Return-Path: Received: (qmail 6100 invoked from network); 10 Apr 2001 19:16:05 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 10 Apr 2001 19:16:05 -0000 Received: (qmail 13842 invoked from network); 10 Apr 2001 19:15:59 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 10 Apr 2001 19:15:59 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14n3UT-0002NY-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 10 Apr 2001 20:07:49 +0100 Received: from rhenium.btinternet.com ([194.73.73.93] helo=rhenium) by post.thorcom.com with esmtp (Exim 3.16 #2) id 14n3UQ-0002NT-00 for rsgb_lf_group@blacksheep.org; Tue, 10 Apr 2001 20:07:47 +0100 Received: from [213.1.101.1] (helo=j1r9b7) by rhenium with smtp (Exim 3.03 #83) id 14n3U0-0000rG-00 for rsgb_lf_group@blacksheep.org; Tue, 10 Apr 2001 20:07:21 +0100 Message-ID: <002301c0c1f1$4cbce1e0$016501d5@j1r9b7> From: "Derek Atter" To: rsgb_lf_group@blacksheep.org References: <3AD2D0CE.23045.117384@localhost> Subject: Re: LF: Coil Losses Date: Tue, 10 Apr 2001 19:25:31 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2919.6600 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Mike, Re your plan to try a loading coil with thinner Litz wire - CARC still have plenty of Litz in various thinner gauges if you need any. Regards - Derek Atter G3GRO ----- Original Message ----- From: "Mike Dennison" To: Sent: Tuesday, April 10, 2001 9:22 AM Subject: Re: LF: Coil Losses > Yet again, many thanks to Jim for helping to clarify a technical point. > > > One problem with ferrite cores is saturation - if the magnetic flux in > > the core exceeds a certain point, the core effectively loses it's > > magnetism over the peaks in the current waveform in the coil, > > which can give rise to harmonic generation as well as excessive > > heating of the ferrite. If you put a ferrite core into a coil carrying a > > particular current, the magnetic flux density there is in the core > > depends on the shape of the coil and core - a long, thin rod along > > the axis of the core will be subject to much greater flux density than > > a short, fat core. > > Ah. That is probably why my lumps of old broken pot core work well in the > 73kHz coil - I actually used one with the wire still in it and this seemed to have > no bad effect! > > > Another factor that is important when deciding the type of coil to > > make is the voltage it has to withstand. A 7mH coil with, say, 3A @ > > 136kHz going through it has about 18kV across its terminals, So > > insulating an inductor wound on a pot-core would be quite a > > challenge at this level, especially for outdoors use. > > I certainly had not planned to use a pot core as a former, rather to tape bits of > ferrite - probably of the SMPSU grade - to a plastic water pipe and place it > inside the existing drinks bottle former. I expect at least 70 per cent air > spacing. > > I am away at Easter but will do some tests later this month on practical cores, > and will report back to the group. > > I do have an alternative strategy, and that is to get some thinner Litz wire so > the same physical size coil can give greater inductance, but then resistance > may be an issue again. > > > > > Mike, G3XDV (IO91VT) > http://www.lf.thersgb.net > > >