subject:"Re\: \[EVDL\] Bicycle battery"

Yes, if one really wants to protect from cell failure then fuse each cell like
Tesla does.

Sent from my iPad

On Jun 19, 2015, at 1:33 PM, Michael Ross via EV ev@lists.evdl.org wrote:

I said it, because it has come up in papers and journal articles I have
read. Paul agreed with me I think.

The basic Li ion cell does not self discharge - none of them. Once charged
they will just sit there and remain asis until something creates a circuit
for the ions to migrate back to the positive electrode.

I don't understand the mechanism for PbSO4, but they do discharge just
sitting unattached to any circuit - all of them.

What this says is if a cell is having ions migrate back to the positive
electrode that something is wrong. There are all sorts of manufacturing
defects that can cause it, or BMS deficiencies, etc. No amount of
correction to a lead acid will stop it from discharging.

If you tell me that your Thundersky cells shows a loss over time, I don't
disbelieve that - I say instead, they needed more and better design work
and some manufacturing improvement. There is some sort of fault causing an
internal or external parasitic load.

The prismatic, folded page cells, like CALB and TS are not very good in
many respects, Some (all?) bolt the conductive plates onto an aluminum
post with a threaded fastener. Bleh.

Notice that folks like Tesla did not choose that form - even though the
alternative was to make individual connections to 7000 smalls to accomplish
the task.

Those little cylindrical cells have some advantages.

They lend themselves to very automated, read consistent, construction.
Consistency is very important at the pack level.
The cylindrical form is much more stable when subjected to the volumetric
changes that Li ion cells undergo when charging and discharging.
They can't be packed too close that they cannot convect heat well (with
some extra gear to puch air (or other fluids around them).
Internally the cylindrical cells are simpler with less opportunity for
failure.
The connection to a pack by welding is as good as it gets.
And so on.

I am pretty sure in that video by Jeff Dahn I keep alluding to (and
linking) he mentions this characteristic of Li ion cells.

Did you all notice that article Bruce linked to about Tesla funding
research at the Dahn Lab? I am hoing the Tesla will make these results
open to all as they have so many other things in the interest of furthering
the use of EVs.

Look forward for new information, rather than back to the old and less well
done research. Stuff we read from 2009 is quite stale WRT Li cells.

Mike

On Fri, Jun 19, 2015 at 1:15 PM, Willie2 via EV ev@lists.evdl.org wrote:

On 06/19/2015 11:58 AM, Ben Goren wrote:

On Jun 19, 2015, at 9:33 AM, Willie2 via EV ev@lists.evdl.org wrote:

I am curious as to how Paul came to his belief.
His methodology is inadequate to the task -- rather like using a roadside
truck scale to weigh the first four people to pass by and concluding that
all humans weigh exactly 200 pounds.
You may be implying that Paul attempted to deduce self discharge from cell
voltage?

When my first lithium pack was new, I was frequently amazed that NUMEROUS
EV folks with extensive lead experience would put a volt meter to my cells
and proclaim: Why these cells are PERFECTLY balanced! I don't know how
many times I've attempted to explain that it is almost impossible to
determine state of charge from voltage on lithium cells. Other than at the
tails, of course.

Though I don't know that Paul made that mistake.

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Re: [EVDL] Bicycle battery

2015-06-19 Thread Lee Hart via EV


Ben Goren via EV wrote:

I am curious as to how Paul came to his belief.


His methodology is inadequate to the task -- rather like using a
roadside truck scale to weigh the first four people to pass by and
concluding that all humans weigh exactly 200 pounds.

Lee, in comparison, is akin to a long-time general practice physician
who's kept aggregate patient records of vital statistics for decades,
and concludes that...80% more likely to need treatment...


I wouldn't put it that starkly. I'd say it's more like Joe Blow buying 
a new ICE car, and at 3000 miles he sees that the oil level on the 
dipstick is still the same. So he concludes that it doesn't use a drop 
of oil!


So he skips the oil changes. 2 years and 30,000 miles later, the car is 
towed to the dealer, three quarts low and with a wrecked engine.


On the other hand, his mechanic Crusty swears by 3000 mile oil 
changes. That's not always necessary; but it's good insurance. People 
who do this can expect to go 200,000 miles before the engine is using 
any significant amount of oil.


So it's more like the blind men and the elephant. Each sees the same 
data, but come to different conclusions because of their perspective.


I'm not some big company; I'm a lone wolf working in his basement. I 
have to get my batteries cheap; as bargains, or donations, or old, or 
used, or on loan so I don't dare hurt them. That means they aren't 
likely to be prime stock. But that's a good thing! I get to see 
batteries at their WORST, not just at their best.


Another thing...

The storage battery is one of those peculiar things which
appeals to the imagination, and no more perfect thing could
be desired by stock swindlers. Just as soon as a man gets
working on the secondary battery, it brings out his latent
capacity for lying. -- Thomas A. Edison

There are few industries with more BS than the battery
industry. -- Elon Musk

Battery information has been unreliable for a hundred years. 99% of what 
you read is either lying to make money, or the mindless parroting of 
what someone else said.


This mean you should treat everything you read about batteries as BS 
(baloney sandwiches, as Carl Sagan said). You have to *test it for 
yourself*! This is tedious; but not particularly difficult or expensive.


And, you need to keep a skeptical mind. Just because one does X doesn't 
mean that they all do X. It's as if there's a devious little demon 
inside, doing everything in his power to trick you. With only a few 
quick tests, he's likely to lie to you (and get away with it)! So you 
need to be diligent, and repeat your tests in different ways to pry the 
truth out of him. Oh yeah? *Prove* it!


--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

I haven't seen any science from BMS advocates yet. They make lots of 
assumptions based on nothing.

Besides I have a BMS I just don't have a cell level BMS.

I haven't heard the theory on self discharge yet?

Or the rate at which they discharge or an example of someone putting one on the 
shelf for 5 years then measuring the voltage and capacity. Save for Jack 
Richard who boldly did it and published a video. 

I read a lot of papers and I only found one that talks about self discharge 
although I don't agree with the way they use the term because what they really 
verify in the paper is capacity fade.



