Welding current by electrode diameter
The first setting anyone makes, and the one that decides how the rest of the weld behaves. The calculator starts from the diameter and then corrects for the position, the coating and the plate thickness.
How it is worked out
The base figure is I = k · d, where d is the core diameter in
millimetres and k is 30 to 40 A/mm depending on the coating. Rutile electrodes
sit at the lower end of the band, basic ones at the upper end: a basic coating
needs more energy to melt and gives a stiffer arc.
Two corrections follow. Position: −10 % for vertical, −15 % for overhead. Thickness: on plate thinner than about three electrode diameters the current is capped so that the arc does not blow through the joint.
Checking it at the arc
The number is a starting point; the weld tells you the rest. Current too low shows as a narrow, high bead sitting on the surface, slag that will not release and an electrode that keeps freezing. Current too high shows as undercut at the toes, heavy spatter and a coating that glows red and falls away before the electrode is used up.
If you need a table to pin on the wall rather than a calculator, the same figures are laid out in current versus electrode diameter.
Frequently asked questions
Where does the 30–40 A per millimetre rule come from?
From the current density the coating and the core wire can take. Below that the coating does not burn evenly and the arc keeps going out; above it the core overheats, the coating cracks off in the last third of the electrode and the arc starts wandering. The band is empirical but it has held for decades across manufacturers.
Why does the current drop for vertical and overhead work?
Because gravity stops helping. In the flat position surface tension and gravity both hold the pool in the joint; vertical-up and overhead leave only surface tension, so the pool has to be kept small — and a smaller pool means less current, typically 10–15 % below the flat figure.
The machine dial and the actual current disagree. Which do I trust?
The measurement. Dials on cheaper inverters are marked at no load and drift under a long cable run; a clamp meter on the welding lead settles the question in ten seconds. If the reading is far below the dial, check the cable cross-section before blaming the machine.
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