<font face="'PrimaSans BT,Verdana,sans-serif'">Its just my general
"feel" from my experience with TP, and witnessing others experience
with FP. I won't go into all the details on the list because I don't
want to tarnish any particular company, but I have yet to see any of
the 1P packs come close to the longevity of the 4P packs when putting
them through the same punishment.<br><br>I have seen a lot of puffed 5350's, 5300's, 5000's so I guess they all have their limits :)<br><br>Chad<br><br></font><font face="'PrimaSans BT,Verdana,sans-serif'"><br>----- Original Message -----<br>From: Earl Haury <ejhaury@comcast.net><br>Date: Friday, March 14, 2008 9:10 am<br>Subject: Re: [NSRCA-discussion] Batteries<br>To: chad@f3acanada.org, NSRCA Mailing List <nsrca-discussion@lists.nsrca.org><br><br>> Chad, you have a point, however it's important to factor in that <br>> the 1P <br>> packs are also generally higher C rating. My view when <br>> considering batteries <br>> initially was that higher cell count provided more failure <br>> opportunities, <br>> both as individual cell failure and connections. I've <br>> disassembled a number <br>> of "failed", or no longer pattern suitable packs, and <br>> measured individual <br>> cell characteristics.<br>> <br>> Generally, the cells in a lower C pack tend demonstrate an <br>> increase in <br>> impedance, resulting in lower voltage output for a given current <br>> draw over <br>> their lifespan until no longer "pattern viable". During this <br>> time capacity <br>> diminishes - but most cells with high impedance will still <br>> retain 80+% of <br>> their original capacity. Even though these things generate more <br>> heat than <br>> the higher C packs - they tend to handle abuse (as you've found) <br>> partly <br>> because of the retained capacity and partly because of <br>> "performance <br>> limiting" impedance. Post flight imbalance doesn't change too <br>> much as these <br>> packs age - suggesting a similar "aging" of the individual cells.<br>> <br>> Conversely, the high C packs demonstrate very low impedance <br>> initially and <br>> that appears to be retained throughout their life. However, the <br>> cell <br>> capacity appears to drop pretty early and continue to do so over <br>> the pack <br>> life. I've measured some of these with an average capacity loss <br>> of 40% after <br>> 50 flights - that means a 5000 mAh pack is now a 3000 mAh pack. <br>> Even worse - <br>> there is often a good deal of variance from cell to cell. Their <br>> low <br>> impedance will provide little warning (as loss of power) until a <br>> cell is <br>> injured, real easy to do if you try to take 3500 mAh from the <br>> now 3000 pack. <br>> Often one will notice the post flight imbalance increasing as <br>> these packs <br>> age and it will be greater at higher depths of discharge - a <br>> sure sign some <br>> cells are getting weak. OTOH - for blazing power the high C <br>> packs are the <br>> way to go - but there's a price to pay in life, weight, & $$.<br>> <br>> These observations have led me to surmise that a pack with a <br>> high enough C <br>> rating to minimize impedance losses (and accompanying heat) and <br>> a low enough <br>> C rating to allow good capacity retention should provide the <br>> best value for <br>> pattern. I have no idea just what construction parameters / <br>> chemistry <br>> defines these characteristics. I chose to try the FlightPower <br>> F3A packs <br>> because they are mid-C rating and 5350 mAh capacity. So far they <br>> provide <br>> good power and generate no more heat than the high C packs I've <br>> used. I <br>> expect that the extra capacity (above 5000) offers a little <br>> buffer if there <br>> is a capacity decline over their life. I see little balancer <br>> activity with <br>> these packs regardless of depth of discharge (say 3000 mAh vs <br>> 4000 +) so <br>> far, time will tell - we're all still learning.<br>> <br>> Earl<br>> <br>> Team FlightPower<br>> </font><br>