Re: Off-axis primary inductance

To: tesla-at-pupman-dot-com
Subject: Re: Off-axis primary inductance
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of "Terry Fritz (moderator)" <twf-at-verinet-dot-com>)
Date: Sun, 06 Dec 1998 18:13:10 -0700
Approved: twf-at-verinet-dot-com

Hi Mike,

> >  I have constructed two "cores" , both heavily gapped 
> >  internally by recovering 3C8x ferrite cores from old computer SMPS, 
> >  smashing them to bits and stuffing the chips into PVC and acrylic 
> >  piping. 
> 
> Malcolm,
>     I like the idea.   Do you think magnetite would work in place of the
> ferrite?  I don't have much in the way of ferrite cores available, but could
> get pounds of magnetite.   I could mix it with something like sand and even
> grind it to powder if necessary.  I guess my question is whether this
would be
> bad at TC frequencies.  I thought about using this for chokes etc, but have
> never tried it.  I have not heard of anyone trying this, so I expect that
> there is something that makes this a poor choice.
> Mike

If magnetite has the ability to retain magnetism it is a poor choice 
as the hysteresis losses would be high. The better the retentivity, 
the higher the losses. One has to effectively demagnetize the grains 
in operation or, by proxy, there is minimal flux swing in the core 
and hence it would have an induction factor not much higher than air.

Malcolm