Power supply with current and voltage regulation. Voltage regulation in DC circuits Voltage regulation in the welding machine
One of the main components of a truly high-quality one is the correct and precise adjustment of the welding current in accordance with the task. Experienced welders often have to work with metal of different thicknesses, and sometimes the standard min / max adjustment is not enough for a full-fledged job. In such cases, there is a need for multi-stage current adjustment, accurate to the ampere. This problem can be easily solved by including an additional device in the circuit - a current regulator.
The current can be regulated by the secondary (secondary winding) and by the primary (primary winding). In addition, each of the methods for setting up a transformer for welding has its own characteristics, which are important to consider. In this article, we will tell you how the current is adjusted in, we will give diagrams of regulators for welding, we will help you correctly select the welding current regulator for the primary winding for the welding transformer.
There are many ways to adjust the current, and above we wrote about the secondary and primary windings. In fact, this is a very rough classification, since the adjustment is still divided into several components. We will not be able to analyze all the components within the framework of this article, so we will focus on the most popular ones.
One of the most commonly used methods for adjusting the current is to add a secondary winding to the output. This is a reliable and durable way, the ballast can be easily made with your own hands and used at work without additional devices. Often, ballasts are used solely to reduce the current strength.
If you are not ready to put up with these shortcomings, then we recommend that you pay attention to the method when the welding current is adjusted along the primary winding. For these purposes, electronic devices are often used, which can be easily made by hand. Such a device will seamlessly regulate the current through the primary and will not cause inconvenience to the welder during operation.
The electronic regulator will become an indispensable assistant to the summer resident, who is forced to carry out welding in conditions of unstable voltage. Often, houses are simply not supposed to use electrical appliances with more than 3-5 kW, and this is very limiting in work. With the help of the regulator, you can configure your device so that it can work smoothly even with low voltage. Also, such a device is useful for craftsmen who need to constantly move from place to place while working. After all, the regulator does not need to be dragged along like a ballast, and it will never cause injury.
Now we will talk about how to make an electronic regulator from thyristors.
Thyristor regulator circuit
Above you can see a diagram of a simple regulator on 2 thyristors with minima of non-deficient parts. You can also make a regulator on a triac, but our practice has shown that a thyristor power regulator is more durable and works more stably. The assembly diagram is very simple and you can quickly assemble the regulator with minimal soldering skills.
The principle of operation of this regulator is also simple. We have a primary winding circuit into which the regulator is connected. The regulator consists of transistors VS1 and VS2 (for each half-wave). The RC circuit determines the moment when the thyristors open, at the same time the resistance R7 changes. As a result, we get the opportunity to change the current in the primary of the transformer, after which the current changes in the secondary.
Note! The regulator is set under voltage, do not forget about it. To avoid fatal errors and not get injured, it is imperative to isolate all radio elements.
In principle, you can use old style transistors. This is a great way to save money, since such transistors can be easily found in an old radio or at a flea market. But keep in mind that such transistors must be used at an operating voltage of at least 400 V. If you see fit, you can put dinistors in place of the transistors and resistors shown in the diagram. We did not use dinistors, because in this embodiment they do not work very stably. In general, this circuit of the thyristor welding current regulator has proven itself well, and on its basis many regulators have been made that work stably and perform their function well.
You could also see the RKS-801 regulator and the RKS-15-1 resistance welding regulator in stores. We do not recommend making them yourself, as it will take a lot of time and save you a little money, but if you wish, you can make RKS-801. Below you can see the diagram of the regulator and the diagram of its connection to the welder. Open the pictures in a new window to see the text better.
Welding current measurement
After you have made and configured the regulator, it can be used in operation. To do this, you need another device that will measure the welding current. Unfortunately, it will not be possible to use household ammeters, since they are not capable of handling more than 200 amperes. Therefore, we recommend using current clamps. This is a relatively inexpensive and accurate way to read the current value, the operation of the clamps is clear and simple.
