Just wanted some help with the conversion.
The welder is a Miller Thunderbolt XL 225/150 Amp. I have an air cooled TIG torch, gas and regulator. Am I correct to assume that I will need a high-frequency unit and a foot or thumb control to start TIG welding?
Any info would be greatly appreciated.
Thanks

It has been a while since I tried the same thing, but what I found/was told was that even though this is possible, the only way you could control amperage was on the face of the arc welder. It works on the same principles as GTAW, but of course needs the shielding gas etc. I may be mistaken about converting to adjustable amperage, but that is what I found. Sorry I couldn't be more help :)

I assume you will have the same problem with converting stick welder to TIG as you would MIG, the characteristics of the transformer and supply is quite different.
With Stick welder the transformer attempts to supply constant current source as opposed to MIG which is a constant voltage source at a somewhat lower voltage.
The stick welder is higher open circuit voltage which would be no good if this voltage was sustained at the rated current of the welder, therefore in a stick welder, the secondary of the transformer is usually loosly coupled and has a shunt to control the resulting voltage/current. i.e. the voltage starts to collapse as soon as a high current demand is required.
I am not sure what the open circuit requirement of TIG is, Stick welder is typically 70v open circuit and MIG is around 35v.
Al.

I assume you will have the same problem with converting stick welder to TIG as you would MIG, the characteristics of the transformer and supply is quite different.
With Stick welder the transformer attempts to supply constant current source as opposed to MIG which is a constant voltage source at a somewhat lower voltage.

The difference between a cc and cv transformer is the amount of reluctance, and therefore leakage inductance. It's much easier to convert a cv (mig) transformer to cc (stick, tig) than the other way around. CC has more leakage inductance, which can be produced by adding a small (under 1 mm) air gap between the two halves, but since he already has a cc source, this isn't needed.


The stick welder is higher open circuit voltage which would be no good if this voltage was sustained at the rated current of the welder, therefore in a stick welder, the secondary of the transformer is usually loosly coupled and has a shunt to control the resulting voltage/current. i.e. the voltage starts to collapse as soon as a high current demand is required.
I am not sure what the open circuit requirement of TIG is, Stick welder is typically 70v open circuit and MIG is around 35v.
Al.

Because of the ionization potential , the absolute minimum voltage for using argon is about 16. Helium is the highest at ~25 volts. Anything above this is just making it easier to start the arc, which a HF starter does anyways. You'll need to add a power controller that can be adjusted from a foot pedal/torch potentiometer. The easiest method is phase angle control via triac.

Nice explanation js,
I believe that the machine meets the minumum voltage you said for argon.
So your saying that all I need is a footpedal/torch control? I am not familiar with phase angle contriol via triac but I will check it out.
Thanks.