X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from imr-da05.mx.aol.com ([205.188.105.147] verified) by logan.com (CommuniGate Pro SMTP 6.0.3) with ESMTP id 6163199 for lml@lancaironline.net; Thu, 28 Mar 2013 14:12:47 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.105.147; envelope-from=Sky2high@aol.com Received: from mtaomg-db05.r1000.mx.aol.com (mtaomg-db05.r1000.mx.aol.com [172.29.51.203]) by imr-da05.mx.aol.com (Outbound Mail Relay) with ESMTP id DC7A01C0000B4 for ; Thu, 28 Mar 2013 14:12:14 -0400 (EDT) Received: from core-mtc005a.r1000.mail.aol.com (core-mtc005.r1000.mail.aol.com [172.29.235.17]) by mtaomg-db05.r1000.mx.aol.com (OMAG/Core Interface) with ESMTP id 4F18AE000087 for ; Thu, 28 Mar 2013 14:12:14 -0400 (EDT) From: Sky2high@aol.com Full-name: Sky2high Message-ID: <2d255.4963304c.3e85e1fe@aol.com> Date: Thu, 28 Mar 2013 14:12:14 -0400 (EDT) Subject: Re: Hydraulic gear pump failure - Relays To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_2d255.4963304c.3e85e1fe_boundary" X-Mailer: AOL 9.7 sub 19 X-Originating-IP: [205.188.66.134] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1364494334; bh=KnftYoaGwE8NgqgcQGVvU7Ag8DoNag9smc01x8mzMW0=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=kKcPIlq++8H8WTG4so+YhnorJT02wEfOnUNllmFnoDQXaYogPTo2O3tWmXQXvCvrx w4PbIs01jpvfhRSsN7bjDgj94aGdIjfb0vwn6paoxYGb4r4HlYxYS2xeF2NjMYMY0b cTTUbc4RedFgNmDl0IHFxeBsUxt/S4N5m/hiPyjQ= X-AOL-SCOLL-SCORE: 0:2:356217632:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d33cb515487fe48ff --part1_2d255.4963304c.3e85e1fe_boundary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Bill, et al, =20 Relays should have a diode reverse connected across the coil to stop the = =20 voltage surge generated by the field collapse when power is removed from t= he=20 coil. This will help protect the pressure switch contacts. =20 Grayhawk=20 =20 =20 In a message dated 3/28/2013 12:58:55 P.M. Central Daylight Time, =20 super_chipmunk@roadrunner.com writes: =20 Would there be any drawback to using a higher- rated contactor? I found=20 the Lancair part to be a P.O.S.- it was marked continuous duty but when pu= t=20 on a power supply it rapidly overheated and shorted to the case. =20 Instead I=E2=80=99m using an antique 50A Leach B-5B aircraft style that eas= ily =20 operated for hours. The pump supplied with my IV-P draws a maximum of 50A, = so =20 the Leach might be marginal but I think I=E2=80=99ll try it initially. =20 On Colin=E2=80=99s recommendation I also purchased a TYCO LEV100A5ANH , rat= ed 100A=20 that I could use instead, or elsewhere. The Leach draws 0.16A, the TYCO =20 draws 0.25A at 28V. The Lancair- supplied Suco pressure switch is rated for= 4A=20 as best I can determine so either unit should be compatible. =20 I don=E2=80=99t know what other models might use but consider the contact= s =20 inside the pressure switches. If they should get overloaded and weld closed= the=20 effect would be the same as welding the relay points. -Bill Wade =20 =20 =20 From: _Gary Casey_ (mailto:casey.gary@yahoo.com) =20 Sent: Thursday, March 28, 2013 9:36 AM To: _lml@lancaironline.net_ (mailto:lml@lancaironline.net) =20 Subject: [Norton AntiSpam][LML] Re: Hydraulic gear pump failure - Relays =20 =20 =20 Pardon me if I'm jumping into a discussion a little late (and a dollar =20 short), but there might be some confusion on how and why relays are designe= d =20 for intermittent duty. As an example, take a standard master relay. It i= s=20 rated for continuous duty and something like 80 amps. That means the coil= =20 won't overheat if left on forever and that the contacts also won't overhea= t=20 when passing 80 amps and that the contacts won't weld when interrupting 80= =20 amps. It is often the limitations when opening the circuit that=20 determines the rating. Current will try to keep flowing and if the contac= ts don't=20 separate rapidly and with enough force the inevitable arc could create=20 enough heat to weld the contacts and prevent opening. If it is desired to= =20 design a relay in the same package (for cost, size and weight reasons) tha= t can=20 be used intermittently to pass a much higher current the design parameters= =20 are different. More force is required to increase the rate at which the= =20 contacts are opened so a higher force spring is installed. Then more forc= e=20 is required to close the contacts, so fewer turns of heavier wire are used= =20 in the coil (that's right, FEWER turns, but that's another discussion). T= he=20 result is that the relay can now successfully switch maybe 300 amps, but= =20 the coil will overheat after a few minutes of operation. That's the=20 difference between a master and a starter relay. And I have never, ever h= eard of=20 using a relay as the "weak link" in the system. Gary ps: My Lancair list emails now come all messed up (see below). Why is=20 that? Am I doing something wrong? =20 The only caveat with that fix, Fred, is that intermittent relays are ther= =3D e for a purpose. They are supposed to be the weak link in a circuit where = =3D a continuous stuck relay could result in greater problems than a failure.=3D= 20 Does that protective function matter in this circuit?=3D0D Should be considered.=3D0D John=3D0D --part1_2d255.4963304c.3e85e1fe_boundary Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Bill, et al,
 
