Volts and Amps at Power source or at Arc

Date 06-11-2016 03:56

yes I can
have voltage drop
your getting into complex electric here
and complex welding theory
give me some time to run some #'s
and you gave me none....other than wire length
sincerely,
Kent

By js55

Date 06-13-2016 12:36 Edited 06-13-2016 12:38

This is one of those issues that anal retentive inspectors get off on because it makes them look smart.
If you consider where your welder will be referencing the volts then you have your answer.
There is nothing in the codes anywhere that requires you estimate voltage drop for WPS compliance (although with the bullschit ranges in AWS you might have to write multiple WPS's to accommodate). Imaging the nightmare of this. Welders would be required to carry VA meters and every change in cable length would become a quasi essential variable.
THIS IS NOT the intent of the Codes.
What are the chances you run into one of these inspectors? Considering the industry is chockablock full of these buffoons, probably pretty good eventually. Ask him to show you where the Code requires such consideration. Or better, bury his ass in paperwork with numerous missing dotted 'I's, and crossed 'T's' to give him purpose and keep him busy.

By js55

Date 06-14-2016 13:34

I'm still waiting for someone to explain exactly how, if the voltage drop scenario is taken seriously, this to be implemented on the shop floor.
Are we to distribute VA meters to welders now?
Should the codes impose this as an essential variable?
What if another inspector references the gauges on the machine and determines you are out of compliance with the procedure?
How do you accommodate this in AWS?
Write multiple procedures? One for the machine that everyone can see and one for the gun that nobody can see?
And what of gauge calibration on the machine. You have now rendered it irrelevant. Is this how we propose to run a shop? Where the most convenient reference for the welders is now meaningless?
This may make for good discussion for inspectors and engineers but it complicates when it comes to production welding.
The thing is, for me, everyone knows about voltage drop. But to try and do something about it in a production environment is more trouble than its worth.
ITS JUST A NUMBER
Qualify the procedure using the voltages at the machine, and write your procedure for the voltages at the machine, and the welder will reference the voltages at the machine.

By Steelslinger (**)

Date 06-14-2016 13:59 Edited 06-14-2016 14:03

At one shop I used to work at as a welder, the QC would check the machine prior to any PQR or Welder Qualification tests. This calibration would be in combination (and a verification) with Maintenance's own quarterly calibration, at which time they would write down on a label on each of the machines, what that machine's variation was. Anybody using that machine would then know that if you wanted 26 volts and 220 amps, you would have to set it at 26.5 Volts and 230 amps (as an example). We did have a few machines that were off by a fair amount (older machines, with 25' of cable between power source and feeder, plus another 15' to 20' of gun & whip).

Governing bodies such as AISC have requirements that you have the calibration of your equipment checked at specified intervals and a log kept of those periodic calibrations/checks anyway. This just puts the findings right on the machine, rather than just in a log book somewhere.

Adam
- Shop QC/CWI/NDT

By pipewelder_1999 (****)

Date 06-14-2016 01:25 Edited 06-14-2016 01:32

It is my opinion that measurements should be taken at a short distance from the welding. If you qualify a procedure (not sure why you are recording setting for performance) on a given machine, any readings on a subsequent machine may not be accurate depending upon cable lengths/diameter etc.. With a system in which the voltage is displayed at the wire feeder and then in most cases, the voltage difference is negligible for a 12' lead.

Checking actual conditions near the arc can show things such a poor grounding/connections etc... Taking readings at the machine only shows that the machine itself is functioning and not the entire system. Even if a machine is calibrated the entire system may not be accurately represented by the machine reading/settings even if the machine is calibrated.

If I were a 3rd party inspector and tasked with verifying compliance with parameters, chances are EXTREMELY high that I will check at the location the welding is being done. Understand that if a company had a procedure in place that indicated they recorded values at the power source, controlled cable lengths, assured grounding, etc.. then maybe I would reconsider.

In cases where heat input is critical, then its my opinion that the procedures for verifying these parameters should be closely looked at and voltages/amperages should be measured as close to the arc as possible.

