It would probably pretty easy to calculate the primary. The secondary is only three turns of 2AWG welding cable with approximately 12 inch leads. Total cable length with turns through core is approximately four feet. The transformer is not powered on until the secondary is shorted together through two 1/4" copper rods turned down to .060" at the tip onto a zinc or zinc plated metal tab so you are probably looking at maybe 0.5VAC but about 1100 amps, and probably 2.5VAC no load if it were to ever be powered without the tips shorted. I just got my parts from Mouser and building the control board now, and hopefully can get some exact data when I can actually make some test welds with it. Problem is, I recently had basil joint surgery on my left hand (and I'm left handed) and it's in a hard cast with my wrist and most of my hand immobilized, and soldering all those small components is proving to be no fun at all. I couldn't even work on it today because trying to do too much last night, has my hand swollen and hurting.
I've looked for CT's but finding one is proving difficult. they are either for a lot less current, or cost more than I would plan to spend if I wanted to build 20 of these things. Even thought about getting a ferrite toroid core and making one but that many turns through a doughnut is not my kind of fun.
Even considering measuring the primary and trying to do some funky math that would give me something that looked like a secondary current.
I'm also giving serious thoughts to saying p**s on it because I don't really need it, just thought the thing would look better with a meter in it.