Return-Path: Sender: (Marvin Kaye) To: lml Date: Thu, 10 Jul 2003 08:37:15 -0400 Message-ID: X-Original-Return-Path: Received: from [216.229.64.71] (HELO mail.fidnet.com) by logan.com (CommuniGate Pro SMTP 4.1b9) with SMTP id 2470607 for lml@lancaironline.net; Thu, 10 Jul 2003 07:39:32 -0400 Received: (qmail 17804 invoked from network); 10 Jul 2003 11:39:17 -0000 Received: from 216-229-95-162-empty.fidnet.com (HELO shannon) (216.229.95.162) by one.fidnet.com with SMTP; 10 Jul 2003 11:39:17 -0000 Reply-To: From: "Shannon Knoepflein" X-Original-To: "'Lancair Mailing List'" Subject: RE: [LML] Alternator Sizing X-Original-Date: Thu, 10 Jul 2003 07:30:18 -0400 Organization: ISC X-Original-Message-ID: <005f01c346d6$a48dadc0$0700a8c0@shannon> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.2627 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 In-Reply-To: Importance: Normal I agree with Jim, except I'll take that one step further on battery sizing. I subscribe to the Bob N school of thought that an alternator failure shouldn't ruin your day or prevent you from going to your intended destination. With that said, your battery should be sized to be able to power your essesential equipment in a worst case scenario situation. In my case, that's hard IFR, so that includes my ESS EFIS in front of me, AHRS, efis GPS, audio panel, garmin 430 gps/nav/com, transponder, JET 2" attitude indicator, and autopilot.....these are all on my ESS avionics buss fed through a diode and solid state relay by an AV master with an ESS ALT FEED directly from the battery as a further backup. So, say 30 minutes into my flight my primary AND ess alternator fails (honestly, whats the chance of that..thats why the OBAM dual bat dual alt is such a great system). If all fails to get either one going, then I need to have enough battery reserve to keep things going for the remainder of my trip. In my case with the supercharged IO-550, I figure 20 gallons per hour, with an average of 36 for takeoff and climb. 30 minutes into the flight, I've burned 18 gallons. I have 78 gallons of fuel in my Legacy, so that leaves 60 gallons, or 3 hours, or just 2.25 hours with 45 minute reserves, and during this flight, I should be able to cover just about 1000nm, so that should cover any trip I would want to make. So, I need 3 hours of battery. My calculations show I need about 10A continuous during IFR cruise, as long as the autopilot isn't working overboard. (I will have more hard numbers on this as I get more hours and will post the actual amp draws of all my components for everyones future use) So, 10A for 3 hours is 30Ah. I have 2 17Ah batteries in my system, so I should be ok....thats at least the way I planned it anyway. Fortunately, we have the opportunity as OBAM builders to build our system to far outperform the systems that spam can fliers are stuck with. Designing your system where very little can ruin your day only makes sense, as it doesn't cost much more, and it really forces you to understand your system and be a safe pilot when you are forced to use it. --- Shannon Knoepflein <---> kycshann@kyol.net Jim wrote: BTW, the battery should be able to power the essential instruments for 30 minutes.