Do-it-yourself inverter power supply circuit. Powerful do-it-yourself switching power supply

To perform welding work at home, an inverter welding machine is indispensable. The principle of its operation is based on the use of transistors and switches, with the help of which the mains voltage is first transformed into a constant one.

Then the characteristics of the current change (the frequency of the sinusoid increases). These actions lead to a decrease in the voltage value, which leads to a rectification of the current, while the frequency of the current does not change.

The widespread use of these devices is associated with a number of its advantages, which include:

• Small overall dimensions, as well as low weight, which greatly facilitates the work during welding and allows you to place the device in a convenient place;
• The ability to make it yourself, spending a little money. In addition, do-it-yourself assembly allows you to select parts with the necessary characteristics, and in the future it is enough to simply repair the unit or replace parts to adjust the characteristics;
• High efficiency, which allows it to compete with ready-made devices.

The disadvantages of a welding inverter, which is made independently, are:

• Short service life, with incorrectly selected details;
• There is no possibility to implement additional functions, which are able to improve the quality of the weld;
• If necessary, obtain a device of high power an additional cooling system is required, which increases the final cost and dimensions.

It should be noted that self-assembly of the inverter is quite painstaking work., which takes a lot of time and requires certain skills. But modern manufacturers offer a wide selection of components, which greatly facilitates their choice. The selection of parts itself is based on the compatibility of parameters by type and characteristic, as well as on the possibility of simple replacement in the future.

The main elements of the inverter are:

• power unit;
• power unit and its keys.

Basic output features include:

• consumed current, and its maximum value;
• voltage and frequency in the network;
• the value of the welding current at which the seam will be performed.

Preparatory stage

Before you start buying parts for the manufacture of an inverter, you must accurately represent the values ​​​​of the output parameters, as well as have electrical circuits of all elements (general circuit, power supply).

Consider the manufacture of a welding machine with input characteristics:

• mains voltage 220 V;
• frequency 50 Hz;
• current strength 32 A.

The output will be a current converted to a value of 250 A, that is, it has increased its input value by 8 times. With this machine, you can make a weld by placing the electrode less than 1 cm to the workpiece to be welded.

Before proceeding with the assembly of the device, it is necessary to prepare the following materials and tools:

• screwdrivers (flat and cross) of different sizes;
• devices for measuring voltage and current (voltmeter and ammeter), which can be replaced by a modern universal measuring device;
• with a little sting;
• components for soldering (rosin, wire);
• an oscilloscope, the use of which will allow you to control the change in the current sinusoid;
• special steel with suitable electrical parameters;
• cotton and fiberglass fabrics;
• core for transformer;
• transformer windings:
• primary for 100 turns of wire with a diameter of 0.3 mm
• secondary (internal - 15 turns of 1 mm wire, middle - 15 turns of 0.2 mm wire, outer - 20 turns made of 0.35 mm wire);
• textolite;
• bolts and screws;
• transistors with the necessary characteristics;
• wires of different sections;
• power cable;
• electrical tape or special paper.

After completing the preparatory work, you can proceed with the assembly.

Inverter power supply

The board where the inverter power supply is located is assembled separately from the power element of the device. In addition, they need to be separated from each other by a sheet of metal, which is rigidly fixed to the body.

The main element of the power supply is a transformer, which can be made independently. With its help, the voltage that comes from the network will be converted to a safe value for life, and then increase the current strength to perform welding.

The core material can be 7x7 or 8x8 iron. In this case, you can take it as standard plates or cut off the required piece of metal from an existing sheet. The winding is carried out with a copper wire of the PEV brand, since it is this material that provides the required characteristics to the maximum (small cross section with sufficient width).

The use of a different material as a winding may significantly affect the characteristics of the transformer, for example, increase the heating of this part.

The assembly of a transformer consisting of 2 windings begins with the creation of a primary winding. To do this, a wire with a cross section of 0.3 mm is wrapped 100 times on the core. It is important that the winding occupies the entire width of the core. This feature will improve the operation of the inverter during mains voltage fluctuations in the process of further operation.

In this case, each turn should fit snugly against the previous one, while overlap should be avoided. After all 100 turns have been completed, a layer of special insulating paper or fiberglass cloth must be laid. Please note that the paper will darken during operation.

Next, the secondary winding is performed. To do this, you need to take a copper wire with a cross section of 1 mm and make 15 turns, trying to distribute them over the entire width, at an equal distance from each other. After coating them with varnish and drying, they wind the 2nd layer with a copper wire with a cross section of 0.2 mm, also making 15 turns.

They also need to be distributed, as in the previous case, and isolated. The last layer for the secondary winding will be a PEV with a cross section of 0.35 mm, while there will be 20 turns. The last layer must also be insulated.

Frame

Next, proceed to the manufacture of the case. Its size should be commensurate with the dimensions of the transformer and plus 70% for the placement of the remaining parts of the inverter. The body itself can be made of sheet steel with a thickness of 0.5-1 mm.

