Power source

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A welding power source, sometimes referred to as a welding machine or a welder, is a piece of equipment that supplies current and voltage for welding, thermal cutting or thermal spraying.^[1]

Classifications

Two of the most common classifications of welding power sources are constant current and constant voltage.

Constant Current

Constant current power supplies have limited maximum short-circuit currents. They are sometimes referred to as “droopers” due to their negative volt-amp curves. Though different arc lengths may change the voltage in these machines, the amperage (current) will only vary slightly. This is why they are referred to as constant current.^[2]

Constant Voltage

Constant voltage power sources maintain relatively consistent voltages regardless of amperage. This results in a fairly flat volt-amp curve (as opposed to the drooping volt-amp curve of a constant current machine).² The direction of current is another important characteristic of power sources—they may be alternating current (AC) or direct current (DC).

Alternating Current (AC)

Alternating electrical currents reverse direction at regular intervals (e.g., 60 cycles alternating current (AC), or 60 hertz (Hz)).^[3]

Direct Current (DC)

Direct electrical currents do not change direction like alternating currents—their flows remain constant in one direction. DC power sources are available in two varieties.

Direct current electrode negative (DCEN) refers to the direction of current flow through a circuit when an electrode lead is connected to the negative terminal and the work lead is connected to the positive terminal of a DC welding machine.
Direct current electrode positive (DCEP) refers to the direction of current flow through a circuit when the electrode lead is connected to the positive terminal and the work lead is connected to the negative terminal of a DC welding machine. ³