RadioBanter - View Single Post

May 31st 06, 08:31 AM posted to rec.radio.amateur.homebrew

wrote:
I was rummaging around for a core for a small switching power supply
and came across some 1.00" OD, 0.55" ID, 0.39" high (25x14x10 mm)
toroids. A 50 turn coil measures about 1 mH (by measuring resonance
at 200-500 kHz). This appears to indicate a permeability around 600,
by comparing it with various catalogues. But the Q is rather low
(equivalent series resistance is roughly 250 ohms at 500 kHz and 120
ohms at 200 kHz). Doesn't look likely to be good enough for a
switching supply, so they may have to be relegated to EMI jobs (which
I seem to recall they were used for in a piece of equipment I took
apart).

But does anyone have any idea what material they might be ? Doesn't
at first glance appear to be anything similar to what Fair-Rite
makes. There's a good chance it is of Asian origin, I think.

73, Steve VE3SMA

Steve, the usual reason for the apparent low Q is that it is not being
measured at the frequency that will give highest Q. Try fewer turns and
higher frequencies as a first attempt. I've measured many cores this
way. If you like, I can email you an XL spreadsheet with the all the
cores I've measured so far. Switchmode cores seems to have
permeabilities quite a bit higher than 600.
Alan
VK2ADB