To connect the corners, you can use bolts or use special bending machines to bend the sheet to the desired size. If you place a handle on the case for attaching the inverter to a belt or for ease of carrying, this will greatly facilitate the operation of the device in the future.

In addition, the design of the case should provide for fairly easy access to all parts located inside it. It is necessary to make several technological holes on it for switches, a power button, a light signaling of health, as well as cable connectors.

Power section and inverter unit

The power unit for the inverter is a transformer, a feature of which is the presence of 2 cores, which are located next to a small gap, laying a sheet of paper. This transformer is assembled similarly to the previous one. An important detail is that the insulating layer between the turns of the wire must be strengthened, which will prevent voltage breakdown. In addition, gaskets made of PTFE are laid between the layers of wires.

Capacitors that are connected according to the diagram can be attributed to the power part. They are designed to reduce the resonance of transformers, and are also designed to minimize and compensate for current losses in transistors.

The inverter unit of the device is used to convert current, which increases the output frequency. For this, transistors or diodes are used in the inverter. If it is decided to use diodes in this block, then they must be assembled into an oblique bridge according to a special scheme. The outputs from it go to transistors, which are designed to return alternating current at a higher frequency. The diode bridge and transistors must be separated by a partition.

Cooling system

Since all elements of the unit are subject to heat, it is necessary to organize a cooling system that will ensure uninterrupted reliable operation. To do this, you can use coolers from computers, as well as make several additional holes in the case for easy air access into the device. However, there should not be too many such holes to avoid getting excess dust into the case.

Coolers should be located in such a way that they can work to remove air from the device case. Cooling elements need maintenance, such as replacing thermal paste, so access to them should be easy.

There are several parts in the inverter that require mandatory cooling. These are transformers. For their cooling it is reasonable to mount 2 fans. In addition, the diode bridge needs additional cooling. It is mounted on a radiator.

Installing such an element as a temperature sensor, and its further connection to the LED on the case, will allow you to give a signal when an unacceptable temperature is reached and turn off the inverter from the power supply for cooling.

Assembly

The inverter is assembled in the following order:

• on the base of the case there is a transformer, a diode bridge, a control circuit;
• twisting, soldering and fastening all wires together;
• the outer panel displays light indication, start button, cable connector.

When everything is installed, you can check the operation of the device.

Checking work

To check the device, you must use an oscilloscope for this. The inverter is connected to a 220 V network, and then the device checks how the output parameters correspond to the required ones. For example, the voltage should be in the range of 500-550 V. With absolutely correct assembly and correctly selected parts, this value should not cross the threshold of 350 V.

After such measurements and acceptable indicators of the oscilloscope, you can begin to weld. After the first electrode is completely burnt out, it is necessary to measure the temperature on the transformer. If it boils, then the circuit needs to be finalized, the device must be turned off and changes made. Only after measures have been taken to eliminate this defect, it is possible to restart with the same temperature measurement after the end of work.

Operating rules

The welding inverter can be used both for welding parts made of ferrous metal, and for working with non-ferrous. It is useful both in a private house, in the country, and in the garage.

During its operation, it is necessary to monitor the quality of voltage and frequency in the network.

For long-term use of this unit, it is necessary to periodically check the performance of its individual cleaning, carry out preventive measures to clean it from dust and dirt.

When making an inverter yourself, you must:

• have diagrams of all elements of the apparatus;
• choose the right accessories;
• maintain all necessary clearances and carefully isolate the elements;
• comply with safety regulations.

The scope of switching power supplies in everyday life is constantly expanding. Such sources are used to power all modern household and computer equipment, to implement uninterruptible power supplies, chargers for batteries for various purposes, the implementation of low-voltage lighting systems and for other needs.

In some cases, buying a ready-made power supply is not very acceptable from an economic or technical point of view, and assembling a switching power supply with your own hands is the best way out of this situation. Simplifies this option and the wide availability of modern element base at low prices.

The most popular in everyday life are switching sources powered by a standard AC network and a powerful low-voltage output. The block diagram of such a source is shown in the figure.

The mains rectifier CB converts the alternating voltage of the supply network into a constant one and smoothes out the ripples of the rectified voltage at the output. The high-frequency VChP converter converts the rectified voltage into an alternating or unipolar one, having the form of rectangular pulses of the required amplitude.

In the future, such a voltage either directly or after rectification (HV) is supplied to a smoothing filter, to the output of which a load is connected. The VChP is controlled by a control system that receives a feedback signal from the load rectifier.

Such a structure of the device can be criticized due to the presence of several conversion links, which reduces the efficiency of the source. However, with the right choice of semiconductor elements and high-quality calculation and manufacture of winding units, the level of power losses in the circuit is small, which makes it possible to obtain real values ​​of efficiency above 90%.

Schematic diagrams of switching power supplies

Structural block solutions include not only the rationale for choosing circuit implementation options, but also practical recommendations for choosing the main elements.

To rectify the mains single phase voltage use one of the three classic schemes shown in the figure:

• half-wave;
• zero (two-half-wave with a midpoint);
• two-half-wave bridge.

Each of them has advantages and disadvantages that determine the scope.

