X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 25 Jan 2011 16:46:54 -0500 Message-ID: X-Original-Return-Path: Received: from mail-iw0-f180.google.com ([209.85.214.180] verified) by logan.com (CommuniGate Pro SMTP 5.4c2a) with ESMTPS id 4825878 for lml@lancaironline.net; Tue, 25 Jan 2011 10:12:43 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.214.180; envelope-from=mwsletten@gmail.com Received: by iwn37 with SMTP id 37so11876854iwn.25 for ; Tue, 25 Jan 2011 07:12:08 -0800 (PST) DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:references:in-reply-to:subject:date:message-id:mime-version :content-type:x-mailer:thread-index:content-language; b=vFvhVry2q17TL2Lo3+1dNggwLqNWKWA/gmB3Qs9WyvqOgEEqXNmpbN43veNbrE6+T/ LjRFBSlWXXq889YHyPAxorMAzEnPzzPu2O44URiKf+6ByyORtLBo0MzJkD3kRDa2lKyT 35IeLACbnxQbeIrUroReKBx6Z1hKAqp1qJF84= Received: by 10.42.180.65 with SMTP id bt1mr3723591icb.258.1295968328495; Tue, 25 Jan 2011 07:12:08 -0800 (PST) X-Original-Return-Path: Received: from MarkDesktop (dsl-204-13-117-146.hometel.com [204.13.117.146]) by mx.google.com with ESMTPS id 8sm12048605iba.16.2011.01.25.07.11.50 (version=TLSv1/SSLv3 cipher=RC4-MD5); Tue, 25 Jan 2011 07:11:55 -0800 (PST) From: "Mark Sletten" X-Original-To: "'Michael McMahon'" , References: In-Reply-To: Subject: RE: [LML] Re: Lithium Batteries X-Original-Date: Tue, 25 Jan 2011 09:11:51 -0600 X-Original-Message-ID: <005501cbbca2$34a1e4a0$9de5ade0$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0056_01CBBC6F.EA0774A0" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: Acu8AHUNF3czw3CTQtetXbGfz19uYAAnSO+g Content-Language: en-us This is a multipart message in MIME format. ------=_NextPart_000_0056_01CBBC6F.EA0774A0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Michael, Being one yourself, you should know the average, very-independent-minded experimental aircraft builder holds strong opinions, especially in the area of safety. Many share their experiences in that area bluntly and tersely, with the opinion the best approach to guarding safety is "tough love, early and often." I don't really know whether or not that approach is the most effective or not, but I DO know being involved with a community that's concerned with your personal safety is a rare and valuable thing, one that can strongly and positively affect the risks associated with dangerous activities like experimental aviation. So, despite the seemingly intentional sharp edges of some of the comments you've gotten, I hope you are able to round the corners a bit, so to speak, and view them as encouraging words of caution. Speaking for myself, I hope someday to benefit in one way or another from your continued experimentation, I just want you to hold safety as your paramount concern while doing so. Regards, Mark Sletten From: Michael McMahon [mailto:afm528@gmail.com] Sent: Monday, January 24, 2011 1:54 PM To: lml@lancaironline.net Subject: Re: [LML] Re: Lithium Batteries I never claimed to be an expert, and I've never advocated that people start using these batteries; I said I was interested in them and had been doing a lot of research. Tostino is far from the only person reporting that he does not balance his cells. The SECOND link in my post is a thread with several hundred posts on designing, building, and testing cells. Have any of the naysayers read the thread, in depth, or done similar research? As I've written before, I've been researching this for a long time, I'm not relying on one post from one guy who did a few tests, it was just the first I pulled up of many, many similar reports. I also have read, but won't bother to post 15 links, that deep discharging, such as Hamid had done, is different than the minimal discharge we would expect from an engine start. The small discharge contributes to less need to balance the cells. Quite different from the total-loss system in an RC or solar-powered environment. I'm an experimenter. I can't just sit on the sidelines and wait for "someone else" to do the research, testing and development, then jump on the bandwagon. That's why I'm building an experimental aircraft. I thought this forum would be a good place to discuss development and testing of new systems rather than quickly declare it "too risky" for intelligent discussion. Michael On Mon, Jan 24, 2011 at 4:57 AM, wrote: The two worst places to have a fire...boat and plane. A IVP was seriously damaged due to a battery fire. Risk v. Benefit. Jeff Sent from my iPad On Jan 22, 2011, at 6:32 AM, Michael McMahon wrote: It seems there may be some discrepancies between theoretical extremes and real-world experience. Here's a link to one of the forums on which people are reporting on their results (highlights mine): Re: building my own lifepo4 batt question. Error! Filename not specified.by tostino > Fri Sep 17, 2010 6:05 am By doing discharges on the bench with the cells exposed, and being able to tell that each string holds almost exactly the same voltage all the way through the discharge, I am pretty sure I can tell they are not horribly out of balance. I did IR matching of the cells, but no capacity matching 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 test and see how out of balance they got... It went right down to 3.2v/cell (resting) (2.9v under load) without them going out of balance at all, and they then charged right back up to full and stayed balanced. 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 voltage for each cell when I stop the discharge is about 3.5v. I would have killed them by now if it were going to happen, and they would have gone out of balance now if that were going to happen too. I found this thread to be informative and a good place to start on studying people's actual experiences building and using these batteries: http://endless-sphere.com/forums/viewtopic.php?f=2 &t=2633&start=705&hilit=thyristor Michael On Fri, Jan 21, 2011 at 8:35 AM, Hamid Wasti wrote: Michael McMahon wrote: I do not 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 limitations are? When you have a number of cells of any chemistry in series in a battery pack, they all receive exactly the same current when charging. Some cells are a little more efficient than others so they get fully charged before their colleagues in the string. If at that point they continue to receive charging current, they will over-charge. Some chemistries are able to handle this over-charging. Other chemistries like LiPo are very intolerant of this over charging and quite literally blow up. Cell balancing attempts to make sure that the charge on each of the cells in the string is identical so they all get fully charged at the same time, 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 get 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 each individual cell and stop charging when one of the cells gets fully charged. Over time, the discrepancy in th charge state between the most efficient and the least efficient cell in the string will keep increasing, with the usable capacity of the entire pack being controlled by the charge 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 discharged. In real life, you will declare the pack useless and stop using it before you get to that point. If you are willing to live with this diminishing capacity, then cell balancing is indeed not required. Just remember that your pack is no longer going to have the same capacity as the pack 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 rest of the story. Regards, Hamid -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html ------=_NextPart_000_0056_01CBBC6F.EA0774A0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Michael,

