X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from elasmtp-banded.atl.sa.earthlink.net ([209.86.89.70] verified) by logan.com (CommuniGate Pro SMTP 6.0.4) with ESMTP id 6173288 for lml@lancaironline.net; Sun, 31 Mar 2013 19:43:02 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.70; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=UAhonV2Kh5i3QPItBQHPc9662uS573puo87evHaUcFwqy4gX92JwnyU9zVg1WkzZ; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [71.161.208.71] (helo=[192.168.1.24]) by elasmtp-banded.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1UMRtK-0006di-JH for lml@lancaironline.net; Sun, 31 Mar 2013 19:42:27 -0400 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: multipart/alternative; boundary=Apple-Mail-56--80910581 Subject: Re: [LML] Re: Hydraulic gear pump failure - Relays Date: Sun, 31 Mar 2013 19:42:25 -0400 In-Reply-To: To: "Lancair Mailing List" References: Message-Id: X-Mailer: Apple Mail (2.1085) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da940c467ec9564181360d4f739f50cc93be3350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 71.161.208.71 --Apple-Mail-56--80910581 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 TYCO has a variety of models now. Some have ultra-low hold current and = include the diode protection. Others omit the fancy stuff. They = clearly specify their maximum "break" current which is what you want a = lot of it you are trying to interrupt an errant high current circuit. = e.g. in Bill's example, if you had a stuck pressure switch, you could = still shut down the power by pulling the breaker that powers the relay. On Mar 28, 2013, at 2:12 PM, Sky2high@aol.com wrote: Bill, et al, =20 Relays should have a diode reverse connected across the coil to stop the = voltage surge generated by the field collapse when power is removed from = the coil. This will help protect the pressure switch contacts. =20 Grayhawk =20 In a message dated 3/28/2013 12:58:55 P.M. Central Daylight Time, = super_chipmunk@roadrunner.com writes: Would there be any drawback to using a higher- rated contactor? I = found the Lancair part to be a P.O.S.- it was marked continuous duty but = when put on a power supply it rapidly overheated and shorted to the = case. =20 Instead I=92m using an antique 50A Leach B-5B aircraft style that easily = operated for hours. The pump supplied with my IV-P draws a maximum of = 50A, so the Leach might be marginal but I think I=92ll try it initially. =20 On Colin=92s recommendation I also purchased a TYCO LEV100A5ANH , rated = 100A that I could use instead, or elsewhere. The Leach draws 0.16A, the = TYCO draws 0.25A at 28V. The Lancair- supplied Suco pressure switch is = rated for 4A as best I can determine so either unit should be = compatible. =20 I don=92t know what other models might use but consider the contacts = inside the pressure switches. If they should get overloaded and weld = closed the effect would be the same as welding the relay points. -Bill = Wade =20 From: Gary Casey Sent: Thursday, March 28, 2013 9:36 AM To: lml@lancaironline.net Subject: [Norton AntiSpam][LML] Re: Hydraulic gear pump failure - Relays =20 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 determines the rating. Current will try to = keep flowing and if the contacts don't separate rapidly and with enough = force the inevitable arc could create enough heat to weld the contacts = and prevent opening. If it is desired 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. More force is required to increase the rate at which the = contacts are opened so a higher force spring is installed. Then 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 = 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 starter = relay. And I have never, ever heard of 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 = 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.=3D20 Does that protective function matter in this circuit?=3D0D Should be considered.=3D0D John=3D0D --Apple-Mail-56--80910581 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 TYCO = has a variety of models now.   Some have ultra-low hold current and = include the diode protection.   Others omit the fancy stuff.   = They clearly specify their maximum "break" current which is what you = want a lot of it you are trying to interrupt an errant high current = circuit.   e.g. in Bill's example, if you had a stuck pressure = switch, you could still shut down the power by pulling the breaker that = powers the relay.

On Mar 28, 2013, at 2:12 PM, Sky2high@aol.com wrote:

Bill, et al,
 
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=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.co= m writes:
  Would there be any drawback to using a higher- rated = contactor? 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=92m using an antique 50A Leach B-5B aircraft style that = 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=92ll try it initially.
 
On Colin=92s recommendation I also purchased a TYCO LEV100A5ANH , = rated=20 100A 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.
 
  I don=92t know what other models might use but consider = the contacts=20 inside the pressure switches. If they should get overloaded and weld = closed=20 the effect would be the same as welding the relay points.  -Bill=20= Wade
 
Sent: Thursday, March 28, 2013 9:36 AM
Subject: [Norton AntiSpam][LML] Re: Hydraulic gear pump = failure -=20 Relays
 
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 = designed=20 for intermittent duty.  As an example, take a standard master=20 relay.  It is rated for continuous duty and something like 80 = amps. =20 That means the coil won't overheat if left on forever and that the = contacts=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 = flowing and=20 if the contacts don't separate rapidly and with enough force the = inevitable=20 arc could create enough heat to weld the contacts and prevent = opening. =20 If it is desired to design a relay in the same package (for cost, size = and=20 weight reasons) that can be used intermittently to pass a much higher = current=20 the design parameters are different.  More force is required to = increase=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 = fewer=20 turns of heavier wire are used in the coil (that's right, FEWER turns, = but=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 = few=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=3D
e
for=20= a purpose.  They are supposed to be the weak link in a circuit = where=20 =3D
a
continuous=20 stuck relay could result in greater problems than a = failure.=3D20
Does=20 that protective function matter in this circuit?=3D0D
Should=20 be  considered.=3D0D
John=3D0D

= --Apple-Mail-56--80910581--