scope:

Most power supplies used for arc welding are carefully designed to develop the relatively constant electrical output needed to produce acceptable welds with a variety of welding processes. In some cases, as for covered electrode or TIG welding, care is taken to provide an output is essentially constant current. In others, as for MIG or submerged arc welding, better welding control is achieved with constant voltage. Ripple-free output has been a desirable characteristic of motor generators. Rectified transformer machines have the disadvantage of a significant ripple which, generally, has only been tolerated. This is eliminated in more expensive machines by incorporating filter networks. Transient fluctuations are prevented in sophisticated power supplies by using special circuits to regulate the output, and more effective filters are used to eliminate ripple completely. The first radical departure from this philosophy of requiring a stable current of the arc occurred when the short-circuiting process was developed. With this technique, all transfer occurs during relatively rapid short circuits, causing a great deal of ripple. However, the short circuit surges of current are carefully controlled by matching the wire feed speed with the inductance and static output voltage of otherwise conventional constant voltage power supplies. The frequency of short circuiting and the amplitude of short-circuit current surges are determined as much by the welding conditions selected as they are by the basic characteristics of the power supply.