A pure sine wave inverter is necessary to run a welding machine. The inverter will take the DC power from the batteries and convert it into AC power that can be used by the welder. Most welders require at least a 220-volt power source to function properly, so it is important to choose an inverter that can provide this level of power. A pure sine inverter is also necessary if you want to use a generator to power the welder. The inverter will take the AC power from the generator and convert it into DC power that can be used by the welding machine. Always check your pure sine inverter's manual before connecting it to a welding machine to ensure that it is compatible. Also, make sure you size your inverter correctly so that it can handle the power requirements of your welder.