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Re: Inside A Plasma Cutter (Must See Pictures for SSTCers!)

Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net> 

A full history of torch heads for plasma cutters:
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, June 11, 2004 5:32 PM
Subject: Re: Inside A Plasma Cutter (Must See Pictures for SSTCers!)

 > Original poster: Jim Lux <jimlux-at-earthlink-dot-net>
 > At 07:30 AM 6/11/2004 -0600, you wrote:
 > >Original poster: "Jim Mitchell" <Electrontube-at-sbcglobal-dot-net>
 > >Hello John,
 > >
 > >That might explain their rating of 1200v,  I didn't look to see if they
 > >in series,  but 1200X6 would give 7200v of rectfication,  so perhaps the
 > >transformer gives 5kv? out.
 > >
 > >Something I've noticed,  that even IF the ground clamp isn't connected to
 > >the work,  I can still gouge the metal with the torch.  This also lead me
 > >believe that the output is high frequency as well, because we all know
 > >a unrectified flyback will arc to ungrounded metal,  but a rectified
 > >will not (or just make small blue sparks to the metal)
 > >
 > >I guess I can still gouge the metal without being grounded, because the
 > >is being started in the torch head, and then blown out by the air stream.
 > >
 > >It seems plasma cutters are kind of a "mystery device" ;-)
 > >
 > >Regards - Jim Mitchell
 > >----- Original Message -----
 > The plasma cutter I used to use (Thermal Dynamics, as I recall), was about
 > 300V open circuit with inductive "ballasting" + a HV/HF circuit (similar
 > a TC or TIG welder) to start and stabilize the arc.  There were three
 > out of the supply: the ground clamp, the main annular electrode, and the
 > center electrode.  There's a fairly good arc between the center and
 > electrode, creating the plasma that does the cutting (which is blown into
 > the workpiece by the pressurized air (in my case.. they also use H2 in
 > cutters apparently).  There may also be current flow to and through the
 > workpiece to help heat it so that the air blast can blow it out of the way
 > (which is really how a plasma cutter works.. melt the metal and blow it
 > of the way: compare to a cutting torch, which actually burns the metal
 > oxygen)
 > They're really pretty simple devices.  The "art" is in the design of the
 > "torch" to create a stable arc and air flow so that it's controllable and
 > precise.  There's a LOT of interaction between the electrical properties
 > the power supply (in particular, the I/V curve) and the fluid mechanics of
 > the torch, so that the arc is stabilized.  If you look at the inserts in
 > the torch head, there are little slots at an angle and the profile of the
 > inside of the outer electrode looks simple.  IN reality, I suspect that a
 > LOT of trial and error went into that design.