An arc welding power source with a volt-ampere relationship yielding a large welding current change from a small arc voltage change. See also WELDING POWER SOURCE.
A constant voltage power source is capable of providing a range of variations in welding current while maintaining nearly constant voltage. Constant voltage (sometimes called constant potential power sources) have a relatively flat volt-ampere output curve. They have a lower open circuit voltage than machines with the drooping characteristic required for SMAW.
These characteristics are achieved by low impedance transformer design, in which the primary and secondary coil relationships have a very tight magnetic or inductive coupling.
With the development of solid-state devices which can handle high power, the constant voltage output is more easily and economically achieved electronically. This is particularly true of the inverter type power supplies.
Constant voltage welders were developed initially for submerged arc welding. However, their desirable characteristics were noted and quickly adapted for the gas metal arc welding (GMAW) process. The interaction of the drooper power supply and wire feed speed made it difficult to set proper welding conditions. With a constant voltage output, however, setting the welding conditions is far simpler, since the power supply determines the voltage and the wire feed speed determines the current. Additionally, the self-regulating feature provided by the constant voltage machines make it easier for welding operators to maintain a constant arc length with GMAW. These desirable “welder friendly” characteristics apply equally to SAW.