Half wave circuit characterized by ease of implementation and a minimum number of semiconductor components. The main disadvantages of such a rectifier are a significant amount of output voltage ripple (in the rectified one there is only one half-wave of the mains voltage) and a low rectification factor.

Rectification ratio Kv determined by the ratio of the average value of the voltage at the output of the rectifier Udk effective value of the phase mains voltage Uph.

For a half-wave circuit, Kv \u003d 0.45.

To smooth out the ripple at the output of such a rectifier, powerful filters are required.

Zero, or full-wave circuit with a midpoint, although it requires a double number of rectifier diodes, however, this disadvantage is largely offset by a lower level of rectified voltage ripple and an increase in the rectification factor to 0.9.

The main disadvantage of such a scheme for use in domestic conditions is the need to organize the midpoint of the mains voltage, which implies the presence of a mains transformer. Its dimensions and weight turn out to be incompatible with the idea of ​​a small-sized self-made pulsed source.

full wave bridge rectification has the same indicators in terms of ripple level and rectification factor as the zero circuit, but does not require a network. This compensates for the main drawback - twice the number of rectifier diodes, both in terms of efficiency and cost.

To smooth out the ripple of the rectified voltage, the best solution is to use a capacitive filter. Its use allows you to raise the value of the rectified voltage to the amplitude value of the mains (at Uph=220V Ufm=314V). The disadvantages of such a filter are considered to be large values ​​of the pulsed currents of the rectifier elements, but this disadvantage is not critical.

The choice of rectifier diodes is carried out according to the average forward current Ia and the maximum reverse voltage U BM.

Taking the value of the output voltage ripple coefficient Kp=10%, we obtain the average value of the rectified voltage Ud=300V. Taking into account the load power and the efficiency of the RF converter (80% is taken for calculation, but in practice it will turn out higher, this will allow you to get some margin).

Ia is the average current of the rectifier diode, Рн is the load power, η is the efficiency of the RF converter.

The maximum reverse voltage of the rectifier element does not exceed the amplitude value of the mains voltage (314V), which allows the use of components with a value of U BM =400V with a significant margin. You can use both discrete diodes and ready-made rectifier bridges from various manufacturers.

To ensure a given (10%) ripple at the rectifier output, the capacitance of the filter capacitors is taken at the rate of 1 μF per 1 W of output power. Electrolytic capacitors with a maximum voltage of at least 350V are used. Filter capacities for various capacities are shown in the table.

High frequency converter: its functions and circuits

The high-frequency converter is a single-cycle or two-cycle key converter (inverter) with a pulse transformer. Variants of circuits of RF converters are shown in the figure.

Single cycle circuit. With a minimum number of power elements and ease of implementation, it has several disadvantages.

1. The transformer in the circuit operates on a private hysteresis loop, which requires an increase in its size and overall power;
2. To provide output power, it is necessary to obtain a significant amplitude of the pulsed current flowing through the semiconductor switch.

The scheme has found the greatest application in low-power devices, where the influence of these disadvantages is not so significant.

To change or install a new meter yourself, no special skills are required. Choosing the right one will ensure that the current consumed is correctly accounted for and will increase the safety of the home electrical network.

In modern lighting conditions, both indoors and outdoors, motion sensors are increasingly being used. This gives not only comfort and convenience to our homes, but also allows you to save a lot. You can find out practical tips on choosing an installation site, connection diagrams.

Push-Pull Circuit with Transformer Midpoint (Push-Pull). It got its second name from the English version (push-pull) of the job description. The circuit is free from the shortcomings of the single-cycle version, but has its own - a complicated design of the transformer (it is required to manufacture identical sections of the primary winding) and increased requirements for the maximum voltage of the switches. Otherwise, the solution deserves attention and is widely used in do-it-yourself switching power supplies and not only.

Push-Pull Half-Bridge. In terms of parameters, the circuit is similar to the circuit with a midpoint, but does not require a complex configuration of the transformer windings. The inherent disadvantage of the circuit is the need to organize the middle point of the rectifier filter, which entails a fourfold increase in the number of capacitors.

Due to the ease of implementation, the circuit is most widely used in switching power supplies up to 3 kW. At high powers, the cost of the filter capacitors becomes unacceptably high compared to the semiconductor switches of the inverter, and the bridge circuit turns out to be the most profitable.

Push-Pull Bridge. Similar in parameters to other push-pull circuits, but without the need to create artificial "midpoints". The price for this is twice the number of power keys, which is beneficial from an economic and technical point of view for building powerful impulse sources.

The choice of inverter keys is carried out according to the amplitude of the collector (drain) current I KMAX and the maximum collector-emitter voltage U KEMAC. For the calculation, the load power and the transformation ratio of the pulse transformer are used.

However, first you need to calculate the transformer itself. The pulse transformer is made on a core made of ferrite, permalloy or transformer iron twisted into a ring. For powers up to units of kW, ferrite cores of an annular or W-shaped type are quite suitable. The calculation of the transformer is based on the required power and conversion frequency. To exclude the appearance of acoustic noise, it is desirable to move the conversion frequency outside the audio range (make it higher than 20 kHz).

