of the semi-automatic welding machine begins with a voltage check of 5.5 V. When the “Start” button on the capacitor C5 is pressed, the open circuit voltage must exceed 50 V DC, under load - at least 34 V.

On the cathodes of the triacs, relative to the zero of the network, the voltage should not differ by more than 2 ... 5 V from the voltage at the anode, otherwise replace the triac or optocoupler of the control circuit.

If the mains voltage is low, switch the transformer to low voltage taps.

When setting up, safety precautions must be observed.

Download printed circuit boards:

On sale you can see a lot of semi-automatic welding machines of domestic and foreign production used in the repair of car bodies. If you wish, you can save on costs by assembling a semi-automatic welding machine in a garage.

The set of the welding machine includes a housing, in the lower part of which a single-phase or three-phase power transformer is installed, a device for drawing the welding wire is located above.

The device includes a DC electric motor with a gear reduction mechanism, as a rule, an electric motor with a gearbox from a UAZ or Zhiguli car wiper is used here. The copper-plated steel wire from the feed drum, passing through the rotating rollers, enters the wire feed hose, at the exit the wire comes into contact with a grounded product, the resulting arc welds the metal. To isolate the wire from atmospheric oxygen, welding takes place in an inert gas environment. A solenoid valve is installed to turn on the gas. When using the prototype of the factory semi-automatic device, they revealed some shortcomings that prevent high-quality welding: premature overload failure of the output transistor of the motor speed controller circuit; the absence in the budgetary scheme of the engine braking machine on the stop command - the welding current disappears when it is turned off, and the engine continues to feed the wire for some time, this leads to excessive consumption of the wire, the risk of injury, the need to remove excess wire with a special tool.

In the laboratory of "Automation and Telemechanics" of the Irkutsk Regional DTT Center, a more modern wire feed regulator circuit has been developed, the fundamental difference of which from the factory ones is the presence of a braking circuit and a double supply of the switching transistor for inrush current with electronic protection.

Device Specifications:
1. Supply voltage 12-16 volts.
2. Electric motor power - up to 100 watts.
3. Deceleration time 0.2 sec.
4. Start time 0.6 sec.
5. Speed ​​control 80%.
6. Starting current up to 20 amperes.

The circuit diagram of the wire feed controller includes a current amplifier on a powerful field-effect transistor. A stabilized speed setting circuit allows you to maintain power in the load regardless of the mains supply voltage, overload protection reduces the burning of the motor brushes during start-up or jamming in the wire feeder and the failure of the power transistor.

The braking circuit allows almost instantly stop the rotation of the motor.
The supply voltage is used from a power or separate transformer with a power consumption not lower than the maximum power of the wire pulling motor.
The circuit includes LEDs for indicating the supply voltage and the operation of the electric motor.

The voltage from the motor speed controller R3 through the limiting resistor R6 is supplied to the gate of a powerful field-effect transistor VT1. The speed controller is powered by an analog stabilizer DA1, through a current-limiting resistor R2. To eliminate interference possible from turning the slider of the resistor R3, a filter capacitor C1 is introduced into the circuit.

The HL1 LED indicates the on state of the welding wire feed regulator circuit.
Resistor R3 sets the feed rate of the welding wire to the place of arc welding.

Trimmer resistor R5 allows you to choose the best option for controlling the engine speed, depending on its power modification and power supply voltage.

Diode VD1 in the voltage regulator circuit DA1 protects the chip from breakdown if the polarity of the supply voltage is reversed.

The field effect transistor VT1 is equipped with protection circuits: a resistor R9 is installed in the source circuit, the voltage drop across which is used to control the voltage at the gate of the transistor, using the comparator DA2. At a critical current in the source circuit, the voltage through the tuning resistor R8 is supplied to the control electrode 1 of the comparator DA2, the anode-cathode circuit of the microcircuit opens and reduces the voltage at the gate of the transistor VT1, the speed of the motor M1 will automatically decrease.

