How the Arc Pig Works


The Pig lets you strike (ignite) a welding arc without touching the electrode to the workpiece.

While you weld, the Pig monitors weld voltage in real time and fires as needed to re-ignite the arc every AC half-cycle. (This is continuous fire for TIG-welding aluminum.)

Here is how you use it:

  1. Position the electrode 1/8" from the workpiece.
  2. Press the trigger. With most welders, your arc will strike immediately.
  3. With low-voltage welders, push the electrode in closer until the arc ignites.
  4. (Optional) Shout in triumph, and run to show your friends.
  5. Tell your sons how much tougher you had it, scratch starting.

Technical Details

The Pig is a Tesla coil, a form of high-voltage, high-frequency transformer.

The Pig's high-voltage sparks are relatively safe,
because they change polarity millions of times per second.
This is why they are called HF, for High Frequency.

AC Weld Voltage With Pig

When your weld voltage approaches peak OCV (Open Circuit Voltage) the Pig fires a flurry of sparks.

The Pig measures your welder's peak OCV at power-up.
For a clean read, disable lift start and do not touch the workpiece.

With DC weld voltage, the Pig fires at regular intervals.

The Pig monitors weld voltage directly, for reliable ignition even if your weld voltage is phase shifted.

The Pig wires into your weld cables, and draws its power (about 30W) from your welder.

block diagram

The Pig sends sparks to your torch, not to your welder.


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