Do-it-yourself faults and methods for repairing inverter welding machines

Inverter welding machines are becoming increasingly popular among welders due to their compact size, low weight and reasonable prices. Like any other equipment, these devices can fail due to improper operation or due to design flaws. In some cases, you can repair inverter welding machines yourself by studying the design of the inverter, but there are breakdowns that can only be repaired in a service center.

Welding inverter device

Depending on the model, welding inverters operate both from a household electrical network (220 V) and from three-phase (380 V). The only thing that needs to be taken into account when connecting the device to a household network is its power consumption. If it exceeds the capabilities of the electrical wiring, then the unit will not operate if the network is drained.

So, the inverter welding machine includes the following main modules.

Primary rectifier unit. This block, consisting of a diode bridge, is located at the input of the entire electrical circuit of the device. It is this that is supplied with alternating voltage from the mains. To reduce the heating of the rectifier, a heat sink is attached to it. The latter is cooled by a fan (supply fan) installed inside the unit housing. The diode bridge also has overheating protection. It is implemented using a temperature sensor, which breaks the circuit when the diodes reach a temperature of 90°.
Capacitor filter. It is connected in parallel to the diode bridge to smooth out alternating current ripples and contains 2 capacitors. Each electrolyte has a voltage reserve of at least 400 V, and a capacity of 470 μF for each capacitor.
Filter for noise suppression. During current conversion processes, electromagnetic interference occurs in the inverter, which can disrupt the operation of other devices connected to this electrical network. To remove interference, a filter is installed in front of the rectifier.
Inverter. Responsible for converting AC voltage to DC. Converters operating in inverters can be of two types: push-pull half-bridge and full bridge. Below is a diagram of a half-bridge converter with 2 transistor switches, based on devices of the MOSFET or IGBT series, which can most often be seen on inverter devices of the middle price category.

The circuit of a full bridge converter is more complex and already includes 4 transistors. These types of converters are installed on the most powerful welding machines and, accordingly, on the most expensive ones.
Read also: Radiographic testing of welds and technology for its implementation
Just like diodes, transistors are installed on radiators for better heat removal from them. To protect the transistor unit from voltage surges, an RC filter is installed in front of it.
High frequency transformer. It is installed after the inverter and reduces the high-frequency voltage to 60-70 V. Thanks to the inclusion of a ferrite magnetic core in the design of this module, it is possible to reduce the weight and dimensions of the transformer, as well as reduce power losses and increase the efficiency of the equipment as a whole. For example, the weight of a transformer that has an iron magnetic core and is capable of providing a current of 160 A will be about 18 kg. But a transformer with a ferrite magnetic core with the same current characteristics will have a mass of about 0.3 kg.
Secondary output rectifier. It consists of a bridge that contains special diodes that respond to high-frequency current at high speed (opening, closing and recovery takes about 50 nanoseconds), which conventional diodes are not capable of. The bridge is equipped with radiators that prevent it from overheating. The rectifier also has protection against voltage surges, implemented in the form of an RC filter. At the output of the module there are two copper terminals, which ensure reliable connection of the power cable and ground cable to them.
Control board. All operations of the inverter are controlled by a microprocessor, which receives information and controls the operation of the device using various sensors located in almost all components of the unit. Thanks to microprocessor control, ideal current parameters are selected for welding various types of metals. Electronic control also allows you to save energy by supplying precisely calculated and dosed loads.
Soft start relay. To prevent the rectifier diodes from burning out from the high current of charged capacitors during startup of the inverter, a soft start relay is used.

Inverter machines - a new generation of manual welding

Since the beginning of 2000, inverter welding machines have become cheaper and more accessible. To carry out welding work at home, it is enough to have this small and easy-to-use device and good electrodes.

Advantages of inverters

Inverter machines are lightweight, compact in size, and their scope of use and welding quality are higher than those of heavy and bulky welding transformers. They carry out their task in full: they weld cars, gates, pipe structures (for example, greenhouses or gazebos). Working with them is mobile - throwing an extendable belt over your shoulder, welding is carried out in any hard-to-reach places.

When vertical, horizontal or overhead welding, the current is reduced by 10–20%, and when welding at an angle, it is increased by the same amount compared to the normal position.

There are also no problems with the connection; the welding machine operates from a regular electrical network. It's great that it won't stop when the mains voltage drops. If the deviation is within +/- 15%, the device will continue to operate normally. The current value can be adjusted by selecting the power depending on the type and thickness of the metal. All this makes inverters ideal for both beginners and professionals.