Relays should have a diode reverse connected across the coil to stop t= he=20 voltage surge generated by the field collapse when power is removed fr= om=20 the coil.  This will help protect the pressure switch contacts.
 
Grayhawk
 
In a message dated 3/28/2013 12:58:55 P.M. Central Daylight Time,=20 super_chipmunk@roadrunner.com writes:
=
  Would there be any drawback to using a higher- rated contacto= r? I=20 found the Lancair part to be a P.O.S.- it was marked continuous duty but = when=20 put on a power supply it rapidly overheated and shorted to the case.
 
Instead I=E2=80=99m using an antique 50A Leach B-5B aircraft style t= hat easily=20 operated for hours. The pump supplied with my IV-P draws a maximum of 50A= , so=20 the Leach might be marginal but I think I=E2=80=99ll try it initially.
 
On Colin=E2=80=99s recommendation I also purchased a TYCO LEV100A5AN= H , rated=20 100A that I could use instead, or elsewhere. The Leach draws 0.16A, the T= YCO=20 draws 0.25A at 28V. The Lancair- supplied Suco pressure switch is rated f= or 4A=20 as best I can determine so either unit should be compatible.
 
  I don=E2=80=99t know what other models might use but consider= the contacts=20 inside the pressure switches. If they should get overloaded and weld clos= ed=20 the effect would be the same as welding the relay points.  -Bill=20 Wade
 
From: = Gary=20 Casey
Sent: Thursday, March 28, 2013 9:36 AM
Subject: [Norton AntiSpam][LML] Re: Hydraulic gear pump failu= re -=20 Relays
 
Pardon me if I'm jumping into a discussion a little late (and a doll= ar=20 short), but there might be some confusion on how and why relays are desig= ned=20 for intermittent duty.  As an example, take a standard master=20 relay.  It is rated for continuous duty and something like 80 amps.&= nbsp;=20 That means the coil won't overheat if left on forever and that the contac= ts=20 also won't overheat when passing 80 amps and that the contacts won't weld= when=20 interrupting 80 amps.  It is often the limitations when opening the= =20 circuit that determines the rating.  Current will try to keep flowin= g and=20 if the contacts don't separate rapidly and with enough force the inevitab= le=20 arc could create enough heat to weld the contacts and prevent opening.&nb= sp;=20 If it is desired to design a relay in the same package (for cost, size an= d=20 weight reasons) that can be used intermittently to pass a much higher cur= rent=20 the design parameters are different.  More force is required to incr= ease=20 the rate at which the contacts are opened so a higher force spring is=20 installed.  Then more force is required to close the contacts, so fe= wer=20 turns of heavier wire are used in the coil (that's right, FEWER turns, bu= t=20 that's another discussion).  The result is that the relay can now=20 successfully switch maybe 300 amps, but the coil will overheat after a fe= w=20 minutes of operation.  That's the difference between a master and a= =20 starter relay.  And I have never, ever heard of using a relay as the= =20 "weak link" in the system.
Gary
ps:  My Lancair list emails now come all messed up (see=20 below).  Why is that?  Am I doing something wrong?
 
The=20 only caveat with that fix, Fred, is that intermittent relays are=20 ther=3Defor=20 a purpose.  They are supposed to be the weak link in a circuit where= =20 =3Dacontinuous=20 stuck relay could result in greater problems than a failure.=3D20<= BR=20 style=3D"FONT-FAMILY: arial, helvetica, sans-serif; COLOR: rgb(69,69,69);= FONT-SIZE: 13px">Does=20 that protective function matter in this circuit?=3D0DShould=20 be  considered.=3D0DJohn=3D0D
 --part1_2d255.4963304c.3e85e1fe_boundary--