To eliminate the operation of protection against impulse currents that occur when the brushes of the electric motor spark, capacitor C2 is introduced into the circuit.
A wire feed motor is connected to the drain circuit of transistor VT1 with collector spark reduction circuits C3, C4, C5. A circuit consisting of a VD2 diode with a load resistor R7 eliminates the reverse current pulses of the motor.

The two-color LED HL2 allows you to control the state of the electric motor, with a green glow - rotation, with a red glow - braking.

The braking circuit is made on the electromagnetic relay K1. The capacitance of the filter capacitor C6 is chosen to be small - only to reduce the vibration of the armature of the relay K1, a large value will create inertia when braking the motor. Resistor R9 limits the current through the relay winding when the power supply voltage is increased.

The principle of operation of braking forces, without the use of reverse rotation, is to load the reverse current of the electric motor during rotation by inertia, when the supply voltage is turned off, to a constant resistor R8. Recuperation mode - transferring energy back to the network allows you to stop the motor in a short time. At a complete stop, the speed and reverse current will be set to zero, this happens almost instantly and depends on the value of resistor R11 and capacitor C5. The second purpose of capacitor C5 is to eliminate burning of contacts K1.1 of relay K1. After supplying the mains voltage to the control circuit of the regulator, relay K1 will close the circuit K1.1 of the electric motor power supply, the drawing of the welding wire will resume.

The power supply consists of a network transformer T1 with a voltage of 12-15 volts and a current of 8-12 amperes, the VD4 diode bridge is selected for 2x current. If there is a semi-automatic secondary winding of the corresponding voltage on the welding transformer, power is supplied from it.

The wire feed regulator circuit is made on a printed circuit board made of single-sided fiberglass with a size of 136 * 40 mm, except for the transformer and motor, all parts are installed with recommendations for possible replacement. The field-effect transistor is installed on a radiator with dimensions 100 * 50 * 20.

Field-effect transistor analogue of IRFP250 with a current of 20-30 Amperes and a voltage above 200 Volts. Resistors type MLT 0.125, R9, R11, R12 - wire. Install the resistor R3, R5 of the type SP-3 B. The type of relay K1 is indicated on the diagram or No. 711.3747-02 for a current of 70 Amperes and a voltage of 12 Volts, their dimensions are the same and are used in VAZ vehicles.

Comparator DA2, with a decrease in speed stabilization and transistor protection, can be removed from the circuit or replaced with a KS156A zener diode. The VD3 diode bridge can be assembled on Russian diodes of the D243-246 type, without radiators.

The DA2 comparator has a complete analogue of foreign-made TL431 CLP.
Solenoid valve for inert gas supply Em.1 - regular, for a supply voltage of 12 volts.

Adjustment of the circuit of the wire feed regulator of the welding semiautomatic device Start by checking the supply voltage. Relay K1, when voltage appears, should operate, having a characteristic click of the armature.

By increasing the voltage at the gate of the field-effect transistor VT1 with the speed controller R3, check that the speed starts to grow at the minimum position of the resistor R3 slider, if this does not happen, adjust the minimum speed with the resistor R5 - first set the slider of the resistor R3 to the lower position, with a gradual increase in the value of the resistor K5, the engine should gain minimum speed.

Overload protection is set by resistor R8 during forced braking of the motor. When the field-effect transistor is closed by the comparator DA2 during overload, the HL2 LED will go out. Resistor R12 at a power supply voltage of 12-13 Volts can be excluded from the circuit.

The scheme has been tested on different types of electric motors, with similar power, the braking time mainly depends on the mass of the armature, due to the inertia of the mass. The heating of the transistor and diode bridge does not exceed 60 degrees Celsius.

The printed circuit board is fixed inside the body of the semi-automatic welding machine, the engine speed control knob - R3 is displayed on the control panel along with indicators: HL1 on and a two-color engine operation indicator HL2. Power is supplied to the diode bridge from a separate winding of the welding transformer with a voltage of 12-16 volts. An inert gas supply valve can be connected to capacitor C6 and will also be switched on after mains voltage is applied. Power supply of power networks and electric motor circuits should be performed with a stranded wire in vinyl insulation with a cross section of 2.5-4 mm.kv.

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