Set Amps vs. ‘actual amps’

Locobobbie · Fri Jul 31, 2020 8:21 am

Hi Team,
I’m a newly-introduced Newbie, and I have a question. Here are the parameters ;
Machine is a 2005 ( approx) ESSETTI AC/DC TIG transformer machine that has only been used a few times since I bought it new here in Sydney Australia. I’m using a foot pedal, welding up a 40mmx2mm SHS workbench. I’m using 2.4mm 2% thoriated and 1.5% lanthanated tungstens, and both 1.6mm and 2.4mm filled rods. Welds are not pretty, but I’m gradually improving. Here is my question...
When I run practise beads on the ‘flat’, my actual amps match the set amps (ie., 80 amps set = 80 amps actual). Then when I run a practise bead on the ‘flare bevel’ joint ( gap appears to be about .5mm to 1.0mm), my ‘actual amps ‘ drop to around 65 amps. Does not happen on the plain ( square) fillet joints.
I’m managing to do the flare bevel joints ok., but it takes a lot of torch manipulation to get the metal to flow across the gap. I cheat a bit by using the filler wire as a ‘lay wire’, and try to push the puddle around ... sort of a ‘weave’ technique I guess.
Can someone offer me some ideas as to the difference in actual amps on the different welds?
Regards,
Robert

Oscar · Fri Jul 31, 2020 11:27 am

On a CC machine your amperage should not vary all that much, so I'm wondering how you are determining that your actual amps are dropping. Does the machine have a built-in ammeter/display for you to view the welding amps? The only way I see that the amperage falls without the person causing it to do so, is if there is not enough voltage; which I think would be very rare since voltage requirements for TIG are pretty low to begin with.

cj737 · Fri Jul 31, 2020 4:06 pm

If the machine is dropping amps as you describe, and is occurring as you weld across "gaps" the likely cause is long arcing and a poor ground for the arc.

I do have to wonder how you can watch the amp readout and weld at the same time? I've been to Sydney many times, never seen a chameleon strolling through CBD with a welding helmet

Locobobbie · Fri Jul 31, 2020 10:10 pm

Oscar wrote:On a CC machine your amperage should not vary all that much, so I'm wondering how you are determining that your actual amps are dropping. Does the machine have a built-in ammeter/display for you to view the welding amps? The only way I see that the amperage falls without the person causing it to do so, is if there is not enough voltage; which I think would be very rare since voltage requirements for TIG are pretty low to begin with.

Thanks Oscar that all makes sense. The machine has a display and I had my "apprentice" reading and logging the wielding amps as I did the tests.

Regards Robert

Locobobbie · Fri Jul 31, 2020 10:15 pm

cj737 wrote:If the machine is dropping amps as you describe, and is occurring as you weld across "gaps" the likely cause is long arcing and a poor ground for the arc.

I do have to wonder how you can watch the amp readout and weld at the same time? I've been to Sydney many times, never seen a chameleon strolling through CBD with a welding helmet

Thanks Mate. My apprentice was reading the display as I wielded. I assume from what you are saying, that as the arc runs over the gap, the ground is week, the arc lengthens, and the voltage drops. AS does the amps???
Im going to try laying a 3/32 rod in the gap to see if I can maintain a good arc across the gap. Walking around in Sydney these days would probably attract the attention of the nearest SWAT squad

Regards Robert.

Oscar · Fri Jul 31, 2020 10:40 pm

Locobobbie wrote: the arc lengthens, and the voltage drops.

that's an "oxymoron" for TIG welding. When the arc lengthens, the voltage has to increase, for it is what compensates for the extra distance between the tungsten and the workpiece, and thus keeps the arc lit. I know it doesn't answer your question, but perhaps it will get you thinking about other possible solutions.

Spartan · Fri Jul 31, 2020 10:58 pm

I wouldn't worry too much about the displays. Keep a tight arc and push a clean puddle. Nothing wrong with lay wire or weaves when needed or useful so long as your spec allows it.

cj737 · Sat Aug 01, 2020 8:24 am

Oscar wrote:
Locobobbie wrote: the arc lengthens, and the voltage drops.
that's an "oxymoron" for TIG welding. When the arc lengthens, the voltage has to increase, for it is what compensates for the extra distance between the tungsten and the workpiece, and thus keeps the arc lit. I know it doesn't answer your question, but perhaps it will get you thinking about other possible solutions.

If the amps are decreasing across the gap then the voltage too must be decreasing as they are directly proportional. The likely factor is the increase in resistance pulling the amps and voltage down. A simple formula (Ohm’s Law) proves the outcome.

It is my contention that the “gap” is causing a ramp in the resistance as the arc is not grounding as efficiently. Same would be true if the arc gets too long, the resistance climbs higher than the proportional increase in voltage. That raises the volts, but lowers the amps.

Poland308 · Sat Aug 01, 2020 5:24 pm

On any machine there will be a change in amps based on arc length. Most machines I’m aware of have a maximum arc length of about 1/8 in. Not that they won’t make an arc over that it’s just that your amps will be way off over that. Also. Excessive arc length on dc will tend to put more heat into the tungsten and less into the part. So if you have a long arc you will be putting more energy into the arc and tungsten and less into your steel.