The so-called "pliers" at the top of the device wrap around the wire and measure the current. On the body of the device there is a switch for the current measurement limits. Depending on the model and price, different manufacturers make current clamps that can operate in the range from 100 to 500 amperes. Select a device that matches yours.
Clamp meters are an excellent choice if you need to quickly measure the current value without affecting the circuit and without connecting additional elements to it. But there is one drawback: the pliers are absolutely useless in measuring the value. The fact is that direct current does not create an alternating electromagnetic field, so the device simply does not see it. But in working with such a device justifies all expectations.
There is another way to measure current, it is more radical. You can add an industrial ammeter to the circuit of your semi-automatic welding machine that can measure large currents. You can also just temporarily add an ammeter to the break in the welding wire circuit. On the left you can see a diagram of such an ammeter, according to which you can assemble it.
This is a cheap and effective way to measure current, but the use of an ammeter in welding machines also has its own characteristics. It is not the ammeter itself that is added to the circuit, but its resistor or shunt, while the dial indicator must be connected in parallel to the resistor or shunt. If you do not follow this sequence, the device, at best, simply will not work.
Instead of a conclusion
Adjusting the welding current on a semiautomatic device is not as difficult as it might seem at first glance. If you have minimal knowledge in the field of electrical engineering, you can easily assemble a current regulator for a trimistor welding machine on your own, saving on buying this device in a store. Homemade regulators are especially important for home DIYers who are not ready for the extra expense of equipment. Tell us about your experience in making and using a current regulator in the comments and share this article on your social networks. We wish you good luck in your work!
In this material, we will consider ways to adjust the welding current. Current regulator circuits for a welding machine are varied. They have their own advantages and disadvantages. We will try to help the reader choose a current regulator for the welding machine.
General concepts
The principle of arc welding is well known. Let's refresh the basic concepts. To get a welded joint, you need to create an arc. An electric arc occurs when voltage is applied between the welding electrode and the surface of the material to be welded. The arc current melts the metal, a molten pool is formed between the two ends. After cooling the seam, we get a strong connection of the two metals.
In Russia, alternating current is regulated by a frequency of 50 Hz. Power for the welding machine is supplied from the network with a phase voltage of 220 V. Welding transformers have two windings: primary and secondary. The secondary voltage of the transformer is 70 V.
Separate manual and automatic welding modes. In a home workshop, welding is carried out in manual mode. We list the parameters that are changed in manual mode:
- welding current;
- arc voltage;
- welding electrode speed;
- number of passes per seam;
- diameter and brand of the electrode.
The correct choice and maintenance of the necessary parameters throughout the welding process are the key to a high-quality welded joint.
When carrying out manual arc welding, it is necessary to correctly distribute the current. This will allow you to make a quality seam. The stability of the arc directly depends on the magnitude of the welding current. Specialists select it based on the diameter of the electrodes and the thickness of the materials to be welded.
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Types of current regulators
There are more ways to change the current strength during welding operations. Even more circuit diagrams of regulators have been developed. Ways to control the welding current can be as follows:
- installation of passive elements in the secondary circuit;
- switching the number of turns of the transformer windings;
- change in the magnetic flux of the transformer;
- semiconductor control.
Know the advantages and disadvantages of different adjustment methods. Let us name the characteristic features of these types.
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Resistor and choke
The first type of adjustment is considered the simplest. A resistor or inductor is connected in series with the welding circuit. In this case, the change in the current strength and arc voltage occurs due to the resistance and, accordingly, the voltage drop. Craftsmen appreciated a simple and effective way to adjust the current - the inclusion of resistance in the secondary circuit. The device is simple and reliable.
Additional resistors are used to soften the current-voltage characteristic of the power supply. The resistance is made of thick (5-10 mm in diameter) nichrome wire. Powerful wire resistances are used as a passive element.
To regulate the current, a choke is also installed instead of resistance. Due to the introduction of inductance into the AC arc circuit, a phase shift of current and voltage is observed. The current zero crossing occurs at a high transformer voltage, which increases the reliability of re-ignition and the stability of the arc. The welding mode becomes soft, as a result of which we obtain a uniform and high-quality seam.