Sent from my iPhone

 On Jun 19, 2015, at 3:34 PM, Lee Hart via EV ev@lists.evdl.org wrote:
 
 Ben Goren via EV wrote:
 I am curious as to how Paul came to his belief.
 
 His methodology is inadequate to the task -- rather like using a
 roadside truck scale to weigh the first four people to pass by and
 concluding that all humans weigh exactly 200 pounds.
 
 Lee, in comparison, is akin to a long-time general practice physician
 who's kept aggregate patient records of vital statistics for decades,
 and concludes that...80% more likely to need treatment...
 
 I wouldn't put it that starkly. I'd say it's more like Joe Blow buying a 
 new ICE car, and at 3000 miles he sees that the oil level on the dipstick is 
 still the same. So he concludes that it doesn't use a drop of oil!
 
 So he skips the oil changes. 2 years and 30,000 miles later, the car is towed 
 to the dealer, three quarts low and with a wrecked engine.
 
 On the other hand, his mechanic Crusty swears by 3000 mile oil changes. 
 That's not always necessary; but it's good insurance. People who do this can 
 expect to go 200,000 miles before the engine is using any significant amount 
 of oil.
 
 So it's more like the blind men and the elephant. Each sees the same data, 
 but come to different conclusions because of their perspective.
 
 I'm not some big company; I'm a lone wolf working in his basement. I have to 
 get my batteries cheap; as bargains, or donations, or old, or used, or on 
 loan so I don't dare hurt them. That means they aren't likely to be prime 
 stock. But that's a good thing! I get to see batteries at their WORST, not 
 just at their best.
 
 Another thing...
 
The storage battery is one of those peculiar things which
appeals to the imagination, and no more perfect thing could
be desired by stock swindlers. Just as soon as a man gets
working on the secondary battery, it brings out his latent
capacity for lying. -- Thomas A. Edison
 
There are few industries with more BS than the battery
industry. -- Elon Musk
 
 Battery information has been unreliable for a hundred years. 99% of what you 
 read is either lying to make money, or the mindless parroting of what someone 
 else said.
 
 This mean you should treat everything you read about batteries as BS 
 (baloney sandwiches, as Carl Sagan said). You have to *test it for 
 yourself*! This is tedious; but not particularly difficult or expensive.
 
 And, you need to keep a skeptical mind. Just because one does X doesn't mean 
 that they all do X. It's as if there's a devious little demon inside, doing 
 everything in his power to trick you. With only a few quick tests, he's 
 likely to lie to you (and get away with it)! So you need to be diligent, and 
 repeat your tests in different ways to pry the truth out of him. Oh yeah? 
 *Prove* it!
 
 -- 
 The greatest pleasure in life is to create something that wasn't
 there before. -- Roy Spence
 --
 Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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 UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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Re: [EVDL] Bicycle battery

2015-06-19 Thread George Tyler via EV

Have you guys heard of lithium-sulphur cells?
http://www.oxisenergy.com I am travelling in the UK at the moment, and the 
friend I am staying with told me that this company is not far from where we 
are, we are going to arrange a visit.

-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Michael Ross via EV
Sent: Friday, 19 June 2015 8:45 p.m.
To: Cor van de Water; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

Cor,

From an electrochemical point of view, the laptop fires were due to components 
in the cells (electrolyte and separator primarily), that ignited from an 
internal short, but were sustained by the components gassing off oxygen at 
higher temperatures, causing a runaway situation.  More heat = more oxygen = 
more heat=...  If the chemicals/construction didn't self support combustion, 
then little dendritic shorts would be less consequential.

One of the reasons that LFP cells fare better is a much higher temperature when 
self supporting combustion happens. There is about 100°C more head room.  That 
doesn't mean they won't burn up fast though given the right
conditions

The family of lithium ion cell has the capability, when designed and operated 
properly, not to have any loss of charge from just sitting.  This is not true 
for some other battery chemistries - lead acid in particular.
You can't apply  the understanding of one to the other in this respect.

The trickle charge subject is similar.  PbSO4 cells benefit from a light 
trickle charge to make up for the gradual loss of sitting.  The same 
treatment will destroy Li ion cells, but there is no need because they don't 
lose their charge  - if they are made right and their operating systems are 
right.

On Fri, Jun 19, 2015 at 3:05 PM, Cor van de Water via EV ev@lists.evdl.org
wrote:

 Michael,

 I think you are starting to get it, even though you express it in a 
 peculiar way.

 In real life, nothing is 100% pure. Every material and every surface 
 has
 *some* contamination,
 even in a clean room. They just make sure that what is still there is 
 small enough or in low enough numbers that it does not really hurt 
 their yield, but they still need to test every circuit since it still 
 may be unacceptably damaged by the unavoidable contamination.

 Same in battery manufacturing - it only needs to be clean enough that 
 the effect introduced by contamination is low enough not to harm the 
 operation of the cell and for example the self-discharge is within 
 specification.
 Have you ever seen a modern cell manufacturing facility? It is almost 
 as good as a clean room just as all modern electronics production is 
 done in very clean environment just to avoid failures.

 I do not know enough about the chemistry of the battery physics to 
 judge if there is an inherent mechanism of self-discharge. I do know 
 that a lot of battery parameters are a trade-off, for example you can 
 buy batteries with higher power but with lower capacity or you can buy 
 higher capacity with lower power (in the same form factor).
 Similar trade-offs exist between high and low temp operation.
 It may be that the basic chemical reaction does not have a 
 self-discharge mechanism and that a theoretical perfect Li-Ion cell 
 has no self-discharge.
 But that is the same as saying that a theoretical perfectly sealed ICE 
 engine does not need new motor oil ever, because it does not leak. 
 Still I check my oil level from time to time, even though I know that 
 it does not leak now, I could be losing oil and damage the engine if I 
 do not keep an eye on the level once in a while.

 The well-documented laptop Lithium battery fires were actually 
 attributed to excessive contamination of battery cells during 
 production, which could even cause short circuits in the cells and 
 thermal runaway around those (large) contaminations.
 So - the result of this is that no matter how good manufactured, any 
 Li-Ion cell will have some self-discharge. High quality cells will 
 have lower numbers than more sloppy produced cells and variation of 
 self-discharge will also be an indication of quality and consistency 
 of the manufacturing process, but saying that there is no such thing 
 while everyone who is working with batteries tells you that it does 
 exist is, well, denying reality.

