PA140st arc stability

I've just posted under "introduce yourself", and thought I should keep the technical details in a more appropriate thread.

I have just received my second PA140st in three weeks, and have seen the same problems with each machine.

SETUP:

Welding new, clean mild steel in a super nice environment using the tig torch supplied with the unit. Using a gas lens and either a 1/16 2% thoriated or a 3/32 lanthanated electrode with Argon at 10 CFH.

Running on 230VAC on a 50A breaker.

Ground clamp and cable are obviously new and attached securely to a cleaned spot on the workpiece.

The cables are attached properly, workpiece (+) and torch (-).

Output measures approx. 65 VDC at 10 amp setting, and 70.4 VDC at 140 amp setting.

PROBLEM:

An arc cannot be struck at a current setting under 17-18 Amps. There is a tiny spark when the electrode is lifted but no arc is sustained until the current control is past 17 amps.

When the current control is advanced until an arc can be sustained, the output current varies from low to high, and at lower settings it will extinguish at the low point. When the control is advanced to around 25 Amps the arc will sustain but the current varies. The problem seems to be worst at low settings and is partly masked at higher currents although the variations are still there.

The output voltage changes from about 9 VDC to 17VDC at a rate of approximately 1 to 2 Hertz measured at the cables. The high voltage corresponds to the stronger arc, and the low voltage occurs when the arc is smaller.

MORE INFO.

Machine seems to work reliably in stick mode, actually welds very well.

Problem occurs immediately upon start up and does not seem better or worse after a bit of warmup.

I can supply more details if needed, I've practically emptied a tank of Argon fooling with it......

Hope someone has seen this before, I'm completely baffled.

Regards, Neil

This is probably a silly question, but have you checked the consistency of your mains power? Mains power is usually pretty solid, but given that two separate machines have had the same problem, it may suggest something outside the machine causing the issue. If your mains power shows steady when the machine isn't plugged in, another thing you can do is clip some tiny alligator clips to the prongs on the plug, then plug it in to the wall, sandwiching the alligator clips between the plug and the wall. I can usually get the plug in far enough to make contact while still leaving the alligator clips attached. This allows me (or a helper) to monitor the line voltage while welding. Obviously, use some common sense when doing this and don't electrocute yourself or anybody else.

If you care to remove the cover of your machine, you could also clip a multimeter on to the lugs where the power line goes into the machine. This would also allow you to confirm that your plug and your receptacle were wired up correctly.

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Originally Posted by joshuab

This is probably a silly question, but have you checked the consistency of your mains power? Mains power is usually pretty solid, but given that two separate machines have had the same problem, it may suggest something outside the machine causing the issue. If your mains power shows steady when the machine isn't plugged in, another thing you can do is clip some tiny alligator clips to the prongs on the plug, then plug it in to the wall, sandwiching the alligator clips between the plug and the wall. I can usually get the plug in far enough to make contact while still leaving the alligator clips attached. This allows me (or a helper) to monitor the line voltage while welding. Obviously, use some common sense when doing this and don't electrocute yourself or anybody else.

If you care to remove the cover of your machine, you could also clip a multimeter on to the lugs where the power line goes into the machine. This would also allow you to confirm that your plug and your receptacle were wired up correctly.

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Thanks for posting. As soon as I hit "submit" I figured someone would mention mains voltage. The plug is connected to the entrance box via #10 wire and powers a variety of machinery including a 5Hp motor. I have not put a meter on it under load, but have verified 230 VAC at the outlet. I'll do it just to rule out everything.

Just thought of something, maybe I should try it on 110VAC just to see if there's a difference in results.

Neil

Out of curiosity, were all the accessories exchanged as well, or just the machine? The reason I ask, is that there was one report of bad connections inside the DINSE connectors at the ends of the cables. You can pull back the rubber boots to check those, although I really doubt that fits all your symptoms.
I do find that the machine will go much lower on 120 VAC so I tend to use that for low amp welding, but it works fine on 240VAC, just not quite as low. I have never had the overload light even blink. Does this machine have that lamp flashing, or was that just the first machine?
I know I did measure the OCV, voltage under load, and current, when I first got the machine, but I can't remember what they were, so I will have to check again.

