PowerTig 255EXT welding power problem

[Kempy]

I was welding a part and put it on the work bench to finish welding it and the welder stop working made a sound like it was going to work but didn’t. Moved it off the bench to see what happen to the welder holding the part in my hand with the ground clamp still on it and it started working again so I put it back on the bench to finish welding it and it stopped again. Moved it off the bench again and it welds OK.
So on the work bench it will not weld still with the ground camp on the work piece I was welding. Take it off the bench it works on the bench it will not work weld and the ground clamp is always on the piece I am welding, I never take off the part.

So out comes PowerTig 250EX to see if it will work and it dose on or off the bench using the same settings same piece same gun and ground clamp.
The MTS 250S works on or off the bench.
The PowerMig 250 works on or off the bench.
The PowerTig 255EXT will not weld on the work bench.
Tomorrow it will try again.

[Kempy]

Well I pushed the welder to the limit on the pedal and held it to see if it would start then came a bang and I stopped to see what happen. Well there was a lot of smoke coming from my NOMA extension box. It seems that when the grinder was plug in it wanted to use the grinders ground to the extension box not the ground on the welder.
So anyone using a 255EXT with power tools on the same thing you are welding and it is plugged in might have this problem.
Good news is the it did not do anything to the PowerTig 255EXT just the NOMA and the plug on the grinder the welder works just fine.

[Rambozo]

Well I pushed the welder to the limit on the pedal and held it to see if it would start then came a bang and I stopped to see what happen. Well there was a lot of smoke coming from my NOMA extension box. It seems that when the grinder was plug in it wanted to use the grinders ground to the extension box not the ground on the welder.
So anyone using a 255EXT with power tools on the same thing you are welding and it is plugged in might have this problem.
Good news is the it did not do anything to the PowerTig 255EXT just the NOMA and the plug on the grinder the welder works just fine.

Something funny is going on there. There should never be any current flowing through the ground wire. My initial reaction would be phase issues, except that i know your power is all single phase. With the age of the grinder, I wonder if it had some leakage between hot and ground, maybe metal dust inside. Seems like some kinda ground loop or something. Glad to hear that everything is ok.

[Kempy]

Something funny is going on there. There should never be any current flowing through the ground wire. My initial reaction would be phase issues, except that i know your power is all single phase. With the age of the grinder, I wonder if it had some leakage between hot and ground, maybe metal dust inside. Seems like some kinda ground loop or something. Glad to hear that everything is ok.

Good try but I just put my old impact gun on the bench all metal one and the same, so I used a all plastic drill it welded no problem tried an all metal wood cutting saw and no can weld. So it must have something built in the welder to prevent the welder from getting feedback some how I will let the Everlast team figure it out.

[Rambozo]

Good try but I just put my old impact gun on the bench all metal one and the same, so I used a all plastic drill it welded no problem tried an all metal wood cutting saw and no can weld. So it must have something built in the welder to prevent the welder from getting feedback some how I will let the Everlast team figure it out.

Well something is not right for sure. The welding output should be totally isolated from the mains and from ground. At worst massive line noise inductance or back EMF might trip an error code, but it should never do anything like that. I don't understand exactly what you are describing, but you should be able to measure between things and find out if you have some strange ground loop going on. Is the metal table grounded, or have anything connected to it that can complete a circuit?

[Rambozo]

I must have missed your first post. Ok so from the picture, I guess the table is grounded via the grinder's power cord. So the welder was putting power through that. That is not right at all and means the isolation in the welder is not 100%. Some how there is some leakage between the welding circuit and the input power. Out of curiosity were you welding with AC or DC?

[Kempy]

I would say if we don’t have a schematics of the welder it is hard to tell what the welder is thinking when something goes wrong it might have diodes that will not let it feedback and like Rambozo said it will take the easiest path. By the looks of the plug the black wire shorted to the ground because of grinding dust and with HF to help the jump it said a short cut here I come. I am not an electrician but I understand most of the theory of AC and DC and some of the parts that go with it if I have a schematics of what is going on.
As I said earlier in the forum the factory will figure it out and fix it as Duncan told me all the testing is done with the cover off and then it is put back on at the end and test again on a cart without a grinder or power tools plug in on it. Sh_t happens but the factory is aware of it now and will fix it and so far it is an isolated problem.

