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<DIV><FONT face=Arial>Chris</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Thanks for the info - pretty much answer's the puffing
question.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Let me add my thoughts / observations as to why things can
not be all good with charging / balancing related to pattern packs and the
common chargers we use.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV>
<DIV><FONT face=Arial>So what about "charge abuse"? My observations suggest that
balancing equipment doesn't always do what is expected. Many balancers
function by drawing charge current away from the high cell(s) which allows
the low cells to "catch up". Part of the problem lies with the
balancers capacity to divert that charge current - usually 300 - 500mAh -
which isn't sufficient when charging at 5A. If the
charger primarily terminates on total pack voltage, the high cell(s) are
pushed too high until the average reaches the target pack voltage. This
will often leave the weak cell low and some too high and won't be noted
unless the individual cell voltages are observed. (The way to charge packs
packs with large imbalance is at a rate that doesn't exceed the diversion
capacity of the balancer - takes time.) On a good note, most systems will
terminate charge (with notification) if the high cells are pushed too far -
still not good for them (especially without consideration for temperature)
but an important safety feature that should prevent charging eruptions as well
as providing notification that something isn't right. </FONT><FONT
face=Arial>Then there are chargers that balance by either charging each cell
independently or by adding current to the low cells to help them "catch
up". This is a good strategy and that appears ideal except for issues
with connectors / leads.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>A common problem is that both balance methods can be
compromised by the balance leads / connectors themselves which can result in the
balancer actually misbalancing the pack. The connectors are small and of
materials that will oxidize over time. They also tend to lose tension with use.
Both the looseness and oxidation results in a poor connection. A marginal
connection will prevent the balancer from "seeing" the correct voltage and will
become worse as balance current flows. (Ever have a "balance lead not connected"
or "incorrect cell count" report - these are indications that the connectors are
not doing their job. This all is 10X true if charging at 5A is attempted through
these faulty connections! Additionally, the balance leads themselves are small
gauge wire of low strand count (not very flexible) which often results in
several strands breaking from the connector with use. Eventually the wire might
break off - in the meantime it's a resistor in the balancing circuit! I've also
seen extensions (have all the same problems) where only a couple of strands were
captured in crimping to the connector! The good news is that much of this can be
avoided with maintenance and observation. Contact cleaners will help keep the
connections clean, the some female connectors can be removed from the housing
(one at a time if on the batt) and "bent" back closed when they loosen. Check
connections on new leads / extensions and always fix the problem if some lead
"wiggling" is needed to make the charger happy.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Earl</FONT></DIV></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>---- Original Message ----- </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=f3aflyer7@gmail.com href="mailto:f3aflyer7@gmail.com">Scott
Pavlock</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">General pattern discussion</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, December 05, 2010 7:59
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] "Sick"
Lipo Packs</DIV>
<DIV><BR></DIV>Chris ,<BR><BR>Great article!<BR>Were can we find the rest of
it.<BR><BR>
<DIV class=gmail_quote>On Sat, Dec 4, 2010 at 8:36 PM, Chris <SPAN
dir=ltr><<A
href="mailto:cjm767driver@hotmail.com">cjm767driver@hotmail.com</A>></SPAN>
wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: rgb(204,204,204) 1px solid; MARGIN: 0pt 0pt 0pt 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV bgcolor="#ffffff" text="#000000">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>
<P><I>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.</I></P>
<P><I>Here's the science. You have three ingredients that are functional in
a LiPo battery. The rest is wrapping and wiring attachments.</I></P>
<UL>
<LI><I>Cathode: LiCoO2 or LiMn2O4</I>
<LI><I>Separator: Conducting polymer electrolyte</I>
<LI><I>Anode: Li or carbon-Li intercalation compound</I> </LI></UL>
<P><I>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.</I></P>
<P><I>Remember your chemistry class? Note the absolute <B>lack of any
hydrogen atoms in the reaction</B>. None, zero, zip, nada. If you have
<B>water inside your battery</B> -- 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.</I></P>
<P><I>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.</I></P>
<P><I>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.</I></P>
<P><I>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.</I></P>
<P><I>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.</I><BR></P><I>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.</I>
<P><I>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...</I></P>
<P><I>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.</I></P>
<P><I>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.</I></P>
<DIV style="FLOAT: right"><I><INS
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<P><I>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.</I></P>
<DIV>
<DIV></DIV>
<DIV class=h5><BR><BR>On 12/4/2010 8:23 PM, Stuart Chale wrote:
<BLOCKQUOTE type="cite">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>
<BLOCKQUOTE type="cite">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
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