[NSRCA-discussion] Batteries

[Earl Haury]

Chad

Sure - nothing wrong with going with what provides the highest comfort level. Given the same technology - and often the same manufacturer - the differences between brands can come down to service provided. As you say - they all have their limits. We on the gulf coast are envious of your ambient temps for battery life (you can keep it for human life.) :) I've noted much better life from batts used during our "winter" than the heat of our summer.

At least we get a bit of a break with the shorter F3A sequences (the Masters guys need all the capacity they can get). 

Earl
  ----- Original Message ----- 
  From: Chad Northeast 
  To: nsrca-discussion at lists.nsrca.org 
  Sent: Friday, March 14, 2008 10:44 AM
  Subject: Re: [NSRCA-discussion] Batteries


  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.

  I have seen a lot of puffed 5350's, 5300's, 5000's so I guess they all have their limits :)

  Chad


  ----- Original Message -----
  From: Earl Haury <ejhaury at comcast.net>
  Date: Friday, March 14, 2008 9:10 am
  Subject: Re: [NSRCA-discussion] Batteries
  To: chad at f3acanada.org, NSRCA Mailing List <nsrca-discussion at lists.nsrca.org>

  > Chad, you have a point, however it's important to factor in that 
  > the 1P 
  > packs are also generally higher C rating. My view when 
  > considering batteries 
  > initially was that higher cell count provided more failure 
  > opportunities, 
  > both as individual cell failure and connections. I've  
  > disassembled a number 
  > of  "failed", or no longer pattern suitable packs, and 
  > measured individual 
  > cell characteristics.
  > 
  > Generally, the cells in a lower C pack tend demonstrate an 
  > increase in 
  > impedance, resulting in lower voltage output for a given current 
  > draw over 
  > their lifespan until no longer "pattern viable". During this 
  > time capacity 
  > diminishes - but most cells with high impedance will still 
  > retain 80+% of 
  > their original capacity. Even though these things generate more 
  > heat than 
  > the higher C packs - they tend to handle abuse (as you've found) 
  > partly 
  > because of the retained capacity and partly because of 
  > "performance 
  > limiting" impedance. Post flight imbalance doesn't change too 
  > much as these 
  > packs age - suggesting a similar "aging" of the individual cells.
  > 
  > Conversely, the high C packs demonstrate very low impedance 
  > initially and 
  > that appears to be retained throughout their life. However, the 
  > cell 
  > capacity appears to drop pretty early and continue to do so over 
  > the pack 
  > life. I've measured some of these with an average capacity loss 
  > of 40% after 
  > 50 flights - that means a 5000 mAh pack is now a 3000 mAh pack. 
  > Even worse - 
  > there is often a good deal of variance from cell to cell. Their 
  > low 
  > impedance will provide little warning (as loss of power) until a 
  > cell is 
  > injured, real easy to do if you try to take 3500 mAh from the 
  > now 3000 pack. 
  > Often one will notice the post flight imbalance increasing as 
  > these packs 
  > age and it will be greater at higher depths of discharge - a 
  > sure sign some 
  > cells are getting weak. OTOH - for blazing power the high C 
  > packs are the 
  > way to go - but there's a price to pay in life, weight, & $$.
  > 
  > These observations have led me to surmise that a pack with a 
  > high enough C 
  > rating to minimize impedance losses (and accompanying heat) and 
  > a low enough 
  > C rating to allow good capacity retention should provide the 
  > best value for 
  > pattern. I have no idea just what construction parameters / 
  > chemistry 
  > defines these characteristics. I chose to try the FlightPower 
  > F3A packs 
  > because they are mid-C rating and 5350 mAh capacity. So far they 
  > provide 
  > good power and generate no more heat than the high C packs I've 
  > used. I 
  > expect that the extra capacity (above 5000) offers a little 
  > buffer if there 
  > is a capacity decline over their life. I see little balancer 
  > activity with 
  > these packs regardless of depth of discharge (say 3000 mAh vs 
  > 4000 +) so 
  > far, time will tell - we're all still learning.
  > 
  > Earl
  > 
  > Team FlightPower
  > 



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