Power Sources & Characteristic Curves
Why the machine regulates differently depending on the process — drooping and constant characteristic
AI generated The power source is the heart of every welding system: it delivers current and voltage. But not every source regulates the same — TIG and stick need a drooping characteristic, MIG/MAG a constant one. Whoever understands the difference understands why their behaves the way it does.
The power source is the heart of every welding system. It delivers what keeps the alive: current (amps) and voltage (volts). Together they make up the power — P = U · I. The current determines how much material melts off, and the voltage determines how long and stable the burns.
The key term is the characteristic curve: it describes how voltage changes when current rises or falls. And there are two basic types that belong to two different welding process worlds.
Drooping characteristic (constant current) — for TIG and stick
Here, voltage drops when current rises. That means the source keeps current as constant as possible, even if your hand trembles a bit and the constantly changes.
Why is that important? With TIG and stick, you guide the or the by hand — the arc length inevitably fluctuates. With a drooping characteristic, the current stays almost the same anyway, penetration is uniform, and the weld bead stays clean. The welder sets the current on the machine; the voltage adjusts itself to the arc length.
Constant characteristic (constant voltage) — for MIG/MAG
Here, voltage stays almost constant, and current adapts. That's the basis of the famous self-regulation in MIG/MAG : the is fed at a constant speed. If the wire stick-out gets shorter, current rises, the wire burns off faster — and the stick-out self-corrects. If it gets longer, current drops, the wire burns off slower. The thus stabilizes itself automatically.
Add the second relationship you should have a feel for: Longer = higher . If you lift the torch, voltage rises and the gets wider and flatter; if you dip down, it drops and penetration gets deeper. That's exactly why you can see on the voltage display how long your is right now.
For practice, that means: with TIG/stick you set the current, with MIG/MAG the voltage (and wire feed speed). The machine does the rest — provided it has the right characteristic for your process.