At the same time, it must be remembered that at frequencies close to 100 kHz, losses in ferrite magnetic circuits increase significantly. The calculation of the transformer itself is not difficult and can be easily found in the literature. Some results for various power sources and magnetic cores are shown in the table below.

The calculation was made for a conversion frequency of 50 kHz. It is worth noting that when operating at a high frequency, the effect of current displacement to the surface of the conductor takes place, which leads to a decrease in the effective winding area. To prevent this kind of trouble and reduce losses in conductors, it is necessary to wind from several cores of a smaller cross section. At a frequency of 50 kHz, the permissible diameter of the winding wire does not exceed 0.85 mm.

Knowing the load power and the transformation ratio, it is possible to calculate the current in the primary winding of the transformer and the maximum collector current of the power switch. The voltage on the transistor in the closed state is selected higher than the rectified voltage supplied to the input of the RF converter with a certain margin (U KEMAH>=400V). Based on this data, keys are selected. Currently, the best option is to use IGBT or MOSFET power transistors.

For rectifier diodes on the secondary side, one rule must be observed - their maximum operating frequency must exceed the conversion frequency. Otherwise, the efficiency of the output rectifier and the converter as a whole will be significantly reduced.

Video on the manufacture of the simplest switching power supply

In most modern electronic devices analog (transformer) power supplies are practically not used, they were replaced by pulse voltage converters. To understand why this happened, it is necessary to consider the design features, as well as the strengths and weaknesses of these devices. We will also talk about the purpose of the main components of pulsed sources, we will give a simple implementation example that can be assembled by hand.

Design features and principle of operation

Of the several ways to convert voltage to power electronic components, two of the most widely used can be distinguished:

1. Analog, the main element of which is a step-down transformer, in addition to the main function, it also provides galvanic isolation.
2. impulse principle.

Let's take a look at the difference between these two options.

PSU based on power transformer

Consider a simplified block diagram of this device. As can be seen from the figure, a step-down transformer is installed at the input, with its help the amplitude of the supply voltage is converted, for example, from 220 V we get 15 V. The next block is a rectifier, its task is to convert the sinusoidal current into a pulsed one (the harmonic is shown above the symbolic image). For this purpose, rectifier semiconductor elements (diodes) connected in a bridge circuit are used. Their principle of operation can be found on our website.

The next block plays two functions: it smoothes the voltage (a capacitor of the appropriate capacity is used for this purpose) and stabilizes it. The latter is necessary so that the voltage does not “fall through” with increasing load.

The given block diagram is greatly simplified, as a rule, this type of source has an input filter and protective circuits, but this is not essential for explaining the operation of the device.

All the disadvantages of the above option are directly or indirectly related to the main structural element - the transformer. First, its weight and dimensions limit miniaturization. In order not to be unfounded, we give as an example a 220/12 V step-down transformer with a rated power of 250 W. The weight of such a unit is about 4 kilograms, dimensions are 125x124x89 mm. You can imagine how much a laptop charger based on it would weigh.

Secondly, the price of such devices sometimes many times exceeds the total cost of other components.

Impulse devices

As can be seen from the block diagram shown in Figure 3, the principle of operation of these devices differs significantly from analog converters, first of all, by the absence of an input step-down transformer.

Figure 3. Structural diagram of a switching power supply

Consider the algorithm of such a source:

• Power is supplied to the surge protector, its task is to minimize network interference, both incoming and outgoing, resulting from operation.
• Next, a unit for converting a sinusoidal voltage into a pulsed constant and a smoothing filter come into operation.
• At the next stage, an inverter is connected to the process, its task is to form rectangular high-frequency signals. Feedback to the inverter is carried out through the control unit.
• The next block is IT, it is necessary for automatic generator mode, supply voltage to the circuits, protection, controller control, as well as the load. In addition, the task of IT is to provide galvanic isolation between high and low voltage circuits.

Unlike a step-down transformer, the core of this device is made of ferrimagnetic materials, this contributes to the reliable transmission of RF signals, which can be in the range of 20-100 kHz. A characteristic feature of IT is that when it is connected, it is critical to turn on the beginning and end of the windings. The small dimensions of this device make it possible to manufacture devices of miniature size, as an example, we can cite the electronic piping (ballast) of an LED or energy-saving lamp.

• Next, the output rectifier comes into operation, since it operates with a high-frequency voltage, the process requires high-speed semiconductor elements, therefore, Schottky diodes are used for this purpose.
• At the final phase, smoothing is performed on an advantageous filter, after which the voltage is applied to the load.

Now, as promised, we will consider the principle of operation of the main element of this device - the inverter.

How does an inverter work?

RF modulation can be done in three ways:

• frequency-pulse;
• phase-pulse;
• pulse width.

In practice, the latter option is used. This is due both to the simplicity of execution and the fact that PWM has a constant communication frequency, unlike the other two modulation methods. A block diagram describing the operation of the controller is shown below.

