# Plasma cutting with a MIG / Lift TIG (conversion question) ?



## graham-xrf (Aug 12, 2021)

I ask this from a start point of sheer ignorance, and because I figure that the difference seems hardly more than screwing on a plasma cutting torch and changing the gas to shop air, or maybe adapting a plasma cutting end bits onto a recycled old TIG torch. So far as I can tell, a settable 200A machine would not know the difference on the business end, and could be used.

Folk here are very practical, but I know the devil is in the detail. So I ask, is any of this notion just plain stupid? What might be involved, if it can or should be done at all?

I am guessing that if there is a hangup, it most likely will be to do with starting the arc?


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## General Zod (Aug 16, 2021)

Not possible.  Welders cannot produce the arc voltage needed to sustain a plasma cutting arc.  That simple.


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## matthewsx (Aug 17, 2021)

That would explain why plasma cutters are so fiendishly expensive.


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## graham-xrf (Aug 19, 2021)

General Zod said:


> Not possible.  Welders cannot produce the arc voltage needed to sustain a plasma cutting arc.  That simple.


Thanks much Z, that's good to know.

For one who starts out not knowing anything, just looking at everything searched, and seeing the principle of operation, nowhere I found was this explicitly stated.

Clearly the variety of common settable plasma currents were usually less than the 200A available from my machine.
When one looks at (say) the cheap, lightweight, and it has to be said, damn tiny things like the $150 HERO CUT from Amazon, there seemed every reason for me to think that such a conversion would hardly be more than using a plasma torch on a basically TIG machine, and going for shop air! There is even a video out there on how to adapt an old TIG torch to use Plasma cut consumables.

A TIG arc is already a plasma state, so if it is the VOLTAGE that makes the difference, then naturally one would ask, exactly how high does it need to get?  If the voltage has to be higher (to suit plasma cutting), then, for a given power, the current has to be lower. For a whole bunch of those admittedly crap-looking Chinesium kits, they do not look as if they are "higher power", and clearly 50A to 80A is enough to cut some sheet metal.

I do note that at the prices some import plasma cutters can now be had, it seems hardly worth messing with an ill-judged "conversion".  The cheapest of the "better rated" plasma cutters on Amazon seem to cost around $270.


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## Janderso (Aug 19, 2021)

graham-xrf said:


> A TIG arc is already a plasma state, so if it is the VOLTAGE that makes the difference, then naturally one would ask, exactly how high does it need to get? If the voltage has to be higher (to suit plasma cutting), then, for a given power, the current has to be lower


This made my head hurt.


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## pontiac428 (Aug 19, 2021)

Arc start is like 400v, and the plasma arc is around 60v, plus plasma cutting heads focus the gas and arc into a very tight cone.  Plasma cutters weren't really a thing in the days of analog electrics, it took those great digital innovations of the 70's and 80's and switching power supplies to bring the technology to the shop.  Must be something to that.  I own a robust but somewhat simple plasma machine from the 90's, and that thing is stuffed full of circuit boards to provide the control to sustain a stable cutting arc.  My transformer TIG would be too "dumb" to work as a plasma power supply for sure.


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## graham-xrf (Aug 19, 2021)

Janderso said:


> This made my head hurt.


This is easy!
Power(Watts) = Voltage x Current.

You know from the start how much power the kit can deliver (e.g.2kW) , and the input voltage (e.g. 220 VAC)
The current it takes from the socket will be 2000/220 = 9.09Amps
Expect that because it is not 100% efficient, it may take about 10Amps or so.

Now move to the other end. Take out (say) 60Amps.

The most volts the machine could ever muster to deliver that continuously would be 2000/60 = 33Volts.
We know this is not what really happens. The plasma machine switching regulator winds up 200V to 400V (no current yet) and starts the arc.
In milliseconds, that high voltage collapses to a much lower voltage sustained across the arc.
The machine then controls the current in the arc, millisecond by millisecond.

Any other numbers (voltage x current)  giving an answer exceeding the power of the machine gets you something for nothing - impossible!
If there is one thing we know about energy done with electrons, it is that the amounts are exact, and unforgiving. There is so escaping a simple multiplication!


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## graham-xrf (Aug 19, 2021)

pontiac428 said:


> Arc start is like 400v, and the plasma arc is around 60v, plus plasma cutting heads focus the gas and arc into a very tight cone.  Plasma cutters weren't really a thing in the days of analog electrics, it took those great digital innovations of the 70's and 80's and switching power supplies to bring the technology to the shop.  Must be something to that.  I own a robust but somewhat simple plasma machine from the 90's, and that thing is stuffed full of circuit boards to provide the control to sustain a stable cutting arc.  My transformer TIG would be too "dumb" to work as a plasma power supply for sure.


