Electronic welding current regulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

 Comments on the article

The author of the proposed article shares his experience in creating an electronic welding current controller (ERST) for multi-station electric welding. Firms specializing in the field of welding equipment today produce several models of ERST. But their cost is such that sometimes calls into question the economic efficiency of the use of these devices. For example, Lincoln Electric's ERST Multi-Weld 350 costs over $3000. The proposed device is much cheaper than analogues, and due to its close to 100% efficiency, even with one-shift operation, it will pay off within a year only due to energy savings. The possibility provided in it to select the optimal load characteristic for the work performed ensures the best quality of the weld, practically eliminates metal spatter. With a step-down transformer and a rectifier of sufficient power, ERST can also become the basis of a welding machine for a home workshop.

At those industrial enterprises where electric welding occupies one of the main places in the technological cycle (for example, at shipbuilding and ship repair plants), multi-station welding is traditionally used. Several welding jobs (posts) are fed from one powerful source of direct or alternating current with a voltage of 50 ... load characteristics and regulation of welding current. The advantages of such an organization of welding work are simplicity, safety, and savings in production space and equipment. Unfortunately, the overall efficiency of the system does not exceed 80...30%, because rheostats dissipate a significant part of the energy in the form of heat.

The achievements of modern electronics make it possible to manufacture an ERST - a functional analogue of a ballast rheostat with improved performance and an efficiency close to 100%. This not only saves energy, but also allows you to connect much more welding stations to one power source without exceeding its load capacity.

The conventional welding transformer is designed only for certain types of welding (manual, semi-automatic, automatic, consumable electrode, non-consumable electrode). Until recently, the creation of a universal source was hindered by the fact that its external characteristic was determined mainly by the design of the transformer. To obtain a rigid load characteristic, the transformer windings are made cylindrical, and the falling one is disk. Some flexibility could be achieved by using magnetic amplifiers and transformers of a special design (with a magnetic shunt), but this had to be paid for by a significant increase in the mass and dimensions of the sources. In an electronic welding source, the load characteristic of any required type is formed not parametrically, but due to feedback on the voltage and current of the load.

The efficiency of the proposed ERST is at least 92%. It operates at a primary source voltage of 50...80 V and allows continuous welding with a current of 10...315 A. A short-term increase in welding current up to 350 A is allowed. Operational adjustment of the slope of the load characteristic from steeply falling to hard is provided. This makes ERST suitable for both manual and semi-automatic welding. The device is equipped with protection against reverse polarity of the supply voltage, its excessive increase and decrease, overcurrent and overheating, which guarantees reliable operation in industrial conditions.

The operation of the ERST is based on the conversion of a constant input voltage into a pulse of adjustable duty cycle with the help of a semiconductor interrupter, followed by filtering - the selection of the constant component of the pulses. Due to the fact that the field-effect transistors of the interrupter have a very small resistance in the open state, and a very large resistance in the closed state, the power dissipated by them is relatively small.

The ERST scheme is shown in fig. 1. Terminal X1 is connected to the positive of the primary source. Its minus and the HZ clamp are connected to the part to be welded, which plays the role of a common wire. The welding electrode holder is connected to terminal X2.

(click to enlarge)

Capacitors C1, C2 and C3-C22 eliminate the influence of the output impedance of the source and the inductance of the connecting wires on the operation of the ERST. Immediately after applying voltage to the ERST, these capacitors begin to charge through the limiting resistor R2 and the diode located in the charging and supply voltage control unit (A2). When the capacitors are fully charged and provided that the voltage between the X1 and XZ terminals is normal (50 ... 80 V), the HL1 "Ready" LED lights up, and inside the A2 block the relay is activated, closing the contacts that supply voltage to the ERST switching circuit.

To turn it on, just press the SB1 "Start" button. A triggered KM1 contactor will bypass the button with KM 1.1 contacts. Through the closed power contacts KM1.2, the source voltage will be supplied to the capacitors C1 - C22, bypassing the charging circuit. Thanks to the resistor P1, the KM1 contactor will remain triggered (and the ERST on) until the SB2 "Stop" button is pressed. If the input voltage goes beyond the permissible limits during the operation of the ERST, it will be turned off by the open contacts of the relay of block A2.

