[NSRCA-dist7] LiPo cell configuration

Thu Sep 18 09:51:57 AKDT 2008

This is exactly what happened to my pack that caught on fire last Friday Scott. I had a good feeling a cell or two was bad as my performance was down on this pack pretty good, but I figured I'd use it as a 5 minute trimming practice pack.. I assume it got really hot in flight as I had the stick pegged most of the 3 or 4 minutes that it was in the air. It was super hot and one cell was split open when I took the belly pan off. I won't use my other packs now that are down on "noticeable power anymore. Too much at risk to keep flying them for me. Had I had a Cellpro charger, I might have never flown that pack that day. 

Chris          

--- On Thu, 9/18/08, Scott <scottcov at comcast.net> wrote:
From: Scott <scottcov at comcast.net>
Subject: Re: [NSRCA-dist7] LiPo cell configuration
To: "'CA, AZ, HI, NV, UT'" <nsrca-dist7 at lists.nsrca.org>
Date: Thursday, September 18, 2008, 1:49 AM

Don, I have 4 5300's that 
are the one's I have been using for a long time (years). Mine too, pull my plane 
well, but comparing them to new packs, the drop off in performance over time has 
been so subtle I notice little difference until I compare them to new packs. The 
difference is very evident. However, my larger concern is fire.. as I place more 
demand on cell BANKS that may be bad (or going bad), the heat builds up much 
more.. and the potential for fire, in my mind, increases. This happens when 
charging and discharging (flying). Imagine a cell or TWO being puffed inside a 
4s BANK of cells inside the black heat shrink. There is a chance you would not 
see this unless you are looking close.. which I have done, and have replaced 
these packs. The stress on the remaining good cells within the 4s bank is 
extreme. Things have been pretty quiet lately regarding fires with LiPo, but we 
must not forget the potential is still there and using old packs (any packs for 
that matter), where the IR has increased, is concerning to me. I have 2 packs 
(5300) that run hot and I don't think I'd fly them in 90 degree plus outside 
temps as they would really come down hot after a flight. The new packs (5200's) 
are not even warm to the touch. Oh, just FYI, I have replaced my 5000 V2 Extreme 
pack with the new 5200 cells. I am not recommending the 5200's yet, they are too 
new yet, but it seems they have good potential. Also, here  is San Jose, 
the outside temp's are rarely over 90.. but up in Sac or AZ, this happens much 
more often. If I lived in these areas I'd be a bit more concerned. 

sc

From: nsrca-dist7-bounces at lists.nsrca.org 
[mailto:nsrca-dist7-bounces at lists.nsrca.org] On Behalf Of 
AtwoodDon at aol.com
Sent: Wednesday, September 17, 2008 9:31 
PM
To: nsrca-dist7 at lists.nsrca.org
Subject: Re: 
[NSRCA-dist7] LiPo cell configuration

Scott, like you, my TP5300s (4P) configuration have lasted into my 3rd 
season flying electric.  Yep, they are tired but will still pull my plane 
vertical as far as I need, just not quite as much gusto.  All my other 
batteries are 1P configurations but I have not seen that show significantly 
better or worse balancing challenges.  I agree, the 1P configuration would 
make it easier to detect a single cell developing higher IR.

I have one FP5350 (2 5S packs) as well as 2 TrueRC 5000 mah packs (each 2 
5S packs).  The FPs have been solid with about 75 flights, no issues, 
pretty easy to balance while charging.  The 2 TrueRC packs need a little 
more balancing during charge but everything finishes out fine.  They have 
less than 30 flights each.

I did check one of the TrueRC packs on Jim's Cellpro and all 10 cells were 
in the 3.5 milli ohm range, one cell was slightly higher at about 4 if I 
remember correctly.  The new Cellpro 10s is interesting and there is a 
very good review and subsequent discussion about it on RC Groups.

Don

In a message dated 9/17/2008 9:05:48 P.M. Pacific Daylight Time, 
scottcov at comcast.net writes:

  Hey Electric 
  Guys,

  I'd be interested in what 
  LiPo battery configuration you are using.. 5S2P, 5S4P, 5S1P... other. Why?.. 
  read on. I believe the less "P" you have in the battery the easier to balance 
  and possibly the longer life you will get due to better cell balancing before 
  charging. I have recently converted to a new cell by TP, some of you saw this 
  at the Hollister contest. The 5S2P, 5200 pack, is working great. Jim Oddino 
  and I checked the internal cell resistance, which was around 3milli-ohms (if I 
  recall correctly). This battery puts out 156A burst, the older 5s4p, 5300 pack 
  put out 109A burst. My thinking is this, the lower "P" pack you have the 
  easier to keep the battery in balance. If you have a 4p pack, any one of the 
  4p cells can degrade over time, causing the 4p 'bank' to not supply as much 
  sustained current - causing the whole battery to be weaker. Jim and I played 
  with a Cellpro 10S charger, and I think we concluded that it would be 
  difficult for any charger to determine if any one cell in a 4p bank 
  was going bad (you can only monitor the bank IR, not the individual cell 
  within the bank). However, if you had a 1p 10S pack, you could easily tell if 
  the cell was gaining resistance as it aged. On a 2p pack, the resistance 
  CHANGE may not show up as easily as a 1p pack but much easier than a 4p pack. 
  We are trying to determine here when a 5S pack is getting weak (yes, we can 
  see as we fly - but if we could determine as it happens, perhaps we can 
  correct this by charging differently). Jim O mentions he has not seen a 
  battery with as low of internal resistance readings as the new TP pack, which 
  equates to more power, less heat in use, and I hope longer life. I will 
  mention here that my 5300, 5s4p packs have lasted 2-3 years and many, 
  many flights, but they are getting old.. and the new packs may last 
  3-4 years.. they are also around $250 each.. a reduction in price from the 
  5s4p packs. I believe even newer technology will soon show us a 10s1p 
  pack from TP - and some may have this now from other 
  manufacturers.

  I'd be interested in your 
  opinions on this topic.

  Scott

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