Medium Frequency Small Size DC Welding Machine for Electrical Copper Relay / Shunt DESCRIPTION MF DC Inverter Spot Welder is one of the newest resistant welding technology The three-phase power supply, through rectified by a special inverter, is converted into 1000Hz AC voltage and then is transmitted to a medium frequency transformer so the current is rectified in order to supply DC welding current. The advantage is that it helps to greatly reduce the energy of iron core