 To supply the electrical power necessary for arc welding processes , a variety of different power supplies can be used . The most common welding power supplies are constant current power supplies and constant voltage power supplies . In arc welding , the length of the arc is directly related to the voltage , and the amount of heat input is related to the current . Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding , because they maintain a relatively constant current even as the voltage varies . This is important because in manual welding , it can be difficult to hold the electrode perfectly steady , and as a result , the arc length and thus voltage tend to fluctuate . Constant voltage power supplies hold the voltage constant and vary the current , and as a result , are most often used for automated welding processes such as gas metal arc welding , flux cored arc welding , and submerged arc welding . In these processes , arc length is kept constant , since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current . For example , if the wire and the base material get too close , the current will rapidly increase , which in turn causes the heat to increase and the tip of the wire to melt , returning it to its original separation distance . 
