Clarify TIG Polarity....

[BillC]

My old welder was physically switched from AC - DC - DC reverse. With this 255 EXT;DC TIG, the torch is negative with positive ground - and with AC TIG, the torch goes to positive - with negative ground. Correct? But if you were only welding with AC TIG - why would it matter if the torch was hooked to negative? High frequency arc start?

I used to be concerned about asking dumb questions - I've gotten too old to care any more! And memory - OK but fleeting.

Thanks!

[Rambozo]

My old welder was physically switched from AC - DC - DC reverse. With this 255 EXT;DC TIG, the torch is negative with positive ground - and with AC TIG, the torch goes to positive - with negative ground. Correct? But if you were only welding with AC TIG - why would it matter if the torch was hooked to negative? High frequency arc start?

I used to be concerned about asking dumb questions - I've gotten too old to care any more! And memory - OK but fleeting.

Thanks!

Nope, you leave the torch in negative for AC, too. It sorta does matter, because there are a few features that would be confused by swapping the torch and your AC balance control would be backwards, or forwards if you are used to a Miller. Everlast marks the AC balance in percent positive, whereas Miller marks there's in percent negative, and not on a linear scale as well, at least in the older machines. The only time you need to swap cables is for stick welding or the rare time you might want reverse polarity (DCEP) TIG.

[BillC]

Rambozo,

Thanks greatly. Never used (as I recall) a Miller only the Lincoln transformer machine. I still have it but it's in a storage spot that doesn't occupy my trifling home shop space (that's a big welder). Arc3 in Hampton seems eager to work on (restore) that old welder..... I'll learn this 255EXT and as someone near and dear says 'you will be happy!'

[BillC]

OK - while on the CK website I found some data about this TIG polarity - seems it does make a difference even with IGBT machines - maybe.....:


Could it be that the 'balance' on AC may be confusing with the torch on negative.... Looks like the HV arc start may be affected too. Is this data correct for our Everlast machines?

[Rambozo]

You can see why the balance control would be reversed if you swap the connections. But in reality you are always using more negative than positive for the electrode on AC squarewave. 50% is like full cleaning mode, and you go down from there. Some machines like Everlast are calibrated in percent, some have just a low to high or a 1 - 10 scale. Early squarewave machines that used that had #3 marked as the balanced setting. With your 255EXT you will find that 30% is a good starting point. go down from there on really clean metal for extra penetration, and up on not so clean, for more cleaning action.
Also these machines can only make square waves, so all the other wave shapes are done by tweaking the amplitude during the rising and falling edges to simulate the other shapes. I haven't checked on a scope, but they could very well make some of the waves asymmetric to improve welding performance, and you would lose that if the cables were swapped. With digital it's easy to get the wave to change shape millisecond to millisecond. Something an analog machine could never do. Things like the advanced pulse AC on your machine, that mixes DC into an AC wave to get way more welding power than a typical 250 class machine, and without having to use expensive helium. Digital opens up all kinds of possibilities. Just be aware when reading about general information that some manufacturers use different terminology for the AC balance control. If you see anything higher than 50%, that machine is doing percent negative where Everlast does percent positive. So just invert the percentage to convert. If you see 70% think 30% on yours.