Erractic arc at low AC setting

I have been welding and fabricating for over 45 years, and professionally for more than 30. I have been certified under numerous AWS and ASME procedures in the nuclear industry. However I am new to inverters, having just purchased an Everlast Powertig 255 EXT. I am having trouble with arch stability at low settings on aluminum, specifically beverage cans. I can run a nice bead and have no problem welding two together with my old Miller 250 HF set on 25 amps. That’s using a WP 26 torch that is stiff as a board, a 3/32 tungsten and either a 3/32 or 1/16 filler.

Most of the time the arc pops repeatedly like it keeps going into the HF start mode and will not focus at the end of the tungsten. I've read the manual several times, spoke to Ray in technical, tried numerous cups, tungsten sizes, argon flows, and machine settings. I don't have this issue on heavier aluminum or in DC mode even on very low settings. The 255 EXT has many features and settings that should make I much easier to control while welding thin aluminum. I don't know if I am unable to set the machine properly or if something is wrong with it. I tried setting it at 25 amps, sine wave and 60 Hz which is the only setting for my old miller HF machine and got no improvement in arc performance.

Help or suggestions will be greatly appreciated.

What is your AC balance setting? What terminal do you have your torch in?

I've tried everything from 0 to 35. The torch is in the left side negative terminal.

Welcome. Hopefully the forum will be repaired soon so that we can upload pictures.
Are you sharpening the tungsten to a point about the same angle as a sharp pencil ?
A smaller tungsten or a sharper point help for low amp starts... at least with inverters. I don't know about the old transformer machines. My 250 ex has a hard time starting an arc at low amps unless the tungsten is pointed.
What type tungsten are you using? 2% lanthanated (blue) works well for just about everything. Never use pure tungsten (green) with an inverter.

Yes, that was going to be my next question. Tungsten and tip shape for aluminum?

The most stable wave form for starts will be the advanced square wave. Frequency should be around 120 for low end starts in my opinion. The arc will be more stable.

Another issue with wandering is work clamp placement. If it's not on the metal you are welding, you can get wandering of the arc, particularly at low amps.

Exact same problem as original poster with a four month old PP256s. Everything works beautifully on it except for low amp AC TIG. Once it gets above 20-30 or so amps it smooths right out and the welds are top notch. I have used two different torches (9 and 26), lanthanated and ceriated tunstens, and several different pieces of Al to practice on. Same results. Tungsten shape has no effect. All pieces of stock were thoroughly cleaned with SS brush and acetone. Ground clamped directly to piece.

This is exactly what it acts like:
https://www.youtube.com/watch?v=r54KHm18pMM Skip to 3:07. Does it at start up of the arc, as well as when tapering off. You can hear the HF points buzzing when this happens.

Unit is not rated for low amp tig. Rated for only 20 amps minimum...with best starts around 25 amps. Nothing you can do about it. You can read even see it on your spec panel on the unit. We've highlighted this several times as a tradeoff on this unit. The 256 units, S, ,or Si, aren't a 250EX with a plasma cutter added.

Quote:

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Originally Posted by punisher

This is exactly what it acts like:
https://www.youtube.com/watch?v=r54KHm18pMM Skip to 3:07. Does it at start up of the arc, as well as when tapering off. You can hear the HF points buzzing when this happens.

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"Mr.Tig" at his finest ;)

Amazes me how a guy with So Little ability to Tig weld calls himself that!

Yeah,

I'm not an old pro like Sage Hill with AC TIG, but I've had the lower-output EXT unit (210), as your/his new 255EXT. And though I haven't tried welding aluminum cans together, I do think the AC arc gets stable pretty quickly beyond its 5 amp starts on the Square wave, i.e. around 20 amps or less, with about 30% AC balance, a sharp tungsten, and around 120-200 Hz on AC frequency. The Triangle wave seem pretty cool for a finer bead too. Of course, AC TIG still seem noisy to me, compared to the calm and quiet DC TIG arcs. Also, I'm liking the 5356 filler rod better than 4043.

Please let us all hear how it goes with your new 255EXT, as I'm diggin' my 210EXT, but maybe can learn some new settings that you will discover, which could make it even better for me too.

Hey, look, the EDIT feature on the Forum here seems to work fine again. Maybe things here on the Forum are pretty good again. Whee...!

Maybe something here could help with your aluminum can welding.

https://www.youtube.com/watch?v=eX_sepp9T_M