X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [206.46.252.42] (HELO vms042pub.verizon.net) by logan.com (CommuniGate Pro SMTP 5.0c2) with ESMTP id 717950 for flyrotary@lancaironline.net; Sat, 10 Sep 2005 18:23:51 -0400 Received: from verizon.net ([71.99.169.87]) by vms042.mailsrvcs.net (Sun Java System Messaging Server 6.2 HotFix 0.04 (built Dec 24 2004)) with ESMTPA id <0IMM00B1AGVKLZO1@vms042.mailsrvcs.net> for flyrotary@lancaironline.net; Sat, 10 Sep 2005 17:23:45 -0500 (CDT) Date: Sat, 10 Sep 2005 18:23:40 -0400 From: Finn Lassen Subject: Re: [FlyRotary] Re: Overvoltage control (help Ed A) In-reply-to: To: Rotary motors in aircraft Message-id: <43235CEC.2090702@verizon.net> MIME-version: 1.0 Content-type: multipart/alternative; boundary=------------010900080206080609020107 X-Accept-Language: en-us, en References: User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax; PROMO) This is a multi-part message in MIME format. --------------010900080206080609020107 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Jim Sower wrote: > Finn Lassen wrote: > >> If one or all of the main rectifier diodes in the alternator shorts >> out, you will have an alternating current (voltage) feeding the >> battery and other loads. I sure hope that the "overvoltage" detector >> will recognize this and kill the voltage to the field winding or >> disconnect the wire from the B+ terminal. I'm not sure that ANY OV >> protection devices will detect failed diodes. Which one have I missed? > None that I know of :( >> I suspect that the regulators in our alternators are very reliable, >> providing they are adequately cooled. That would be one advantage for >> having a external regulator: it can be mounted in a cooler location. >> On the other hand, I don't know how reliable those "cheap" ford >> regulators are... Looking at the automotive industry in general, I'm >> confident that they design their regulators to perform adequately >> inside the alternator. > Within certain specified temp limits. Do we know those? I think Tracy mentioned that electronics expected life goes down exponentially with temp increases over 120F... I think the importance of this subject is directly related to the $ amount of avionics you have in your plane. Well, due to the fact that we fly "electric" planes, safety is a factor too. You'll want to be able to diconnect a failing alternator and continue flying on the battery. Time for me to modify my electrical system... Finn --------------010900080206080609020107 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Jim Sower wrote:
Finn Lassen wrote:
If one or all of the main rectifier diodes in the alternator shorts out, you will have an alternating current (voltage) feeding the battery and other loads. I sure hope that the "overvoltage" detector will recognize this and kill the voltage to the field winding or disconnect the wire from the B+ terminal.   I'm not sure that ANY OV protection devices will detect failed diodes.  Which one have I missed?
None that I know of :(
I suspect that the regulators in our alternators are very reliable, providing they are adequately cooled. That would be one advantage for having a external regulator: it can be mounted in a cooler location. On the other hand, I don't know how reliable those "cheap" ford regulators are... Looking at the automotive industry in general, I'm confident that they design their regulators to perform adequately inside the alternator. 
Within certain specified temp limits. Do we know those? I think Tracy mentioned that electronics expected life goes down exponentially with temp increases over 120F...

I think the importance of this subject is directly related to the $ amount of avionics you have in your plane.
Well, due to the fact that we fly "electric" planes, safety is a factor too. You'll want to be able to diconnect a failing alternator and continue flying on the battery. Time for me to modify my electrical system...

Finn

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