X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 28 Mar 2013 09:36:20 -0400 Message-ID: X-Original-Return-Path: Received: from nm29.bullet.mail.ne1.yahoo.com ([98.138.90.92] verified) by logan.com (CommuniGate Pro SMTP 6.0.3) with ESMTPS id 6162326 for lml@lancaironline.net; Thu, 28 Mar 2013 08:47:17 -0400 Received-SPF: none receiver=logan.com; client-ip=98.138.90.92; envelope-from=casey.gary@yahoo.com Received: from [98.138.226.176] by nm29.bullet.mail.ne1.yahoo.com with NNFMP; 28 Mar 2013 12:46:42 -0000 Received: from [98.138.89.248] by tm11.bullet.mail.ne1.yahoo.com with NNFMP; 28 Mar 2013 12:46:42 -0000 Received: from [127.0.0.1] by omp1040.mail.ne1.yahoo.com with NNFMP; 28 Mar 2013 12:46:42 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 526603.69924.bm@omp1040.mail.ne1.yahoo.com Received: (qmail 4236 invoked by uid 60001); 28 Mar 2013 12:46:42 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Rocket-MIMEInfo:X-Mailer:Message-ID:Date:From:Reply-To:Subject:To:MIME-Version:Content-Type; b=J6KsWiSoOwflKKzaLxlz+x89i16MM0pcqvcOp/ZZ0d2Y6EoqLAeLiSsq+32V3aPfMMKgmshKPI+4QpM7sEhHPRkUxYGH0uy2PGHglSEaqa+mfdBtWnd30H2/tLXdHm6pqtE9BJZH3NEv4WZ8sLbkMvUQsRwsdB2jeBQAWeNa4c8=; X-YMail-OSG: _5qIMR0VM1mops.iCywODRpwJMhCsBTn27ckRKMxuqSfKcr Up_7CvEAOuowuFIxedzRy7nAJ3PzQpOvlOP0i04zbumhHPqntKND02AQUYSp pF9IQiv6d5dRuAcPYfgBPHhHLntsO.EnDEWPXdT59XUg7udwdhimO8qU2ZxR oA9oqFmSBmQ7N5bhD1iSDT0sWR4unnzcTkB6N5wLvu251P42rxJ_1TBvJ0mm c7wt4Ro8vlwbHiR215pIrrxqnK5SN43S1R.72kEjYWRHsG8qv8FwxTY9mKiq SIPgAZYwJYTTEOH_cKDMlSpkThAvN_7K_ECwfjoGh828K5xIos15R_mE7qSD TcDJ2ff2OH7l.zvXWlxCiVBLyDhNY7UFoYsa5gPK1_MocBoL8XxmGQeMFzPS IDlZZeAHnpvpUbhB25wBw.KNEl0xhztfdIh.x9MEiNjYPhrjnFSW0TRdYjcR paE0.orzcD6BerqRzzBj4OIWhtynY41pUr3.keRCbcuo5MaGZdDsk6Iq96n8 3hA-- Received: from [24.252.55.109] by web120106.mail.ne1.yahoo.com via HTTP; Thu, 28 Mar 2013 05:46:41 PDT X-Rocket-MIMEInfo: 002.001,UGFyZG9uIG1lIGlmIEknbSBqdW1waW5nIGludG8gYSBkaXNjdXNzaW9uIGEgbGl0dGxlIGxhdGUgKGFuZCBhIGRvbGxhciBzaG9ydCksIGJ1dCB0aGVyZSBtaWdodCBiZSBzb21lIGNvbmZ1c2lvbiBvbiBob3cgYW5kIHdoeSByZWxheXMgYXJlIGRlc2lnbmVkIGZvciBpbnRlcm1pdHRlbnQgZHV0eS4gwqBBcyBhbiBleGFtcGxlLCB0YWtlIGEgc3RhbmRhcmQgbWFzdGVyIHJlbGF5LiDCoEl0IGlzIHJhdGVkIGZvciBjb250aW51b3VzIGR1dHkgYW5kIHNvbWV0aGluZyBsaWtlIDgwIGFtcHMuIMKgVGhhdCBtZWEBMAEBAQE- X-Mailer: YahooMailWebService/0.8.139.530 X-Original-Message-ID: <1364474801.94313.YahooMailNeo@web120106.mail.ne1.yahoo.com> X-Original-Date: Thu, 28 Mar 2013 05:46:41 -0700 (PDT) From: Gary Casey Reply-To: Gary Casey Subject: Re: Hydraulic gear pump failure - Relays X-Original-To: Lancair Mailing List MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-96787742-518321993-1364474801=:94313" ---96787742-518321993-1364474801=:94313 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Pardon me if I'm jumping into a discussion a little late (and a dollar shor= t), but there might be some confusion on how and why relays are designed fo= r intermittent duty. =A0As an example, take a standard master relay. =A0It = is rated for continuous duty and something like 80 amps. =A0That means the = coil won't overheat if left on forever and that the contacts also won't ove= rheat when passing 80 amps and that the contacts won't weld when interrupti= ng 80 amps. =A0It is often the limitations when opening the circuit that de= termines the rating. =A0Current will try to keep flowing and if the contact= s don't separate rapidly and with enough force the inevitable arc