Constant power welding machine

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Traditionally, Stick and TIG welding have been done using constant current (CC). When using CC, the welding machine will provide a constant current as long as the arc exists. From physics, we know that the arc voltage is determined by the arc length. When the distance is increased between the tip of the TIG torch (or electrode in Stick mode) and the material being welded, the arc voltage increases while the current remains constant. Then as the welding power (current times arc voltage) increases, a hotter puddle is produced. Good welding results using Constant Current depends greatly on having a very steady hand, especially on thin material.

Constant Power Welding Machines offer advantages for Stick (SMAW) and TIG (GTAW) welding. When the arc length between the work piece and the tip of the TIG torch (electrode) is increased, the arc voltage increases just as it does in a constant current machine. The difference is that the Constant Power machine will sense the increase in arc voltage and will automatically decrease the current, allowing the welding power (= puddle temperature) to remain constant. Even those with an unsteady hand can weld very thin material using Constant Power without causing burn-through.

Welding machines that provide Constant Power characteristics are big motor-generator welders, where the mechanical mass rotation keeps the output power constant. This is the reason that these big welding machines have been preferred for very precise TIG welding, such as in the nuclear industry. Now there are inverter welders on the market that mimics these constant power characteristics in a small portable package.^[1]

References

1. http://www.arconweld.com/welding_faq/faq.htm