When I use the kickbox I made, I apply the DC voltage to the CT secondary and measure on the high side. Never saw it done in this fashion. Better meter movement when stepping it up vs stepping it down.
it fries, then it doesn't, anymore. it's DC only when it stabilizes after exponentialy increasing (because of the inductance, which resists to change of current by inducing it's own, contra voltage, right?) to the steady value...which is defined by the dc resistance of the winding. one plus the other=impedance, right? until then, ....what happens when you switch the battery off, during the current rising? ...think of it as a quasi - square signal, more of a series of pulses really, being fed to the tr.