MIG welding Arc voltage control, the energy source is given and the wire-feed unit delivers speed control of the welding wire, in MIG it is equivalent to the welding process. Many traditional wire feed systems control the wire feed speed through the thyristor control PCB and the DC motor to offer control of the Armature volts and therefore the RPM of the engine. The wire feed motor spindle is equipped with a feed roller and then additional pressure roller, the variable spring is placed to gently catch the wire and force it up to a MIG torch length