X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 17 Apr 2009 19:44:17 -0400 Message-ID: X-Original-Return-Path: Received: from vms173017pub.verizon.net ([206.46.173.17] verified) by logan.com (CommuniGate Pro SMTP 5.2.13) with ESMTP id 3584271 for lml@lancaironline.net; Fri, 17 Apr 2009 01:00:08 -0400 Received-SPF: pass receiver=logan.com; client-ip=206.46.173.17; envelope-from=tom.gourley@verizon.net Received: from jacky0da39824a ([71.111.126.146]) by vms173017.mailsrvcs.net (Sun Java(tm) System Messaging Server 6.3-7.04 (built Sep 26 2008; 32bit)) with ESMTPA id <0KI800EHWB749X9B@vms173017.mailsrvcs.net> for lml@lancaironline.net; Thu, 16 Apr 2009 23:59:29 -0500 (CDT) X-Original-Message-id: <35166780329C425F9BD26FFD7964F526@jacky0da39824a> Reply-to: "Tom Gourley" From: "Tom Gourley" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: spike suppresion diodes X-Original-Date: Thu, 16 Apr 2009 21:59:22 -0700 MIME-version: 1.0 Content-type: multipart/alternative; boundary="----=_NextPart_000_002E_01C9BEDE.995BB0B0" X-Priority: 3 X-MSMail-priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 090416-0, 04/16/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_002E_01C9BEDE.995BB0B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Just as a clarification - the "spike suppression diodes" do not protect = the electrical system from high voltage spikes; they protect the = switched device, which in this case is the solenoid coil of the relay = being turned off, and the switch itself. The coil really doesn't care, = and the switch is designed to tolerate the resulting arc. The normal = wiring (I'm no good at putting graphics in an email so I'll do it = "verbally.") Goes from the battery and all your expensive electronics to = the switch, to the relay coil, and to ground(return). The high voltage = spike exists only between the switch and relay coil, no where else. Gary is correct. When current to the relay coil is interrupted the = inductance of the coil will cause a voltage spike at the coil. How big = depends on the inductance of the coil and the amount of current that was = flowing when the switch was opened. Whether or not the switch will = tolerate this depends on the switch. Personally I think a diode across = the coil is a good idea, just be sure it's installed the right way. I = don't see the need for anything fancier than a diode, something like a = 1N540x (where x is 4, 5, 6, 7, or 8). If you want to protect larger = parts of your electrical system against voltage transients you will need = something fancier than a diode. Tom Gourley ------=_NextPart_000_002E_01C9BEDE.995BB0B0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Just as a clarification - the "spike suppression diodes" do not = protect=20 the electrical system from high voltage spikes; they protect the = switched=20 device, which in this case is the solenoid coil of the relay being = turned off,=20 and the switch itself.  The coil really doesn't care, and the = switch is=20 designed to tolerate the resulting arc.  The normal wiring (I'm no = good at=20 putting graphics in an email so I'll do it "verbally.") Goes from the = battery=20 and all your expensive electronics to the switch, to the relay coil, and = to=20 ground(return).  The high voltage spike exists only between the = switch and=20 relay coil, no where else.
 
Gary is correct.  When current to = the relay=20 coil is interrupted the inductance of the coil will cause a voltage = spike at the=20 coil.  How big depends on the inductance of the coil and the amount = of=20 current that was flowing when the switch was opened.  Whether or = not the=20 switch will tolerate this depends on the switch.  Personally I = think a=20 diode across the coil is a good idea, just be sure it's installed = the right=20 way.  I don't see the need for anything fancier than a diode, = something=20 like a 1N540x (where x is 4, 5, 6, 7, or 8).  If you want to = protect larger=20 parts of your electrical system against voltage transients you will need = something fancier than a diode.
 
Tom Gourley
 
 
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