In the included ERST, the power supply unit A1 will work. It serves to obtain galvanically isolated voltages required to power the A3 and A4 units. In addition, block A1 generates a three-phase voltage of 220 V 50 Hz for M1 and M2 fans blowing heat sinks of powerful semiconductor devices.

The main functional unit of the ERST - a step-down voltage converter - consists of a switching transistor (a battery of field-effect transistors VT1-VT20), a discharge diode (VD9-VD48 connected in parallel) and a smoothing filter (choke L1, capacitor banks C27-C36). Those who wish to understand the operation of the converter in more detail can be recommended to use the literature [1, 2].

Insulated gate field effect transistors have a positive temperature coefficient of open channel resistance. This circumstance favors a uniform distribution of the current load between the transistors, allowing them to be connected in parallel. Resistors R3-P.22 suppress parasitic oscillations of the control voltage.

The diodes KD213B, which form the discharge diode of the converter, are characterized by a rather long recovery time of the reverse resistance. Sometimes by the time the switch is opened, they do not have time to close completely. To avoid undesirable consequences, transistors and diodes are separated by winding I of transformer T1, the inductance of which (1,7 μH) limits the rate of rise of the "through" current, preventing it from reaching a dangerous value. After the discharge diode is completely closed, the energy accumulated in the magnetic field of the transformer will return to the power source - the pulse induced in the transformer winding II will recharge the capacitors C1 and C2 through the VD8 diode. And with a sharp load shedding, the ERST battery of VD49-VD54 diodes will provide recovery (return to the source) of the energy accumulated in the magnetic field of the inductor L1.

Block A4 measures the output current and voltage of the ERST and generates control pulses, changing their duty cycle in such a way as to provide the form of the load characteristic of the ERST specified by the controls "Slope" and "Level". These pulses through block A3, which amplifies them in power, are fed to the gate of the switching transistor (VT1-VT20). In addition, block A3 contains protection units that prohibit the opening of the switching transistor until the end of the regeneration cycle of transformer T1 and in case of overheating. It is signaled by the HL2 LED.

Capacitors C1 and C2 are oxide K50-18, the rest are film K73-17. Resistors R1, R2 - PEV-25, R3-R32 - MLT indicated in the power diagram. Resistor R33 is a unified external shunt 75SHISV-500 to a 500 A ammeter. Shunts of other types, rated for the specified current, with a voltage drop at a rated current of 75 mV, are also suitable. Powerful shunt leads equipped with large diameter bolts are included in the welding current flow circuit. The wires of all other circuits are connected to the test leads with smaller diameter bolts.

Transistors VT1-VT20 and diodes VD9-VD48 are installed on two heat sinks, the active surface area of ​​each of which is 3400 cm2. Fans M1 and M2 - 1,25EV-2,8-6-3270U4 with a total capacity of 560 m3/h blow heat sinks. In the air flow created by the fans, there are also resistors R23-R32, which dissipate significant power.

The KM1 contactor is taken from the KEMPPI LHF-500 oscillator. Its winding is rewound to a voltage of 50 V (the original one is rated for 24 V). You can use another contactor (for example, from those used in electric cars) that can switch a direct current of at least 200 A. In extreme cases, a unified electromagnetic starter of the fourth or fifth magnitude is suitable, all groups of power contacts of which are connected in parallel.

Having selected a contactor, it is necessary to measure the DC voltage Uc at which it operates. If it is significantly below 50 V or more than this value, the contactor winding will have to be rewound. Removing the existing winding, count the number of its turns w, and measure the wire diameter d. New values ​​are calculated by the formulas:

Transformer T1 is wound on a U-shaped magnetic core made of M2000NM ferrite from a line transformer TVS110AM (TVS110LA) of a tube TV series UNT47 / 59. Non-magnetic spacers 3 mm thick are inserted into each of the joints of the magnetic circuit. Primary winding - two turns of a bundle of 236 enameled wires with a diameter of 0,55 mm. Secondary winding - 16 turns of a bundle of ten of the same wires. To ensure maximum connection between the windings, the secondary is placed in the volume of the primary. To prevent inter-turn or inter-winding short circuits, the secondary winding wire harness must be protected before winding with varnished cloth tape or fluoroplastic film.

