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

Alan Peake wrote:

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

Alan, are the ferrite toroids used to filter the output of pc power
supplies or the ac input of microwave ovens useful for other applications?

Or is the ferrite material lossy like the small ferrite beads used for emi
reduction on wires?

Regards,

Mike Monett

Alan, are the ferrite toroids used to filter the output of pc power
supplies or the ac input of microwave ovens useful for other applications?

The PC PSU filter toroids seem to be optimized for the 25KHz -85KHz
range so any applications you have for this frequency range could use
them. Similarly, the AC input to the oven is probably 50/60HZ so those
toroids would be better at the lower audio frequencies.

Or is the ferrite material lossy like the small ferrite beads used for emi
reduction on wires?

Not quite sure about beads - ordinary ferrite material has fairly
constant permeability up to a frequency determined by the ferrite mix,
then drops off. Beads tend to have an impedance peak at some desired
frequency range - e.g. 100-200MHz
Alan

Alan Peake wrote:

The PC PSU filter toroids seem to be optimized for the 25KHz -85KHz
range so any applications you have for this frequency range could use
them. Similarly, the AC input to the oven is probably 50/60HZ so those
toroids would be better at the lower audio frequencies.

Not quite sure about beads - ordinary ferrite material has fairly
constant permeability up to a frequency determined by the ferrite mix,
then drops off. Beads tend to have an impedance peak at some desired
frequency range - e.g. 100-200MHz
Alan

Thanks very much - that encourages me to try them and see how well
they perform.

Regards,

Mike Monett

Ferrites have as many vices as they have virtues.

Ferrite salesmen cleverly make virtues out of vices.

Reg Edwards wrote:
Ferrites have as many vices as they have virtues.

Ferrite salesmen cleverly make virtues out of vices.
================================================
But an electronics 'homebrewer' can find out characteristics anyway ,
through experimentation.

Frank GM0CSZ / KN6WH

Reg Edwards wrote:
Ferrites have as many vices as they have virtues.

Ferrite salesmen cleverly make virtues out of vices.
================================================
But an electronics 'homebrewer' can find out characteristics anyway
,
through experimentation.

Frank GM0CSZ / KN6WH
====================================

Only if he has first-class laboratory facilities.

And samples vary widely in their characteristics, one from another.

The best way of using one is to wind some wire on it. If it works in
your particular circuit then consider yourself lucky.
----
Reg.