Re: Toroid core material

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

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Weazel,

On 25 Jul 2003, at 5:29, Tesla list wrote:

 > Original poster: "J. B. Weazle McCreath by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>
 >
 >
 > Hello Coilers,
 >
 > I've some info and a question for my fellow coilers regarding various
 > materials used in making toroid cores and their usefulness as chokes
 > in TC service.
 >
 > As an RF filter in the hot lead of my PDT was a three turn choke that
 > I'd wound on a toroid core removed from an old computer power supply.
 > After a minute or so run time of the coil, the core material was hot
 > to the point of being uncomfortable to hold onto.  This indicated it
 > was pretty lossy, so I tried another core which had started life as
 > an 88 mH. "telephone choke coil" and noticed no heating even after
 > several minutes run time of the coil.
 >
 > It would seem that we need to choose the core material carefully for
 > this type of use.  The big question is, what is the core material of
 > the computer PS toroid and of the 88 mH. toroid?  They are obviously
 > quite different in composition, no doubt due to the frequencies they
 > where chosen to work at in their original uses.  I suspect that the
 > computer toroid worked in the 10's of kHz. range while the telephone
 > one likely was for voice frequencies of less than 3 kHz.

The toroid from the computer supply would have been an iron powder
core. This core has a low permeability/induction factor and a
distributed airgap. It is designed for chokes whose windings carry a
high level of DC and is used for both energy storage and load
balancing in these supplies. It will lose a lot of power if you
impress high levels of flux change on it. The other core would
undoubtably have been a signal grade ferrite (3B7 or something
similar).

Malcolm

 > 73, Weazle, VE3EAR/VE3WZL
 >
 > Details of my "Hyperbaric Gap" and Tesla coil are at:
 > http://www.hurontel.on.ca/~weazle
 >
 >
 >