welding power supply

A welding power supply is an electrical device that provides an electrical current to perform welding procedures which require electricity. Typically welding requires high current, over 80 amps, and can go 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 manualy. 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 watts 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 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. Modern transformer machines may be of the inverter type which converts the utility power into high frequency AC then internally use a much smaller and more efficient transformer. Inverter machines have high output, low weight, and small size.

Generator and alternator

Welding machines may also use generators or alternators to convert mechanical engery into electrical energy. Modern machines of this type are usually driven by an internal combustion engine but older designs, before the advent of inexpensive solid state technology, may use an electric motor to drive the alternator or generator. In this configuration the utility power is converted first into mechanical engergy then back into electrical energy to achieve the step-down effect similiar to a transformer.