 Hope this clarifies,

 Cor van de Water
 Chief Scientist
 Proxim Wireless

 office +1 408 383 7626 Skype: cor_van_de_water
 XoIP   +31 87 784 1130 private: cvandewater.info
 www.proxim.com

 This email message (including any attachments) contains confidential 
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 received this message in error, please delete it and notify the 
 sender.  Any unauthorized use, disclosure, distribution, or copying of 
 any part of this message is prohibited.

 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Michael Ross

Re: [EVDL] Bicycle battery

2015-06-19 Thread EVDL Administrator via EV

On 19 Jun 2015 at 23:00, Michael Ross via EV wrote:

 Self discharge would be where the capacity has not decreased, but the
 amount available in the cell is less - very hard to measure accurately the
 actual charge level with normal DIY instrumentation when the change is small.

Did you read Lee Hart's earlier post?

http://www.evdl.org/archive/index.html#nabble-td4676242i40|a4676355

That is EXACTLY what he measured.

If one is trying to determine self discharge by measuring voltage, that 
probably won't yield a valid answer.  Though I'm no electrochemist, my 
understanding is that one can't reliably judge a lithium cell's SOC (or any 
other type of cell's, really) by its voltage, except in very limited 
circumstances.  

Perhaps this paper would help.  Anyone here have an IEEE login?

Self-discharge losses in lithium-ion cells

http://ieeexplore.ieee.org/xpl/login.jsp?tp=arnumber=1269687url=http%3A%2F%
2Fieeexplore.ieee.org%2Fiel5%2F62%2F28408%2F01269687.pdf%3Farnumber%3D1269687

http://v.gd/0IqfFJ

The self-discharge losses in several lithium-ion cell designs have been 
measured by three different methods. The losses are separated into time-
dependent and state-of-charge dependent contributions. For most cycling 
conditions, the time-dependent self-discharge losses are dominant; however, 
after several months of stand on open circuit or float charge, the state-of-
charge dependent losses become significant. The self-discharge rate has been 
found to not increase monotonically with state-of-charge, but to drop 
somewhat at intermediate states of charge. The implications of these 
measurements for maintaining balanced cell capacities in batteries and 
establishing optimum storage voltage levels for batteries are discussed.

Or perhaps this one :

Investigation on the Self-discharge of the LiFePO4/C nanophosphate battery 
chemistry at different conditions 

http://ieeexplore.ieee.org/xpl/login.jsp?tp=arnumber=6940762url=http%3A%2F%
2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6940762

http://v.gd/gfBgE2

In this paper the self-discharge of the nanophosphate LiFePO4/C is studied 
at different temperature, SOC conditions and at different SOH levels of the 
battery. Moreover, cell to cell differences in self-discharge caused by the 
manufacturing tolerances are investigated.

Or maybe here.  

http://iopscience.iop.org/0957-4484/24/42/424009/

In this paper, Raman spectroscopy was used to study the surface phase 
change during charge and self-discharge on a more localized scale for three 
morphologies of LiFePO4 ...

Curiously the following page says that LiFePO4 has a HIGHER self discharge 
rate than other Li chemistries.  However, it doesn't explain why nor does it 
give any references, so I'm skeptical.

http://batteryuniversity.com/learn/article/types_of_lithium_ion

The following paper discusses how to simulate the effect of self-discharge 
in LiFePO4 cells, but doesn't explain the chemistry which might cause it.

http://www.dsea.unipi.it/Members/huriaw/journal-paper

I found a paper which references yet another paper as stating that LiFePO4 
self discharge is on the order of 8%(!) per month.  The referenced paper is 
A.  Chih-Chiang Hua  and B.  Zong-Wei  Syue, Charge  and Discharge 
Characteristics  of  Lead-Acid Battery and LiFePO4 Battery.: The 2010 
International Power Electronics Conference.

Here is the referenced paper.

ftp://213.176.96.142/ieee345c50ff-abaf-20141124102512.pdf

Regrettably it simply states this as a fait accompli, but fails to explain 
the electrochemical mechanism for self discharge.

I spent way too much of my time on this research tonight, and that was just 
on the web.  I haven't even hit the library yet!  

However, I found many discussions of self discharge in lithium cells of all 
types, including LiFePO4.  Most of these were either comparisons of LiFePO4 
with other chemistries, or were discussing ways to compensate for the cell 
imbalance that results when these cells are used in batteries.  

I was able to find only one reference which even suggested that lithium 
cells might not have a self discharge.  In fact it was very similar to the 
statement made recently on the EVDL that lithium cells have no specific 
mechanism for self discharge.

http://electricvehiclesnews.com/Technology/Lithium-ion_battery.htm

According to one manufacturer, lithium-ion cells (and, accordingly, dumb 
lithium-ion batteries) do not have any self-discharge in the usual meaning 
of this word. What looks like a self-discharge in these batteries is a 
permanent loss of capacity ...

Unfortunately the author doesn't give any reference for this statement. He 
doesn't even identify the one manufacturer.  

Of course if one desperately wants to believe that lithium batteries don't 
self-discharge, maybe one website with no references is sufficient.  ;-)

As for actual lithium cells that normal people can buy ...

This spec sheet from a LiFePO4 manufacturer specifies a self-discharge rate

Re: [EVDL] Bicycle battery

2015-06-19 Thread Michael Ross via EV

What I saw Rickard talk about was packs of somewhat uncertain provenance -
the Israeli Better Place packs weren't they? He sort of knew when the got
shelved before he bought them and inferred capacity fade from how they
seemed to him after delivery. And he also had a bath of charged CALB cells
he shelved. I guess he knew pretty much about the CALB cells. I think he
said capacity dropped about 1% a year. It is worth asking, what happened
between when the cells were made when and they landed in Missouri? A
scientific study would require some traceability.

