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A welding power supply is a device that provides an electrical current to perform welding. Welding usually requires high current (over 80 amps) and it can need above 12,000 amps in spot welding. Low current can also be used; welding two razor blades together at 5 amps with gas tungsten arc welding is a good example. A welding power supply can be as simple as a car battery and as sophisticated as a modern machine based on silicon controlled rectifier technology with additional logic to assist in the welding process.

Contents 1 Classification 2 Machine construction 2.1 Transformer 2.2 Generator and alternator 2.3 Inverter 3 References

Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine will vary its output voltage to maintain a steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible with a voltage sensing wire feeder.

The nature of the CV machine is required by gas metal arc welding and flux-cored arc welding because the welder is not able to control the arc length manually. If a welder attempted to use a CV machine to weld with shielded metal arc welding the small fluctuations in the arc distance would cause wide fluctuations in the machine's output. With a CC machine the welder can count on a fixed number of amps reaching the material to be welded regardless of the arc distance but too much distance will cause poor welding.

Most welding machines are of the following designs:

A transformer style welding machine converts the high voltage and low current electricity from the utility into a high current and low voltage, typically between 17 to 45 volts and 190 to 590 amps. This type of machine typically allows the welder to select the output current by either moving the core of the transformer in and out of the magnetic field or by allowing the welder to select from a set of taps on the transformer. These machines are typically the least expensive to purchase for hobbyist use.

Welding machines may also use generators or alternators to convert mechanical energy into electrical energy. Modern machines of this type are usually driven by an internal combustion engine but some older machines may also use an electric motor to drive the alternator or generator. In this configuration the utility power is converted first into mechanical energy then back into electrical energy to achieve the step-down effect similar to a transformer. Because the output of the generator can be direct current, these older machines can produce DC from AC without any need for rectifiers of any type.

Since the advent of high-power semiconductors such as the IGBT, it is now possible to build a switching power supply capable of coping with the high loads of arc welding. These are known as inverter welding units. These supplies generally convert utility power to high voltage and store this energy in a capacitor bank; a microprocessor controller then switches this energy into a second transformer as needed to produce the desired welding current. The frequency of switching is very high- typically at least 10,000 Hz and often much higher. Because of this high frequency, inverter-based welding machines can be much more efficient than transformer-based machines.

The actual IGBTs in an inverter based machine are controlled entirely in software, by a microcontroller, so the electrical characteristics of the welding power can be changed by software in real time updates. Typically the controller software will implement features such as pulsing the welding current, variable ratios and current densities through a welding cycle, variable frequencies, and automatic spot-welding; all of which would be prohibitively expensive in a transformer-based machine but require only program space in software-controlled inverter machine.

Metalworking
Welding
Arc welding: Shielded metal (MMA) | Gas metal (MIG) | Flux-cored | Submerged | Gas tungsten (TIG) | Plasma
Other processes: Oxyfuel | Resistance | Spot | Forge | Ultrasonic | Electron beam | Laser beam
Equipment: Power supply | Electrode | Filler metal | Shielding gas | Robot | Helmet
Related: Heat-affected zone | Weldability | Residual stress | Arc eye | Underwater welding
See also: Brazing | Soldering | Metalworking | Fabrication | Casting | Machining | Metallurgy | Jewelry

• http://www.millerwelds.com/education/articles/articles31.html - Miller Electric news release on IGBT technology for welding inverters 8 April 2003

• http://www.lincolnelectric.com/knowledge/articles/content/inverter.asp -Inverter Based Welding Power Supplies for Welding Aluminum By Frank G. Armao, The Lincoln Electric Company ( Lincoln Electric tutorial on inverter-based welding machines )