This method is widely used due to its reliability, availability in manufacture and low cost. The disadvantages include a small control range and difficulty in restructuring the parameters. To make such a design is within the power of everyone. Transformers of the TS-180 or TS-250 type are often used from old tube TVs, from which the primary and secondary windings are removed and the choke winding is wound with the required cross section. The cross section of the aluminum wire will be about 35-40 mm, copper - up to 25 mm. The number of turns will be in the range of 25-40 pieces.
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Switching the number of windings
Voltage regulation is carried out by changing the number of turns of the winding. This changes the transformation ratio. The welding current regulator is easy to operate. For this method of adjustment, it is necessary to make taps when winding. Switching is carried out by a switch that can withstand high current and mains voltage. Disadvantages of switching turns: it is difficult to find a switch that can withstand a load of a couple of hundred amps, a small current adjustment range.
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Core magnetic flux
The current parameters can be influenced by the magnetic flux of the power transformer. The regulation of the strength of the welding current is carried out due to the mobility of the windings, changing the gap or introducing a magnetic shunt. When the distance is reduced or increased, the magnetic fluxes of the two windings change, as a result of which the current strength will also change. The magnetic flux method is practically not used due to the complexity of manufacturing the transformer core.
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Semiconductors in the current regulation circuit
Figure 1. Scheme of the welding current regulator.
Semiconductor devices have made a real breakthrough in the welding business. Modern circuitry allows the use of powerful semiconductor switches. Thyristor circuits for regulating welding current are especially common. The use of semiconductor devices is replacing inefficient control circuits. These solutions increase the current regulation limits. Large and heavy welding transformers containing a huge amount of expensive copper have been replaced with light and compact ones.
An electronic thyristor regulator is an electronic circuit necessary to control and adjust the voltage and current that are supplied to the electrode at the welding site.
For example, consider a thyristor regulator. The scheme of the welding current regulator is shown in fig. 1.
The circuit is based on the principle of a phase current regulator.
The adjustment is carried out by applying a control voltage to solid-state relays - thyristors. Thyristors VS1 and VS2 open alternately when signals are received at the control electrodes. The supply voltage of the control pulse generation circuit is taken from a separate winding. Then it is converted into a constant voltage by a diode bridge on VD5-VD8.
A positive half-wave charges capacitance C1. The charge time of the electrolytic capacitor is formed by resistors R1, R2. When the voltage reaches the required value (more than 5.6 V), the dinistor is opened, formed by the VD6 zener diode and the VS3 thyristor. Next, the signal passes through the diode VD3 or VD4. With a positive half-wave, the thyristor VS1 opens, with a negative half-wave, VS2 opens. Capacitor C1 will discharge. After the beginning of the next half-cycle, the thyristor VS1 closes, and the capacitance is charged. At this moment, the key VS2 opens, which continues to supply voltage to the electric arc.
Adjustment comes down to setting the range of welding current trimming resistance R1. As you can see, the welding current adjustment scheme is quite simple. The availability of the element base, ease of adjustment and control of the regulator allow the manufacture of such a welding machine independently.
You will need
- - transistors type P416, GT308;
- - variable resistor SP-2;
- - MLT resistors;
- - capacitors MBT or MBM 400 V
Instruction
Make a secondary winding when winding welding. Change the current by switching the number of turns. This is the best option. But this method can only be used to adjust the current; it is not used to adjust it over a wide range. It is worth saying that this method is associated with certain problems. First of all, due to the fact that the control device passes a significant current, which leads to its bulkiness, and for the secondary circuit it is impossible to select standard switches that would withstand currents up to 200 A. The primary winding circuit is a completely different matter, since the currents here are 5 times weaker.
Assemble the thyristor regulator. The element base is available, it is easy to manage, does not need to be configured, and has proven itself well in the process. Power adjustment is carried out by periodically switching off the I-th winding of the welding transformer for a given period of time at each half-cycle of current. In this case, the average value of the current decreases.
