X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 24 Jan 2011 07:57:11 -0500 Message-ID: X-Original-Return-Path: Received: from web36905.mail.mud.yahoo.com ([209.191.85.73] verified) by logan.com (CommuniGate Pro SMTP 5.4c2a) with SMTP id 4822977 for lml@lancaironline.net; Sat, 22 Jan 2011 15:09:18 -0500 Received-SPF: none receiver=logan.com; client-ip=209.191.85.73; envelope-from=chris_zavatson@yahoo.com Received: (qmail 72592 invoked by uid 60001); 22 Jan 2011 20:08:45 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=bmuO//Clcn/0zfgQ5kxWo4Fox/iy7T3HKlKRFdNuGw3vBKcJOunT5kCLUptdG8eaQzcD2JbjGyvydXoktwX63TgM/5rMaFE69w+UTOpO4IAiOYyXtIMWwZOKvL5FfR63OM+FRiSarlmpZ6OFe+/Wl+8Me96Qen2kGt93Yd6+1lQ=; X-Original-Message-ID: <205291.72415.qm@web36905.mail.mud.yahoo.com> X-YMail-OSG: ozLcWu4VM1kz2m_ZC5VkmAk0ZoPeCiw_NsCX2_pyki_mBZw Xo8TN29lFpXO.NYpTfi0yHBkRRTrl8WLHhWtmFpbUPX9LYm6YuYkVPPaxzZH rWZ5m3nlmkj7nnViKaRWhjCqOe78dHIM8uPLAtkhLURYhsICv5GmQ_07riWk QDlRe0N9nySVJ74hOuL6MqUmqjbmfd.nT_50Fzln9tnxL50eZqeKDMbypncI kDCXkBfD_PIlCtpfQRBBODYkSykhYSiRH3xco.kmyC3bnWxvJ05OTx4ULKGk uc33VZ51VQpHlZWMYaiugfoiTA._4MsUnx91lsJBCcMJmluAQwuQaeL_ZLKt C.qFuQ2k- Received: from [149.32.192.35] by web36905.mail.mud.yahoo.com via HTTP; Sat, 22 Jan 2011 12:08:45 PST X-Mailer: YahooMailRC/555 YahooMailWebService/0.8.107.285259 References: X-Original-Date: Sat, 22 Jan 2011 12:08:45 -0800 (PST) From: Chris Zavatson Subject: Re: [LML] Re: Lithium Batteries X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1086322102-1295726925=:72415" --0-1086322102-1295726925=:72415 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Note that the author matched the cells he used in the pack=0A"I did IR matc= hing of the cells....... when I built the pack,............. "=0AAlso, I wo= uld like to see the results after a few dozen cycles -and after two =0Ayear= s of use..=0A"I did a few 100% dod cycles "=0AThe voltages a guaranteed to = start diverging.=0AUntil the dangers associated with over charging are reso= lved (without balancing =0Acircuitry), I plan on avoiding Li-Ion in my plan= e.=A0 I like Li-Ion in for its =0Apower density and stiffness and have used= them in ground vehicles=A0in some very =0Alarge battery=A0packs. When conf= ined in a cockpit however, I prefer to carry along =0Aa battery with a more= benign failure mode.=0Agive them a few more years,=0A=0AChris Zavatson=0AN= 91CZ=0A360std=0Awww.N91CZ.com=0A=0A=0A=0A=0A_______________________________= _=0AFrom: Michael McMahon =0ATo: lml@lancaironline.net=0A= Sent: Sat, January 22, 2011 4:32:27 AM=0ASubject: [LML] Re: Lithium Batteri= es=0A=0AIt seems there may be some discrepancies between theoretical extrem= es and =0Areal-world experience.=A0 Here's a link to one of the forums on w= hich people are =0Areporting on their results (highlights mine):=0A=0ARe: b= uilding my own lifepo4 batt question.=0A>by tostino =BB Fri Sep 17, 2010 6:= 05 am =0A>By doing discharges on the bench with the cells exposed, and bein= g able to tell =0A>that each string holds almost exactly the same voltage a= ll the way through the =0A>discharge, I am pretty sure I can tell they are = not horribly out of balance. I =0A>did IR matching of the cells, but no cap= acity matching when I built the pack, so =0A>there is a little room for dev= iation i'm sure, but it is not much I assure you, =0A>or I would have a rea= lly out of balance pack at this point.I did a few 100% dod =0A>cycles on th= e bench to test and see how out of balancethey got... It went right =0A>dow= n to 3.2v/cell (resting) (2.9v under load) without them going out of =0A>ba= lanceat all, and they then charged right back up to full and stayed balance= d.=0A>=0A>You seem so certain that i'll kill my cells if I didn't have a ce= ll level LVC =0A>(with out the buffer space I provide it). My LVC is set to= 46v with a 14s pack. =0A>That means that it is 3.28v/cell. The resting vol= tage for each cell when I stop =0A>the discharge is about 3.5v. I would hav= e killed them by now if it were going to =0A>happen, and they would have go= ne out of balancenow if that were going to happen =0A>too.