AC or DC

[Chris_]

Hey guys, i'm thinking of getting one of these 'el cheapo' tig kit adapters for my old transformer MMA unit to do a little light duty aluminium work.

But, theres no point me doing that if my rig is DC yeah?

So how do i find out if it is AC or DC. Can you even get AC from old copper wound transformers?

Here is a piccy for those that are good a deciphering hieroglyphics

Cheers
Chris

 

[shenion]

Looks like an AC only unit, most low-end units are. If it was DC, the output terminals would be marked + and -.

 

[Drains]

Even if it was AC (which it ain't), you'd still need a High Frequency unit to make it work.

 

[shenion]

Si, why would you say it is DC?

If this is the same, it is definitely AC:

 

[irondarren]

never seen an old transformer type that isnt AC yet, you can be 99% sure any welder that looks like that is AC

 

[mishka]

Yes, its AC. On the plate, the little diagram with the overlapping circles shows single-phase AC input ("1~"), AC output ("~"). For DC it would show something like an equals sign ("=").

 

[Chris_]

AC? Woohoo, so does that mean if i get my self a bottle of argon, and one of those tig torch kit things i can do a little crude scratch start aluminium tig welding?

Shenion, similar,

Can i ask, what amperage does does yours go to on 230v single phase? i think i need to beef up the garage electrics, it keeps popping fuses.

Cheers for your help guys.
Chris

 

[snowcat]

Your need H/F whatever on A/C......The duty cycle on a little arc would proberbly give you issues as well.

 

[Chris_]

Does that mean you cannot just use scratch/lift start with AC?

Anyone know if you can buy a HF start torch that just takes a gas supply and power?

 

[snowcat]

You need the H/F on A/C because theres a 0v point at the middle of the wave therfore you would keep loseing the arc.....You can buy stand alone H/F units..

 

[piman]

Hello Snowcat,

all A\C voltages have the zero point whatever the frequency (H/F = High Frequency). (And just to confuse things, with most A\C circuits there is current flowing at zero volts and no current flowing at some voltage due to the current and voltage waves not being synchronised)

I must admit I don't know why you need high frequency for aluminium though.

Alec

 

[irondarren]

Its not hf for alluminium but HF to run the AC tig, DC tig is fine and will hold a constant arc because its DC power at 20 odd volts, but because AC reduces to 0 volts and then changes polarity, its that point at 0 volts where there is no power to hold a spark.

 

[snowcat]

Its not hf for alluminium but HF to run the AC tig, DC tig is fine and will hold a constant arc because its DC power at 20 odd volts, but because AC reduces to 0 volts and then changes polarity, its that point at 0 volts where there is no power to hold a spark.

thats what I was attempting to get at, wraping presents at the mo...so distractions a planty

 

[shenion]

Chris_

My Airco is on a 50A breaker. At its full load (470A) it specs a 108A input at 220V. So 50A should give about 220A; probably a bit more as I bet it gets real inefficient at its full load.

50A is about all you can get on a standard 220V plug here (this is a range/oven plug). I would have to hardwire it for more. Don't expect to need to though I have found 100A RV plugs though if need be.

Yours says 40A at full tilt. I would bet a 32A would do whatever you would need.

Keep an eye out on ebay for the HF start units. I see them go fairly cheap at times.

You can try without HF start, but on AC you will probably find the arc may drop every few seconds or you have to keep the torch real close to the work.

 

[piman]

Hello Darren,

I'm afraid this doesn't make sense, I must be missing something. Surely H\F must be A.C not D.C.?

Alec

 

[irondarren]

HF is high frequency, it is artifically created. on my IFL 200 phf inverter you have HF mode and non HF mode. in HF mode you hold the torch a few millimeter from the work piece and a high voltage spark jumps and creates and arc, because it is a DC current and the voltage is constant the arc can be maintained. in scratch start/non hf mode you scratch the tungsten acrossed the work piece and lift it off, as you lift off the arc is maintained. In AC the voltage goes from positive welding voltage (depends on the amperage setting) to negative welding voltage, there is the point where it changes polarity that there is no voltage what so ever acrossed the tungsten at this point the arc will stop, but it wont restart as the voltage picks back up. HF creates an artifical spark that restarts the arc as the voltage begins to rise, thus giving the illusion of a constant arc. in reality in AC welding on TIG, its weld electrode positive, arc drop due to 0 voltage, polarity change to electrode negative, HF spark kick in to create an arc, voltage build then lower, arc break at 0 etc etc

 

[shenion]

The HF is AC, it is a signal added to the welding voltage.

For DC welding, the HF is only needed for starting. My Airco has 3 settings:

Off - arc/MIG or scratch start
Start - HF runs for about 3 seconds then shuts off. Used for DC welding. Once started the arc will be maintained by the current. Event hough this is DC that returns to 0 every half cycle, the reactor (inductor) will keep the current flowing until the voltage rises back up.
Continuous - HF on all the time. Used for AC TIG. As mentioned before, the zero voltage crossings will cause the arc to stop and restart. The arc will usually restart, but will not restart until the voltage gets high enough. The HF start makes the arc more continuous.

 

[Drains]

Si, why would you say it is DC?

If this is the same, it is definitely AC:

Erm, what I meant was, er, you need HF to Make AC work.

As for the rest of whatever I said.... :full

 

[irondarren]

Si,
As for the rest of whatever I said.... :full

To much xmas cheer was it Si

 

[Chris_]

Aha, clear as mud.

Not doubting anything you pro's have said so far but....

...How come when stick welding with this unit (AC) I get a nice stable arc all day long, with no HF stuff?

I suppose it probable has something to do with the big lump of molten metal almost touching the surface?