X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 18 Apr 2006 00:36:25 -0400 Message-ID: X-Original-Return-Path: Received: from smtp106.sbc.mail.mud.yahoo.com ([68.142.198.205] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with SMTP id 1071594 for lml@lancaironline.net; Tue, 18 Apr 2006 00:01:44 -0400 Received-SPF: none receiver=logan.com; client-ip=68.142.198.205; envelope-from=elippse@sbcglobal.net Received: (qmail 79787 invoked from network); 18 Apr 2006 04:00:59 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@70.237.145.44 with login) by smtp106.sbc.mail.mud.yahoo.com with SMTP; 18 Apr 2006 04:00:59 -0000 X-Original-Message-ID: <000501c6629c$b50d0f30$2c91ed46@Computerroom> From: "Paul Lipps" X-Original-To: Subject: field breaker trip X-Original-Date: Mon, 17 Apr 2006 21:01:01 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C66262.083BC650" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2869 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C66262.083BC650 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Often the overvoltage protection is what's referred to as a "crowbar", = meaning that it shorts out the field supply, like a crowbar across the = wires, to trip the field breaker, often an SCR, silicon = controlled-rectifier. A lot of transistors and SCRs have operating = points that change with temperature. A simple crowbar would have a 15V = zener diode connected from the alternator output to the SCR's gate. Once = the voltage rises high enough for the zener to conduct, the SCR conducts = and stays on, putting a short on the field input supply. ------=_NextPart_000_0002_01C66262.083BC650 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Often the overvoltage protection is what's = referred to as=20 a "crowbar", meaning that it shorts out the field supply, like a crowbar = across=20 the wires,  to trip the field breaker, often an SCR, silicon=20 controlled-rectifier. A lot of transistors and SCRs have operating = points that=20 change with temperature. A simple crowbar would have a 15V zener diode = connected=20 from the alternator output to the SCR's gate. Once the voltage rises = high enough=20 for the zener to conduct, the SCR conducts and stays on, putting a short = on the=20 field input supply.
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