Electronic packages for medical, communications, defense, and other applications are often hermetically sealed into metal containers using projection welding. However, current projection welding machines may not reliably seal packages with weld perimeters exceeding 7.6 cm (3.0 in), and also may expel metallic particles into the package. This paper describes a novel low-impedance projection welding device that can reliably weld large packages with up to 25.4 cm (10.0 in) weld perimeters with zero weld expulsion and zero weld defects, using half the energy required by traditional machines. The device does not rely on conventional power supplies and transformers, and delivers ≫120kA of weld current while operating from standard electrical outlet (110V, 15A circuits), and requires no external bus bars or cooling system. The system architecture can be easily scaled upward to significantly increase the delivered weld current and hermetically seal packages with weld perimeters greater than 25.4 cm (10.0 in). A commercial version of this device has welded more than 1 million medical, communications, and military electronic packages with zero customer returns. Data is presented showing the weld parameters for a variety of commercial and military hermetic electronic packages.