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Ron,<br>
<br>
(The use of the word "you" in the following does not mean you
personally Ron)<br>
<br>
I think that the way we run the batteries, we will never get many
hundreds or thousands of cycles from them. If you put aside the
marketing hype, no battery can supply what the typical r/c guy
demands from it over many many hundreds of flights. We sometimes
over discharge (at a high rate too), run them at sub optimal temps,
charge improperly, etc. etc. etc. With the advent of cheap
batteries for our purposes, we treat the packs as utterly disposable
and as a result get poor performance and life cycle life in return.
My first set of TP 5300 Pro-lites cost me $650 for a set and believe
me, I read the directions 10 times and talked with lots of
knowledgeable people before I attempted to run them the first time
and then followed the instructions and suggestions to a "T". Those
packs made it to 175 useful cycles because due to the price, I
treated them like gold. Now, guys don't have that investment and
don't use the same level of care but are still surprised when they
don't last a long time. <b>Every single time</b> you over charge,
over discharge, run a 50 degree battery right from your trunk, etc
you damage the pack. Period. It does not usually show up
immediately so you think it's ok and keep doing things that damage
the pack until at flight 35 or 40, it starts to swell during a
perfectly normal flight and the user thinks the packs just swelled
up for no reason since they were not abusing it THAT flight, but the
damage had already been done. <br>
<br>
I am not saying at all that it's blame the user for all battery
failures as there are some that are genuinely bad and have a defect
of some sort, but you cannot abuse them over time and expect them to
last. Again, these batteries are still very fragile and our usage of
them is very, very extreme and the utmost care needs to be heeded to
get maximum life and performance from them. I am guilty too as I am
not as diligent as I once was with the $650 set, and as a result
sometimes get a reduced lifespan from a pack but we all justify it
by saying that they were relatively cheap anyways. I submit we can
all get much better life and performance if we took better care of
our packs, but that takes time and effort and diligence. There is a
very good reason why some people get long life from their packs and
others get much, much less from their identical brand packs.<br>
<br>
Chris Moon<br>
<br>
<br>
On 12/5/2010 12:00 AM, Ron Van Putte wrote:
<blockquote cite="mid:00AC9773-0702-41B4-9178-BF0C07A09FB9@cox.net"
type="cite">Yeah. Now my head feels like my belly felt on
Thanksgiving afternoon.
<br>
<br>
However, it begs the question of what over discharging or
discharging too quickly actually is. I can understand going past
the mah rating as over discharging. Can discharging to 75%, 85%
or 95% of the mah rating be considered over discharging, if the
rate of discharge is under the C rating?
<br>
<br>
Ron VP
<br>
<br>
On Dec 4, 2010, at 8:21 PM, John Fuqua wrote:
<br>
<br>
<blockquote type="cite">First good explanation of why Lipos swell
that I have seen. Thanks for the insight.
<br>
<br>
<br>
<br>
From: <a class="moz-txt-link-abbreviated" href="mailto:nsrca-discussion-bounces@lists.nsrca.org">nsrca-discussion-bounces@lists.nsrca.org</a>
[<a class="moz-txt-link-freetext" href="mailto:nsrca-discussion-bounces@lists.nsrca.org">mailto:nsrca-discussion-bounces@lists.nsrca.org</a>] On Behalf Of
Chris
<br>
Sent: Saturday, December 04, 2010 7:37 PM
<br>
To: General pattern discussion
<br>
Subject: Re: [NSRCA-discussion] "Sick" Lipo Packs
<br>
<br>
<br>
<br>
Stu is right, all cells in the pack were subjected to the same
overcharge or over discharge and will also fail as the first
cell did. One event will probably not show up as a swelled cell
but it is the overcharge / over discharge over many cycles that
will result in swelling. Notice the article says that max
voltage is temp related, and most chargers don't make this
adjustment so even with a "good" balance charger, you can still
overcharge.
<br>
<br>
Chris
<br>
<br>
Part of a good article:
<br>
<br>
This was the common problem with many cheap Chinese LiPos of
around 2005-2008. Most are better now, but it's the #1 cause of
premature LiPo failure: water contamination in the plant. Many
of China's LiPo factories are on the coast, where the altitude
is very low and the humidity is high. You can't run the humidity
too low on the assembly floor, because you're working with
volatile chemicals that could explode in the presence of a
spark, and you can't run it too high because then you end up
with a worthless LiPo that swells on first use.
<br>
<br>
Here's the science. You have three ingredients that are
functional in a LiPo battery. The rest is wrapping and wiring
attachments.
<br>
<br>
Cathode: LiCoO2 or LiMn2O4
<br>
Separator: Conducting polymer electrolyte
<br>
Anode: Li or carbon-Li intercalation compound
<br>
I'm going to be a little vague in my language here. The
chemicals involved vary according to manufacturers, so I don't
want to make any assumptions.
<br>
<br>
Remember your chemistry class? Note the absolute lack of any
hydrogen atoms in the reaction. None, zero, zip, nada. If you
have water inside your battery -- and virtually all batteries
have a little bit -- you've got problems. When the chemical bond
of H20 is broken by electrolysis and heat, you end up with free
oxygen. You also have free-roaming hydrogen that typically ends
up bound to your anode or cathode, whichever side of the
reaction it's on and depending on the state of charge of your
battery.