Turn on the main elements of the regulator (thyristors) in parallel and opposite each other. They will be opened in turn by current pulses, which are formed by transistors VT1, VT2. When power is applied to the regulator, both are closed, capacitors C1 and C2 start through the variable R7. When the avalanche breakdown voltage of the transistor is reached on one of them, the latter will open the way for the discharge current of the capacitor connected to it. After that, the corresponding thyristor, connecting the load to the network. At the beginning of the next half-cycle, everything repeats, but vice versa, in reverse polarity.
Adjust the torque of the thyristors by changing the resistance of the variable resistor R7 from the beginning to the end of the half-cycle. This leads to a change in the total current in the I-th winding of the welding transformer. To decrease or increase the adjustment range, change the resistance of the variable resistor R7 up or down, respectively.
Replace resistors R5, R6, which are included in the base circuits and transistors VT1, VT2, which operate in avalanche mode, with dinistors. Connect the anodes of the dinistors to the extreme terminals of the resistor R7, and connect the cathodes to the resistors R3 and R4. For a current regulator assembled on dinistors, use devices such as KN102A. Use transistors like P416, GT308 as VT1, VT2, but you can replace them with modern low-power high-frequency ones with similar parameters. Use a variable resistor type SP-2, type MLT. Capacitors of the MBT or MBM type with an operating voltage of 400 V. The regulator is not adjusted, just make sure that the transistors are stable in avalanche mode.
An important design feature of any welding machine is the ability to adjust the operating current. In industrial devices, different methods of current regulation are used: shunting with the help of various types of chokes, changing the magnetic flux due to the mobility of the windings or magnetic shunting, the use of active ballast resistance stores and rheostats. The disadvantages of such an adjustment include the complexity of the design, the bulkiness of the resistances, their strong heating during operation, and inconvenience when switching.
The most optimal option is to make it with taps even when winding the secondary winding and, by switching the number of turns, change the current. However, this method can be used to adjust the current, but not to adjust it over a wide range. In addition, adjusting the current in the secondary circuit of the welding transformer is associated with certain problems.
Thus, significant currents pass through the control device, which leads to its bulkiness, and for the secondary circuit it is almost impossible to select such powerful standard switches that they can withstand currents up to 200 A. Another thing is the primary winding circuit, where the currents are five times less.
After a long search through trial and error, the best solution to the problem was found - a well-known thyristor regulator, the circuit of which is shown in Fig. 1.
With the utmost simplicity and availability of the element base, it is easy to manage, does not require settings and has proven itself in work - it works only like a "clock".
Power control occurs when the primary winding of the welding transformer is periodically switched off for a fixed period of time at each half-cycle of current. In this case, the average value of the current decreases.
The main elements of the regulator (thyristors) are connected opposite and parallel to each other. They are alternately opened by current pulses generated by transistors VT1, VT2. When the regulator is connected to the network, both thyristors are closed, capacitors C1 and C2 begin to charge through the variable resistor R7. As soon as the voltage on one of the capacitors reaches the avalanche breakdown voltage of the transistor, the latter opens, and the discharge current of the capacitor connected to it flows through it.
Following the transistor, the corresponding thyristor opens, which connects the load to the network. After the beginning of the next, opposite in sign, half-cycle of the alternating current, the thyristor closes, and a new capacitor charging cycle begins, but in reverse polarity. Now the second transistor opens, and the second thyristor reconnects the load to the network.
By changing the resistance of the variable resistor R7, you can control the moment the thyristors are turned on from the beginning to the end of the half-cycle, which in turn leads to a change in the total current in the primary winding of the welding transformer T1. To increase or decrease the adjustment range, you can change the resistance of the variable resistor R7 up or down, respectively.
