Inside a 35 Amp Plasma Cutter

 

An upcoming project will be to build a very large (<100 Amps) plasma cutter from salvage parts.  These devices are available commercially but even low power units are very expensive.  The design seems simple being little more than a welder with a compressed air fitting.  We were able to acquire a 35 Amp imported unit for about half of the usual cost.  Weighing about 100 lbs., the majority of its mass is the heavy−current welding type transformer and the associated wirewound inductor.  Additionally, there is a large corn cob resistor, a couple of bridge rectifiers, and gas control apparatus that completes the internal workings of the plasma cutter.  The following photos demonstrate the simplicity of the design:

 

Here we see the left side of the unit open to reveal a 2-level design. The lower level contains the main trnasformer, a smaller single winding transformer used as unductive ballast, a cooling fan, a very large resistor and 2 bridge rectifiers that are not visible as they are attached to bottom of the upper level shelf for heat sinking. The upper level is comprised of electrical input terminations, switching, the gas flow apparatus, and control circutry.

This is a closeup of the main transformer (right) and the wirewound inductor (left).

Here we see the right side of the unit open. Notable here is the large corn cob resistor suspended from the upper deck. On the upper level, the gas intake apparatus can bee seen on the right and output connections on the left.

This is a closeup of right side lower level (left).

Here we see the upper deck of the unit in closeup. The front panel is on the right in this picture.

This photo is also of the upper control desk but is shot from the back of the unit looking toward the front.