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Originally Posted by NWD43

Thanks for posting. As soon as I hit "submit" I figured someone would mention mains voltage. The plug is connected to the entrance box via #10 wire and powers a variety of machinery including a 5Hp motor. I have not put a meter on it under load, but have verified 230 VAC at the outlet. I'll do it just to rule out everything

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Your mains is probably fine. I just figured it was worth mentioning. Trying on 110v isn't a bad idea. I'm sure someone from Everlast will chime in tomorrow, when they're back in the office. Or you could take the initiative and call in and ask for tech support.

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Originally Posted by Rambozo

Out of curiosity, were all the accessories exchanged as well, or just the machine? The reason I ask, is that there was one report of bad connections inside the DINSE connectors at the ends of the cables. You can pull back the rubber boots to check those, although I really doubt that fits all your symptoms.
I do find that the machine will go much lower on 120 VAC so I tend to use that for low amp welding, but it works fine on 240VAC, just not quite as low. I have never had the overload light even blink. Does this machine have that lamp flashing, or was that just the first machine?
I know I did measure the OCV, voltage under load, and current, when I first got the machine, but I can't remember what they were, so I will have to check again.

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I replaced the whole kit. Both machines work fairly similarly but the second one seems to be just a touch better. I know there must have been a cable problem in the past because the phone tech really grilled me about checking the cable connections. Just for fun I rigged up a ground cable that's about 4 times heavier than the std. one, and bolted the end to the workpiece just to see. Can't even strike an arc on the end of the ground cable! I'll wait a bit to see if there is any comment from the company folks before I call tech support again. Neil

Not sure, but the issue still sounds like a connection issue.

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Originally Posted by performance

Not sure, but the issue still sounds like a connection issue.

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Since the machine stick welds fine, maybe that points towards a problem with the TIG torch?

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Originally Posted by performance

Not sure, but the issue still sounds like a connection issue.

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Assuming that it IS a connection issue, what sort of test do you recommend? I have tried two ground cables, a series of clamps, two Everlast tig torches, one Weldcraft size 17 torch (which works perfectly on my Lincoln), two different gas lenses, two sizes of cup, and two sizes of electrode. I'm running out of things to change and the performance is EXACTLY the same with any of the above parts. The problem seems to be in the lift-start circuitry. I have switched to stick mode and sacrificed the electrode a bit during arc-start, but the arc is stable and it welds OK.

Is there any other test that I can run? I'm a 30 year electrical design engineer with a lot of test equipment at my disposal so I can do almost anything needed and am not afraid to do some serious testing. It would be easy to simply send it back for a refund but I'd REALLY like to understand how my results can be so different from everyone else.

One interesting point: Most of the comparison tests I've seen are all being run at higher currents than what I need. Is it a lot trickier to use these machines at low currents?

Still hoping for that magically simple answer, Neil

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Originally Posted by NWD43

The problem seems to be in the lift-start circuitry. I have switched to stick mode and sacrificed the electrode a bit during arc-start, but the arc is stable and it welds OK.

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You know, I didn't realize you were talking about the TIG torch when you said it welds fine in stick mode. You may already know this, but what you're describing is known as scratch-start TIG, and it's been a standard way of running a TIG torch off of a stick welder for years. HF is required for AC TIG, and as you point out, lift start or HF will help preserve your electrodes, but scratch start is tried and true.

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One interesting point: Most of the comparison tests I've seen are all being run at higher currents than what I need. Is it a lot trickier to use these machines at low currents?

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I have a PA160-STH. Not the exact same machine as yours, but not a high-end purpose-built TIG welder either. It's rock solid at whatever output I set it to, high or low. None of this wavering that you talk about. I don't typically weld at low amperage, and I use HF start when I do, so I can't speak to how its lift start works at low amperage.

It's so weird that you have two machines with exactly the same problem. It sounds like you're no stranger to welding, and like you have ruled out many of the obvious things except for the machine itself.