[Kempy]

Problem solved it weld OK even with the grinder plugged in change the white and black to see if it made a difference and it did not all is well.

[Rambozo]

That totally explains it. That was one side of the output bonded right to the case ground. So when your table was grounded via the ground wire on your grinder or other power tool that has a grounded case, you had a nice big ground loop. I am somewhat surprised that the machine could not detect that it had an internal short to ground on one of the outputs. Out of curiosity, was the short on the bus that fed the torch lead or the work clamp? There really should be more of an air gap between something like that and the case. I know it's pretty tight in there, but is there a chance that something got bent, and there is room to bend it back away from the case? Relying on a thin piece of tape or even heatshrink in direct contact with the case is not good. Especially if there can be HF on that.

[RichardH]

Does the picture here include a GFCI on either the grinder's or the welder's outlet? I would have expected them to trip. (I know GFCI detects an imbalance between hot-hot or hot-neutral currents; do they also trip if current is detected on ground?)

Considering how the current smoked the 120v receptacle, it'd be wise to inspect the ground wiring from the 120v receptacle back to the panel's bus, and do the same for the 240v circuit, particularly the ground wires inside the welder.

I'm trying to grasp why the electrical path would prefer the building ground over the heavy ground clamp wire. It'd guess it's because the short was actually on the torch lead, so a path existed from the ground clamp, to the building ground via the grinder, through the case, and to the torch lead. This would have been a much lower resistance path than through a spark gap to the torch electrode, which would explain why it wouldn't strike an arc, yet current was flowing through the grinder as soon as you hit the pedal.

My $.02,
Richard

[Rambozo]

Does the picture here include a GFCI on either the grinder's or the welder's outlet? I would have expected them to trip. (I know GFCI detects an imbalance between hot-hot or hot-neutral currents; do they also trip if current is detected on ground?)

Considering how the current smoked the 120v receptacle, it'd be wise to inspect the ground wiring from the 120v receptacle back to the panel's bus, and do the same for the 240v circuit, particularly the ground wires inside the welder.

I'm trying to grasp why the electrical path would prefer the building ground over the heavy ground clamp wire. It'd guess it's because the short was actually on the torch lead, so a path existed from the ground clamp, to the building ground via the grinder, through the case, and to the torch lead. This would have been a much lower resistance path than through a spark gap to the torch electrode, which would explain why it wouldn't strike an arc, yet current was flowing through the grinder as soon as you hit the pedal.

A GFCI on the grinder wouldn't have helped, as they do not break the ground line even if it tripped. A GFCI on the welder circuit might not have tripped either. Hard to say as the balance between hot lines should have still been ok. I'm not really sure as I am not sure of the ground current detection system used in a modern one. Last time I took one apart, they were still just called a GFI and didn't do anything but watch for imbalance between conductors via a small transformer. In theory the welding output is completely isolated from the input, so the GFCI might not even detect it. The ground wire to the grinder was no doubt a terminal bolted tightly to the chassis, and the grinder was bolted to the table so that ground path was pretty good. The point of highest resistance was probably the oxide layer on the plug and outlet, hence where it went poof. Combine that with the ground clamp of the welder being on a dirty part of the table or part, and a layer of oxides here and there, and the resistance could be much higher. You can see why ground loops can do the damnedest things. The torch lead bonded to the case does seem to be the best fit with what happened, though.

[kafer]

did you resolve your problem?
I have a 255ext on order and soon to arrive and I have a steel bench that I weld on
I also have my grinder and drill press on the same bench

[performance]

did you resolve your problem?
I have a 255ext on order and soon to arrive and I have a steel bench that I weld on
I also have my grinder and drill press on the same bench

See post 17, just a wire had rubbed against the cover...when it was on the final assembly after testing.

[Kempy]

See post 17, just a wire had rubbed against the cover...when it was on the final assembly after testing.

Mark
Just saw you post and for Kafer to look at post #17 just finished welding a snowmobile ski's and a titanium exhaust system will put pic's later. The weld is working just great.

[kafer]

thanks appreciate the quick responce