I didn't hear JR say they self discharged, but that could be memory fade.
He might have known the SOC of the CALBs at t=0. But he probably had to
measure voltage (not reliable perhaps), and again I am not admitting the
capacity decreases were due to self discharge. They may look the same but
they are not. Self discharge would be where the capacity has not
decreased, but the amount available in the cell is less - very hard to
measure accurately the actual charge level with normal DIY instrumentation
when the change is small.

On Fri, Jun 19, 2015 at 5:28 PM, Paul Dove via EV ev@lists.evdl.org wrote:

I haven't seen any science from BMS advocates yet. They make lots of
assumptions based on nothing.

Besides I have a BMS I just don't have a cell level BMS.

I haven't heard the theory on self discharge yet?

Or the rate at which they discharge or an example of someone putting one
on the shelf for 5 years then measuring the voltage and capacity. Save for
Jack Richard who boldly did it and published a video.

I read a lot of papers and I only found one that talks about self
discharge although I don't agree with the way they use the term because
what they really verify in the paper is capacity fade.

--
To invent, you need a good imagination and a pile of junk.
Thomas A. Edison
http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 585-6737 Land
(919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google Phone
(919) 631-1451 Cell

michael.e.r...@gmail.com
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Re: [EVDL] Bicycle battery

2015-06-19 Thread Peri Hartman via EV


Paul,

I'm not following you, here.  How can you have 4v open circuit applied 
to anything?  You could measure 4v open circuit across a power supply 
or, for that matter, a disconnected battery.   But, I thought, the 
moment you connect it to something, you no longer have an open circuit.  
Unless, of course, the grounds of the two systems aren't connected.


In the latter case, though - if the grounds aren't connected - I don't 
see how 4v or 100v would make any difference.  There cannot be any 
current flowing and thus no voltage being applied.


Peri

-- Original Message --
From: Paul Dove via EV ev@lists.evdl.org
To: Cor van de Water cwa...@proxim.com; Electric Vehicle Discussion 
List ev@lists.evdl.org

Sent: 19-Jun-15 4:10:52 AM
Subject: Re: [EVDL] Bicycle battery

That's what Boeing said but it's interesting that these batteries are 
used in many applications and none of them had fires. Open circuit 
voltage is what needs to be considered not max charge voltage,


I haven't tried this but I may just to prove a point. If you hold 4 
volts on one of these cells indefinitely it will burn. Which is what 
they were doing. Also it was a starter battery so they didn't use much 
to start the APU and then is held 4 volts on the cells.


Sent from my iPad

 On Jun 18, 2015, at 11:47 PM, Cor van de Water via EV 
ev@lists.evdl.org wrote:


 Paul, the 29.6V is not the max charge voltage of the pack. It is the 
nominal voltage:

 8 x 3.7V (these were Cobalt cells) = 29.6V
 So the max 32V on the bus is actually only 4V per cell and that means 
that they keep those cells

 below max charge voltage of 4.2V
 So, it was not possible that the battery was over-charged, unless a 
cell shorted and the 32V

 was applied to 7 cells in series instead of 8!

 Cor van de Water
 Chief Scientist
 Proxim Wireless

 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com


 This email message (including any attachments) contains confidential 
and proprietary information of Proxim Wireless Corporation.  If you 
received this message in error, please delete it and notify the 
sender.  Any unauthorized use, disclosure, distribution, or copying of 
any part of this message is prohibited.



 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove 
via EV

 Sent: Thursday, June 18, 2015 8:21 PM
 To: Cor van de Water via EV
 Subject: Re: [EVDL] Bicycle battery

 We already covered how to tell is a cell has internal defects. You 
drain the cell to 2.5 volts and then if the cell voltage rises it's 
good if it keeps falling don't use it. I did think this up This is 
what NASA does. I read it in one of their presentations. I can dig it 
up if you like.


 As for the Dreamliner I followed that carefully. My favorite chart 
that they presented to the FAA said

 - the only thing that causes lithium battery fires is overchargeing
 - we can find no evidence we are over charging
 - therefore the cause of the fire is unknown

 One of those statements has to be wrong. And the fire was the 
evidence of overcharging.


 The open circuit voltage of their battery was 29.6 volts. The system 
voltage was 32 volts. They were charging the cells the whole time the 
APU was running and wondering why it burned.


 As for laptops they were overcharging as well. The paper I read the 
designer claimed that leaving a small amount of current flowing or 
trickle charge as they call it would not hurt lithium batteries.


 Sent from my iPad

 On Jun 18, 2015, at 9:59 PM, Cor van de Water via EV 
ev@lists.evdl.org wrote:


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Re: [EVDL] Bicycle battery

2015-06-19 Thread Lee Hart via EV


Cor van de Water via EV wrote:

I would be very surprised if DeWalt does not have a BMS on their Lithium packs,
all power tool packs with Lithium that I have opened always come with a BMS
which both checks every cell and turns off any current flow above max and
under min voltage levels.


The last DeWalt lithium pack I saw open did indeed have a BMS. It was 
the usual switchable shunt across each cell. In fact, most of the 
controller was inside the battery pack too, rather than in the tool.


--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

2015-06-19 Thread tomw via EV

/That is a reason I don't use a cell level BMS. With a cell level BMS like
the miniBMS there is a constant drain on the cells running the BMS boards
and it is nearly impossible to make sure that each board uses the _exact_
same current regardless of voltage in the cell./

The constant drain is less 4mA with about +/-20% variability, so the
difference between cells is at most  2 microamp.

/Furthermore, boards like the miniBMS expect that you will balance at the
end of every charge and last I saw, that balance voltage was at 3.6V or so
which is over the theoretical 100% SOC level for LiFePO4 cells which leads
to potential overcharging of the cells on every charge cycle./

Balance voltage on the minibms for LiFePO4 cells has always been 3.5V, from
the very first ones made to the present. Check the original minibms thread
on diyelectriccar if you don't believe it.  I purchased some of the first
boards and am still using them.  Also, 3.6V while charging is not
necessarily over the theoretical max SoC.  According to Whitacre cell rest
voltage of 3.4V is 100% SoC.  The voltage will be higher while charging
while near full charge due to the voltage drop across the cell effective
internal resistance. The higher the charge current, the higher the cell
voltage will be at a given SoC. Of course if you go too high in cell voltage
(4.2V according to Whitacre) you start to break down the electrolyte.  When
I charge my pack to 3.53V average cell voltage, they are at 3.344V average
after  2 hours rest.  CALB and others used to spec charge to 4.1 or 4.2V at
0.05C rate, which would result in a full charge and rest voltage of about
3.4V per cell.  They haven't spec'ed that for years though.  They relaxed it
to 3.6V.  I would guess for longer cell life and the fact that there is
little difference in useable charge.

