Tig welder for plasma cutting?

You guys who know more about welding, 'splain me this:
How come I couldn't use an existing high-frequency/DC TIG welder as a
supply for plasma cutting?
My welder will dial down in amperage to the range most plasma torches
expect, and the HF side will allow auto-strike of the arc.
So, what's the difference in a 'real' plasma cutter?
LLoyd
Reply to
Lloyd E. Sponenburgh
Loading thread data ...
The arc voltage of a plasma cutter is higher than the arc voltage of a welder.
Best Regards Tom.
Reply to
azotic
formatting link

Reply to
Rick
There is a good 10X difference in output voltage between a TIG welder (~30V) and a plasma cutter (~300V), HF for pilot arc starting has largely been replaced with a "blowback" system (contact start internal to the torch essentially), and the control of the entire process is a lot different.
Reply to
Pete C.
formatting link
jsw
Reply to
Jim Wilkins
"azotic" fired this volley in news:k1o556$fua$1 @speranza.aioe.org:
Arc voltage at constant current is a function of the arc gap. The SW-300 is a constant-current source, and provides high frequency to start the arc.
Lloyd
Reply to
Lloyd E. Sponenburgh
"azotic" fired this volley in news:k1o556$fua$1 @speranza.aioe.org:
I didn't mean that last to sound like I didn't agree with you. It's just that the arc gap is quite small in most torches I've seen, and would be POSSIBLE to have an arc at 30-50V, if you can just get it struck first.
A welder certainly would not work on a blow-back start torch, but I wonder if it would work on an old-style one with high frequency to initate the arc.
In my last... _Once the arc has started_, the voltage is a function of gap, given constant current.
Lloyd
Reply to
Lloyd E. Sponenburgh
I believe you need a constant voltage source to generate and sustain a plasma. The pressure and volume of the gas flowing thru the plasma torch is going to determine the voltage needed to establish and maintane a true plasma. Also the gas conductivity is a factor ( air, nitrogen, argon, etc.) in plasma formation. I attempted what you are thinking about doing back in in the 1980's and it did not work with a conventional welder even with the HF set on all the time. I now own an old airco plasma cutter 100A, its old (1970's?) but very servicable with descrete components. The dc power supply that runs the plasma torch produces about 200vdc. I did some reasearch back in the 1980's studying schematics i aquired from several manufactures of plasma cutters and they all ran between 200 to 400vdc to the plasma torch depending on how thick a material they would cut. As i recall the thicker the material the higher the voltage required. Hope this helps.
Best Regards Tom.
Reply to
azotic
I do not have a plasma cutter so treat this as opinion not fact.
But the arc voltage is also a function of pressure. See Pachen curves. So the arc voltage would be higher if the arc gap under pressure.
Dan
Reply to
dcaster
" snipped-for-privacy@krl.org" fired this volley in news:ea9ef946- snipped-for-privacy@b8g2000yqh.googlegroups.com:
Dan, I don't think the 30psi-or-so necessary would elevate the voltage that much... have to look at the tables for dielectric constant of air at different pressures to make sure.
I also checked; my Miller will go to 100V, so it might work for thin materials (Almost everything I cut is 3/8" or less)
LLoyd
Reply to
Lloyd E. Sponenburgh
30 psig is three times the pressure. So the Mean Free Path would be 1/3 as long. So the arc voltage would be three times as high. Unless my memory has failed me.
=20 Dan
Reply to
dcaster
formatting link
formatting link
... my next metalworking toy ... mmm.....
Reply to
Denis G.

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.