Step 13 / 14

How does an inverter welding machine work?

Old welders carried a 20 kg iron transformer; an inverter welder does the same job with a palm-sized ferrite transformer at 50 kHz. Compare idle, welding and stuck-rod states on the diagram, strike the arc in the simulation to see how the control holds the current constant, then identify the parts on the board drawing.

Mains + switch

The thick mains cable and the on/off switch on the back panel. A 160–200 A machine can draw 15–25 A from the mains while welding: that's why it can trip a 16 A breaker and why the arc gets weak on a thin extension lead.

Oscilloscope

Multimeter230 V AC, ≈0.3 A idle

Tap a block to see what it does and what you'd measure there.

⚡ Arc simulation: the machine that holds the current constant

Set the current, strike the arc, move the electrode closer and further away. On the chart the machine's 'drooping' characteristic (orange) crosses the arc line (blue): that's the operating point. When the arc length changes the voltage changes but the current stays almost the same; the control board does this by adjusting the pulse width.

Arc length:

Current setting (knob)120 A

Voltage

66.0 V

Current

0 A

Arc power

0.00 kW

From the mains: ≈40 W, ≈0.2 A

Primary pulses (PWM)%85

≈50 kHz in reality (20 µs per period); shown slowed down.

Idle: ≈66 V at the holder (OCV). With no current flowing the control sees 'too little current' and opens the pulses fully, but only a small magnetising current flows through the transformer.

⚠ A real arc gives off intense UV and infrared light: even a few seconds with the naked eye causes 'arc eye' (burning, gritty eyes). Always use a DIN 10–11 welding mask, gloves and long cotton sleeves, and protect people around you. The ≈66 V at the holder is dangerous with wet hands.

🔧 Inside the welder: what's where?

This drawing isn't a photo; it follows the typical layout of 120–250 A inverter MMA welders. The top edge is the back panel (cable entry, fan), the bottom edge the front panel (sockets, current knob). Tap a region, pick a mode above and follow which terminal of which part the energy passes through.

Energy path:

Tap a region to see what it does and how to spot it on the board.

📷 Real-world view

A compact inverter MMA (stick) welding machine

An electrode holder, its cable and different covered welding electrodes

Stick (MMA) arc welding with a welding helmet and gloves

Fotoğraf: Just a Man, CC BY 4.0, Wikimedia CommonsFotoğraf: Triddle, Kamu malı, Wikimedia CommonsFotoğraf: Weldscientist, CC BY-SA 4.0, Wikimedia Commons

🔒 This content is in the repair pack

The repair pack unlocks all interactive content in one go: diagrams and current flows, the Repair Workshop, simulations, concepts, IC guides, the Component Library and comparison guides. One sample in every section is free.

Repair pack: 5,000 ₺, members get 10% off → 4,500 ₺. Or 1-week access for 1,000 ₺.

⚠ Safety: The DC bus capacitors stay above 300 V for minutes after unplugging: discharge them through a resistor and measure before touching. Always do the first power-up after a repair through a 100–200 W incandescent bulb in series. Never look at the arc with the naked eye: the UV burns your eyes, use a DIN 10–11 mask.

Next step: Step 14How does a PLC (programmable logic controller) work?→

Go further

Repair Workshop: find the welder fault by measuring First power-up after repair: series bulb The same idea: IGBT bridge, NTC and relay in a VFD Topology: forward converter PWM controller: SG3525 pins Concept: current sensing Concept: dead time Component: NTC thermistor