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Date: Sat, 27 Feb 2016 20:03:36 +0000
Message-ID: <CAA8k23TjT+E28CUm6Bp6JXcBGNuc=xGwXYdtGupxQ+zUCyHD=A@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: MF: EbNaut
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Why not just twist together some multi-filar turns and use all the sirface
area you can for cooiling?

I  use standard ETD54  type  SMPSU cores for 400 Watts at 475kHz and 700
Watts on 137kHz and they barely get warm.  I think the ferrite type is
EC90, but the cores are quite old, and may be EC85.    Those are just
standard transformer winding used for isolation and impedance changing.

Andy  G4JNT

On 27 February 2016 at 17:36, Paul Nicholson <vlf0403@abelian.org> wrote:

> On again.
>
>  Freq: 477690.00000 Hz
>  Chars: 15
>  Symbols: 0.5 seconds
>  Code: 8K19A
>  Duration: 496 seconds, 00:08:16
>  Repeat: XX:00 XX:20 XX:40
>
> I rewound the transformer, the primary windings are the braid
> of coax and the secondary is the series connected coax cores.
> FETs running a lot cooler now and the only thing getting
> warm is the coax.   DC in 27V at 3.8A and getting the same
> antenna volts as yesterday with 150W in so that's a lot better.
> The cause of last night's high unloaded current was a shorted
> secondary turn - the insulation had melted.
>
> I'm a bit worried about using coax like this, the inner will be
> at the temperature of the braid plus its own temperature rise.
> I expect a short from primary to secondary when the dielectric
> of the tightly wound coax coil softens.   I'd like to find some
> flat braid with high temperature insulation.
>
> The toroid I'm using is this one
>
>  http://uk.rs-online.com/web/p/ferrite-rings/2120803/
>
> which I picked because I found a MF PA design on the web which
> used it.  It's the wire that's producing the heat, not the core.
>
> --
> Paul Nicholson
> --
>
>

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<div dir=3D"ltr">Why not just twist together some multi-filar turns and use=
 all the sirface area you can for cooiling?<div><br></div><div>I =C2=A0use =
standard ETD54 =C2=A0type =C2=A0SMPSU cores for 400 Watts at 475kHz and 700=
 Watts on 137kHz and they barely get warm.=C2=A0 I think the ferrite type i=
s EC90, but the cores are quite old, and may be EC85. =C2=A0 =C2=A0Those ar=
e just standard transformer winding used for isolation and impedance changi=
ng. =C2=A0=C2=A0</div><div><br></div><div>Andy =C2=A0G4JNT<br><div class=3D=
"gmail_extra"><br><div class=3D"gmail_quote">On 27 February 2016 at 17:36, =
Paul Nicholson <span dir=3D"ltr">&lt;<a href=3D"mailto:vlf0403@abelian.org"=
 target=3D"_blank">vlf0403@abelian.org</a>&gt;</span> wrote:<br><blockquote=
 class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc soli=
d;padding-left:1ex">On again.<br>
<br>
=C2=A0Freq: 477690.00000 Hz<br>
=C2=A0Chars: 15<br>
=C2=A0Symbols: 0.5 seconds<br>
=C2=A0Code: 8K19A<br>
=C2=A0Duration: 496 seconds, 00:08:16<br>
=C2=A0Repeat: XX:00 XX:20 XX:40<br>
<br>
I rewound the transformer, the primary windings are the braid<br>
of coax and the secondary is the series connected coax cores.<br>
FETs running a lot cooler now and the only thing getting<br>
warm is the coax.=C2=A0 =C2=A0DC in 27V at 3.8A and getting the same<br>
antenna volts as yesterday with 150W in so that&#39;s a lot better.<br>
The cause of last night&#39;s high unloaded current was a shorted<br>
secondary turn - the insulation had melted.<br>
<br>
I&#39;m a bit worried about using coax like this, the inner will be<br>
at the temperature of the braid plus its own temperature rise.<br>
I expect a short from primary to secondary when the dielectric<br>
of the tightly wound coax coil softens.=C2=A0 =C2=A0I&#39;d like to find so=
me<br>
flat braid with high temperature insulation.<br>
<br>
The toroid I&#39;m using is this one<br>
<br>
=C2=A0<a href=3D"http://uk.rs-online.com/web/p/ferrite-rings/2120803/" rel=
=3D"noreferrer" target=3D"_blank">http://uk.rs-online.com/web/p/ferrite-rin=
gs/2120803/</a><br>
<br>
which I picked because I found a MF PA design on the web which<br>
used it.=C2=A0 It&#39;s the wire that&#39;s producing the heat, not the cor=
e.<br>
<br>
--<br>
Paul Nicholson<br>
--<br>
<br>
</blockquote></div><br></div></div></div>

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