The device operation algorithm is as follows:

The master frequency generator generates a series of rectangular signals, the frequency of which corresponds to the reference one. Based on this signal, U P of a sawtooth shape is formed, which is fed to the input of the comparator K PWM. The second input of this device is supplied with the signal U US coming from the control amplifier. The signal generated by this amplifier corresponds to the proportional difference between U P (reference voltage) and U PC (control signal from the feedback circuit). That is, the control signal U US, in fact, is a mismatch voltage with a level that depends both on the current on the load and on the voltage on it (U OUT).

This implementation method allows you to organize a closed circuit that allows you to control the output voltage, that is, in fact, we are talking about a linear-discrete functional unit. At its output, pulses are formed, with a duration depending on the difference between the reference and control signal. Based on it, a voltage is created to control the key transistor of the inverter.

The process of stabilization of the output voltage is carried out by monitoring its level, when it changes, the voltage of the regulating signal U PC changes proportionally, which leads to an increase or decrease in the duration between pulses.

As a result, there is a change in the power of the secondary circuits, which ensures the stabilization of the output voltage.

To ensure safety, galvanic isolation between the supply network and the feedback is required. As a rule, optocouplers are used for this purpose.

Strengths and weaknesses of impulse sources

If we compare analog and pulse devices of the same power, then the latter will have the following advantages:

• Small size and weight, due to the absence of a low-frequency step-down transformer and control elements that require heat dissipation using large radiators. Through the use of high-frequency signal conversion technology, it is possible to reduce the capacitance of the capacitors used in the filters, which allows the installation of smaller elements.
• Higher efficiency, since the main losses are caused only by transients, while in analog circuits a lot of energy is constantly lost during electromagnetic conversion. The result speaks for itself, an increase in efficiency up to 95-98%.
• Lower cost due to the use of less powerful semiconductor elements.
• Wider input voltage range. This type of equipment is not demanding on frequency and amplitude, therefore, connection to networks of various standards is allowed.
• Availability of reliable protection against short circuit, overload and other emergency situations.

The disadvantages of impulse technology include:

The presence of RF interference, this is a consequence of the operation of the high-frequency converter. Such a factor requires the installation of a filter that suppresses interference. Unfortunately, its operation is not always efficient, which imposes some restrictions on the use of devices of this type in high-precision equipment.

Special requirements for the load, it should not be reduced or increased. As soon as the current level exceeds the upper or lower threshold, the output voltage characteristics will begin to differ significantly from the standard ones. As a rule, manufacturers (recently even Chinese) provide for such situations and install appropriate protection in their products.

Scope of application

Almost all modern electronics is powered by blocks of this type, as an example we can give:

We assemble a pulsed power supply unit with our own hands

Consider a simple power supply circuit, where the above principle of operation is applied.

Designations:

• Resistors: R1 - 100 Ohm, R2 - from 150 kOhm to 300 kOhm (selected), R3 - 1 kOhm.
• Capacitances: C1 and C2 - 0.01 uF x 630 V, C3 -22 uF x 450 V, C4 - 0.22 uF x 400 V, C5 - 6800 -15000 pF (selected), 012 uF, C6 - 10 uF x 50 V, C7 - 220 uF x 25 V, C8 - 22 uF x 25 V.
• Diodes: VD1-4 - KD258V, VD5 and VD7 - KD510A, VD6 - KS156A, VD8-11 - KD258A.
• Transistor VT1 - KT872A.
• Voltage stabilizer D1 - chip KR142 with index EH5 - EH8 (depending on the required output voltage).
• Transformer T1 - a w-shaped ferrite core with dimensions of 5x5 is used. The primary winding is wound with 600 turns of wire Ø 0.1 mm, the secondary (terminals 3-4) contains 44 turns Ø 0.25 mm, and the last - 5 turns Ø 0.1 mm.
• Fuse FU1 - 0.25A.

The setting is reduced to the selection of R2 and C5 ratings, which provide excitation of the generator at an input voltage of 185-240 V.

It is quite possible to make a welding inverter with your own hands, even without in-depth knowledge in electronics and electrical engineering, the main thing is to strictly adhere to the scheme and try to understand well how such a device works. If you make an inverter, the technical characteristics and efficiency of which will differ little from those of serial models, you can save a decent amount.

You should not think that a home-made device will not give you the opportunity to effectively carry out welding work. Such a device, even assembled according to a simple scheme, will allow you to weld with electrodes with a diameter of 3-5 mm and an arc length of 10 mm.

Characteristics of a homemade inverter and materials for its assembly

Having assembled a welding inverter with your own hands according to a fairly simple electrical circuit, you will receive an effective device with the following technical characteristics:

• the value of the consumed voltage - 220 V;
• the strength of the current supplied to the input of the device - 32 A;
• the current generated at the output of the device is 250 A.

A scheme with such characteristics includes the following elements:

• power unit;
• power key drivers;
• power block.

