How many kVA spot welder do I need?

Roughly 15–25 kVA for thin mild steel up to about 1 + 1 mm (0.0394 inch), and 50 kVA or more for 2 + 2 mm (0.0787 inch) and galvanised sheet.

What is an MFDC spot welder?

A medium-frequency inverter welder giving steadier DC current, better welds on coated steels and lower power draw.

Can one machine do projection welding?

Press-type machines with flat platens can; rocker-arm machines generally cannot.

Spot welding machine: types, kVA, sheet thickness

A spot welding machine joins overlapping sheets by squeezing them between copper electrodes and passing a high current for a fraction of a second. Pedestal machines with a rocker or press-type arm suit workshop parts; portable guns reach large assemblies; press-type machines also do projection welding of nuts and studs. Machines are rated in kVA.

Quick facts

Main types: Rocker arm, press type (pneumatic), portable gun, multi-spot
Rating: About 10–150 kVA
Sheet thickness: About 0.5 + 0.5 mm (0.0197 inch) up to 3 + 3 mm (0.118 inch) in mild steel
Control: Timer with squeeze, weld and hold times; inverter (MFDC) on newer machines
Electrodes: Water-cooled copper alloy tips
Air: Needed for pneumatic types

Main parts

Welding transformer (AC or medium-frequency DC)
Arms and copper electrodes
Pneumatic cylinder or foot pedal for squeeze force
Weld timer and current control
Cooling water circuit

Good to know

Electrode tips wear and must be dressed to keep welds consistent
Galvanised and stainless sheet need different settings from mild steel
Aluminium needs much higher current and special machines
Longer arms reduce the current available at the tips

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Questions

How many kVA spot welder do I need?: Roughly 15–25 kVA for thin mild steel up to about 1 + 1 mm (0.0394 inch), and 50 kVA or more for 2 + 2 mm (0.0787 inch) and galvanised sheet.
What is an MFDC spot welder?: A medium-frequency inverter welder giving steadier DC current, better welds on coated steels and lower power draw.
Can one machine do projection welding?: Press-type machines with flat platens can; rocker-arm machines generally cannot.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 23 October 2026.