[NSRCA-discussion] Batteries

[Chad Northeast]

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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