Inverter air plasma cutters are the most widely installed class of plasma power source in metal fabrication today. IGBT inverter technology replaces the heavy line-frequency transformer, and ordinary compressed air serves as the plasma gas, driving the cost per cut on carbon steel, stainless, aluminium and copper down to a fraction of laser or flame. The Icyrobot LGK-IGBT family spans seven current classes from 65 A to 400 A and works equally well handheld or bolted onto a CNC cutting table.
If you are specifying your first plasma power source, or matching a source to an existing cutting table, start here. The guide below covers sizing logic, real capability limits and the total cost of ownership.
Why "inverter" is the dividing line
Conventional plasma sources step 380 V down through a line-frequency transformer: bulky, copper-heavy, inefficient at no load, and easily over 100 kg for a 100 A machine. An inverter first rectifies mains AC to DC, then chops it above 20 kHz with IGBT modules, steps it down through a high-frequency transformer and rectifies again. Raising the frequency by two orders of magnitude shrinks the transformer roughly in inverse proportion, which delivers:
- 60–70% less machine weight — a 200 A unit is a two-person carry and can ride on a gantry;
- Far finer control — stepless current preset, programmable current ramp-up, and much lower arc-strike shock on electrode and nozzle;
- Wide mains tolerance — stable starting on generator power, remote sites and ageing plants with voltage swing;
- 100% duty cycle — the hard requirement for continuous industrial duty.
The capability envelope of air plasma: three gas choices
"Air plasma" simply means compressed air is the plasma gas. The advantage is that the gas is effectively free; the trade-off is a nitrided/oxidised film on the cut face. Swapping gases on the same power source changes the result dramatically:
| Plasma gas | Carbon steel edge | Stainless edge | Cut speed | Gas cost | Best for |
|---|
| Compressed air | Good, light dross | Dark, needs grinding | Medium | Very low | Carbon steel, cost-sensitive shops |
| Oxygen | Best, bright and near dross-free | Not suitable | Fast | Medium | High-quality carbon steel |
| Nitrogen / argon-hydrogen | Fair | Best, bright as-cut finish | Fast | High | Stainless and aluminium |
So: mostly carbon steel with occasional stainless → air plasma is the most economical choice. If stainless exceeds roughly a third of your throughput and you need a grind-free edge, look at a high-performance machine with a gas console. The full decision path is written up in Plasma Gas Selection for Stainless: Air vs Oxygen vs Nitrogen vs Argon-Hydrogen.
Sizing by current class: a reference table
The figures below are typical industry ranges for each current class; always confirm against the machine's own datasheet. The rule that matters is that your everyday plate thickness should sit inside the "quality cut" band, not the "maximum cut" band — running permanently at the limit degrades speed, squareness and consumable life all at once.
| Model | Rated output | Quality cut (mild steel, ref.) | Typical supply | Typical duty |
|---|
| LGK-65IGBT | 65 A | 12–18 mm | 1-ph 220 V / 3-ph 380 V | Sheet metal, ductwork, site repair |
| LGK-85IGBT | 85 A | 18–22 mm | 1-ph 220 V / 3-ph 380 V | General maintenance, farm equipment, scrap |
| LGK-100IGBT | 100 A | 22–28 mm | 3-ph 380 V | Steel structures, pressure vessels, erection |
| LGK-130IGBT | 130 A | 28–35 mm | 3-ph 380 V | Medium plate, batch cutting |
| LGK-200IGBT | 200 A | 40–50 mm | 3-ph 380 V | Heavy fabrication, main CNC table source |
| LGK-300IGBT | 300 A | 55–65 mm | 3-ph 380 V | Heavy plate, risers, demolition |
| LGK-400IGBT | 400 A | 65–80 mm | 3-ph 380 V | Extra-heavy plate, underwater, heavy dismantling |
The complete sizing walkthrough — pierce rating, cut speed, compressor flow matching and duty-cycle maths — is in How to Size an Air Plasma Cutter by Plate Thickness: 6 mm to 80 mm.
Handheld vs mechanised: same source, different package
The LGK-IGBT family supports both a handheld torch and a mechanised torch on a cutting table. The difference is not in the power source but in three external conditions:
- Torch — straight handheld torch versus a machine torch with a lifter, initial height sensing and collision protection;
- Arc voltage height control (THC) — mandatory on CNC, otherwise uneven plate means crashed torches or lost arc;
- Arc starting — high-frequency start is reliable but noisy; mechanised cells generally prefer a non-HF or contact start.
We ran the numbers on "should we put this on a table?" in CNC Plasma Table vs Handheld Cutting: Throughput and Payback.
Where the money actually goes
For a 200 A machine running three productive hours a day, electricity is only about 15% of total cost. Electrodes and nozzles account for 40–55%, with compressed air and labour making up the rest. The levers that matter:
- Current ramp-up to soften arc-strike shock (standard across the LGK-IGBT range);
- Hold gas pressure and flow inside the process window — low pressure is the number one cause of abnormal nozzle erosion;
- Dry, oil-free air. Oil and water in the supply can halve electrode life. Use ISO 8573 compressed-air quality classes as your purchasing spec;
- Constant standoff — for handheld work, use a standoff guide or roller bracket.
Diagnostics are covered in Plasma Consumables: Electrode & Nozzle Life, Failure Signs and Cost per Hole.
Frequently asked questions
Can air plasma cut stainless steel? Why does the edge go black?
Yes. Oxygen and nitrogen in the air react with the molten metal at temperature, leaving an oxide/nitride film that looks grey-black. If the part is to be welded, grind the layer off; if appearance matters, switch to nitrogen or an argon-hydrogen mix.
Does a 100% duty cycle mean non-stop cutting?
It means that at the rated ambient temperature the source can deliver full rated current continuously without thermal shutdown. The torch has its own thermal limit, and a handheld torch at high current will still get hot — rotate torches or add water cooling for continuous work.
How much current can single-phase 220 V deliver?
Limited by service capacity and voltage drop, single-phase is generally comfortable up to 65–100 A. At 130 A and above, specify three-phase 380 V, and on site check transformer capacity and cable cross-section.
Can it drive a robot cell?
Yes, but specify a non-HF start model plus analogue or digital control interfaces. HF start interferes with robot controllers — state your automation requirement up front.
Need help sizing? Send us your thickness distribution, material mix and daily arc-on time; our engineers will return a machine and accessory list within one business day. See Contact.
