AC or DC

[shenion]

Yes, I get real nice arcs with the Airco on AC with stick. However, I use DC as it has a cleaner weld.

With stick you have the flux "burning" producing an ionized gas. It stays ionized well through the 0 crossings so the arc starts right back up on the next cycle.

With pure argon, the gas ionization stops quickly. So, after the arc stops, the voltage needs to get past the ionization start voltage.

Yes, the big molten tip helps. You also run higher currents. With TIG you can run very low currents (mine goes down to 5 amps.) HF is real important on low current.

I have also seen mention that the Al oxide interferes with the arc.

 

[piman]

Hello all,

thanks for the clarification, so the H\F is in addition (superimposed) to the basic welding supply, that makes sense.

Alec

 

[snowcat]

Hello all,

thanks for the clarification, so the H\F is in addition (superimposed) to the basic welding supply, that makes sense.

Alec

got in in one the H/F is simply used to carry the welding current...To add to the confused, my kemmpi set will switch off the H/F if required...some sets can do this if they "carry" well...

D/C stick is fine for lower amps, but can cause arc wander and undercut when the sets are running hot say above 200amps... hence the need for A/C arc

 

[Drains]

Square wave AC tig sets can switch the HF off after arc starting, as the square wave form goes from + to - quick enough for the arc not to break.

 

[mishka]

Today's word is "quenching".

As Shenion said, in Argon the usual 50Hz AC main current goes through the zero-point slow enough that the arc is quenched by the Argon and the conductive plasma goes away. So when the main current starts up again there is no conductive path and no current flows. End of welding.

HF is a High Frequency high voltage signal added to the output of the power source. Typical values are about 10,000V at about 1MHz. But it is current limited so it won't kill you (but will give a nasty "zapp" in the ear ).

Because the HF is also high voltage it is able to jump the gap between the TIG tip and the workpiece, generating a little spark sufficient to ionize enough Argon to allow the main current to take over and ionize the gas and continue the weld. This happens fast enough that you and the weld pool never notice the tiny delay between the HF arc striking and the main arc current taking over.

I think a lot of the theory of this was worked out in the days of Marx rectifiers.

 

[Chris_]

Aha. Well thank you learned people for imparting a little wisdom in this thread.

I shall now go and trawl ebay for a few bits and bobs to buy

Cheers
Chris

 

[The right]

Could someone tell me which this ac or dc... i'm still new in this hobby...

 

[premmington]

Could someone tell me which this ac or dc... i'm still new in this hobby...

It is AC...

Look at the top line of the rating plate! It shows single phase transformer Legrand from AC voltage to AC voltage

The only thing on the rating plate that says DC is in percentage which means duty cycle.

Being able to read welder rating plates is a good skill for buying used welders!

 

[The right]

It is AC...

Look at the top line of the rating plate! It shows single phase transformer Legrand from AC voltage to AC voltage

The only thing on the rating plate that says DC is in percentage which means duty cycle.

Being able to read welder rating plates is a good skill for buying used welders!

What if, there is no rating plat on mig.. it only show the input... but not output. Is there other way to know it output ac or dc

 

[pedrobedro]

That welder has been discussed before, I knew it looked familiar.

 

[penfold]

What if, there is no rating plat on mig.. it only show the input... but not output. Is there other way to know it output ac or dc

I'm confused; if it's a MIG then it's DC, all(well, domestic/hobby ones anyway) MIGs are DC. Is there a picture I'm not seeing?

 

[penfold]

Appearing in a christmas cracker near you, soon...