OK, I checked again and here is what I found. Open circuit voltage is right at 69 volts and is bang on over the whole amp range. There is some thermal drift over time, but it's less than .1 volt and again is constant over the whole amp range. This is the same in stick mode and TIG mode, BTW.

Attachment 11865 Attachment 11866 Attachment 11867 Attachment 11868

So clearly you have a problem with your machine and how far you want to dive into it is up to you. Very odd that you got two bad ones.

Mine is very stable down to 10 amps on 240VAC sorry I forgot to check on 120VAC, but as I recall it will go down to 7 or 8 on 120VAC. The actual output is a little higher than what is displayed, and that is pretty consistent everywhere. Checking under load, the output is very stable with just a little droop at longer arc lengths. In the low range it can handle arc lengths up to about 15 volts before it cuts out. With the panel set to 10 amps, a short arc would yield 13.6 amps @ 11.5 volts, while a super long arc would be 12.2 amps @ 14.8 volts. At the 15 amp setting the results are about the same 18.9A @ 11.5V vs 18.0A @ 13.3V

Attachment 11870 Attachment 11869 Attachment 11872 Attachment 11871

You answered my one other question about checking in stick mode. I frequently forget to flip the switch, and not only will the automatic hot start take it's toll on the tungsten, but the auto arc force also plays with the amperage and causes some of what you describe. I wonder if that is not being switched out on your machine? As the voltage goes down it will crank up the current but it is not reflected in the panel display reading.


BTW joshuab, using this kind of machine is stick mode is not quite the same as a normal scratch start setup on a true CC machine. There is that annoying auto hot start and auto arc force that can't be turned off. Also HF is not required on all AC TIG. True sinewave needs HF on all the time to stabilize the arc through the zero crossings, especially at low power. Squarewave machines can get by with just HF start or none at all since they have very rapid zero crossings.

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Originally Posted by Rambozo

OK, I checked again and here is what I found. Open circuit voltage is right at 69 volts and is bang on over the whole amp range. There is some thermal drift over time, but it's less than .1 volt and again is constant over the whole amp range. This is the same in stick mode and TIG mode, BTW.

Attachment 11865 Attachment 11866 Attachment 11867 Attachment 11868

So clearly you have a problem with your machine and how far you want to dive into it is up to you. Very odd that you got two bad ones.

Mine is very stable down to 10 amps on 240VAC sorry I forgot to check on 120VAC, but as I recall it will go down to 7 or 8 on 120VAC. The actual output is a little higher than what is displayed, and that is pretty consistent everywhere. Checking under load, the output is very stable with just a little droop at longer arc lengths. In the low range it can handle arc lengths up to about 15 volts before it cuts out. With the panel set to 10 amps, a short arc would yield 13.6 amps @ 11.5 volts, while a super long arc would be 12.2 amps @ 14.8 volts. At the 15 amp setting the results are about the same 18.9A @ 11.5V vs 18.0A @ 13.3V

Attachment 11870 Attachment 11869 Attachment 11872 Attachment 11871

You answered my one other question about checking in stick mode. I frequently forget to flip the switch, and not only will the automatic hot start take it's toll on the tungsten, but the auto arc force also plays with the amperage and causes some of what you describe. I wonder if that is not being switched out on your machine? As the voltage goes down it will crank up the current but it is not reflected in the panel display reading.


BTW joshuab, using this kind of machine is stick mode is not quite the same as a normal scratch start setup on a true CC machine. There is that annoying auto hot start and auto arc force that can't be turned off. Also HF is not required on all AC TIG. True sinewave needs HF on all the time to stabilize the arc through the zero crossings, especially at low power. Squarewave machines can get by with just HF start or none at all since they have very rapid zero crossings.

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Thanks for taking the time do do the testing! I have inserted a high-wattage shunt (1 ohm) in series with the ground lead and measured the current under various conditions:

Dial set to minimum (11A), with electrode touching work the current is 8.17A
Dial set to 30, current measures 20.5A
Dial set to 50, current measures 27A

With dial set to 20 (the lowest setting that will establish an arc, current measures 9.7 to 10.1A
In order to get 20 A of measured current, dial must be set to 40A

Here's the interesting part- with the 1 ohm shunt in place, the variations in current and the flashing duty cycle lamp go away!

