Welding Position:

Direct current is rather better than AC for vertical and overhead welds because lower amperage might be used. With appropriate electrodes, however, satisfactory welds might be made in all positions with AC.

Metal Thickness

Sheet metal and heavy sections both can be welded using DC. The welding of sheet metal along AC is less desirable than with DC. Arc conditions at low current levels needed for thin materials are less stable on AC power than on DC power.

Generally review of a welding application will indicate whether alternating or direct current is most appropriate. Power sources are available as AC, DC, or combination AC/DC units. The power source for the SMAW procedure must be a constant-current type instead of a constant voltage type, because it is hard for a welder to hold the constant arc length needed with constant-voltage power sources.