Welding power source
A welding power source is used to generate the high electrical current required for arc welding . The simplest welding power source is a welding transformer in the form of a short-circuit-proof leakage field transformer which supplies alternating current . In the case of welding power sources that supply direct current , this transformer is also supplemented with a rectifier .
Electronic welding power sources - special forms of inverters , which are also referred to as "welding inverters" - do not require a stray field transformer, but use electronic processes similar to a switched-mode power supply .
In the welding transformer, the alternating current of the network with high voltage and low amperage is converted into an alternating current with low voltage and high amperage, as it is required for welding .
The maximum welding current is preselected by taps on the primary coil of the mains transformer . In many cases, a movable yoke is also used between the secondary and the primary coil, whereby the welding current can be adjusted by the magnetic shunt.
Welding transformers are stray field transformers . Its current / voltage characteristic is gently falling and at zero voltage (short circuit), slightly more flows than the set welding current. The open circuit voltage is around 50 volts, so there is no risk of electric shock.
Small welding transformers for 2 to 4 kW or a welding current of 50 to 125 amps already weigh over 30 kg. With the advent of inverter welding machines, these heavy machines have disappeared from the market.
It also consists of a mains transformer with current limitation and a downstream rectifier . The rectifier converts the alternating current into direct current. This is the only way to use three-phase current for welding. In addition, in many cases direct current is better suited for welding than mains alternating current. The supply from the three-phase network means that significantly higher outputs can be achieved than with single-phase operation. The residual ripple is lower (4% compared to almost 50% for alternating current).
A downstream smoothing throttle serves to reduce the residual ripple and decisively determines the welding properties , e.g. B. the ignition of the arc and the formation of spatter. It maintains the current for a short time even when the arc voltage is higher than that of the welding power source.
Welding converters consist of an electric motor, usually operated with three-phase alternating current, which drives a controllable direct current generator via a shaft. These devices were mainly built at a time when powerful electronics were not yet available. Converters are characterized by a low level of ripple, but their mechanical components make them more susceptible to failure and more maintenance-intensive than welding rectifiers. With the advent of power electronics, these devices disappeared from the market. However, they stayed in the upper power or current class for some time or - fed from the overhead line - in the maintenance of tram networks. The rotating components make these devices louder than modern welding rectifiers.
In addition to pure converters, there are combination devices in which the generator is optionally driven by an electric motor or a combustion engine. They are designed for use on construction sites and can be operated with a combustion engine if the power supply is insufficient. However, they are louder than in electrical operation.
Devices in which the generator is operated exclusively by a combustion engine are, however, also colloquially referred to as converters .
Internal combustion engine powered welding power sources
Combustion engine-powered welding machines are available for use on construction sites where there is no or hardly an adequate power connection. With them, an internal combustion engine drives a generator, with large devices almost always a diesel. A direct current generator is almost always used, which is suitable for manual electrode welding due to its falling characteristic. The internal combustion engine makes the devices very loud.
In addition, there are power generators on the market which, in addition to the usual mains voltage of 230/400 V, also have a connection with a lower voltage and adjustable current for welding.
The welding inverter is an electronic welding power source. Inverter welding machines are built for all arc welding processes such as electrode , MIG / MAG , plasma and tungsten inert gas welding . The devices are connected to the mains with one or three phases, depending on their performance. The basic principle of an inverter corresponds to a switched-mode power supply . The mains voltage is first rectified, chopped up with the help of power semiconductors with a frequency between 20 kHz and 150 kHz and transformed to a lower voltage via a relatively small transformer. The welding current must then be rectified using suitable diodes. The size of transformers of the same power is approximately inversely proportional to their operating frequency, i. H. the higher the frequency, the smaller and lighter the transformer and the entire welding machine can be built. The efficiency of inverter welding machines is better than that of other welding power sources. Due to the higher working frequency, highly dynamic welding processes can be controlled much better. Various comfort functions can also be implemented:
- Shortly before the short circuit, the system delivers the set maximum current, which prevents the electrode from sticking / welding on and annealing.
- Arc force control
- Electronic control of the arc , which automatically increases the set current value when the arc becomes shorter. The arc power is kept almost constant.
- Hot start
- Prevents the stick electrode from sticking by briefly increasing the set welding current and warms up the start of the weld seam more quickly.