Transistors VT1, VT2, operating in avalanche mode, and resistors R5, R6 included in their base circuits, can be replaced with dinistors. The anodes of the dinistors should be connected to the extreme terminals of the resistor R7, and the cathodes should be connected to the resistors R3 and R4. If the regulator is assembled on dinistors, then it is better to use devices such as KN102A.
Variable resistor type SP-2, the rest type MLT. Capacitors of the MBM or MBT type for an operating voltage of at least 400 V.
A properly assembled regulator does not require adjustment. You just need to make sure in the avalanche mode (or in the stable inclusion of dinistors).
Attention! The device has a galvanic connection to the network. All elements, including thyristor heat sinks, must be isolated from the case.
The design of a convenient and reliable DC regulator is proposed. Its voltage range is from 0 to 0.86 U2, which allows this valuable device to be used for various purposes. For example, for charging high-capacity batteries, powering electric heating elements, and, most importantly, for welding with both a conventional electrode and stainless steel, with smooth current adjustment.
Schematic diagram of the DC regulator.
A graph explaining the operation of a power unit made according to a single-phase asymmetric bridge circuit (U2 is the voltage coming from the secondary winding of the welding transformer, alpha is the thyristor opening phase, t is time).
The regulator can be connected to any welding transformer with secondary winding voltage U2=50. 90V. The proposed design is very compact. The overall dimensions do not exceed the dimensions of a conventional unregulated bridge type rectifier; for DC welding.
The regulator circuit consists of two blocks: control A and power B. Moreover, the first is nothing more than a phase-pulse generator. It is made on the basis of an analogue of a unijunction transistor, assembled from two semiconductor devices of n-p-n and p-n-p types. With the help of a variable resistor R2, the direct current of the structure is regulated.
Depending on the position of the slider R2, the capacitor C1 is charged here up to 6.9 V at different rates. When this voltage is exceeded, the transistors open sharply. And C1 begins to discharge through them and the winding of the pulse transformer T1.
A thyristor, to the anode of which a positive half-wave approaches (the impulse is transmitted through the secondary windings), opens at the same time.
As a pulse, you can use industrial three-winding TI-3, TI-4, TI-5 with a transformation ratio of 1:1:1. And not only these types. For example, good results are obtained by using two two-winding transformers TI-1 with a series connection of the primary windings.
Moreover, all the named types of TI allow isolating the pulse generator from the control electrodes of thyristors.
There is only one “but9raquo;. The power of the pulses in the secondary windings of the TI is insufficient to turn on the corresponding thyristors in the second (see diagram), power block B. The way out of this “conflict9raquo; situation was found elementary. To turn on the powerful ones, low-power thyristors with high sensitivity to the control electrode were used.
The power unit B is made according to a single-phase asymmetric bridge circuit. That is, thyristors work here in one phase. And the shoulders on VD6 and VD7 during welding work like a buffer diode.
Installation? It can also be mounted mounted, based directly on a pulse transformer and other relatively “large-sized”9raquo; schema elements. Moreover, the radio components connected to this design, as they say, are at least-minimorum.
The device starts working immediately, without any adjustments. Get yourself one - you won't regret it.
A. CHERNOV, Saratov. Model designer 1994 No. 9.
Category: "Electronic homemade products"
Simple electronic welding current controller, circuit
Often you have to weld metal of different thicknesses and use electrodes of different diameters, and in order for welding to be of high quality, it is necessary to adjust the welding current so that the seam lies evenly and the metal does not splatter. But, it is quite problematic to regulate the current of the secondary winding of the welding transformer, because. it can reach up to 180-250A.
As an option, nichrome spirals are used to adjust the welding current, including them in series in the circuit of the primary or secondary winding of the welding transformer, or inductors. It is inconvenient to regulate the current in this way, and the regulator itself is cumbersome. But there is another way out - to make an electronic welding current controller that would regulate the current in the primary winding of the welding machine.