Video: testing a homemade inverter device

How welding inverters work

The inverter unit connects parts with direct current using electric arc welding with a coated electrode. The big plus is that at the very beginning of the process there are no power surges in the network to which the device is connected. The storage capacitor ensures uninterrupted electrical circuit and soft ignition of the arc with its further automatic maintenance. When connected to an electrical outlet, the alternating mains voltage with a frequency of 50 Hz is converted first into direct voltage and then into high-frequency modulated voltage. Then, using a high-frequency transformer, the current increases, the voltage decreases, and the output current is rectified. The device provides adjustment of the welding current value and protection against overheating.

The inverter device first rectifies and modulates the input current, and then increases its strength by reducing the voltage until the arc appears

The basic operating mode of inverter welding machines is MMA. This is manual arc welding with piece coating electrodes. For welding steel and cast iron products using direct or alternating current, a diameter of 1.6–5.0 mm is used.

The devices differ in power and operating cycle duration . The second indicator is the period during which it is allowed to cook at the maximum permissible power in order to prevent the device from overheating. It is designated by the letters PV (on period) and is determined as a percentage relative to a time unit of 10 minutes. For example, if the device indicates a PV of 60%, this means that it can be cooked for 6 minutes and then turned off for 4 minutes. Sometimes the welding cycle is set to 5 minutes. Then a PT value of 60% means a work period of 3 and a rest period of 2 minutes. PV and duty cycle indicators are indicated in the instructions for each device.

How does an inverter work?

Below is a diagram that clearly shows the principle of operation of a welding inverter.

So, the operating principle of this welding machine module is as follows. The primary rectifier of the inverter receives voltage from the household electrical network or from generators, gasoline or diesel. The incoming current is alternating, but when passing through the diode block it becomes constant. The rectified current is supplied to the inverter, where it is converted back into alternating current, but with changed frequency characteristics, that is, it becomes high-frequency. Next, the high-frequency voltage is lowered by a transformer to 60-70 V with a simultaneous increase in current. At the next stage, the current again enters the rectifier, where it is converted into direct current, after which it is supplied to the output terminals of the unit. All current conversions are controlled by a microprocessor control unit.

Causes of inverter failures

Modern inverters, especially those made on the basis of an IGBT module, are quite demanding in terms of operating rules. This is explained by the fact that when the unit operates, its internal modules generate a lot of heat. Although radiators and a fan are used to remove heat from power components and electronic boards, these measures are sometimes not enough, especially in inexpensive units. Therefore, you need to strictly follow the rules that are indicated in the instructions for the device, which imply periodically turning off the unit to cool down.

This rule is usually called “On Duration” (DS), which is measured as a percentage. Without observing the PV, the main components of the device overheat and fail. If this happens to a new unit, then this breakdown is not subject to warranty repair.

Also, if an inverter welding machine operates in dusty rooms, dust settles on its radiators and interferes with normal heat transfer, which inevitably leads to overheating and breakdown of electrical components. If the presence of dust in the air cannot be eliminated, it is necessary to open the inverter housing more often and clean all components of the device from accumulated contaminants.

But most often inverters fail when they operate at low temperatures. Breakdowns occur due to the appearance of condensation on the heated control board, resulting in a short circuit between the parts of this electronic module.

Repair features

A distinctive feature of inverters is the presence of an electronic control board, so only a qualified specialist can diagnose and repair faults in this unit . In addition, diode bridges, transistor units, transformers and other parts of the electrical circuit of the device may fail. To carry out diagnostics yourself, you need to have certain knowledge and skills in working with measuring instruments such as an oscilloscope and a multimeter.

From the above, it becomes clear that, without the necessary skills and knowledge, it is not recommended to start repairing the device, especially electronics. Otherwise, it can be completely damaged, and repairing the welding inverter will cost half the cost of a new unit.

Advantages of Welding Zone

Mandatory free installation diagnostics to identify problems.
Communicating diagnostic results to clients immediately after testing.
Use of original components - all new parts will be compatible with those already installed.
Mandatory testing. Any Foxweld repair ends with checking the functionality of the equipment, and only then the equipment is sent back.

If you need urgent repair of welding equipment in Moscow, please contact us by phone.

Main malfunctions of the unit and their diagnostics

As already mentioned, inverters fail due to the impact of external factors on the “vital” units of the device. Also, malfunctions of the welding inverter can occur due to improper operation of the equipment or errors in its settings. The most common malfunctions or interruptions in the operation of inverters are:

The device does not turn on

Very often this breakdown is caused by a faulty network cable of the device. Therefore, you first need to remove the casing from the unit and ring each cable wire with a tester. But if everything is in order with the cable, then more serious diagnostics of the inverter will be required. Perhaps the problem lies in the standby power supply of the device. The method of repairing the “duty room” using the example of a Resanta brand inverter is shown in this video.

Welding arc instability or metal spattering

This malfunction may be caused by incorrect current setting for a certain electrode diameter.

Advice! If there are no recommended current values on the packaging for the electrodes, then it can be calculated using the following formula: for each millimeter of equipment there should be a welding current in the range of 20-40 A.