"Welding Machine Calibration" in my opinion is a farce in any case in which variations of a few amps or a half a volt at the arc is going to affect the quality of the weld. Calibration of equipment used to measure the electrical output however may be something that could be an asset.

Not sure what kind of discussions go on in the code committee meetings in which this is decided to be something that adds quality to welds. However since I have not attended any, I am part of the problem.

There are many variables that affect the quality of the weld. Usually there is a usable range listed on a WPS that allows for some variation in "real life". Sometimes there isn't as much "rocket science" to welding as we think. Then sometimes there may be a little. It just depends on the industry, how critical the components are, and the "brains" that went into the project specifications and related codes.

Have a great day.

Gerald Austin

By kcd616

Date 06-14-2016 03:37

let us start simple
metal to be welded? (I think mild steel)
size of filler wire?
size of welding and ground cable?
I know what you want
to get your answer you need to give more information
we share here
but $$$$$$$$$ pays the bills
share with us we share with you
give some to get some
just IMHO
sincerely,
Kent
btw: spelled it out, check @ the arc
and make up for voltage drop?????????????? UP THE AMPS!!!!!!!!!!!!!!

By 803056

Date 06-13-2016 23:04 Edited 06-13-2016 23:07

Todays lesson boys and girls is the importance of arc voltage and other useful welding parameters.

Does it make a difference whether the voltage is measured at the machine using the meters on the machine or at the arc? The answer is yes, if the welding leads are relatively long and causes a significant voltage drop. One may encounter problems in the field, in a fabrication facility where the power supply is some distance from the actual welding, or in a shipyard where long welding leads are used. Not only is the length of the welding lead an issue, but the diameter of the welding leads can also result in excessive voltage drop.

As an example to illustrate:

31 volts are required across the arc for a specific diameter electrode.
The welding leads, with connections, results in a 4 volt drop due to the length of the leads.

A total dynamic voltage of 35 volts is needed to produce an acceptable weld. The question becomes what power supply will provide the required voltage while under load. The sidebar note is that open circuit voltage does not provide the voltage under load, it is the voltage at the terminals when the machine is powered, but no welding is being performed.

The equation that provides the information we are seeking is:

I = (V-20)/0.04 making the substitution I = (35-20)/0.04 or I = 15/0.04 = 375 amps: therefore purchase a 400 amp power supply to ensure sufficient voltage at the arc is available.

Not everyone uses a manual welding process where the arc voltage is a function of the arc length maintained by the welder. Semiautomatic welding processes such as FCAW or GMAW requires a relatively narrow optimum range for the arc voltage which is set with a twist of the knob on the welding machine. The arc voltage should not be set by "feel". The arc voltage should be set in accordance with the electrode manufacturer's recommendations. Two electrodes, both having the same classification, made by two different manufacturers will rarely use the same voltage or wire feed speed range. Each has optimum values for voltage, WFS, and electrode extension that produces the "best" results. The difference is because each manufacturer uses sheet metal having different thicknesses for the tubular electrode and they tweak the chemistry of the flux. As a result, each will have different parameters, i.e., values for electrode extension (CTWD), arc voltage, and wire feed speeds. Granted, the ranges for the parameters from both manufacturers might have some overlap, but there is little likelihood both will utilize the same optimum parameters.

Woe to the welder that set the parameters based on what he used on the "last job" unless by chance he is using the same electrode made by the same manufacturer. Even when the electrode is manufactured by the same company, even when the electrode is the same classification, there may be differences in the optimum parameters for electrodes with different "trade names".

When long welding leads are used, it is best to measure the voltage drop across the arc as near to the gun or the electrode holder to ensure the arc voltage is reasonably accurate.

Does arc voltage, wire feed speed, welding amperage, etc. make a difference? It certainly does in my world. Using the proper welding parameters go a long way in minimizing poor or unacceptable weld quality. If you are welding to the Farm Code and if the quality standard is somewhat lax, set the machine by feel and hope for the best.