could cre= ate enough heat to weld the contacts and prevent opening. =A0If it is desir= ed to design a relay in the same package (for cost, size and weight reasons= ) that can be used intermittently to pass a much higher current the design = parameters are different. =A0More force is required to increase the rate at which the contacts are opened so a higher force spring is installed. =A0Th= en more force is required to close the contacts, so fewer turns of heavier = wire are used in the coil (that's right, FEWER turns, but that's another di= scussion). =A0The result is that the relay can now successfully switch mayb= e 300 amps, but the coil will overheat after a few minutes of operation. = =A0That's the difference between a master and a starter relay. =A0And I hav= e never, ever heard of using a relay as the "weak link" in the system.=0AGa= ry=0Aps: =A0My Lancair list emails now come all messed up (see below). =A0W= hy is that? =A0Am I doing something wrong?=0A=0AThe only caveat with that f= ix, Fred, is that intermittent relays are ther=3D=0Ae=0Afor a purpose.=A0 T= hey are supposed to be the weak link in a circuit where =3D=0Aa=0Acontinuou= s stuck relay could result in greater problems than a failure.=3D20=0ADoes = that protective function matter in this circuit?=3D0D=0AShould be=A0 consid= ered.=3D0D=0AJohn=3D0D=0A ---96787742-518321993-1364474801=:94313 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Pardon me if I= 'm jumping into a discussion a little late (and a dollar short), but there = might be some confusion on how and why relays are designed for intermittent= duty.  As an example, take a standard master relay.  It is rated= for continuous duty and something like 80 amps.  That means the coil = won't overheat if left on forever and that the contacts also won't overheat= when passing 80 amps and that the contacts won't weld when interrupting 80= amps.  It is often the limitations when opening the circuit that dete= rmines the rating.  Current will try to keep flowing and if the contac= ts don't separate rapidly and with enough force the inevitable arc could cr= eate enough heat to weld the contacts and prevent opening.  If it is d= esired to design a relay in the same package (for cost, size and weight reasons) that can be used intermittently to pass a much higher curr= ent the design parameters are different.  More force is required to in= crease the rate at which the contacts are opened so a higher force spring i= s installed.  Then more force is required to close the contacts, so fe= wer turns of heavier wire are used in the coil (that's right, FEWER turns, = but that's another discussion).  The result is that the relay can now = successfully switch maybe 300 amps, but the coil will overheat after a few = minutes of operation.  That's the difference between a master and a st= arter relay.  And I have never, ever heard of using a relay as the "we= ak link" in the system.
Gary
ps:  My Lancair list = emails now come all messed up (see below).  Why is that?  Am I do= ing something wrong?

The only caveat with that fix, Fred, is that i= ntermittent relays are ther=3D
e
for a pur= pose.  They are supposed to be the weak link in a circuit where =3D
a
= continuous stuck relay could result in greater pro= blems than a failure.=3D20
Does that protective function matter in this circuit?=3D0D
Should be  considered.=3D0= D
John=3D0D
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