Welding speed should also be taken into account. The smaller it is, the lower the current value must be set on the control panel of the unit. In addition, to ensure that the current strength corresponds to the diameter of the additive, you can use the table below.

Welding current is not adjustable

If the welding current is not regulated, the cause may be a breakdown of the regulator or a violation of the contacts of the wires connected to it. It is necessary to remove the unit casing and check the reliability of the conductor connections, and, if necessary, test the regulator with a multimeter. If everything is in order with it, then this breakdown can be caused by a short circuit in the inductor or a malfunction of the secondary transformer, which will need to be checked with a multimeter. If a malfunction is detected in these modules, they must be replaced or rewound by a specialist.

High power consumption

Excessive power consumption, even if the device is without load, most often causes an interturn short circuit in one of the transformers. In this case, you will not be able to repair them yourself. You need to take the transformer to a mechanic to rewind it.

The electrode sticks to the metal

This happens if the network voltage drops. To get rid of the electrode sticking to the parts being welded, you will need to correctly select and configure the welding mode (according to the instructions for the device). Also, the voltage in the network may sags if the device is connected to an extension cord with a small wire cross-section (less than 2.5 mm2).

Often, a drop in voltage causing electrode sticking occurs when using a power extension cord that is too long. In this case, the problem is solved by connecting the inverter to the generator.

Overheat light on

If the indicator is on, this indicates overheating of the main modules of the unit. The device may also turn off spontaneously, which indicates that the thermal protection has tripped. To prevent these interruptions in the operation of the unit from occurring in the future, it is again necessary to adhere to the correct duty cycle (ST). For example, if duty cycle = 70%, then the device should operate in the following mode: after 7 minutes of operation, the unit will be given 3 minutes to cool down.

In fact, there can be quite a lot of different breakdowns and the reasons that cause them, and it’s difficult to list them all. Therefore, it is better to immediately understand what algorithm is used to diagnose a welding inverter in search of faults. You can learn how to diagnose the device by watching the following training video.

Repair Svarog TIG 200 P AC/DC

Diagnostics:

The first thing that needed to be done was to connect the device and check it for welding.
As described above, the welder welded flawlessly on direct current and gas was supplied. the current was regulated.

But when switching on to alternating current, we found problems:

A black spot formed on the surface of the metal, which in no way wanted to heat the metal and create a weld pool.

And why this happens - now we’ll figure it out

Let's figure out what should happen during welding in order to weld aluminum correctly.

Aluminum

is a metal more difficult to heat treat than iron. The main reason for this is the instantaneous formation of a thin oxide film on its surface upon contact with oxygen. This film has a melting point several times higher than pure aluminum. During the welding process, argon prevents the oxidation of aluminum, displacing oxygen. The filler wire, which is made from aluminum, melts under the influence of an arc and forms a weld.

When welding aluminum, it is alternating current that has won the love and respect of specialists. In order to understand why this happens, you need to delve a little into the technical details.

When connected

direct current of reverse polarity, cathodic cleaning of the oxide film occurs, but the welding temperature increases significantly. As a result, even such a refractory metal as tungsten, from which the electrode is made, begins to gradually deteriorate. If you connect direct current of direct polarity, it cannot penetrate the oxide film, but provides a more stable arc.

It is the polarity switching

current ensures a high-quality result of your work. This means that the choice is obvious - you need to use alternating current.

Welding aluminum permanently

current is used much less frequently.
This method is much more difficult
, and you also need to use pure helium instead of argon, which costs several times
more
.

So look at the pictures:

Now it becomes clear why the aluminum could not warm up correctly and form a weld pool during the welding process.

It is because of the oxide film

, which could not melt.

Let's start disassembling the welding inverter and check the readings on an oscilloscope when welding with alternating current.

And as we already know from theory, we need two half-cycles, positive and negative.

AC voltage welding inverter design:

The last block diagram shows the same AC voltage module and the control driver of this module

.
There we will look for our malfunction. We check power transistors
for malfunctions with a simple
tester
; very often the transistors overheat because of this, a so-called breakdown occurs, which the tester can show.
But in this device, all the power parts are working properly
.
Then we’ll connect the oscilloscope
directly to the control driver of the AC power module and check the signals.
As it turned out, there was no signal on one of the driver channels. The control board is faulty
.

Why was the control board damaged, you ask?

You can find many reasons for failure:

— Possibly a poor-quality installed electronic component (tired of working)

— It is likely that there is high-frequency ignition

, which somehow affects electronics.

— But in this inverter TIG welding

most likely this was due to the huge amount of
metal dust and shavings
that covered all the electronics in a thick layer.

SO CLEAN AND BLOW OUT YOUR WELDING EQUIPMENT SOMETIMES!!!!!

Well, if you can’t cope, bring it to us and we will be happy to help you with this difficult task))))))