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PREFACE:

Arc welding with coated electrodes is a manual process where the heat source consists of the electric arc. When the arc strikes between the coated electrode (by means of an electrode holder) and the piece to be welded (base material), it generates heat which causes rapid melting of both the base material and electrode.

The purpose of the power source is to feed the electric arc, which is present between the base material and the electrode, through the output of a current sufficient in quantity to keep the arc struck. 

Electrode welding is based on the constant current principle i.e. the current delivered by the power source should not vary when the operator moves the electrode towards the piece.

 Themain construction property of the source is therefore tokeep the current unchanged in the presence of variations in arc length as the electrode moves closer to or away from the piece: the more constant the current, the more stable results the arc and the simpler the operator's work.

 Inside the power source, there is usually a weldingcurrent adjustment device, of a mechanical (e.g a magnetic shunt) or electronic type (SCR systems or inverter systems).