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Simpleton 29th June 2005 11:03 AM

Ferrite bead help
I just dismatled a computer PSU, and it had a yeallow ferrite bead, which i stripped down, around 3cm diametre, 1cm heght and 5mm thick.

Do you know what type of material it is made off? I would like to use it as a choke, but need to knwo the permeabilty of it for calculations sake.

Thank you very much

BrianL 29th June 2005 01:16 PM

First, that is not a ferrite bead. Beads are tiny. I've usually
heard them referred to as donuts. But enough for semantics.

At this point it is almost impossible to figure out what you
have. Ferrites that are good at very low frequencies (like
audio frequencies) are often somewhat conductive when
measured with an Ohm meter. But most ferrites are
highly insulative. There are many formulations for
varying applications and it's almost impossible to tell them
apart. Sometimes the manufacturers color-code them with
paint so the yellow might be a clue. But one brand's yellow
might be another's green. Given that you found this in
a computer power supply, the range of unknown far East
vendors becomes large and the problem more difficult.

I would imagine you can use it as some sort of hash filter
for an AC line, much as it was likely used in the computer,
but to put it to any other use requires significant expensive
instrumentation to measure properties as you try to wind
something -- and then you may not get what you want as
the material may not be suitable.

You'd be better buying or getting free samples of ferrites
with known properties.

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