 =

Being one yourself, you should know the average, very-independent-minded = experimental aircraft builder holds strong opinions, especially in the area of = safety. Many share their experiences in that area bluntly and tersely, with the opinion the = best approach to guarding safety is “tough love, early and = often.” I don’t really know whether or not that approach is the most effective or not, = but I DO know being involved with a community that’s concerned with your = personal safety is a rare and valuable thing, one that can strongly and positively = affect the risks associated with dangerous activities like experimental = aviation.

 =

So, despite the seemingly intentional sharp edges of some of the comments = you’ve gotten, I hope you are able to round the corners a bit, so to speak, and = view them as encouraging words of caution. Speaking for myself, I hope someday to = benefit in one way or another from your continued experimentation, I just want = you to hold safety as your paramount concern while doing so.

 =

Regards,

 =

Mark Sletten

 =

 =

 =

From:= Michael = McMahon [mailto:afm528@gmail.com]
Sent: Monday, January 24, 2011 1:54 PM
To: lml@lancaironline.net
Subject: Re: [LML] Re: Lithium Batteries

 

I never claimed to = be an expert, and I've never advocated that people start using these = batteries; I said I was interested in them and had been doing a lot of research.

Tostino is far from the only person reporting that he does not balance = his cells.  The SECOND link in my post is a thread with several hundred = posts on designing, building, and testing cells.  Have any of the = naysayers read the thread, in depth, or done similar research?  As I've written = before, I've been researching this for a long time, I'm not relying on one post = from one guy who did a few tests, it was just the first I pulled up of many, = many similar reports.

I also have read, but won't bother to post 15 links, that deep = discharging, such as Hamid had done, is different than the minimal discharge we would = expect from an engine start.  The small discharge contributes to less need = to balance the cells.  Quite different from the total-loss system in = an RC or solar-powered environment.

I'm an experimenter.  I can't just sit on the sidelines and wait = for "someone else" to do the research, testing and development, = then jump on the bandwagon.  That's why I'm building an experimental = aircraft.  I thought this forum would be a good place to discuss development and = testing of new systems rather than quickly declare it "too risky" for intelligent discussion.

Michael

On Mon, Jan 24, 2011 at 4:57 AM, <vtailjeff@aol.com> = wrote:

The two worst places to have a fire...boat and = plane. A IVP was seriously damaged due to a battery fire. Risk v. = Benefit. 

 

Jeff

Sent from my iPad


On Jan 22, 2011, at 6:32 AM, Michael McMahon <afm528@gmail.com> wrote:

It seems there may be some discrepancies between = theoretical extremes and real-world experience.  Here's a link to one of the = forums on which people are reporting on their results (highlights = mine):

Re: building my own lifepo4 batt = question.

Error! = Filename not specified.by tostino » Fri Sep 17, 2010 6:05 am =

By doing discharges on the bench with the cells = exposed, and being able to tell that each string holds almost exactly the same = voltage all the way through the discharge, I am pretty sure I can tell they are not horribly out of balance. I did IR matching of the cells, but no capacity matching 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 test and see how out of balance they got... It = went right down to 3.2v/cell (resting) (2.9v under load) without them going = out of balance at all, and they then charged right back up to full and stayed balanced.

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 voltage for each cell when = I stop the discharge is about 3.5v. I would = have killed them by now if it were going to happen, and they would have gone = out of balance now if that were going to happen too.


I found this thread to be informative and a good place to start on = studying people's actual experiences building and using these batteries:  http://endless-sphere.com/forums/viewtopic.php?f=3D2&am= p;t=3D2633&start=3D705&hilit=3Dthyristor


Michael

On Fri, Jan 21, 2011 at 8:35 AM, Hamid Wasti <hwasti@lm50.com> wrote:

Michael McMahon wrote:


I do not 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
limitations are?

When you have a number of cells of any chemistry in series in a = battery
pack, they all receive exactly the same current when charging. Some
cells are a little more efficient than others so they get fully = charged
before their colleagues in the string. If at that point they continue = to
receive charging current, they will over-charge. Some chemistries = are
able to handle this over-charging. Other chemistries like LiPo are = very
intolerant of this over charging and quite literally blow up. Cell
balancing attempts to make sure that the charge on each of the cells = in
the string is identical so they all get fully charged at the same = time,
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 = get
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 each individual cell and = stop
charging when one of the cells gets fully charged. Over time, the
discrepancy in th charge state between the most efficient and the = least
efficient cell in the string will keep increasing, with the usable
capacity of the entire pack being controlled by the charge 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 discharged. In real life, = you
will declare the pack useless and stop using it before you get to = that
point. If you are willing to live with this diminishing capacity, = then
cell balancing is indeed not required. Just remember that your pack = is
no longer going to have the same capacity as the pack 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 rest of the = story.



Regards,

Hamid



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