/If you stop charging without the balancing taking place and/or let the
pack sit for extended periods of time then the different current draw of
each board working 24/7 introduces an imbalance in the SOC of the cells in
the pack./ 

I do partial charges without any shunting  70% of the time.  When I do
charge to 3.53V per cell to get shunting, the first cells start shunting
about 10 minutes before charging terminates, and by end of charge all shunt
LEDs are on.  The highest cells reach about 3.55V.  I've let the car sit for
over 2 weeks while away for work or on vacation and the pack voltage reads
the same voltage when I return as when I left.  The next full charge there
may be several cells that don't shunt, but they all do after a couple of
full charges. The pack has 5 1/2 years and about 45,000 miles on it.

I think you have to keep the scale of things in mind.  These effects are
small.  I've found them inconsequential in daily operation of the vehicle. 
I think the main effect on cell life is temperature.  I expressed concern
about that several years ago when the Whitacre video first came out and he
said don't exceed 50C to 60C.  I questioned then which was the limit,
pointing out that 50C was a big problem for a place like Phoenix. But I am
not going to let the car sit in hot weather.  I use it as my daily driver. 
If hot weather shortens the pack life, then so be it. I want to see how it
operates as a car, not a hobby. Yesterday the cells were at about 105F (41C)
after about 75 miles driving in about 96F ambient.  That's pretty typical
for the last 5 years during June - August, but I have measured as high as
116F (47C).





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Re: [EVDL] Bicycle battery

2015-06-19 Thread Lee Hart via EV


Cor van de Water via EV wrote:

I have Lithium cells (CALB 180Ah) sitting in my garage since 1.5 years
and have measured their self-discharge and plotted it in an Excel spreadsheet.
I can *see* their self-discharge.
I can *see* effect from ambient temperature on the change in self-discharge 
rate...
I can *see* differences up to a factor 2 in self-discharge between cells...


I've done the same thing with Thundersky. The results were the same, 
except that the self-discharge rates differed by more than 4:1.


Additionally, the self-discharge rate is dramatically faster at higher 
states of charge. The closer it gets to 0 SOC, the slower the 
self-discharge rate.


Since the voltage-vs-state of charge curve is so flat from about 20-80% 
SOC, voltage alone is a poor indicator of state of charge. This will 
fool you into thinking there is no self-discharge, because the voltage 
won't change enough to measure between these SOCs.


To determine how much charge was lost over time, I fully charge the 
cells. Then let them sit in parallel for a day. Then remove the 
connections, and wait X days. Then measure the amphour capacity of each 
cell. Recharge the cells, and repeat the process, but with successively 
larger values of X. So for example, I might find that a 60ah cell yields:


- 60ah for X = 1 day after charging
- 58ah for X = 30 days after charging
- 56ah for X = 6 months after charging
- 54ah for X = 1 year after charging

Now, 10% a year is a pretty low self-discharge rate. 6ah per year 
corresponds to an 8ma self-discharge current. The problem is that it 
varies so much between cells. It means the cells can drift 10% apart per 
year. This won't matter in the short term, but it adds up over time.


I'm also testing a set of A123 cells. The self-discharge rate is 
similar, but the differences between cells is much smaller; less than 
2:1. I'm coming up on the 2-year point for them next month.


--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

2015-06-19 Thread Willie2 via EV


On 06/19/2015 10:58 AM, Lee Hart via EV wrote:

Cor van de Water via EV wrote:

I have Lithium cells (CALB 180Ah) sitting in my garage since 1.5 years
and have measured their self-discharge and plotted it in an Excel 
spreadsheet.

I can *see* their self-discharge.
I can *see* effect from ambient temperature on the change in 
self-discharge rate...
I can *see* differences up to a factor 2 in self-discharge between 
cells...


I've done the same thing with Thundersky. The results were the same, 
except that the self-discharge rates differed by more than 4:1.


Additionally, the self-discharge rate is dramatically faster at higher 
states of charge. The closer it gets to 0 SOC, the slower the 
self-discharge rate.


Since the voltage-vs-state of charge curve is so flat from about 
20-80% SOC, voltage alone is a poor indicator of state of charge. This 
will fool you into thinking there is no self-discharge, because the 
voltage won't change enough to measure between these SOCs.


To determine how much charge was lost over time, I fully charge the 
cells. Then let them sit in parallel for a day. Then remove the 
connections, and wait X days. Then measure the amphour capacity of 
each cell. Recharge the cells, and repeat the process, but with 
successively larger values of X. So for example, I might find that a 
60ah cell yields:


- 60ah for X = 1 day after charging
- 58ah for X = 30 days after charging
- 56ah for X = 6 months after charging
- 54ah for X = 1 year after charging

Now, 10% a year is a pretty low self-discharge rate. 6ah per year 
corresponds to an 8ma self-discharge current. The problem is that it 
varies so much between cells. It means the cells can drift 10% apart 
per year. This won't matter in the short term, but it adds up over time.


I'm also testing a set of A123 cells. The self-discharge rate is 
similar, but the differences between cells is much smaller; less than 
2:1. I'm coming up on the 2-year point for them next month.


Thanks for the methodology for REALLY measuring self discharge.  I was 
quite taken aback when Paul claimed there was none!  All cell 
manufacturers make claims on low self discharge but, as far as I know, 
no manufacturer claims no self discharge.  I am curious as to how Paul 
came to his belief.


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Re: [EVDL] Bicycle battery

2015-06-19 Thread Ben Goren via EV

On Jun 19, 2015, at 9:33 AM, Willie2 via EV ev@lists.evdl.org wrote:

 I am curious as to how Paul came to his belief.

His methodology is inadequate to the task -- rather like using a roadside truck 
scale to weigh the first four people to pass by and concluding that all humans 
weigh exactly 200 pounds.