<br>
<br>
Now, this is a pretty unstable situation that's exacerbated by
any over-discharge or over-charge condition creating metallic
lithium in your cell. The end result is Lithium Hydroxide: 1
atom of lithium, one atom of hydrogen, and one atom of oxygen.
<br>
<br>
But you still have a free oxygen atom floating around inside the
battery casing, that typically combines with one other oxygen
atom -- O2, or what we sometimes think of as "air" -- or two
other oxygen atoms, to form a characteristic tangy,
metallic-smelling substance called "ozone", or O3. Gases expand
with heat and contract with cold. Chuck a swollen battery in the
freezer and it might come out rock-hard again... until it heats
up. It's not frozen, it just got cold enough that the gases
inside didn't take up much space at all.
<br>
<br>
And that free O2 or ozone is just waiting to pounce and oxidize
some lithium on the slightest miscalculation on your part. The
modest over-discharge during a punch-out, or running the battery
a little too low or letting it get a little too hot, or running
the voltage up to 4.235v/cell on a cold day when the actual
voltage limit per cell is more like 4.1v. All of these create
the perfect storm for a puffy battery to quickly turn itself
into a ruined battery or an in-flight fire.
<br>
<br>
Understanding the role of free oxygen in your battery, from
water and other causes, is CRUCIAL to understanding why
batteries fail, and why sometimes you can get by with flying a
puffy battery, and sometimes you can't.
<br>
<br>
If a Lithium battery is overcharged or charged too quickly, you
end up with LOTS of excess free lithium on the anode (metallic
lithium plating), and free oxygen on the cathode. A free oxygen
atom is small enough to freely traverse the separator without
carrying an electric charge, resulting in lithium OXIDE on the
anode. Lithium "rust", in reality. Useless to us at this point,
just dead weight being carted around inside your battery's
wrapper.
<br>
<br>
But lithium oxide uses fewer oxygen atoms than existed in the
ionized state, so you end up with, again, FREE OXYGEN. And
people wonder why if you over-charge a LiPo underwater, it still
ignites despite the lack of open air...
<br>
<br>
If it's over-discharged or discharged too quickly, the reverse
is true, but you end up with Lithium Oxide on the cathode, but
at a lower rate because there's simply less there. Basically, an
abused battery quickly develops corrosion on both poles of the
battery inside the wrapper. And the more it's abused, the worse
it gets as the resistance goes up and it still gets driven hard.
<br>
<br>
This, by the way, is the most common cause of swelling today for
our aircraft when flown with a high-quality pack (not knock-off
eBay leftovers from expensive Chinese mistakes of 2004-2009).
The reality is, these kinds of cells, regardless of their 'C'
rating, are built for use where they last for several hours...
not several minutes. While the chemistry if used as designed is
good for thousands of cycles, we're driving them so far out of
spec that we're lucky to get hundreds of cycles out of them.
<br>
<br>
In most cases, too, our batteries are under-specced. If
slow-charged and slow-discharged, many of these packs would
often hold considerably more mAh than we think they do. That's
one of the reasons we get the performance we do from them.
Higher-C-rated packs also often introduce gelled electrolyte
into the separator, and carbon or phosphorous nano-structures on
the anode and cathode mixtures rather than the "pound it out
thin and hope it's mixed right" approach used with sheets of
anodes & cathodes today.
<br>
<br>
<br>
<br>
On 12/4/2010 8:23 PM, Stuart Chale wrote:
<br>
<br>
Been there done that but my experience is that before long
additional cells will fail and the cycle will continue. With
the cost of the lower priced packs, ie: Zippy's I would no
longer bother :)
<br>
<br>
On 12/4/2010 6:45 PM, Ron Van Putte wrote:
<br>
<br>
<br>
Those of you who use lithium polymer battery packs to power
their competition airplanes are familiar with "puffed" packs. I
recently had four elderly 5S packs "puff". We all know that's
not good, but what I'd like to know is what's actually
happening.
<br>
<br>
I know it's probably not wise for consumers to take lithium
polymer packs apart, but that's exactly what I did with four
packs. I discovered that in three of the "puffed" packs, only a
single cell was "puffed". In the last pack, there were two
"puffed cells. I did a little arithmetic and quickly discovered
that I could make three "unpuffed" packs from the good cells I
had. So, I unsoldered the "puffed" cells from the four packs
and cannibalized one pack to make three 5S packs from what I had
left. This process is obviously for the timid or the careless.
I was careful and had no mishaps. However, I would suggest that
anyone who says "Oops" a lot should not attempt doing this.
<br>
<br>
The three 5S packs I have left are "rock solid". Experienced
electric-pilots will know just what I mean.
<br>
<br>
I have flown these packs and they seem to perform just as they
did in their "youth".
<br>
<br>
My questions are: Why do lithium polymer cells "puff"? What is
the likely future of my recovered 5S packs?
<br>
<br>
Ron VP
<br>
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