X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 10 [X] Return-Path: Sender: To: lml Date: Wed, 20 Dec 2006 22:30:30 -0500 Message-ID: X-Original-Return-Path: Received: from jrcda.com ([69.36.178.59] verified) by logan.com (CommuniGate Pro SMTP 5.1.3) with ESMTP id 1696577 for lml@lancaironline.net; Wed, 20 Dec 2006 21:57:25 -0500 Received-SPF: none receiver=logan.com; client-ip=69.36.178.59; envelope-from=hwasti@starband.net Received: from [127.0.0.1] (cbl-238-61.conceptcable.com [207.170.238.61] (may be forged)) (authenticated) by jrcda.com (8.11.6/8.11.6) with ESMTP id kBL2uc116105 for ; Wed, 20 Dec 2006 19:56:38 -0700 X-Original-Message-ID: <4589F7DD.3090408@starband.net> X-Original-Date: Wed, 20 Dec 2006 18:56:29 -0800 From: "Hamid A. Wasti" User-Agent: Thunderbird 1.5.0.9 (Windows/20061207) MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: [LML] Re: electric attitude indicators References: In-Reply-To: Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Zavatson, Christopher J (US SSA) wrote:

Hamid,

Where did this come from?:

 

For the batteries in question here, the very definition of the nominal battery capacity designation is the number of amps that can be discharged for one hour.  This definition is provided in the battery manufacturer’s literature – see Gill and Concorde websites.

I was not aware that this discussion was restricted to Gill and Concorde batteries.  While the definition of "Amp-Hour" is the number of amps that a battery can deliver for one hour, the industry standard is to report this at C/20 or "when discharged over 20 hour" rate.  While individual manufactures may choose to use different rates, be it 1C rate or C/6 or even C/100 rate, the industry standard is C/20 and that is what one need to assume unless one reads the data sheet and verifies that it is something else.  If you looked up the specific data for your particular manufacturer, you are way ahead of most of the crowd who have installed a "25Ah" battery -- the one that has "25" in its name.

Note that the ‘25’ in Gill ‘G-25’ does not mean 25 Ah, just as the ‘25’ in Concorde’s ‘RG-25XC’ does not mean 25 Ah. 

I suspect that that is news to many listers, most A&P's and almost all certified bird pilots.

The Gill G-25 is rated at 18 Ah

A quick calculation using typical numbers indicates that a battery rated at 18Ah at a 1C rate, would be rated at about 25Ah at C/20 rate.  It is just speculation on my part, but I wonder if the the G-25 at one time used to be rated as 25Ah till they decided to change the reporting standard to more conservative numbers.

All that said, even using the battery's 1C rate as specified by the manufacturer, if you are planning on any of the following:

 -other than a brand new battery
 -other than a fully charged battery (like one that was used to start the engine 30 minutes ago)
 -operating at other than the specified temperature (around room temperature)
-loading with anything more than the 1C current drain

you better figure out how much you need to derate the battery.  A simple division of the 1C capacity by your current consumption is going to give you a wildly optimistic number.  My point remains, when you do all of that, you may come up with a number that may surprise you.

Regards,

Hamid