Lee, in comparison, is akin to a long-time general practice physician who's 
kept aggregate patient records of vital statistics for decades, and concludes 
that, among his patients, those over age 50 with weight and waist-to-hip ratios 
more than three standard deviations from average are 80% more likely to need 
treatment for a cardiovascular condition, and far less likely to have an 
history of regular vigorous physical activity. He then compares his own data 
set with Census Bureau and NIH statistics and concludes that, adjusted for 
variations in the demographics of his patients, they're all pretty much on the 
same page in terms of observations.

But in Paul's world, that's all bunk because everybody weighs exactly 200 
pounds, as confirmed by his own measurements, so all that stuff about diet and 
exercise is equal bunk.

b
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Re: [EVDL] Bicycle battery

2015-06-19 Thread Willie2 via EV


On 06/19/2015 11:58 AM, Ben Goren wrote:

On Jun 19, 2015, at 9:33 AM, Willie2 via EV ev@lists.evdl.org wrote:


I am curious as to how Paul came to his belief.

His methodology is inadequate to the task -- rather like using a roadside truck 
scale to weigh the first four people to pass by and concluding that all humans 
weigh exactly 200 pounds.
You may be implying that Paul attempted to deduce self discharge from 
cell voltage?


When my first lithium pack was new, I was frequently amazed that 
NUMEROUS EV folks with extensive lead experience would put a volt meter 
to my cells and proclaim: Why these cells are PERFECTLY balanced!  I 
don't know how many times I've attempted to explain that it is almost 
impossible to determine state of charge from voltage on lithium cells.  
Other than at the tails, of course.


Though I don't know that Paul made that mistake.

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Re: [EVDL] Bicycle battery

I just report what I observe. My cells don't self discharge. Only had one 
reverse and as I said that was a loose connection.

I don't know of anyone who claims their cells went to zero sitting on a shelf. 
Unless they were defective it should never happen. However, there's probably a 
low percentage of defective cells produced. Irrelevant to the workings of a 
battery pack since they can be tested prior to building the pack

Sent from my iPad

 On Jun 19, 2015, at 2:05 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Michael,
 
 I think you are starting to get it, even though you express it in a peculiar 
 way.
 
 In real life, nothing is 100% pure. Every material and every surface has 
 *some* contamination,
 even in a clean room. They just make sure that what is still there is small 
 enough or in
 low enough numbers that it does not really hurt their yield, but they still 
 need to test
 every circuit since it still may be unacceptably damaged by the unavoidable 
 contamination.
 
 Same in battery manufacturing - it only needs to be clean enough that the 
 effect introduced
 by contamination is low enough not to harm the operation of the cell and for 
 example the
 self-discharge is within specification.
 Have you ever seen a modern cell manufacturing facility? It is almost as good 
 as a clean room
 just as all modern electronics production is done in very clean environment 
 just to avoid
 failures.
 
 I do not know enough about the chemistry of the battery physics to judge if 
 there is an
 inherent mechanism of self-discharge. I do know that a lot of battery 
 parameters are a
 trade-off, for example you can buy batteries with higher power but with lower 
 capacity
 or you can buy higher capacity with lower power (in the same form factor).
 Similar trade-offs exist between high and low temp operation.
 It may be that the basic chemical reaction does not have a self-discharge 
 mechanism
 and that a theoretical perfect Li-Ion cell has no self-discharge.
 But that is the same as saying that a theoretical perfectly sealed ICE engine 
 does not 
 need new motor oil ever, because it does not leak. Still I check my oil level 
 from time to
 time, even though I know that it does not leak now, I could be losing oil and 
 damage
 the engine if I do not keep an eye on the level once in a while.
 
 The well-documented laptop Lithium battery fires were actually attributed to 
 excessive
 contamination of battery cells during production, which could even cause 
 short circuits
 in the cells and thermal runaway around those (large) contaminations.
 So - the result of this is that no matter how good manufactured, any Li-Ion 
 cell will have
 some self-discharge. High quality cells will have lower numbers than more 
 sloppy produced
 cells and variation of self-discharge will also be an indication of quality 
 and consistency
 of the manufacturing process, but saying that there is no such thing while 
 everyone who is
 working with batteries tells you that it does exist is, well, denying reality.
 
 Hope this clarifies,
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and 
 proprietary information of Proxim Wireless Corporation.  If you received this 
 message in error, please delete it and notify the sender.  Any unauthorized 
 use, disclosure, distribution, or copying of any part of this message is 
 prohibited.
 
 
 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Michael Ross via EV
 Sent: Friday, June 19, 2015 11:34 AM
 To: Willie2; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery
 
 I said it, because it has come up in papers and journal articles I have read. 
  Paul agreed with me I think.
 
 The basic Li ion cell does not self discharge - none of them.  Once charged 
 they will just sit there and remain asis until something creates a circuit 
 for the ions to migrate back to the positive electrode.
 
 I don't understand the mechanism for PbSO4, but they do discharge just 
 sitting unattached to any circuit - all of them.
 
 What this says is if a cell is having ions migrate back to the positive 
 electrode that something is wrong.  There are all sorts of manufacturing 
 defects that can cause it, or BMS deficiencies, etc.  No amount of correction 
 to a lead acid will stop it from discharging.
 
 If you tell me that your Thundersky cells shows a loss over time, I don't 
 disbelieve that - I say instead, they needed more and better design work and 
 some manufacturing improvement.  There is some sort of fault causing an 
 internal or external parasitic load.
 
 The prismatic, folded page cells, like CALB and TS are not very good in many 
 respects,  Some (all?) bolt the conductive plates onto an aluminum post with 
 a threaded fastener

Re: [EVDL] Bicycle battery

Subject: Re: [EVDL] Bicycle battery

I said it, because it has come up in papers and journal articles I have
read. Paul agreed with me I think.

The basic Li ion cell does not self discharge - none of them. Once
charged they will just sit there and remain asis until something creates a
circuit for the ions to migrate back to the positive electrode.

I don't understand the mechanism for PbSO4, but they do discharge just
sitting unattached to any circuit - all of them.

The prismatic, folded page cells, like CALB and TS are not very good in
many respects, Some (all?) bolt the conductive plates onto an aluminum
post with a threaded fastener. Bleh.

