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From: "Dave G3WCB" <ganymede444@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Date: Thu, 20 Nov 2008 19:28:16 -0000
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Subject: RE: LF: Re: 3C85/90 Toroids <more>
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Paul-Henrik, LF,

You are correct. 3C85 is a ferrite, and has been widely used in transformer
cores at LF, as reported by G0MRF and others. I have no experience of the
material personally, as I have never been able to find any, and have been
forced to use other "street" ferrite from PC PSUs, ferrite EMC sleeves or
"slugs", etc. Two 40mm long 25mm dia ferrite sleeves taped together in
"binocular" style work fine at 400W on 137 kHz

>From this I conclude that the core material for transformers isn't too
important, providing it isn't too lossy, and can provide a reasonable
inductance (turns per mH).

I have never tried T200-2 as a core transformer material. I suspect that it
would not be too lossy, but because the permeability is much lower than
ferrite, you would have to put a lot of turns on the core to get a suitably
high inductance.

T130-2 and T200-2 powder iron cores do indeed make good inductors for the
low-pass filters. None of the "street ferrite" I tried worked, and in most
cases got fiercely hot. Air-cored inductors work well, but need to be wound
with quite thick wire to keep the copper lossed low. In my 400W LF TX, I got
more output with the T200-2 inductors than the air-cored conductors because
I could reduce the length of wire needed for the inductors, and reduce
losses due to resistance of the wire.

I've never tried T200-3 or any other mix.

73, Dave G3WCB IO91RM

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Paul-Henrik
Sent: 20 November 2008 15:11
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: 3C85/90 Toroids


I forgot to mention one important thing in my last reply:

>From the earlier discussions on this subject I got the impression that
T130-3
and T200-2 cores were suggested as alternatives to the 3C85/3C90.

The mixes #2 and #3 are powder iron, not ferrite as the 3F3 and 3C85/3C90. I
beleive they are poorly suited as power transformers on LF/MF but make good
inductors for low-pass filters on 136 and 500kHz. This is true at least for
the
#2 mix. On 500kHz I remember seeing reports of severe LPF heating with the
#3
mix, I will have to check again on that.

Some of the gurus please correct me if I'm wrong here. I just wanted to
press
the "pause and think again" button before someone possibly orders inductor
cores to use for a transformer.

I'm still a beginner/learner in this game, the above is just how I see
things
today.

73's

Paul-Henrik


Quoting "Johan H. Bodin" <jh.bodin@telia.com>:

> Yes, 3F3 is even better than 3C85/3C90 for power transformation at a few
> hundred
> kHz. The 3F3 cores, if coloured, are light blue. Philips sold their
ferrite
> business to Ferroxcube: http://www.ferroxcube.com/
>
> 73
> Johan SM6LKM
>
>
> Paul-Henrik wrote:
> > Have a look at Ferroxcube (Philips) cores of 3F3 material. As far as I
can
> > interpret datasheets for these, they should work fairly well as
> transformers up
> > to 500kHz with a DC component and up to 1MHz without DC.
>
>