Hall effect switch - pilot arc control

It seems fairly clear that pilot arc control is a little less straightforward than simply connecting the torch shield to the torch electrode. Although that works (and is how Parkside connect their conversion kit), it causes damage to the consumables and seems to rob some of the arc current.

The more professional way to control the pilot arc is to detect when the main arc is established, at which point the torch pilot connection is opened. This requires a DC current sensor controlling a beefy high voltage contactor. The contactor needs to be rated to open under load (up to 50A perhaps) and withstand a high voltage, perhaps approaching 200Vdc.

This needs to be measured at the torch connection - but configured so that it only sees the main arc current, not the pilot arc current.

Here's a Hall effect switch, fresh from China, c/o Amazon:

Again, rude not to take a peek inside. Actually looks pretty decent.

That 16 pin SOIC STC8G1K08 is actually an 8 bit micro, based on the 8051. It doesn't need an external crystal.

And the SO-8 device is an XL1509 buck regulator, also Chinese:

Here's how we need to connect up the torch with the Hall effect switch so that it detects the main arc current but not the pilot arc:

Just need a contactor and some elbow grease. Found this, which probably isn't rated for the application but perhaps it might survive if I connect the 4 sets of contacts in parallel:

It says "250Vdc, max 0.5A open". Hmm. I must see if I can find an EV contactor somewhere, as they are rated for opening high-ish DC currents. True, the only time it should open with more than a few volts on the contacts would be if the Hall switch tried to open the contactor when the pilot arc alone was lit. Not sure if that is a real condition to cater for.

Here's what a pilot arc torch looks like in action: