Strange problem with MIG

I have a small Lincoln MIG (sp130?). Today I was doing a little tack
and it stubbed and then wouldn't feed. It looked like it had burned
back and was stuck to the tip. I pulled it off and it just kept coming!
WTF?? I looked under the hood and the wire was broken. Looking
closely at the break, I could see that it had burned through - there
were tiny balls on both ends. And it wasn't just one point - the wire
had been heated in several spots over 6" or so.
How can this be!? The wire is hot when the trigger is pulled (Duh).
But it is only hot relative to the the ground lead, which is isolated
from everything. I did some poking around with a VOM and found nothing
strange, even with the power on and trigger pulled. I wasn't feeding
wire, but that shouldn't matter.
I can't believe that the wire was on the spool like that, but I can't
think of how the machine could have done it either.
Any help will be greatly appreciated,
Bob
Reply to
Bob Engelhardt
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I think I know what happened. I was welding on a stand for a miter saw. The saw was bolted to the stand and plugged in. The saw frame was grounded (in house wiring sense) through it's 3-prong plug and then so was the stand. As was the welder case, through its 3-prong plug. So the saw stand and the welder case are connected through the house wiring ground. Since the welding ground was attached to the saw stand, it was equivalently attached to the welder case.
Now I put a keep-dry chamber on my welder, around the spool - see
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wire is isolated from the chamber and case by the rubber seals on the slit opening. *Except* in the far corner. There the wire could touch the vertical edge of the slit, when it is unwinding from the far side of the spool. So the wire was hot (trigger pulled), it touched the chamber, which is grounded, and burned through.
It will be easy enough to add a seal to the corner of the slit, but what I'm most worried about is that when this happened, I had welding currents through the case of my welder. I've heard that this is VERY BAD. That it can damage the welder electronics. I hope not. And I'm going to be more careful about where I attach the welding ground. Maybe I should disconnect the welder's ac ground and eliminate any possibility of welding currents in the case.
Bob
Reply to
Bob Engelhardt
I have the lincoln sp-85. Good little machine. Its a black color. I use a full size roll of wire.
I looked at yours, it looks similar, wire feeder, wing nut spring, rollers, except its black paint...
I doubted the purchase, cause it was only 110, but it works very well, for over 8 years of use. Just replace the nozzle/tip, and keep welding. I use a flowmeter on the gas bottle.
xman
Reply to
xmradio
not shure what to tell you but i have a SP135p and it's been a very good machine iv'e never had any problems with it yet
Reply to
chopper
Many bases of wire feeder are hot. If your drag tension is too loose on the wire spool the spool will over run or coast after you stop welding. If the slack is large enough it will hang and contact some part of the feeder that has welding current the next time you pull the trigger.
I have a small Lincoln MIG (sp130?). Today I was doing a little tack and it stubbed and then wouldn't feed. It looked like it had burned back and was stuck to the tip. I pulled it off and it just kept coming! WTF?? I looked under the hood and the wire was broken. Looking closely at the break, I could see that it had burned through - there were tiny balls on both ends. And it wasn't just one point - the wire had been heated in several spots over 6" or so.
How can this be!? The wire is hot when the trigger is pulled (Duh). But it is only hot relative to the the ground lead, which is isolated from everything. I did some poking around with a VOM and found nothing strange, even with the power on and trigger pulled. I wasn't feeding wire, but that shouldn't matter.
I can't believe that the wire was on the spool like that, but I can't think of how the machine could have done it either.
Any help will be greatly appreciated, Bob
Reply to
R. Zimmerman
I have the lincoln sp-85. Good little machine. Its a black color. I use a full size roll of wire.
I looked at yours, it looks similar, wire feeder, wing nut spring, rollers, except its black paint...
I doubted the purchase, cause it was only 110, but it works very well, for over 8 years of use. Just replace the nozzle/tip, and keep welding. I use a flowmeter on the gas bottle.
xman
Reply to
xmradio
Its a not uncommon baffler, this one. You probably had a short at the spool end of the wire to ground. Current would have travelled down the power cable to the contact tip; fed into the wire and back along the length of the torch to the grounding point, thus heating the wire evenly until it melted in a couple of places. You've probably also 'heat-treated' the torch liner, if it was a metal one.
Reply to
Philip Mitchell

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