The magnetic circuit of the inductor L1 - Sh32x80 is made of sheet transformer steel with a thickness of 0,35 mm. The winding of the throttle is eight turns of a bundle of 330 enameled wires with a diameter of 0,55 mm. The magnetic core is assembled end-to-end. A non-magnetic gasket 1,6 ... 1,7 mm thick is inserted into its gap.

BLOCK A1

The block diagram of the ERST power supply is shown in fig. 2. The unstabilized input voltage through the protection unit is supplied to a linear stabilizer that supplies 15 V to all low-power units of the block, and to a switching regulator, the output of which is a 36 V DC voltage that the half-bridge inverter converts into an alternating frequency of approximately 12,5 kHz. The protection node mentioned above will shut down the unit if, as a result of a malfunction or failure, the output voltage of the switching regulator exceeds the permissible value.

The supply of a half-bridge inverter with a stabilized voltage provides group voltage stabilization on the secondary windings of the transformer T1. Rectifiers 1 and 2 isolated from the common ERST wire and from each other feed blocks A4 and A3. The three-phase inverter converts the DC voltage 270 V from the output of the rectifier 3 into AC three-phase 220 V, 50 Hz to power the fans blowing the heat sinks of powerful semiconductor devices ERST.

The node used in [3] served as a prototype of a powerful stage of a switching voltage stabilizer. Its simplified diagram is shown in Fig. 3. Control pulses of positive polarity are fed to the base of the transistor VT2. In the pauses between them, this transistor is closed and the voltage of the capacitor C1, charged during the pulse preceding the pause, is applied in the opening polarity to the gate-source section of the transistor VT3 through the resistor R2. Transistor VT1 is open, and the rising current flowing through its channel and inductor L1 charges the capacitor eC3. The energy accumulated by capacitor C2 is partially spent on charging the gate-source capacitance of transistor VT1. Diode VD1 is needed to prevent the discharge of capacitor C2 through transistor VT1.

The transistor VT2, open with a control pulse, connects the gate of the transistor VT1 to a common wire. The latter closes, and the current of the inductor L1, decreasing, continues to flow through the opened diode VD2. The voltage at the source of the transistor VT1 and on the right (according to the diagram) plate of the capacitor C2 in this state is equal to the direct voltage drop across the VD2 diode, which is negative relative to the common wire. The capacitor C1 is charged along the VD2R2 circuit.

There are many microcircuits for controlling field and bipolar transistors of single-ended and push-pull inverters. But usually their output signals are "tied" to the potential of the common wire, which makes it problematic to use such microcircuits in bridge and half-bridge inverters. The fact is that the control electrodes of the "upper" transistors of the output stages of such inverters are under a large and, as a rule, alternating voltage relative to the common wire.

Chips-drivers of bridge and half-bridge inverters [4] due to the high cost have not yet become widespread among radio amateurs. They prefer to solve this problem in their own way, using, as a rule, optical or transformer isolation of control circuits [5, 6].

However, such a decoupling is by no means necessary. A possible scheme of a half-bridge inverter with control circuits without it is shown in fig. 4. Opposite-phase pulse sequences Uy1 and Uy2 come from the SHI controller.

The main disadvantage of the node assembled according to this scheme is that it is operational only when the supply voltage Up1 does not exceed the maximum allowable voltage between the gate and the source of the field-effect transistor VT3. The fact is that as a result of the reaction of an active-inductive or active-capacitive load, the voltage at the source of the transistor VT3 can lag behind or lead the control gate in phase, which leads to the appearance of short-term negative gate-source voltage pulses, the amplitude of which reaches the supply voltage Up1.

On fig. 5 shows additional elements that correct the noted drawback. Diode VD2, opening with a negative voltage polarity between the gate and source of the transistor VT3, limits it to a very low level, equal to the direct voltage drop across the open diode. Excess voltage extinguishes the resistor R8.

Capacitor C1 in this case is charged through the diode VD1 directly from the power source. Resistor R4 (see Fig. 4), which usedlessly dissipated quite a lot of power, was excluded from the new version of the node.

