Return-Path: Received: from spdmgaac.compuserve.com ([149.174.206.136]) by ns1.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-64832U3500L350S0V35) with ESMTP id com for ; Sat, 29 Jul 2000 23:41:18 -0400 Received: (from mailgate@localhost) by spdmgaac.compuserve.com (8.9.3/8.9.3/SUN-1.9) id XAA27308 for lancair.list@olsusa.com; Sat, 29 Jul 2000 23:47:40 -0400 (EDT) Date: Sat, 29 Jul 2000 23:47:07 -0400 From: Lynda Frantz Subject: Using diodes for battery isolation Sender: Lynda Frantz To: "INTERNET:lancair.list@olsusa.com" Message-ID: <200007292347_MC2-ADF1-6DF7@compuserve.com> X-Mailing-List: lancair.list@olsusa.com Reply-To: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> In analyzing the reliability of a diode being used for battery isolation consider the following happening: The alternator fails resulting in a temporary 50 Volts over voltage. The overvoltage causes the over voltage protector "crowbar" to trip the alternator field deactivating the alternator. Will your diode survive this transient without shorting out? If so the backup battery will continue to power your essential bus for the expected duration while you are getting the aircraft saftely back on the ground. If not the backup battery is powering the primary bus and the backup battery may not last as long as expected. If your isolation diode is only rated for 30V forward bias perhaps you should look for another. Unfortunately, diodes usually fail in the shorted mode which is not good when they are being used to isolate critical systems. We must consider failure mode possibilities else the system may not work as expected. Jim Frantz >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>