Lincoln sp125plus mig welder

A statement made by a manufacturer like "weld up to 3/8" in one pass" is pretty vague.

I would judge a machines capability based on highest possible output in amperage and also by duty cycle. In wire fed welders, 130 amps will usually be enough to join 3/8" material. You can do it in one pass or more. Joining thicker material than that is not advised. Not even on multiple passes. The mass of the parent material draws too much energy from the arc, and heat generated is not sufficient enough to overcome and produce a good weld bead.

I would assume that when you see an ad that says "Up to 3/8" in one pass" that probably means you're at maximum output. If someone at that place of business can't answer your welding questions to your satisfaction, don't buy a welder there. There will be other questions that come up and it's hard to ask them from someone who didn't get your business but probably deserved it based on service.

If I haven't answered your question to your satisfaction, please e-mail me in regard to that and I will take another stab at it.
steve

You might want to be sure the polarity is set to DC-. Another important factor is the stick out. I don't know why some of these manufacturers don't provide more info on parameters for their product. The stick out for your wire is probably about 1/4" to 3/8". Try the shorter length first and increase your arc length slowly. As you do this, listen carefully to the sound to determine the point at which the spatter increases. When you find that point, shorten the arc length until you obtain the smoothest arc. That's your proper stick out. Wire fed machines are volt sensitive. The longer the arc length, the higher the voltage. The higher the voltage, the more spatter and the less penetration you get.

You also need to control moisture in the electrode. Open arc continous electrodes are just as susceptible to moisture pick-up as covered electrodes.

Another consideration is line loss if you are using an extension cord. If the fan speed pulls down when you strike the arc, that is indicative of line loss.

Finally, direction of travel is a factor. Wire welders penetrate when pushed. Stick welders penetrate when pulled. That's why you burn thru on thin sections when dragging a SMAW electrode. Pushing eliminates most of it.
HTH
Steve

You mentioned your Bobcat. If the wire welder starts to run the way you like, you can use it for a portable machine by running it off the Bobcat. You have power to spare. 5000 watts of auxilliary power will run a 125 amp machine at full power.
Steve