Gotta think about this while waiting for CA to wake up....... Neil

Internally Rambozo, that is a much different machine that you have than the newer ones with the rocker switch...though performance should not be vastly different.

It sounds as if the display has some calibration issues.

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Originally Posted by Rambozo

BTW joshuab, using this kind of machine is stick mode is not quite the same as a normal scratch start setup on a true CC machine. There is that annoying auto hot start and auto arc force that can't be turned off. Also HF is not required on all AC TIG. True sinewave needs HF on all the time to stabilize the arc through the zero crossings, especially at low power. Squarewave machines can get by with just HF start or none at all since they have very rapid zero crossings.

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You're 100% right. These were details that I chose to leave out.

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Originally Posted by performance

It sounds as if the display has some calibration issues.

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According to the phone tech. if the duty cycle/OT lamp lights it indicates an internal problem with the machine. Have another one on the way for the third and final test. A product review of the PA140 on Amazon related the exact same problem but the reviewer was so inexperienced that he thought it was just a normal characteristic of the machine. I'm learning things I probably should already know about price/performance expectations.

With crossed fingers, Neil

We've had very very few issues out of the 140ST...or any of the powerarc welders.

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Originally Posted by performance

We've had very very few issues out of the 140ST...or any of the powerarc welders.

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I believe what you say because one of the things that enticed me to buy this model was the lack of much negative stuff on the forums.

I got the new one today (Amazon is AMAZING as far as returns go) and fired it up as fast as I could. This one seems to work much better than the other two. I tried a bunch of stuff at around 20 Amps and it works very well. Unlike the others, I can strike an arc at an indicated 10 Amps, but the duty cycle lamp flashes and the arc goes out. As soon as I increase the current to about 12 on the display it works OK, so it's an improvement but still not "as advertized" performance. I tried some 22 gauge stainless and cannot reduce the current enough to do nice work, big disappointment since that's typically the kind of thing I do. Gotta keep remembering I can't compare it to the Lincoln.....

I have heard several times from tech support that the duty cycle lamp should NOT light at any time other than to indicate over-temperature. If it does then something is wrong. Since the lamp always lights during lift-arc starts, I assumed that was normal (book does not mention this) but should never light otherwise. Since the lamp flashes during low-current operation, I'm sure that the problem is with the lift-arc circuitry.

I'm kind of sick of yappin' about this. Just wish the units would work as they should, but every time I get too picky I remember the price, and being a veteran of the product development business I know that when the money comes out something is traded off. I'll probably keep this one since it does most of what I want and I need the portability.

Thanks to all for the generous help and advice, Neil

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Originally Posted by NWD43

I believe what you say because one of the things that enticed me to buy this model was the lack of much negative stuff on the forums.

I got the new one today (Amazon is AMAZING as far as returns go) and fired it up as fast as I could. This one seems to work much better than the other two. I tried a bunch of stuff at around 20 Amps and it works very well. Unlike the others, I can strike an arc at an indicated 10 Amps, but the duty cycle lamp flashes and the arc goes out. As soon as I increase the current to about 12 on the display it works OK, so it's an improvement but still not "as advertized" performance. I tried some 22 gauge stainless and cannot reduce the current enough to do nice work, big disappointment since that's typically the kind of thing I do. Gotta keep remembering I can't compare it to the Lincoln.....

I have heard several times from tech support that the duty cycle lamp should NOT light at any time other than to indicate over-temperature. If it does then something is wrong. Since the lamp always lights during lift-arc starts, I assumed that was normal (book does not mention this) but should never light otherwise. Since the lamp flashes during low-current operation, I'm sure that the problem is with the lift-arc circuitry.

I'm kind of sick of yappin' about this. Just wish the units would work as they should, but every time I get too picky I remember the price, and being a veteran of the product development business I know that when the money comes out something is traded off. I'll probably keep this one since it does most of what I want and I need the portability.