Notice that folks like Tesla did not choose that form - even though the
alternative was to make individual connections to 7000 smalls to accomplish
the task.

Those little cylindrical cells have some advantages.

I am pretty sure in that video by Jeff Dahn I keep alluding to (and
linking) he mentions this characteristic of Li ion cells.

Look forward for new information, rather than back to the old and less
well done research. Stuff we read from 2009 is quite stale WRT Li cells.

Mike

On Fri, Jun 19, 2015 at 1:15 PM, Willie2 via EV ev@lists.evdl.org wrote:

On 06/19/2015 11:58 AM, Ben Goren wrote:

On Jun 19, 2015, at 9:33 AM, Willie2 via EV ev@lists.evdl.org wrote:

I am curious as to how Paul came to his belief.
His methodology is inadequate to the task -- rather like using a
roadside truck scale to weigh the first four people to pass by and
concluding that all humans weigh exactly 200 pounds.
You may be implying that Paul attempted to deduce self discharge from
cell voltage?

When my first lithium pack was new, I was frequently amazed that
NUMEROUS EV folks with extensive lead experience would put a volt
meter to my cells and proclaim: Why these cells are PERFECTLY
balanced! I don't know how many times I've attempted to explain that
it is almost impossible to determine state of charge from voltage on
lithium cells. Other than at the tails, of course.

Though I don't know that Paul made that mistake.

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To invent, you need a good imagination and a pile of junk.
Thomas A. Edison
http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 585-6737 Land
(919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google
Phone
(919) 631-1451 Cell

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To invent, you need a good imagination and a pile of junk.
Thomas A. Edison
http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html

A public-opinion poll is no substitute for thought

Re: [EVDL] Bicycle battery

2015-06-19 Thread Michael Ross via EV

I said it, because it has come up in papers and journal articles I have
read. Paul agreed with me I think.

I don't understand the mechanism for PbSO4, but they do discharge just
sitting unattached to any circuit - all of them.

The prismatic, folded page cells, like CALB and TS are not very good in
many respects, Some (all?) bolt the conductive plates onto an aluminum
post with a threaded fastener. Bleh.

Notice that folks like Tesla did not choose that form - even though the
alternative was to make individual connections to 7000 smalls to accomplish
the task.

Those little cylindrical cells have some advantages.

I am pretty sure in that video by Jeff Dahn I keep alluding to (and
linking) he mentions this characteristic of Li ion cells.

Look forward for new information, rather than back to the old and less well
done research. Stuff we read from 2009 is quite stale WRT Li cells.

Mike

On Fri, Jun 19, 2015 at 1:15 PM, Willie2 via EV ev@lists.evdl.org wrote:

On 06/19/2015 11:58 AM, Ben Goren wrote:

On Jun 19, 2015, at 9:33 AM, Willie2 via EV ev@lists.evdl.org wrote:

I am curious as to how Paul came to his belief.

His methodology is inadequate to the task -- rather like using a roadside
truck scale to weigh the first four people to pass by and concluding that
all humans weigh exactly 200 pounds.

You may be implying that Paul attempted to deduce self discharge from cell
voltage?

Though I don't know that Paul made that mistake.

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--
To invent, you need a good imagination and a pile of junk.
Thomas A. Edison
http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 585-6737 Land
(919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google Phone
(919) 631-1451 Cell

Re: [EVDL] Bicycle battery

2015-06-19 Thread Cor van de Water via EV

Michael,

I think you are starting to get it, even though you express it in a peculiar 
way.

In real life, nothing is 100% pure. Every material and every surface has *some* 
contamination,
even in a clean room. They just make sure that what is still there is small 
enough or in
low enough numbers that it does not really hurt their yield, but they still 
need to test
every circuit since it still may be unacceptably damaged by the unavoidable 
contamination.

Same in battery manufacturing - it only needs to be clean enough that the 
effect introduced
by contamination is low enough not to harm the operation of the cell and for 
example the
self-discharge is within specification.
Have you ever seen a modern cell manufacturing facility? It is almost as good 
as a clean room
just as all modern electronics production is done in very clean environment 
just to avoid
failures.

I do not know enough about the chemistry of the battery physics to judge if 
there is an
inherent mechanism of self-discharge. I do know that a lot of battery 
parameters are a
trade-off, for example you can buy batteries with higher power but with lower 
capacity
or you can buy higher capacity with lower power (in the same form factor).
Similar trade-offs exist between high and low temp operation.
It may be that the basic chemical reaction does not have a self-discharge 
mechanism
and that a theoretical perfect Li-Ion cell has no self-discharge.
But that is the same as saying that a theoretical perfectly sealed ICE engine 
does not 
need new motor oil ever, because it does not leak. Still I check my oil level 
from time to
time, even though I know that it does not leak now, I could be losing oil and 
damage
the engine if I do not keep an eye on the level once in a while.

The well-documented laptop Lithium battery fires were actually attributed to 
excessive
contamination of battery cells during production, which could even cause short 
circuits
in the cells and thermal runaway around those (large) contaminations.
So - the result of this is that no matter how good manufactured, any Li-Ion 
cell will have
some self-discharge. High quality cells will have lower numbers than more 
sloppy produced
cells and variation of self-discharge will also be an indication of quality and 
consistency
of the manufacturing process, but saying that there is no such thing while 
everyone who is
working with batteries tells you that it does exist is, well, denying reality.

Hope this clarifies,

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
proprietary information of Proxim Wireless Corporation.  If you received this 
message in error, please delete it and notify the sender.  Any unauthorized 
use, disclosure, distribution, or copying of any part of this message is 
prohibited.


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Michael Ross via EV
Sent: Friday, June 19, 2015 11:34 AM
To: Willie2; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

I said it, because it has come up in papers and journal articles I have read.  
Paul agreed with me I think.

The basic Li ion cell does not self discharge - none of them.  Once charged 
they will just sit there and remain asis until something creates a circuit for 
the ions to migrate back to the positive electrode.

I don't understand the mechanism for PbSO4, but they do discharge just sitting 
unattached to any circuit - all of them.

