Abstract: A D.C. welder includes an engine-driven D.C. generator, a polarity-revers switch which can change the direction of current flow through the field winding of that generator to provide a positive or negative polarity at the welder output terminals, a circuit that automatically permits only uni-directional current flow through that field winding during the starting of the engine, and a further circuit that energizes a solenoid to close contacts which enable that generator to operate as the starting motor for that engine but which thereafter de-energizes that solenoid and then keeps it de-energized until the engine is at, or close to, rest.

Abstract: The electric generator of the present invention has a plural-section main nding; and it uses uni-directional devices to permit current to flow through various sections of that winding as the rotor poles move away from various of the stator poles of that generator but to prevent current flow through those various sections as those rotor poles approach those stator poles. By preventing current flow through those various sections, as those rotor poles approach those stator poles, the present invention relieves the field winding of all need of overcoming the magnetomotive force of that main winding. As a result, fewer ampere turns are needed to enable that field winding to provide the magnetomotive force for that main winding.In some preferred embodiments of the present invention, an exciting winding has sections thereof that are wound on poles which have turns of the field winding wound thereon.