Return-Path: Sender: (Marvin Kaye) To: lml Date: Wed, 23 Jul 2003 00:05:06 -0400 Message-ID: X-Original-Return-Path: Received: from wind.imbris.com ([216.18.130.7] verified) by logan.com (CommuniGate Pro SMTP 4.1) with ESMTP id 2501330 for lml@lancaironline.net; Tue, 22 Jul 2003 22:23:02 -0400 Received: from starband.net (cda131-235.imbris.com [216.18.131.235]) by wind.imbris.com (8.11.6/8.11.6) with ESMTP id h6N2Pab42346 for ; Tue, 22 Jul 2003 19:25:37 -0700 (PDT) X-Original-Message-ID: <3F1DF27C.1050108@starband.net> X-Original-Date: Tue, 22 Jul 2003 19:27:08 -0700 From: "Hamid A. Wasti" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20030208 Netscape/7.02 X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: Re: [LML] Re: Essential Busses References: Content-Type: multipart/alternative; boundary="------------030900000202040600030102" --------------030900000202040600030102 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Shannon Knoepflein wrote: > This is all close. I show 10A, but close enough. > Are you saying that you actually measure 10A in your 14V airplane, or are you challenging the math? > With this considered, I'm confident in the batteries providing their > full 17Ah. > No they won't unless you cut your current load to 1.7A. Here's why: I am not familiar with your particular batteries, but the "standard" is to report the "rated" battery capacity at the C/20 rate (draining the battery at 1/20th of its amp-hour rating). As you drain the battery at higher currents, the available capacity decreases. I do not have the discharge curves for your battery, but using the curves for Panasolic Sealed Lead Acid batteries, at 0.5C load and 68F temperature, only 65% of the "rated" capacity is available. At 1C, this goes down to 55%. > Also, the cabin of the aircraft rarely gets below 50 degrees F, > probably more like 60 F, so I don't see that as an issue. > The temperature really depends upon where you mont your batteries. If they are mounted in the cabin, somethig in the 50F to 70F is a reasonable estimate. But keep in mind that even at 50F, you loose another 5% of the rated capacity. I am not familiar with the battery location for all the various models, but for example in my Mooney, the battery is mounted in the tail and I am willing to believe that after a 3 hour flight with a -10F OAT, the battery would be close to that temperature. As the syaing goes, the devil is in the details. There are a lot of little details that you need to look at and take into consideration. Unfortunately, not all the information is readily available and often the people selling the products are not too keen about revealing it. More often than not, the person at the company you can actually get to talk to, most probably does not know that much more than you anyway. Hamid --------------030900000202040600030102 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Shannon Knoepflein wrote:

This is all close. I show 10A, but close enough.

Are you saying that you actually measure 10A in your 14V airplane, or are you challenging the math?

With this considered, I’m confident in the batteries providing their full 17Ah.

No they won't unless you cut your current load to 1.7A. Here's why: I am not familiar with your particular batteries, but the "standard" is to report the "rated" battery capacity at the C/20 rate (draining the battery at 1/20th of its amp-hour rating). As you drain the battery at higher currents, the available capacity decreases. I do not have the discharge curves for your battery, but using the curves for Panasolic Sealed Lead Acid batteries, at 0.5C load and 68F temperature, only 65% of the "rated" capacity is available. At 1C, this goes down to 55%.

Also, the cabin of the aircraft rarely gets below 50 degrees F, probably more like 60 F, so I don’t see that as an issue.

The temperature really depends upon where you mont your batteries. If they are mounted in the cabin, somethig in the 50F to 70F is a reasonable estimate. But keep in mind that even at 50F, you loose another 5% of the rated capacity. I am not familiar with the battery location for all the various models, but for example in my Mooney, the battery is mounted in the tail and I am willing to believe that after a 3 hour flight with a -10F OAT, the battery would be close to that temperature.

As the syaing goes, the devil is in the details. There are a lot of little details that you need to look at and take into consideration. Unfortunately, not all the information is readily available and often the people selling the products are not too keen about revealing it. More often than not, the person at the company you can actually get to talk to, most probably does not know that much more than you anyway.

Hamid --------------030900000202040600030102--