Inverter vs. Transformer MIG Welders – What’s the Difference?

Kevin is working on the bottom of one of his Shitake Agave garden sculptures, comparing his Miller Millermatic 251 MIG welder to Longevity’s ProMTS 200 multifunction (“MIG, TIG, Stick”) welder.

Kevin says there are three big differences that come to mind immediately. Transformers are big, heavy, durable machines that you put on a skid and leave somewhere or put on wheels. Inverter based MIG machines tend to be smaller, suitcase sized machines, something you can pick up and carry. Some are so small they come with a shoulder strap.

You also get more functionality from inverter machines. Kevin gives the example of the burn back function on this particular welder. Burn back is when you let go of the trigger and the welder sends a little charge into the end of the wire to burn wire the back to the same length every time, helping make your welds more consistent. His old Miller doesn’t have that function.

Another big difference is cost. The ProMTS costs about $1,000 on the Longevity Web site, whereas Kevin thinks he spent just under $4,000 for his Miller when he bought it about 10 years ago. Perhaps as important, Kevin shows the power cords of both machines and says inverters are much less expensive to run. The ProMTS can even run on 110 volts!

Next, Kevin fires up both welders, setting them at 220 volts. The Longevity sets its own wire speed at 137 inches, while Kevin has adjusted the Miller to feed about the same, although the Miller’s panel says 302. Kevin says the two welders just display wire feed differently.

As he gets ready to do some test welds, Kevin suggests you listen for the difference in the sound between the two welders. First he welds with the Longevity, then he welds with the Miller.

Next, Kevin shows you the welds from the two machines, as well as a few TIG welds, all on the same metal, very thick hardened steel. Kevin says he can’t see much of a difference between welds from the two MIG welders, although the Longevity’s wirefeed may have been a little higher and the Miller’s voltage may have been a bit higher. Kevin says the two welders seem to be comparable as far as the actual welding.