Return-Path: Received: from cdihost.cdicorp.com ([207.79.152.5]) by ns1.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-64832U3500L350S0V35) with SMTP id com for ; Mon, 31 Jul 2000 18:03:25 -0400 Received: from HQ-EDI by cdihost.cdicorp.com via smtpd (for ns1.olsusa.com [205.245.9.2]) with SMTP; 31 Jul 2000 22:09:50 UT Received: from cdim-pts-mail.cdicorp.com (CDIM-PTS-MAIL [172.17.131.3]) by hq-edi.cdicorp.com with SMTP (Microsoft Exchange Internet Mail Service Version 5.5.2650.21) id QAHZ2SX5; Mon, 31 Jul 2000 18:09:48 -0400 Received: by CDIM-PTS-MAIL with Internet Mail Service (5.5.2650.21) id ; Mon, 31 Jul 2000 18:09:48 -0400 Message-ID: From: "Rumburg, William" To: 'dfs' , Lancair List Subject: RE: Backup Electrical Power Date: Mon, 31 Jul 2000 18:09:43 -0400 X-Mailing-List: lancair.list@olsusa.com Reply-To: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> > Sorry Bill, you've skipped a decimal point in your figuring the Ampere > Hour > (AH) rating af a battery. Figuring your way, would make it a 120 Ampere > Hour > battery instead of 12 AH! > The bottom line is: A 12 AH battery will deliver 1.2 amps for ~10+ hours, > 12 > amps for maybe 45 minutes and it goes down from there. > Dan Schaefer Dan - I should have gone to Oshkosh and stayed out of trouble...I had thought that the diode would be the only component in my design open to question, but my misunderstanding of battery capacity created another. Well, this has turned into a good, worthwhile discussion. You're absolutely correct, I miscalculated battery capacity! Manufacturer's most commonly design their lead-acid batteries for a ten hour discharge, but some are designed for shorter or longer discharge times. I again spoke with Concorde and was surprised to learn that their aircraft batteries are optimized (and rated) for one hour discharge, which is pretty nearly matched to the time we might need to fly on backup power (a battery having a discharge time optimized for one to three hours would be most efficient for our purposes, but this does not mean that a battery designed for a longer discharge time could not be used for backup). Another consideration is that battery terminal voltage decays as the battery is discharged and the question arises at what level the voltage will be insufficient to spin the gyros and they "flag". Manufacturer's supply a chart to show voltage decay as the battery discharges; however, activating the backup battery while on the ground and noting the time and voltage when the gyros "flag" will be the only accurate measure of your battery's endurance. To choose a backup battery, we would of course have to first determine the required current for critical devices (i.e. attitude and turn coordinator gyros, electronic ignition). 5 to 10 amps is a good, liberal estimate (electric gyros are labeled for running current). Two to three hours should be the minimum time they must operate. So, your demand would be 10 to 30 A-H and that would be the minimum battery capacity. I checked and found a Johnson Controls "Dynasty" 30 A-H battery that should be an ideal backup battery. In fact, it's designed for that purpose in the telecommunications industry. It's a sealed RG battery and will supply 8 amps for 3 hours to a minimum of 11.4 volts. It's 7-3/4" L x 5-1/4" W x 6-3/4" H, weighs 27 lbs and should fit the area forward of the right side rudder pedals on the 320. Bill Rumburg N403WR (Sonic bOOm) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 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. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>