Envelope-to: dave@picks.force9.co.uk Delivery-date: Wed, 14 Sep 2005 17:57:48 +0100 Received: by pih-mxcore10.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1EFaZv-0008JU-96 for dave@picks.force9.co.uk; Wed, 14 Sep 2005 17:57:47 +0100 Received: from post.thorcom.com ([193.82.116.20]) by pih-mxcore10.plus.net with esmtp (PlusNet MXCore v2.00) id 1EFaZu-0008JI-Nn for dave@picks.force9.co.uk; Wed, 14 Sep 2005 17:57:47 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1EFaZh-0003BI-J5 for rs_out_1@blacksheep.org; Wed, 14 Sep 2005 17:57:33 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1EFaZg-0003B9-TD for rsgb_lf_group@blacksheep.org; Wed, 14 Sep 2005 17:57:32 +0100 Received: from smtp811.mail.ukl.yahoo.com ([217.12.12.201]) by relay2.thorcom.net with smtp (Exim 4.51) id 1EFbF6-000380-Rl for rsgb_lf_group@blacksheep.org; Wed, 14 Sep 2005 18:40:28 +0100 Received: (qmail 70119 invoked from network); 14 Sep 2005 16:57:19 -0000 Received: from unknown (HELO Main) (Alan.Melia@81.131.122.106 with login) by smtp811.mail.ukl.yahoo.com with SMTP; 14 Sep 2005 16:57:18 -0000 Message-ID: <005001c5b94d$440ab560$87468351@Main> From: "Alan Melia" To: rsgb_lf_group@blacksheep.org References: <000601c5b922$0e59f410$268cf8d4@standalone> <000601c5b932$848f14c0$87468351@Main> <000c01c5b937$cbdc9d20$045bfea9@d4f8d8> Date: Wed, 14 Sep 2005 17:49:03 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 Subject: LF: Re: Re: Re: Current Transformers (off topic, but expertise probably here) Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Yes its possible that wall-warts are designed differently to chassis mounting door-stops of the 1950s. I suppose the "no load" current is vital to keeping the current down, and the cores are usually pretty minimal for the declared current rating. I must admit I have not personally had one catch fire yet. Ok the 5 turns looks right....I could not understand the 0.3 from one. Alan ----- Original Message ----- From: "Andy Talbot" To: Sent: 14 September 2005 15:22 Subject: LF: Re: Re: Current Transformers (off topic, but expertise probably here) > Rik - Oops. typing mistake there - the 0.3V came from 5 turns put on to > test, so the 4000 turn primary was correct. > Alan - I don't see how a rule of thumb can give a fixed number of tuurns > per volt. the critical parameter for sizing a transformer is based on > cross-sectional area, and for a sinusoidal device V = 4.44.F.N.A.B. > > I use this equation a lot for ferrite (and its SMPSU varient, V.t = N.A.B) > and it works fine, but not sure what sort of B is alloed in iron - for this > small transformer it looks as if Bcould be up to 1 Tesla pk. > > Andy > > > > -- > No virus found in this outgoing message. > Checked by AVG Anti-Virus. > Version: 7.0.344 / Virus Database: 267.10.21/96 - Release Date: 2005-09-10 > >