Before you start assembling a homemade inverter, you need to prepare working tools and elements for creating electronic circuits. So, you will need:

• Screwdriver Set;
• soldering iron for connecting elements of electronic circuits;
• hacksaw for metal work;
• threaded fasteners;
• sheet metal of small thickness:
• elements from which electronic circuits will be formed;
• copper wires and strips - for winding transformers;
• thermal paper from the cash register;
• fiberglass;
• textolite;
• mica.

For home use, inverters are most often assembled that operate on a standard 220 V electrical network. However, if necessary, you can make a device that will operate on a three-phase electrical network with a voltage of 380 V. Such inverters have their advantages, the most important of which is a higher Efficiency compared to single-phase devices.

power unit

One of the most important elements of the power supply is a transformer, which is wound on a SH7x7 or 8x8 ferrite. This device, which provides a stable voltage supply, is formed from 4 windings:

• primary (100 turns of PEV wire with a diameter of 0.3 mm);
• the first secondary (15 turns of PEV wire with a diameter of 1 mm);
• the second secondary (15 turns of PEV wire with a diameter of 0.2 mm);
• third secondary (20 turns of PEV wire with a diameter of 0.3 mm).

To minimize the negative impact of voltage drops that regularly occur in the electrical network, the winding of the transformer windings should be performed across the entire width of the frame.

After completing the primary winding and insulating its surface with fiberglass, a layer of shielding wire is wound around it, the turns of which should completely cover it. The turns of the shield wire (it must have the same diameter as the primary winding wire) are made in the same direction. This rule is also relevant for all other windings formed on the transformer frame. The surfaces of all windings wound on the transformer frame are also isolated from each other using fiberglass or ordinary masking tape.

In order for the voltage supplied from the power supply to the relay to be in the range of 20–25 V, it is necessary to select resistors for the electronic circuit. The main function of the welding inverter power supply is to convert AC to DC. For these purposes, the power supply uses diodes assembled according to the "oblique bridge" scheme.

During operation, the diodes of such a bridge get very hot, so they must be mounted on radiators, which can be used as cooling elements from old computers. To mount the diode bridge, it is necessary to use two radiators: the upper part of the bridge is attached to one radiator through a mica gasket, the lower part through a layer of thermal paste to the second one.

The conclusions of the diodes from which the bridge is formed must be directed in the same direction as the conclusions of the transistors, with the help of which the direct current will be converted into high-frequency alternating current. The wires connecting these terminals should be no longer than 15 cm. Between the power supply and the inverter unit, which is based on transistors, there is a sheet of metal attached to the body of the device by welding.

Power block

The basis of the power unit of the welding inverter is a transformer, due to which the value of the high-frequency voltage decreases, and its strength increases. In order to make a transformer for such a block, it is necessary to select two cores Ш20х208 2000 nm. Newsprint can be used to provide a gap between them.

The windings of such a transformer are not made of wire, but of a copper strip 0.25 mm thick and 40 mm wide.

Each layer is wrapped with cash register tape to provide thermal insulation, which demonstrates good wear resistance. Secondary winding The transformer is formed from three layers of copper strips, which are isolated from each other using a fluoroplastic tape. The characteristics of the transformer windings must comply with the following parameters: 12 turns x 4 turns, 10 kv. mm x 30 sq. mm.

Many people try to make step-down transformer windings from thick copper wire, but this is not the right solution. Such a transformer operates on high-frequency currents, which are forced out to the surface of the conductor without heating its interior. That is why, for the formation of windings, the best option is a conductor with a large surface area, that is, a wide copper strip.

Plain paper can also be used as a thermal insulation material, but it is less wear-resistant than cash register tape. From elevated temperature, such a tape will darken, but its wear resistance will not suffer from this.

The transformer of the power unit will become very hot during its operation, therefore, for its forced cooling, it is necessary to use a cooler, which can be used as a device previously used in the computer system unit.

inverter unit

Even a simple welding inverter must perform its main function - to convert the direct current generated by the rectifier of such an apparatus into alternating current high frequency. To solve this problem, power transistors are used that open and close at a high frequency.

Schematic diagram of the inverter unit (click to enlarge)

The inverter unit of the apparatus, which is responsible for converting direct current to high-frequency alternating current, is best assembled on the basis of not one powerful transistor, but several less powerful ones. Such a constructive solution will allow to stabilize the current frequency, as well as to minimize noise effects during welding.

The electronic also contains capacitors connected in series. They are necessary to solve two main tasks:

• minimization of resonant emissions of the transformer;
• reducing losses in the transistor block that occur when it is turned off and due to the fact that the transistors open much faster than they close (at this moment, current losses may occur, accompanied by heating of the transistor block keys).

Cooling system

The power elements of the home-made welding inverter circuit become very hot during operation, which can lead to their failure. To prevent this from happening, in addition to the radiators on which the most heated blocks are mounted, it is necessary to use fans responsible for cooling.

If you have a powerful fan available, you can get by with one by directing the air flow from it to a step-down power transformer. If you are using low-power fans from older computers, you will need about six of them. At the same time, three such fans should be installed next to the power transformer, directing the air flow from them to it.