The welding current regulator for a home-made welding machine is still very useful in cases where you have to weld metal in places where the power grid is weak, in villages for example. As a rule, they limit the current consumption for each house by setting the input machine to 16 A, i.e. it is impossible to turn on the load more than 3.5 kW. And a good welding machine, welding with electrodes with a diameter of 4-5 mm, consumes 6-7, or even 8 kW.
Therefore, we reduced the welding current and at the same time reduced the current consumption of the matcher, so we invested in those 3.5 kW and welded what you need with a “troika”.
Here is a simple circuit of such a regulator on 2 thyristors and it has a minimum of non-deficient parts. It can be done on 1 triac, but, as practice has shown, it is more reliable on thyristors.
The welding current regulator works as follows: a regulator is connected in series to the primary winding circuit, which consists of two controlled thyristors VS1 and VS2 (T122-25-3, or E122-25-3), for each half-wave. The opening moment of the thyristors is determined by the RC circuit (R7, C1, C2). By changing the resistance R7, we change the opening moment of the thyristors and thereby change the current in the primary winding of the transformer, and therefore the current in the secondary winding also changes.
Transistors can be used of the old model - P416, GT308, they can be easily found in old receivers or televisions, and capacitors are used of the MBT or MBM type for an operating voltage of at least 400 V.
Transistors VT1, VT2 and resistors R5, R6, connected as shown in the diagram, are an analogue of dinistors and in this embodiment they work better than dinistors, but with a strong desire, instead of VT1, R5 and VT2, R6, you can put ordinary dinistors - type KN102A.
When assembling and adjusting the welding current regulator, do not forget that the control takes place under a voltage of 220V. Therefore, in order to prevent electric shock, all radio elements, as well as thyristor heat sinks, must be isolated from the case!
In practice, the above electronic welding current regulator has proven itself well.
The material from the Radioamator magazine was taken as a basis. - 2000. - No. 5 “Do-it-yourself welding transformer”.
Recently I was talking with my teacher at the university, and, to my misfortune, revealed my amateur radio talents. In general, the conversation ended with the fact that I undertook to assemble a thyristor rectifier with a smooth current regulator for his welding “donut”9. Why is this needed? The fact is that alternating voltage cannot be welded with special electrodes designed for constant, and given that welding electrodes come in different thicknesses (most often from 2 to 6 mm), then the current value must be proportionally changed.
Choosing a circuit for a welding regulator, I followed the advice of -igRomana- and settled on a rather simple regulator, where the current is changed by applying pulses to the control electrodes, which are formed by an analog of a powerful dinistor assembled on a KU201 thyristor and a KS156 zener diode. See the diagram below:
Despite the fact that an additional winding with a voltage of 30 V was required, I decided to make it easier, and in order not to touch the welding transformer itself, I installed a small additional 40 watt. Thus, the prefix-regulator has become completely autonomous - you can connect it to any welding transformer. The remaining parts of the current regulator were assembled on a small board made of foil textolite, the size of a pack of cigarettes.
As a base, I chose a piece of vinyl plastic, where I screwed the TS160 thyristors themselves with radiators. Since there were no powerful diodes at hand, two thyristors had to be forced to perform their function.
It is also attached to a common base. Terminals are used to input the 220 V network, the input voltage from the welding transformer is supplied to the thyristors through M12 screws. We remove the constant welding current from the same screws.
The welding machine is assembled, it's time for testing. We apply a change from the torus to the regulator and measure the output voltage - it almost does not change. And it shouldn’t, since at least a small load is needed to accurately control the voltage. It can be a simple 127 (or 220 V) incandescent lamp. Now, even without any testers, you can see a change in the brightness of the lamp filament, depending on the position of the resistor-regulator engine.
So it’s clear why the second tuning resistor is indicated according to the scheme - it limits the maximum value of the current that is supplied to the pulse shaper. Without it, the output already from half of the engine reaches the maximum possible value, which makes the adjustment not smooth enough.
To correctly adjust the range of current change, it is necessary to bring the main regulator to the maximum current (minimum resistance), and gradually reduce the resistance with the trimmer (100 Ohm), until its further decrease leads to an increase in welding current. Capture this moment.