Literature

1. Nyvelt G. et al. REA power supply sources. Directory. - M.: Radio and communication, 1986, p. 306-328.
2. Semenov B. Power electronics for amateurs and professionals. Moscow: Solon-R, 2001, pp. 126-140.
3. Count R. Electronic circuits. 1300 examples. - M.: Mir, 1989, p. 424.
4. International Rectifier's Shortform Catalogue, 50th Anniversary Edition. March 1997, p. 136-139.
5. Dubrovsky A. Regulator of rotation frequency of three-phase asynchronous motors. - Radio, 2001, No. 4, p. 42, 43.
6. Fields I. Converter for powering household equipment. - Radio, 2003, No. 1, p. 29-32.

Author: V.Volodin, Odessa, Ukraine

See other articles Section welding equipment.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

The threat of space debris to the Earth's magnetic field 01.05.2024

More and more often we hear about an increase in the amount of space debris surrounding our planet. However, it is not only active satellites and spacecraft that contribute to this problem, but also debris from old missions. The growing number of satellites launched by companies like SpaceX creates not only opportunities for the development of the Internet, but also serious threats to space security. Experts are now turning their attention to the potential implications for the Earth's magnetic field. Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics emphasizes that companies are rapidly deploying satellite constellations, and the number of satellites could grow to 100 in the next decade. The rapid development of these cosmic armadas of satellites can lead to contamination of the Earth's plasma environment with dangerous debris and a threat to the stability of the magnetosphere. Metal debris from used rockets can disrupt the ionosphere and magnetosphere. Both of these systems play a key role in protecting the atmosphere and maintaining ... >>

Solidification of bulk substances 30.04.2024

There are quite a few mysteries in the world of science, and one of them is the strange behavior of bulk materials. They may behave like a solid but suddenly turn into a flowing liquid. This phenomenon has attracted the attention of many researchers, and we may finally be getting closer to solving this mystery. Imagine sand in an hourglass. It usually flows freely, but in some cases its particles begin to get stuck, turning from a liquid to a solid. This transition has important implications for many areas, from drug production to construction. Researchers from the USA have attempted to describe this phenomenon and come closer to understanding it. In the study, the scientists conducted simulations in the laboratory using data from bags of polystyrene beads. They found that the vibrations within these sets had specific frequencies, meaning that only certain types of vibrations could travel through the material. Received ... >>

Random news from the Archive Logitech Reach webcam on articulating arm 15.09.2023 Logitech has unveiled an innovative webcam called Reach, featuring an articulating arm that allows you to precisely adjust the camera's position and move it smoothly during video conferencing. The manufacturer claims that Reach will significantly improve the interactivity of online meetings and will become an indispensable tool for education and streaming. Reach will be available in two versions: a standard version for placement on a desktop and a clamp-style version that allows you to attach the camera to the edge of a table. Both versions come with a flexible tripod arm, which is similar to those used for microphones and other cameras. This hand ensures smooth movement of the camera vertically and horizontally, and also allows you to rotate the camera itself. The main features of Reach are its smoothness and stability, which makes it unique among similar devices. Manufacturers claim that such devices typically do not allow the user to quickly and accurately adjust the desired camera position, but Reach will change this practice. The Reach webcam itself is a Logitech StreamCam model released in 2020, capable of recording 1080p video at 60 frames per second. It is equipped with autofocus and supports 4,3x zoom. If the camera fails, you can replace it with a new StreamCam rather than purchasing a complete kit with bracket. Logitech Reach will initially be available on the Indiegogo Enterprise crowdfunding platform. According to The Verge, the company has not yet decided on the design-to-price ratio, which could range from $299 to $399 (excluding discounts for crowdfunding participants).

Other interesting news:

▪ Suction cup holder for transferring grafts and biosensors

▪ Antiseptic from water

▪ Smartphones HTC Desire HD and Z

▪ Benefits of children's music lessons

▪ carbene record

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Digital technology. Article selection

▪ article by Michel Paul Foucault. Famous aphorisms

▪ article Where and when were video record players sold? Detailed answer

▪ article Auxiliary worker of the energy-mechanical shop. Standard instruction on labor protection

▪ article Refinement of the speed controller for three-phase asynchronous motors. Encyclopedia of radio electronics and electrical engineering

▪ article The mysterious disappearance of an egg in a bag. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024