To prevent overheating of a homemade welding inverter, you should also use a temperature sensor by installing it on the hottest radiator. Such a sensor, if the radiator reaches a critical temperature, will turn off the flow of electric current to it.
In order for the inverter ventilation system to work effectively, properly executed air intakes must be present in its case. The grilles of such intakes, through which air flows will flow into the device, should not be blocked by anything.

Do-it-yourself inverter assembly

For a home-made inverter device, you need to choose a reliable case or make it yourself, using sheet metal with a thickness of at least 4 mm. As a base on which the welding inverter transformer will be mounted, you can use a getinaks sheet with a thickness of at least 0.5 cm. The transformer itself is mounted on such a base using brackets that you can make yourself from copper wire with a diameter of 3 mm.

To create electronic circuit boards of the device, you can use foil textolite with a thickness of 0.5–1 mm. When installing magnetic circuits that will heat up during operation, it is necessary to provide for gaps between them necessary for free air circulation.

For automatic control, you will need to purchase and install a PWM controller in it, which will be responsible for stabilizing the welding current and voltage. To make it convenient for you to work with your home-made device, it is necessary to mount controls in the front of its body. Such bodies include a toggle switch for turning on the device, a variable resistor knob with which the welding current is regulated, as well as cable clamps and signal LEDs.

Diagnostics of a homemade inverter and its preparation for work

Doing is half the battle. An equally important task is its preparation for work, during which the correct functioning of all elements is checked, as well as their settings.

The first thing to do when testing a homemade welding inverter is to apply 15 V to the PWM controller and one of the cooling fans. This will allow you to simultaneously check the performance of the controller and avoid its overheating during such a test.

After the capacitors of the device are charged, a relay is connected to the electrical supply, which is responsible for closing the resistor. If voltage is applied directly to the resistor, bypassing the relay, an explosion may occur. After the relay trips, which should happen within 2-10 seconds after the voltage is applied to the PWM controller, you need to check if the resistor has closed.

When the relays of the electronic circuit work, the PWM board should form rectangular pulses to the optocouplers. This can be checked using an oscilloscope. The correct assembly of the diode bridge of the device must also be checked; for this, a voltage of 15 V is applied to it (the current strength should not exceed 100 mA).

The transformer phases may have been connected incorrectly during the assembly of the device, which may lead to incorrect operation of the inverter and strong noise. To prevent this from happening, the correct connection of the phases must be checked; for this, a two-beam oscilloscope is used. One beam of the device is connected to the primary winding, the second - to the secondary. The phases of the pulses, if the windings are connected correctly, should be the same.

The correctness of the manufacture and connection of the transformer is checked using an oscilloscope and connecting electrical devices with various resistances to the diode bridge. Focusing on the noise of the transformer and the readings of the oscilloscope, they conclude that it is necessary to refine the electronic circuit of a home-made inverter apparatus.

To check how much you can continuously work on a homemade inverter, you need to start testing it from 10 seconds. If the radiators of the device do not heat up during operation of this duration, you can increase the period to 20 seconds. If such a time period did not negatively affect the state of the inverter, you can increase the duration of the welding machine up to 1 minute.

Maintenance of a homemade welding inverter

In order for the inverter device to serve for a long time, it must be properly maintained.

In the event that your inverter has stopped working, you need to open its cover and blow out the insides with a vacuum cleaner. Those places where dust remains can be thoroughly cleaned with a brush and a dry cloth.

The first thing to do when diagnosing a welding inverter is to check the voltage supply to its input. If the voltage is not supplied, you should diagnose the performance of the power supply. The problem in this situation may also be that the fuses of the welding machine have blown. Another weak link of the inverter is the temperature sensor, which, in the event of a breakdown, must not be repaired, but replaced.

When performing diagnostics, it is necessary to pay attention to the quality of the connections of the electronic components of the device. Poorly made connections can be determined visually or using a tester. If such connections are identified, they must be corrected so as not to encounter further overheating and failure of the welding inverter.

Only if you pay due attention to the maintenance of the inverter device, you can count on the fact that it will serve you for a long time and will enable you to perform welding work as efficiently and efficiently as possible.

2 , average rating: 5,00 out of 5)

I decided to devote a separate article to the manufacture of a DC AC boost converter for 220V. This, of course, is remotely related to the topic of LED spotlights and lamps, but such a mobile power source is widely used at home and in the car.

• 1. Assembly options
• 2. The design of the voltage converter
• 3. Sinusoid
• 4. An example of the filling of the converter
• 5. Assembly from UPS
• 6. Assembly from ready-made blocks
• 7. Radio constructors
• 8. Schemes of powerful converters

Assembly options

There are 3 best ways to make a 12 to 220 inverter with your own hands:

1. assembly from prefabricated blocks or radioconstructors;
2. production from an uninterruptible power supply;
3. use of amateur radio circuits.

The Chinese can find good radio designers and ready-made blocks for assembling converters DC into alternating 220V. For the price, this method will be the most expensive, but it takes a minimum of time.

