Hi

How can one obtains the BH curve of a randomly picked transformer core?

Thank you

 

Prepare a small example of it and measure it in a vibrating sample magnetometer.

Sorry, but that's what we did in industry -- most people won't have access to such equipment. You could build your own looper, however -- that's what a couple engineers I used to work with did.

 

What would one expect the BH curve of a core of a Mig welder to look. i.e. points of remanence and coercevity? and would it be narrow or wide curve?

My best guess would be a very narrow curve and very low remanence and coercivity.