Thanks John - my searches have started to yield the detail in plasma technology.
The "resistance" in a plasma ionized gas is indeed unstable, wobbling about near zero, flaring up and subsiding as the molten metal under it moves. It takes very high speed switching regulated current control to keep the arc going.

A good example of plasma from crude AC volts is in a fluorescent lamp tube. When the gas in the tube ionizes, the tube becomes a near short circuit which, left to itself, would pop all the house fuses instantly. The only thing that limits the current is the ballast choke in series, basically lots of turns of fine wire on an iron magnet core. The choke provides inductance, which acts to limit the current in AC circuits by it's impedance. The actual resistance in the wire is low, so the choke does not get very hot. Sadly, what chokes can do is frequency-conscious, so they do not work for DC currents.


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## General Zod (Aug 19, 2021)

A high quality plasma cutter will sustain 100V to 140V at the arc.


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## graham-xrf (Aug 20, 2021)

General Zod said:


> A high quality plasma cutter will sustain 100V to 140V at the arc.


Yes - I was reading that it could be typically 125V to 140V, though this might be a pulse average, or peaks in re-establishing the arc when regulating. What I was after was, with that 100V,  what is the current, or average current, or instantaneous regulated current during a switcher ON period, anything!

This is because even 100V x 50A is *5kW*, and I know the little plasma cutters sold do not boast this power, so this scenario is impossible - unless we are missing something!

An exact appreciation of what goes on in a plasma, and the ups and downs of voltage and current, and how this adds up to the energy being delivered, is not what we have.

I do get it that the question may involve a deeper understanding of plasma cutter operation and design, and that may not be a reasonable expectation here. That's OK. Folk here have provided me enough answers, especially that plasma cutting requires a different type of machine, and that a regular TIG cannot do it. I have seen an advertisement for a (cheapish) machine that can be switch selected to provide Plasma, or TIG, or stick weld, and this makes sense. If there are enough modern electronics inside, (ref @pontiac428 ) then one can design a special product that does this.


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## General Zod (Aug 20, 2021)

Not sure what you are getting at here.  My "little" 55A plasma cutter consumes well over 9 kW at full tilt cutting thick material.  A typical plasma cutting arc is DC, non-pulsed.


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## Aaron_W (Aug 20, 2021)

graham-xrf said:


> Yes - I was reading that it could be typically 125V to 140V, though this might be a pulse average, or peaks in re-establishing the arc when regulating. What I was after was, with that 100V,  what is the current, or average current, or instantaneous regulated current during a switcher ON period, anything!
> 
> This is because even 100V x 50A is *5kW*, and I know the little plasma cutters sold do not boast this power, so this scenario is impossible - unless we are missing something!
> 
> ...



I've read that some of these multi process welder plasma machines are the source of distrust for multi process welders. Both cheap and unreliable, because apparently the plasma function really does not get along with the welder side of the electronics and the gained a reputation for having a very short service life. Even with MP welders becoming popular ones including plasma cutters are limited to cheap imports. I don't think any of the big manufacturers offer one. There may be a good reason for that.


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## graham-xrf (Aug 22, 2021)

Aaron_W said:


> I've read that some of these multi process welder plasma machines are the source of distrust for multi process welders. Both cheap and unreliable, because apparently the plasma function really does not get along with the welder side of the electronics and the gained a reputation for having a very short service life. Even with MP welders becoming popular ones including plasma cutters are limited to cheap imports. I don't think any of the big manufacturers offer one. There may be a good reason for that.


My instincts follow yours. I accept that if the task is any form of "welding", the basic inverter controlled energy source can easily be arranged to suit different types of welding, MIG, TIG, etc. It is clearly possible to offer a welder that can do MIG and TIG and stick welding as a multi-option, with various software control configurations. Of course, these may be sold in any combination.

When it comes to plasma cutting, a multi-modes machine becomes quite awkward. Plasma really is better with a dedicated machine. It's not that it can't be done. The question is whether it should be done. This is, I think, better a case of designing something to do one thing well.

*Starting a plasma*
What is involved in plasma cutting is first the approximately 10kV radio frequency start spark, This is the same gadget as installed on switched start TIG, but this time is synchronized to a gas delivery pressure control. Depending on how sophisticated the plasma cutter is, so will the gas control timing be controlled. Traditionally, the shield gas in the outer stream is retained, and a pilot arc is started between the electrode and the nozzle using a switching designed for only this job. The start sequence also sends in _pre-flow_ gases set at a much lower pressure so as not to blow out the arc. The gas has to be flowing before the arc starts, or the life of the torch parts becomes negligible.

