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

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
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

The arc voltage of a plasma cutter is higher than the arc voltage
of a welder.

Best Regards
Tom.
--
http://fija.org/

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
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

http://www.hypertherm.com/en/Trainin..._is_plasma.jsp

"Lloyd E. Sponenburgh" wrote:

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

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.

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
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

http://bbs.homeshopmachinist.net/thr...-Plasma-cutter

jsw

"azotic" fired this volley in news:k1o556$fua$1
@speranza.aioe.org:

The arc voltage of a plasma cutter is higher than the arc voltage
of a welder.


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

"azotic" fired this volley in news:k1o556$fua$1
@speranza.aioe.org:

The arc voltage of a plasma cutter is higher than the arc voltage

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

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
"azotic" fired this volley in news:k1o556$fua$1
@speranza.aioe.org:

The arc voltage of a plasma cutter is higher than the arc voltage

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

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.
--
http://fija.org/

On Aug 30, 1:05*pm, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

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

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

" fired this volley in news:ea9ef946-
:

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, 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

On Aug 30, 4:02*pm, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

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.



LLoyd

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.


Dan

On Aug 30, 11:17*am, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:
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

http://www.thefabricator.com/article...plasma-cutting
http://webtools.delmarlearning.com/s...h08_rev_CP.pdf

.... my next metalworking toy ... mmm.....