Now the tests themselves, so to speak, for iron. As intended, the current is normally regulated from zero to maximum, however, the output is not constant, but rather a pulsed direct current. In short, the DC electrode did not cook, and does not cook as it should.
We'll have to add a block of capacitors. For this, there were 5 pieces of excellent electrolytes for 2200 microfarads 100 V. Connecting them with two copper strips in parallel, I got just such a battery.
We are conducting tests again - the DC electrode seems to have begun to cook, but a bad defect was discovered: at the moment the electrode touches, a microexplosion and sticking occurs - this is the capacitors being discharged. Obviously, you can't do without a throttle.
And then luck did not leave us with the teacher - in the supply room there was just an excellent DR-1C choke, wound with a 2x4 mm copper bus on W-iron and having a weight of 16 kg.
Quite another matter! Now there is almost no sticking and the DC electrode cooks smoothly and efficiently. And at the moment of contact, there is not a microexplosion, but rather a slight hiss. In short, everyone is happy - the teacher is an excellent welding machine, and I am getting rid of stuffing my head with an archimute object that has nothing to do with electronics :)
How to make a simple current regulator for a welding transformer
An important design feature of any welding machine is the ability to adjust the operating current. In industrial devices, different methods of current regulation are used: shunting with the help of various types of chokes, changing the magnetic flux due to the mobility of the windings or magnetic shunting, the use of active ballast resistance stores and rheostats. The disadvantages of such an adjustment include the complexity of the design, the bulkiness of the resistances, their strong heating during operation, and inconvenience when switching.
The most optimal option is to make it with taps even when winding the secondary winding and, by switching the number of turns, change the current. However, this method can be used to adjust the current, but not to adjust it over a wide range. In addition, adjusting the current in the secondary circuit of the welding transformer is associated with certain problems.
Thus, significant currents pass through the control device, which leads to its bulkiness, and for the secondary circuit it is almost impossible to select such powerful standard switches that they can withstand currents up to 200 A. Another thing is the primary winding circuit, where the currents are five times less.
After a long search through trial and error, the best solution to the problem was found - a well-known thyristor controller, the circuit of which is shown in Fig. 1.
With the utmost simplicity and availability of the element base, it is easy to manage, does not require settings and has proven itself in work - it works just like a “clock”.
Power control occurs when the primary winding of the welding transformer is periodically switched off for a fixed period of time at each half-cycle of current. In this case, the average value of the current decreases.
The main elements of the regulator (thyristors) are connected opposite and parallel to each other. They are alternately opened by current pulses generated by transistors VT1, VT2. When the regulator is connected to the network, both thyristors are closed, capacitors C1 and C2 begin to charge through the variable resistor R7. As soon as the voltage on one of the capacitors reaches the avalanche breakdown voltage of the transistor, the latter opens, and the discharge current of the capacitor connected to it flows through it.
Following the transistor, the corresponding thyristor opens, which connects the load to the network. After the beginning of the next, opposite in sign, half-cycle of the alternating current, the thyristor closes, and a new capacitor charging cycle begins, but in reverse polarity. Now the second transistor opens, and the second thyristor reconnects the load to the network.
By changing the resistance of the variable resistor R7, you can control the moment the thyristors are turned on from the beginning to the end of the half-cycle, which in turn leads to a change in the total current in the primary winding of the welding transformer T1. To increase or decrease the adjustment range, you can change the resistance of the variable resistor R7 up or down, respectively.
Transistors VT1, VT2, operating in avalanche mode, and resistors R5, R6 included in their base circuits, can be replaced with dinistors. The anodes of the dinistors should be connected to the extreme terminals of the resistor R7, and the cathodes should be connected to the resistors R3 and R4. If the regulator is assembled on dinistors, then it is better to use devices such as KN102A.
Variable resistor type SP-2, the rest type MLT. Capacitors of the MBM or MBT type for an operating voltage of at least 400 V.