*The Pilot Arc*
A little arc is first established betwwen parts inside the torch cup. As this precursor arc starts, the electronics increases the pilot arc current to about 18A to perhaps 22A, but it is a very brief pulse thing. The controlled current has to be in series with electronic ballast. The actual voltage across the arc ionized gas is low, and variable. The ionized pre-flow gas is pushed out of the nozzle, so hot plasma touches the work. At this point, the arc current can complete the external circuit back to the welder via the fat positive ground lead. As the external current increases past a minimum value, chosen to be around 7A to 10A in most designs, the pilot arc circuit cuts off the in-torch return route that was shunting the external path. The external arc current is still ramping up. Keep in mind that all this happens very quickly.

*The Main Arc*
At this stage, the gas pressure control ramps the gas pressure to the correct value for the torch settings. Various cups, nozzles and work thickness settings have the corresponding correct pressure. At the same time, the current control adjusts the arc current to the final cutting current value, typically 50 Amps or more, and keeps adjusting to have it stabilized there.

By now, the metal is melting and the central air gas column is cutting through. The air that is coming through had better be _dry_, and_ clean_, or you may expect difficulties.

I expect there may be variations to this, depending on what tricks modern electronics can make happen. All the above I have found from searching and study, and none of it need necessarily be known to an experienced plasma cutter user, other than perhaps an appreciation that making it all happen just right might best be done with a machine dedicated to plasma cutting. Arguably, this path also helps with the costs. I trawled this stuff to help me choose, because on something like this, I want to only choose once. Even before I have made my first plasma cut, I don't want to start out working my way through various purchases, discovering from experience which I should not have gone for!


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## durableoreo (Aug 23, 2021)

matthewsx said:


> That would explain why plasma cutters are so fiendishly expensive.



There's a lot of detail in the torch.  Basically, an arc is struck and the plasma is guided down to the work in a vortex of the working gas.  

There are plenty of Chinesium units that can be purchased for around 400 $ (last I checked).


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## RJSakowski (Aug 24, 2021)

The Everlast multiprocess seem to have a good reputation.  No personal experience though.




__





						Multi Process Welders - Multiprocess Welding Machines - Everlast
					

multiprocess welders from Everlast, full line of TIG/Stick/Plasma machines. Everlast Power Equipment is the leader in inverter welder technology and multiprocess welding machines




					www.everlastgenerators.com


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## pontiac428 (Aug 24, 2021)

Aww, we should all know better by now... If an all-in-one machine craps out, you've got nothing to work with until you fix it or toss it (all in one dumpster).  At least with discrete machines, you can still use the others when one is broken.  And if you buy a good machine with local dealer support (they come in blue, usually) you can get the parts, schematics, and service you need to repair it long after it is out of production- decades, even.

I studied Chinese long enough to learn how to recognize the words, "no warranty express or implied" on a product box.  It's on all of them, just look for the scribbles that look like chicken scratch.  Caveat emptor.


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## Aaron_W (Aug 24, 2021)

pontiac428 said:


> Aww, we should all know better by now... If an all-in-one machine craps out, you've got nothing to work with until you fix it or toss it (all in one dumpster).  At least with discrete machines, you can still use the others when one is broken.  And if you buy a good machine with local dealer support (they come in blue, usually) you can get the parts, schematics, and service you need to repair it long after it is out of production- decades, even.
> 
> I studied Chinese long enough to learn how to recognize the words, "no warranty express or implied" on a product box.  It's on all of them, just look for the scribbles that look like chicken scratch.  Caveat emptor.



In general sentiment I tend to agree with this about multi-in one machines, but I will say the foot print is quite appealing. I have TIG, stick and MIG  in a foot print only slightly larger than MIG alone (machine is marginally larger and there is a second tank for TIG). In my shop that is huge, errr it is not huge.   I would struggle finding space for 3 separate welders.

Blue and Red are each making several 3 in 1 machines. Both even offer some some 300A+ units intended for industrial use. Lincoln has an $11,000 815A multi-process machine so the idea of one welder to do it all is even gaining acceptance by professionals, it is not just a hobby machine thing.

My Miller 3 in 1 is basically two distinct welders (TIG / Stick and MIG) in the box sharing one power supply. Switching from one to the other is as simple as pulling the trigger, no need to swap leads or change settings.


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## pontiac428 (Aug 24, 2021)

Yeah, I understand the footprint thing. I always thought my way out of that was to upgrade to switching/digital welders... Some day.


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