Field work means generator work. Turn the machine's output current and voltage into the kW and kVA the generator actually has to deliver — with a margin that keeps the lights on mid-bead.
kW out → kW in → kVA
Output ÷ efficiency = input · Input ÷ power factor = apparent power
The machine's arc runs on output watts, but the generator has to supply the input — a bigger number once efficiency and power factor take their cut. Apparent power (kVA) is what generators are rated in.
Three-phase input current: S ÷ (V × √3). Single-phase: S ÷ V. The √3 is the difference between the two systems.
A 60% duty cycle machine doesn't need a 60%-sized generator. Here's why.
Over a 10-minute window, a 60% duty cycle machine arcs for 6 minutes. The average demand is lower — that matters for fuel economy and generator cooling.
The generator must carry the full load the moment the arc strikes — duty cycle never erases that peak. A generator sized on average demand sags or trips exactly when the puddle needs the amps.
Modern inverter welders draw non-sinusoidal current and can demand high inrush at start-up. Check the machine's actual input-current rating — it's the number the generator must satisfy.
Not an exact specification. The actual generator requirement must be verified against the welding machine manufacturer's input-current requirements and the generator manufacturer's specifications before purchase or use.
The machine's input current at its rated output is printed on the nameplate — the single most trustworthy number for sizing. Use it to verify this estimate.
Rated kVA assumes clean conditions. Hot sites, high altitude, and long cable runs reduce what a generator can actually deliver — the margin is there for a reason.
When in doubt between two generator sizes, take the larger one. An undersized unit costs more in downtime and damaged loads than the price difference ever will.
Use your calculated power requirements to get an equipment recommendation for your application.
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