Welding power supply
1546777
220003283
2008-06-17T20:55:06Z
Zedla
1669622
rm non-specific ext link
[[Image:Welding power supply-Miller-Syncrowave350LX-front-triddle.jpg|thumb|right|A high output constant current welding power supply for use with [[GTAW]] and [[Shielded metal arc welding|SMAW]]]]
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.
==Classification==
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.
==Machine construction==
Most welding machines are of the following designs:
===Transformer===
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 [[Ampere|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.
===Generator and alternator===
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.
===Inverter===
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 switching frequency is very high - typically 10,000 Hz or higher. The high frequency inverter-based welding machines can be more efficient and have better control than non-inverter welding machines.
The IGBTs in an inverter based machine are controlled 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.
==References==
*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 )
[[Category:Arc welding]]
[[Category:Power supplies]]
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