The second way is to upgrade an uninterruptible power supply (UPS), which, without a battery, is sold in large quantities on Avito and costs from 100 to 300 rubles.

The most difficult option is assembly from scratch, you can’t do without amateur radio experience. You have to make printed circuit boards, select components, a lot of work.

Voltage Converter Design

Consider the design of a conventional step-up voltage converter from 12 to 220. The principle of operation for all modern inverters will be the same. The high-frequency PWM controller sets the operating mode, frequency and amplitude. The power part is made on powerful transistors, the heat from which is removed to the body of the device.

A fuse is installed at the input to protect the car battery from short circuit. A thermal sensor is attached next to the transistors, which monitors their heating. In case of overheating of the 12v 220v inverter, an active cooling system is activated, consisting of one or more fans. In budget models, the fan can run constantly, and not only at high load.

Power transistors at the output

sinusoid

The waveform at the output of the automobile inverter is formed by a high-frequency generator. The sinusoid can be of two types:

1. modified sinusoid;
2. pure sine wave, pure sine wave.

Not every electrical appliance can work with a modified sine wave that has a rectangular shape. Some components in the mode of operation change, they can heat up and start to scribble. Similar can be obtained by dimming led lamp, whose brightness is not adjustable. The crackling and flashing starts.

Expensive DC AC step-up voltage converters 12v 220v have a pure sine output. They are much more expensive, but electrical appliances work great with it.

An example of the filling of the converter

..

Assembly from UPS

In order not to invent anything and not buy ready-made modules, you can try a computer uninterruptible power supply, abbreviated as IPB. They are rated for 300-600 watts. I have an Ippon with 6 outlets, 2 monitors, 1 system unit, 1 TV set, 3 surveillance cameras, video surveillance management system. I periodically switch to operating mode by disconnecting from the mains 220 so that the battery is discharged, otherwise the service life will be greatly reduced.

Colleagues of electricians connected an ordinary car acid battery to an uninterruptible power supply, worked perfectly continuously for 6 hours, watched football in the country. The UPS usually has a built-in gel battery diagnostic system that detects its low capacity. How she will react to the automobile is unknown, although the main difference is the gel instead of acid.

UPS stuffing

The only problem is that the uninterruptible power supply may not like jumps in the car network with the engine running. For a real radio amateur, this problem is solved. Can only be used with the engine off.

Mostly UPSs are designed for short-term operation when 220V is lost in the outlet. With long-term continuous operation, it is very desirable to install active cooling. Ventilation is useful for a stationary version and for a car inverter.

Like all devices, it will behave unpredictably when starting the engine with a connected load. The starter of the car strongly squanders the Volts, at best it will go into protection as if the battery fails. At worst, there will be jumps at the 220V output, the sinusoid will be distorted.

Assembly from prefabricated blocks

To assemble a stationary or car inverter 12v 220v with your own hands, you can use ready-made blocks that are sold on Ebeee or from the Chinese. This will save time on board fabrication, soldering and final setup. It is enough to add a case and wires with crocodiles to them.

You can also buy a radio designer, which is equipped with all radio components, all that remains is to solder.

Approximate price for autumn 2016:

1. 300w - 400 rubles;
2. 500w - 700 rubles;
3. 1000w - 1500 rubles;
4. 2000w - 1700 rubles;
5. 3000w - 2500 rubles.

To search on Aliexpress, enter a query in the search box "inverter 220 diy". The abbreviation "DIY" stands for DIY assembly.

Board for 500W, output for 160, 220, 380 volts

radio constructors

The radio designer is cheaper than the finished board. The most complex elements may already be on the board. After assembly, it requires almost no setup, which requires an oscilloscope. The spread of parameters of radio components and denominations are well matched. Sometimes spare parts are put in a bag, suddenly, due to inexperience, you will tear off the leg.

Schemes of powerful converters

A powerful inverter is mainly used to connect construction power tools during the construction of a summer house or hacienda. A low-power voltage converter for 500W differs from a powerful one for 5000-10000W in the number of transformers and power transistors at the output. Therefore, the complexity of manufacturing and the price are almost the same, transistors are inexpensive. The power is optimally 3000W, you can connect a drill, grinder and other tools.

I will show several inverter circuits from 12, 24, 36 to 220V. It is not recommended to put such in a passenger car, you can accidentally spoil the electrician. The circuitry of DC-AC converters 12 to 220 is simple, the master oscillator and the power section. The generator is made on the popular TL494 or analogues.

A large number of booster circuits from 12v to 220v for DIY can be found at the link
http://cxema.my1.ru/publ/istochniki_pitanija/preobrazovateli_naprjazhenija/101-4
There are about 140 circuits in total, half of them are step-up converters from 12, 24 to 220V. Power from 50 to 5000 watts.

After assembly, you will need to adjust the entire circuit using an oscilloscope, it is desirable to have experience with high-voltage circuits.

To assemble a powerful 2500 watt inverter, 16 transistors and 4 suitable transformers are required. The cost of the product will be considerable, comparable to the cost of a similar radio designer. The advantage of such costs will be a pure sine output.