=0A=0AI found thi= s thread to be informative and a good place to start on studying =0Apeople'= s actual experiences building and using these batteries:=A0 =0Ahttp://endle= ss-sphere.com/forums/viewtopic.php?f=3D2&t=3D2633&start=3D705&hilit=3Dthyri= stor=0A =0A=0A=0AMichael =0A=0A=0AOn Fri, Jan 21, 2011 at 8:35 AM, Hamid Wa= sti wrote:=0A=0AMichael McMahon wrote:=0A>=0A>=0A>>I do n= ot want to start an argument, =A0but it is frustrating for people to say = =0A>>they don't like ideas based on out-of-date or incomplete data.=0A>>=0A= >>It is even more frustrating when people proposed ideas based on=0A>incomp= lete data. Your "EV guru" friends are correct, you do not HAVE to=0A>cell b= alance a pack, but only as long as you are willing to live with=0A>the limi= tations imposed by that choice. Do you know what those=0A>limitations are?= =0A>=0A>When you have a number of cells of any chemistry in series in a bat= tery=0A>pack, they all receive exactly the same current when charging. Some= =0A>cells are a little more efficient than others so they get fully charged= =0A>before their colleagues in the string. If at that point they continue t= o=0A>receive charging current, they will over-charge. Some chemistries are= =0A>able to handle this over-charging. Other chemistries like LiPo are very= =0A>intolerant of this over charging and quite literally blow up. Cell=0A>b= alancing attempts to make sure that the charge on each of the cells in=0A>t= he string is identical so they all get fully charged at the same time,=0A>m= aximizing the charge that the pack can hold. That maximum number is the=0A>= one everyone throws around and that is the number you will expect to get=0A= >from your battery pack.=0A>=0A>As I mentioned, you do not HAVE to cell bal= ance. For a LiPo or LiFe=0A>pack, you can just monitor the voltage on each = individual cell and stop=0A>charging when one of the cells gets fully charg= ed. Over time, the=0A>discrepancy in th charge state between the most effic= ient and the least=0A>efficient cell in the string will keep increasing, wi= th the usable=0A>capacity of the entire pack being controlled by the charge= in the least=0A>efficient cell. Taking this to the theoretical extreme, at= some point=0A>the pack will not be able to deliver any energy because one = cell will be=0A>fully charged and another will be fully discharged. In real= life, you=0A>will declare the pack useless and stop using it before you ge= t to that=0A>point. If you are willing to live with this diminishing capaci= ty, then=0A>cell balancing is indeed not required. Just remember that your = pack is=0A>no longer going to have the same capacity as the pack that has c= ell=0A>balancing and you must design the rest of your system to account for= that.=0A>=0A>Quoting the late Paul Harvey: Now you know the rest of the st= ory. =0A>=0A>=0A>Regards,=0A>=0A>Hamid=0A>=0A>=0A>=0A>--=0A>For archives an= d unsub http://mail.lancaironline.net:81/lists/lml/List.html=0A>=0A=0A=0A= =0A --0-1086322102-1295726925=:72415 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Note that the author matched the cells he used in the pack
"I = did IR matching of the cells....... when I built the pack,............. "=0A
Also, I would like to see the results after a few dozen cycles = -and after two years of use..
=0A
"I did a few 100% dod cycles "
=0A
The voltages a= guaranteed to start diverging.
=0A
Until the dangers associated w= ith over charging are resolved (without balancing circuitry), I plan on avo= iding Li-Ion in my plane.  I like Li-Ion in for its power density and = stiffness and have used them in ground vehicles in some very large bat= tery packs. When confined in a cockpit however, I prefer to carry alon= g a battery with a more benign failure mode.
=0A
give them a few m= ore years,
=0A
 
