Re: HV probe for primary measurements

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dbarrett1-at-austin.rr-dot-com>

> >
> > What about making a current transformer by winding some wire around a
> > ferrite core?

    This works pretty well with a bit of experimentation. I tried running
one of the lines to my primary through a small (FT-82 size) core from a
computer power supply. With a turns ratio of 1:8 it definitely transforms...
I got like 800 volts into 50 ohms. A single turn was about 1uH, so the coil
was theoretically tapping off 1/30 of my primary current. WAY too much,
probably saturated too.
     Just now I used ran one turn of HV wire through the core and
alligator-clipped it across about 3" of my pancake primary (about 1/10 of a
turn). The core secondary is 2 turns of HV wire soldered to a BNC jack. I
ran 50 ohm coax back to the scope and put a BNC 50 ohm terminator on it
right at the scope.  I got about 20v p-p. I have no idea how much real
current is being measured, but I got nice pretty pictures of the ringdown
and discovered it quenches on the 2nd notch. As far as data per dollar goes,
I'll take it!
    BTW, that core is an Amidon FT-82-77, made for use in roughly the
appropriate freq range.

db