Thanks to all for the generous help and advice, Neil

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You could compare it to a Lincoln, but only to something like an Invertech V155-S

No one has ever mentioned the duty cycle lamp flashing, I do not think that is normal at all. Out of curiosity, have you tried it on 120 volts? I find that for real low amp work, it's much more controllable when running on low voltage. I have added a finger amptrol, and always light up at 10 amps and its very stable. I am wondering just what they changed in the new version. I wasn't expecting it to be a real low amp TIG unit as that is not what it was designed for, but I have been more than pleased with it's performance. On 120v the displayed current was 8 - 9 amps to do this with some .030 MIG wire for filler. Not a great job, but that's more my vision than the machine.

Attachment 11885

It's not just a duty cycle light. It's a overcurrent light as well.

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Originally Posted by performance

It's a overcurrent light as well.

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Does that suggest a supply problem? The mains issue was discussed earlier and ruled out, I thought, but machine number 3...?

It could be an internal resistor value issue. I am not familiar with the revised 140st's internally, but on some of the older ones, there was an adjustment that could be made.

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Originally Posted by DaveO

Does that suggest a supply problem? The mains issue was discussed earlier and ruled out, I thought, but machine number 3...?

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It's absolutely not a mains issue, I can run anything I want to on this circuit without fail. Measures 139VAC under load. I have tried it on 120V and it displays the same performance except for the limitation on high end current. It DOES work better than the other two before it so I'm happy for that.

PERFORMANCE: What is an "over current" lamp? If I set the current to 10A shouldn't the machine supply 10A into the load? How can it supply more than it's set for and then complain that I'm asking for too much current?? I should think that, normally, we get less current than we expect due to I/R losses in the leads, resistance between clamp and work, etc., but never more current than we call for. What part of this do I not understand?

As I said before, I'm prepared to keep and use this thing for all the things it can do, and keep my expectations under control.

Neil

First, it is an analog machine. Every unit has a margin of error in settings overall...Resistors and such have a 10% margin of error...so at times things can go a little over or under. The display is there for general reference and cannot be expected to be spot on. Equivalent models in most name brands do not even offer this feature at all. The overcurrent/overheat light is multi color. It can sense an over current or duty cycle issue, and changes color to reflect that (not sure which color is assigned to which on the newer units. That would be a Ray question).

I have no answer why the overcurrent/voltage or duty cycle light is coming on other than the resistor value is slightly off in the circuit that senses it or the arc initiation...I am not the electronics expert...but I do know some general things about the welders operation and design.

I will say this....that 139 volts under load is too high of voltage for what the machine is rated for 120V +- 10%. This could be causing the issue with the over voltage light flashing on. Is this being supplied by a generator?

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Originally Posted by NWD43

It's absolutely not a mains issue, I can run anything I want to on this circuit without fail. Measures 139VAC under load.

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Holy cow! That's not normal. See below, from ANSI C84.1.

Attachment 11886

You are at least 10 volts over the upper end of the normal range for 120v mains power.

EDIT: Dang it. The forum resized my image so it's not readable. Here's the original link.

http://www.pge.com/includes/docs/pdf..._tolerance.pdf

To sum up, a nominal upper limit for 120v power is around 127 volts. I don't know what you have been running on that circuit "without fail," but you're lucky to not have destroyed it with over-voltage.

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Originally Posted by joshuab

Holy cow! That's not normal. See below, from ANSI C84.1.

Attachment 11886

You are at least 10 volts over the upper end of the normal range for 120v mains power.

EDIT: Dang it. The forum resized my image so it's not readable. Here's the original link.

http://www.pge.com/includes/docs/pdf..._tolerance.pdf

To sum up, a nominal upper limit for 120v power is around 127 volts. I don't know what you have been running on that circuit "without fail," but you're lucky to not have destroyed it with over-voltage.

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Of course you're right!! My error, I meant to say 239VAC for the circuit. The 120V circuit is nominally 120V.

Neil