[NSRCA-dist7] LiPo cell configuration

Thu Sep 18 11:51:55 AKDT 2008

You had a decision many of us will have sooner or later.. to use a known
'going bad' battery for trim flights - and what we may not realize is that
we have to fly almost full stick to get any type of performance from the
pack - thus loading it heavily. A 5 minute, or less, flight at almost full
stick, can be very dangerous - as you found out. The trick to any battery
longevity - meaning years, is to pull out as little current as possible (as
slowly as possible) from the pack during each flight (a more efficient motor
will help this also). You can imagine one extreme, taking say, 1 amp out
slowly, the batteries would last for 10 years (a guess). That said, there is
another battery function that also helps, and that is to get a greater
capacity battery so even though you pull 3000mah (3A) from the battery on a
flight, if the battery were rated at 20Ah (our batteries are rates around
5Ah), taking 3A from this battery would only be taking a fraction of the
total capacity, and not be an issue. However, weight will be an issue with
current battery technology. I think the ladder is where we are headed, with
the increased Burst rating of the newer cells = lower IR. Having a burst of
160A (new 5200's) is much better than a burst of 109A (5300's), and if we
could find a burst rating of 200A, that would be better yet. 

sc

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From: nsrca-dist7-bounces at lists.nsrca.org
[mailto:nsrca-dist7-bounces at lists.nsrca.org] On Behalf Of krishlan
fitzsimmons
Sent: Thursday, September 18, 2008 10:52 AM
To: CA, AZ, HI, NV, UT
Subject: Re: [NSRCA-dist7] LiPo cell configuration

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

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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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