Since I firmly advised ( :-0 ) Mr Stewart yesterday that testing for HF
core loss can only be done with a single winding in place - I decided to
try out my own suggestion.

I had a standard 160 VA toroidal core (with plastic covers ) left over from
an old project - so I would 40 turns of 1mm copper wire onto it, spread
evenly around.

I used a SS amplifier to drive the winding with a 2 ohm WW resistor in
series to allow current sensing - a dual beam scope monitored the drive
voltage and current waveforms. The input level was held at 5 volt rms and
the traces overlapped on the scope screen to allow the relative phase angle
to be measured at each frequency.


Hz phi PF mA mW

50 36 0.8 100 400

100 35 0.82 85 348

300 35 0.82 58 239

1k 29 0.88 42 185

3k 25 0.91 34 155

10k 22 0.93 27 126

30k 23 0.92 21 97

100k 24 0.92 17 78



Points to note:


1. The phase angle is always lagging and fairly constant.

2. Both current and power fall with rising frequency all the way to
00kHz - and beyond.

3. The is no secondary winding to bugger things up.

4. The core was just showing signs of saturation at 50 Hz and 5 volts.

5. The resistance of the winding was 0.16 ohms - making copper loss a
negligible at 1.6 mW at 50 Hz.




............ Phil