A properly assembled regulator does not require adjustment. It is only necessary to make sure that the transistors are stable in the avalanche mode (or that the dinistors are turned on in a stable way).
Attention! The device has a galvanic connection to the network. All elements, including thyristor heat sinks, must be isolated from the case.
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Assembling homemade DC welding machines
- Welding machine: arc characteristic
- Dynamic response
- Possible details and calculations
- circuit diagram
- Welding scheme work:
- The design of the transformer and chokes
- Apparatus design
- Details and materials of the welding device:
- Assembly tools
To make homemade DC welders, you will need a high power power source that converts the nominal voltage of a conventional single-phase network and provides a constant amount (in amps) of the appropriate current to directly start and hold a normal arc.
Schemes of a home-made apparatus for welding on direct current.
The power supply of increased power is a circuit of the following components:
- rectifier;
- inverters;
- current and voltage transformer;
- current and voltage regulators that improve the quality characteristics of the electric arc (thyristors, triacs);
- auxiliary devices.
In fact, based on homemade schemes, the transformer was and remains the source of the electric arc, even if auxiliary units and circuits of various control units are not used.
Homemade apparatus: block diagram
Schematic diagram of the power supply unit of the welding machine.
The power supply is inserted into a suitable plastic or metal box. It is supplied with the necessary elements: connectors, various switches, terminals and regulators. The welding machine can be equipped with carrying handles and wheels.
Such a design of fairly good quality welding can be done independently. The main secret of such a device is a minimal understanding of the welding process, the choice of material, as well as skill and patience in the manufacture of this device.
But to assemble the device yourself, you must at least understand and study the basic skills, the moment of occurrence and burning of the electric arc, and the theory of electrode melting. Know the characteristics of welding transformers and their magnetic circuits.
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Homemade device: transformer
The basis of any welding device circuit is a normal voltage step-down (from 220 V to 45-80 V) transformer. It works in a special arc mode with maximum power. Such transformers are simply obliged to withstand very high currents with a nominal value of about 200 A. Their characteristics must be consistent, the I-V characteristic of the transformer must necessarily fully comply with special requirements, otherwise it cannot be used for arc welding mode.
Welding machines (their designs) vary greatly. The variety of home-made welding transformers is huge, because there are a lot of truly unique solutions in the designs. In addition, home-made transformers are very simple: they do not have additional devices designed to directly adjust the current of the structure that flows:
The design of a homemade semi-automatic welding machine.
- with the help of highly specialized regulators;
- by switching a certain number of coil turns.
The transformer mainly consists of the following elements:
- Metal magnetic circuit. It is carried out by a set of plates made of transformer steel.
- Windings: primary (network) and secondary (working). They come with outputs for adjustment (by switching) or for the device circuit.
When calculating the transformer for the required current, welding is carried out, as a rule, immediately from the working winding, without hanging circuits and various elements of limitation and adjustment. Primary winding must be performed with terminals, taps. They serve to increase or decrease the current (for example, to adjust the transformer at low mains voltage).
The main part of any transformer is its magnetic core. In the manufacture of home-made developments, magnetic circuits are used from decommissioned stators of electric motors, old television and power transformers. Therefore, there is a huge variety of various magnetic circuits developed by craftsmen for such devices.
Welding transformer based on the widespread LATR2 (a).
- dimensions of the magnetic circuit;
- windings - the number of turns;
- voltage level at the input-output;
- I p - current consumed;
- I max - maximum output current.
Additional characteristics are simply impossible to evaluate or measure at home, even with the help of instruments. But just they determine the suitability of the transformer of the apparatus for the formation of a high-quality seam when powered in manual welding mode.
This directly depends on how the transformer "holds the current" and is called the external CVC (VAC) of the power supply.
ВВХ - the dependence of the potentials (U) on the connectors and the welding current, which varies from the load properties of the transformer and from the electric arc.
For hand welding, only a steeply dipping characteristic is used, and in automatic machines, a gently dipping and rigid one is used.