Welder Duty Cycle Calculator

How it works

D₂ = D₁ × (I₁ ÷ I₂)² (capped at 100%); continuous current I₁₀₀ = I₁ × √D₁; weld time per period = D × period

A welder's duty cycle is the share of a 10-minute period (5 minutes on older US ratings) that it can deliver a given current before its thermal protection trips: "200 A at 40%" means four minutes of welding and six of cooling. Because resistive heating rises with the square of the current, backing off the amperage extends the allowable time dramatically — the same machine typically runs continuously at about 63% of its rated current — while pushing above the rating collapses it. Ratings are tested at 40 °C ambient; a hot shop or blocked fan intake trips the cut-out sooner. Hobby inverters advertise high peak amps but often only 20–30% duty there, which matters for long structural seams and for aluminium, which needs high current.

Worked example

A machine rated 200 A at 40% can weld 4 minutes in 10 at 200 A; at 160 A the duty cycle rises to 40% × (200/160)² = 62.5% (6.3 minutes), and at 126 A it runs continuously. At 220 A it drops to 33%.

Frequently asked questions