Best regards - Al

By kcd616

Date 06-14-2016 01:13

Al,
correct
everyone can debate
wire (or lead) size, length of wire (or lead), stinger or gun size and so much more
so much here
this is a can of worms that just got opened
you got the point correct
but so much else to it
can make you really think
sincerely,
Kent

By Lawrence (*****)

Date 06-14-2016 11:25

Thank you Al

One post in the entire thread dedicated to the notion of actually making a good weld.

Rather than being worried about where a 3rd party inspector puts the Fluke meter.... Maybe be worried if you are getting the energy at the production weld that is supposed to be there.

With Self Shielding FCAW becoming more and more useful and relevant in field work, the voltage sensitive electrode wire needs to be understood by the people charged with production weld quality.... Quality manual, standard practices, detailed work instructions, WPS's are all ways to formally skin the cat.

By welderbrent (*****)

Date 06-14-2016 02:13

I tend to agree very whole heartedly with Al and Gerald.

But, as I do not have the education, experience, and science background that they do to word things in the same empirical vernacular lets see if we can put this into my visual comprehension limits:

So, I am working on a job with large electrodes on lap joints running 5/16 - 3/8 single pass fillet welds horizontal and flat. The bank of welders running off the generator unit is on one side of a 600' diameter separator tank for a mining operation. To accommodate the distance from the welders to the edge, down over the side (as it is several feet below ground level to the floor plates), and then allowing for some slack to move around when on the far side, the leads are about 800' long. Yeah, they are HEAVY gauge leads, none of this single '0' stuff.

Now, why would anyone even consider checking the volts and amps at the machine?? :confused:

To make sure you are operating in the correct amperage range pre-qualified by the electrode manufacturer you will only be interested in the volts and amps in the immediate area of the electrode holder. And yes, you better have a real good ground connection as well as good twist connections or you will have so much resistance by the time you get to the business end of things that the whole thing will get hotter than a fully automatic in the hands of a novice shooter whose finger gets a cramp in it from squeezing so hard.

Absolutely everything will come into play to lower volts and amps between the machine and the electrode holder. It is not always as simple as calculating per the formula Al showed. There are many other factors that will have a negative effect upon your WPS compliant values. And, if they aren't high enough, especially after welding for an hour or two, you will not get the weld penetration, contour, or other positive characteristics that would be desirable and acceptable.

I tend to side with Gerald on another point, who really cares about a calibrated machine? The readout at the business end is what counts. And you will normally only get that with a volt/amp meter. Now, in some shop environments with wire feeders that are attached to the power unit and the only distance of concern is a few feet of lead to the gun, The machine readout from a machine that is calibrated should be close enough to not be worthy of mention. Well within acceptable tolerances.

But in my first scenario, the machine's reading or a volt/amp check at the machine is totally worthless.

He Is In Control, Have a Great Day, Brent

By 803056

Date 06-14-2016 02:31 Edited 06-14-2016 02:42

Ditto!

If the welding machine doesn't produce the required voltage at the end of the electrode - no can weld!

It happened on one of my jobs for ESPN in Bristol, CT. The welder had 400 feet of electrode lead and another 400 feet of work lead stretch out. He had an air-cooled Bobcat welding machine (200 amps I believe). The welder couldn't understand why he couldn't maintain an arc. After all, he was only looking for about 130 amps. The machine could put out 200 amps! What gives? He could not fathom the voltage drop due to the length of the welding leads.

On another job, just a couple of weeks ago, the welder was trying to use a FCAW suitcase about 150 feet from the welding machine. This time it was a Lincoln Ranger. Same thing, 150 feet of electrode lead to the work area and another 150 feet of work lead back to the machine. The owner and his two welders couldn't understand why it worked in the shop with 20 feet of welding lead and why it wouldn't work with 300 feet of lead in the field.

I told them they need a power supply capable of more amperage. They couldn't wrap their head around why the machine with higher amperage would produce more dynamic voltage under load.

The less they know, the more money I make. Their pain is my profit.

Best regards - Al

By pipewelder_1999 (****)

Date 06-14-2016 16:15

The REALLY cool thing about it is that the welders didn't need any kind of meter to realize it didn't work! They may not have understood "Why" but they with their little knowledge noticed it pretty quickly.