Toroidal Chokes???? (fwd)

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Toroidal Chokes???? (fwd)
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 15 Feb 1998 20:07:09 -0600
Approved: tesla-at-stic-dot-net

----------
From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Sunday, February 15, 1998 4:46 PM
To:  Tesla List
Subject:  Re: Toroidal Chokes???? (fwd)

A note on the use of ferrites in chokes:

> Date: Sat, 14 Feb 1998 15:48:03 +0000
> From: Gwyn Zucca <gwyn-at-tcbod.demon.co.uk>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Toroidal Chokes???? (fwd)
> 
> In message <Pine.LNX.3.95.980214083807.22208C-100000-at-pupman-dot-com>, Tesla
> List <tesla-at-pupman-dot-com> writes
> >
> >
> >---------- Forwarded message ----------
> >Date: Fri, 13 Feb 1998 23:09:02 -0600
> >From: Zuma <mwise-at-ns.sosis-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: Toroidal Chokes????
> >
> >Can someone tell me what material I should get for toroid chokes?
> >Does it need high permeability or low? Also should I get the largest
> >ones I can find or what? I am wanting chokes in the inductance range 
> >of 50-100mh or is this a non-necessary amount?
> >
> >Chris
> >
> 
> 
> 
> You should use the largest core you can find, this will allow you easy
> winding and better insulation. A large core will be able to handle
> higher flux densities before becoming saturated, this is important.
> I do not think you need to go to such a high inductance, as ringing in
> the choke may become a problem in its own right. As for the material a
> power core material such as Philips 3C85 would be a good choice.

I agree, but beware of using ungapped cores made of this material 
unless the inductance is real high because the lack of airgap will 
allow the cores to saturate easily. Magnetic material is capable of 
storing very little energy. Most is stored in the airgap of gapped 
inductors. A better choice for a core you don't want to stick a gap 
in is a low permeability one as this will have a distributed airgap
(well iron-powder cores do anyway). Of course, low permeability = low 
inductance for a given number of turns so there is a horrible 
tradeoff occurring. Frequency-wise, 3C85 is a good choice. 

Malcolm