=0A
Chris Zavatson
=0A
N91= CZ
=0A
360std
=0A=0A
 
=0A

=0A
=0A
=0AFrom: Michael McMahon <afm528@gmail.com>
To: lml@lancaironline.net
Sent: Sat, January 22, 2011 4:32:27 AM
Subject: [LML] Re: Lithium Batteries
It seems there may be some discrepancies between theoretical e= xtremes and real-world experience.  Here's a link to one of the forums= on which people are reporting on their results (highlights mine):
=0A=0A
=0A

Re= : building my own lifepo4 batt question.=

=0A

3D"Newby = tostino =BB Fri Sep 17, 2010 6:05 am

=0A
By doing dischar= ges on the bench with the cells exposed, and being able to tell that each s= tring holds almost exactly the same voltage all the way through the dischar= ge, I am pretty sure I can tell they are not horribly out of balance. I did IR matching of the cells, but no capacity m= atching when I built the pack, so there is a little room for deviation i'm = sure, but it is not much I assure you, or I would have a really out of balance pack at this point. I did a few 100% dod cycles on the bench to t= est and see how out of balance they got... It went right down to 3.2v/cell (resting) (2.9v un= der load) without them going out of balance at all, and they then charged right back up to full and stayed bala= nced.

You seem so certain that i'll kill my cells if I didn't= have a cell level LVC (with out the buffer space I provide it). My LVC is = set to 46v with a 14s pack. That means that it is 3.28v/cell. The resting v= oltage for each cell when I stop the discharge is about 3.5v. I would have killed them by now if i= t were going to happen, and they would have gone out of balance now if that were going to ha= ppen too.
=0A

I found this thread to= be informative and a good place to start on studying people's actual exper= iences building and using these batteries:  http://endless-sphere.com/= forums/viewtopic.php?f=3D2&t=3D2633&start=3D705&hilit=3Dthyrist= or
=0A

Michael

=0A
= On Fri, Jan 21, 2011 at 8:35 AM, Hamid Wasti <hwasti@lm50.com> wrote:
=0A
=0A
Michael McMahon wr= ote:
=0A

I do no= t want to start an argument,  but it is frustrating for people to say = they don't like ideas based on out-of-date or incomplete data.

It is even more frustrating when people proposed ideas based = on
incomplete data. Your "EV guru" friends are correct, you do not HAVE = to
cell balance a pack, but only as long as you are willing to live with=
the limitations imposed by that choice. Do you know what those
limit= ations are?

When you have a number of cells of any chemistry in seri= es in a battery
pack, they all receive exactly the same current when cha= rging. Some
cells are a little more efficient than others so they get fu= lly charged
before their colleagues in the string. If at that point they= continue to
receive charging current, they will over-charge. Some chemi= stries are
able to handle this over-charging. Other chemistries like LiPo are = very
intolerant of this over charging and quite literally blow up. Cell<= BR>balancing attempts to make sure that the charge on each of the cells in<= BR>the string is identical so they all get fully charged at the same time,<= BR>maximizing the charge that the pack can hold. That maximum number is the=
one everyone throws around and that is the number you will expect to ge= t
from your battery pack.

As I mentioned, you do not HAVE to cell= balance. For a LiPo or LiFe
pack, you can just monitor the voltage on e= ach individual cell and stop
charging when one of the cells gets fully c= harged. Over time, the
discrepancy in th charge state between the most e= fficient and the least
efficient cell in the string will keep increasing= , with the usable
capacity of the entire pack being controlled by the ch= arge in the least
efficient cell. Taking this to the theoretical extreme, at some point
the pack will not be able to deliver any energy = because one cell will be
fully charged and another will be fully dischar= ged. In real life, you
will declare the pack useless and stop using it b= efore you get to that
point. If you are willing to live with this dimini= shing capacity, then
cell balancing is indeed not required. Just remembe= r that your pack is
no longer going to have the same capacity as the pac= k that has cell
balancing and you must design the rest of your system to= account for that.

Quoting the late Paul Harvey: Now you know the re= st of the story. =0A
=0A
=0A


Regards,<= BR>
Hamid



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