Century MIG conversion to TIG

By wamcdonald Date 05-19-2004 02:15

Well I finally got tired of my old Century Mig welder getting jammed with wire. So I decided to convert it to a Tig unit. I bought a cable and gun assemble that fit great. The added a switch on the gun with the wires going to where the switch terminated in the welder. No problem...looks very professional... until I started to weld. I did not realize the how complicated a Tig set-up is, with all that arc start and stabilization stuff. So, my thought now is to inject a high voltage low amp high frequency signal into the welding circuit.

I am thinking using an igition coil driver but I am unsure as to how to integrate this into the low volt high amp welding circuit. My thought is that I have to place the ignition coil output on the ground and gun wires leading out of the welder with either a high power resistor around 10-100 ohms in line to provide current isolation. Another thought would be to use a spark gap of 1/4 to 1/2 inch to provide the isolation. I just don't know how much if any of the current could flow through this gap when arcing. And still one other is to use a combination of both.

Also, I will add a switch selector to allow for AC/DC-/DC+ welding.

Any help would be appreciated.

By billvanderhoof (****)

Date 05-19-2004 07:35

You may have trouble with this. Your mig machine is a constant voltage device. Tig is generally done with a constant current power source.
Bill

By sparx

Date 05-19-2004 12:59

I am not one to say " you can't do that....or it won't work" because I hate it when people say that to me, but...........
It wont work.
As bill says in his post, your machine is a constant voltage machine. I have "cheated" with making a "tig" weld with my mig welder before. a real cheap and easy way to do this, is to take a contact tip, slice it down the middle and bore out the hole to accept a small tungsten, so that when you tighten up the tip, it grabs the tungsten kind of like a collet does in a tig torch. Use pure argon for a shielding gas, (obviously release the drive rolls or remove the wire altogether), use DC electrode negative, and scratch start the tungsten when you pull the trigger on the mig gun.
Having said this, you will get a tough to control welding arc with not too great characteristics.....
The other problem with your machine is the fact that it is DC only. I am sure that you could rig up some sort of high frequency device if you try hard enough and have the right parts, but being a constant voltage machine, I believe this is a waste of time.
Like I said earlier, I hate going to a store and having the guy behind the counter tell me that what I am trying to do won't work..... I usually tell them to just sell me the parts that I want, and I will figure it out for myself......but this is a case where if you really want to try it, good luck.

Sparx

By wamcdonald Date 05-20-2004 16:46

The link below is the basis for the HF signal I wish to inject. I would need to add a power resistor/spark gap to isolate the coil from the high current, at least that is my thought.

http://www.geocities.com/CapeCanaveral/Lab/5322/coildrv.htm