What this says is if a cell is having ions migrate back to the positive 
electrode that something is wrong.  There are all sorts of manufacturing 
defects that can cause it, or BMS deficiencies, etc.  No amount of correction 
to a lead acid will stop it from discharging.

If you tell me that your Thundersky cells shows a loss over time, I don't 
disbelieve that - I say instead, they needed more and better design work and 
some manufacturing improvement.  There is some sort of fault causing an 
internal or external parasitic load.

The prismatic, folded page cells, like CALB and TS are not very good in many 
respects,  Some (all?) bolt the conductive plates onto an aluminum post with a 
threaded fastener.  Bleh.

Notice that folks like Tesla did not choose that form - even though the 
alternative was to make individual connections to 7000 smalls to accomplish the 
task.

Those little cylindrical cells have some advantages.

They lend themselves to very automated, read consistent, construction.
Consistency is very important at the pack level.
The cylindrical form is much more stable when subjected to the volumetric 
changes that Li ion cells undergo when charging and discharging.
They can't be packed too close that they cannot convect heat well (with some 
extra gear to puch air (or other fluids around them).
Internally

Re: [EVDL] Bicycle battery

2015-06-18 Thread Lee Hart via EV


David Nelson via EV wrote:

That is a reason I don't use a cell level BMS. With a cell level BMS
like the miniBMS there is a constant drain on the cells running the
BMS boards and it is nearly impossible to make sure that each board
uses the _exact_ same current regardless of voltage in the cell.
Furthermore, boards like the miniBMS expect that you will balance at
the end of every charge and last I saw, that balance voltage was at
3.6V or so which is over the theoretical 100% SOC level for LiFePO4
cells which leads to potential overcharging of the cells on every
charge cycle. If you stop charging without the balancing taking place
and/or let the pack sit for extended periods of time then the
different current draw of each board working 24/7 introduces an
imbalance in the SOC of the cells in the pack.


Yes, this is a problem in the BMS market. Like quack medicine, it's full 
of customers worried about a problem that they don't understand very 
well. So there are marketeers only too happy to throw together some 
piece of junk that purports to solve it. It doesn't have to actually 
work -- it only needs to *sound* like it works, to separate the customer 
from his money.


So some BMS work -- and some don't. The bad ones are so bad that they 
give the whoel BMS market a bad name.


I've written about this over and over... check my old posts. It mostly 
seems to be of no avail, so I won't repeat myself again. Anything I say 
is overwhelmed by the noise of the internet.

--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

2015-06-18 Thread paul dove via EV

Excerpt:In theory, all batteries are identical. If wired in series, you would
therefore expect them all to charge and discharge equally. But in practice,
there are differences. New batteries that are all the same brand, same model,
same date code (and without lemons or quality control defects) will still
have small differences. Each cell 's self-discharge rate, amphour capacity,
internal resistance, and charge/discharge efficiency will be slightly
different. This makes them drift to different states of charge. For example,
cells with a higher self-discharge rate run down faster just from sitting.
Cells with a lower amphour capacity get more deeply discharged on each cycle,
which lowers their efficiency (so they need a bit more current to fully
recharge). Cells with a higher internal resistance run a little hotter, which
affects their efficiency and self-discharge rate. These differences tend to get
larger over time. If not corrected, you can have a pack with some cells almost
full, and some almost empty!
Ok, here's the deal this is fiction. Self discharge is so low (milivolts over
years) as to be non-existant.Secondly, if they are in series then all current
passing through cells is equal. It is impossible to draw more current from one
cell than another in a series pack. It can short and pass all current or it
can open and pass no current but it cannot discharge faster or slower.
If it has higher resistance then it will cause cells to heat faster that is all.
Please show evidence that your theory is possible.
The only person I spoke with having issues with new cells is when they were
placed in parallel with old cells. In that case the wires melted because the
new cell was handling more of the current. You may damage cells if there is a
big difference in resistance only if you exceed the max current draw from the
cell. If one never approaches the max current draw this will not be an issue.

From: Lee Hart via EV ev@lists.evdl.org
To: Electric Vehicle Discussion List ev@lists.evdl.org
Sent: Thursday, June 18, 2015 10:53 AM
Subject: Re: [EVDL] Bicycle battery

Paul Dove via EV wrote:
That was a very good summary. Cell balancing is something that was
done with other chemistry a and many have tried to apply it to Li Ion
chemistries but it doesn't work with Lithium since cells do self
discharge or drift.

If one wanted to balance them it has to be done below 3.38 volts
otherwise you are still charging the cell. Thanks for your input.

Lithiums need balancing even more than other chemistries! You can only
get by without a BMS if the cells are so well matched that they
accidentally stay in balance. (Do you feel lucky?)

Look at my own balancer at http://www.sunrise-ev.com/balancer.htm
I built it to *use*, not to sell. It doesn't load the cells, or clamp
the voltage at some arbitrary level, and doesn't have failure modes that
murder cells.

It basically does what you would do yourself, if you had the time and
inclination. It measures the voltage of every cell, and charges the ones
that are low.
--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

2015-06-18 Thread Lee Hart via EV


Paul Dove via EV wrote:

That was a very good summary. Cell balancing is something that was
done with other chemistry a and many have tried to apply it to Li Ion
chemistries but it doesn't work with Lithium since cells do self
discharge or drift.

If one wanted to balance them it has to be done below 3.38 volts
otherwise you are still charging the cell. Thanks for your input.


Lithiums need balancing even more than other chemistries! You can only 
get by without a BMS if the cells are so well matched that they 
accidentally stay in balance. (Do you feel lucky?)


Look at my own balancer at http://www.sunrise-ev.com/balancer.htm
I built it to *use*, not to sell. It doesn't load the cells, or clamp 
the voltage at some arbitrary level, and doesn't have failure modes that 
murder cells.


It basically does what you would do yourself, if you had the time and 
inclination. It measures the voltage of every cell, and charges the ones 
that are low.

--
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Bicycle battery

2015-06-18 Thread Roland via EV

   
This is why I have my lead cobalt cells or Li Ion pre balance at the factory.  
Its seems they do that any more unless you double the cost of the cell. 

 

When I received my new Li Ion cells from Nissan, all of them read between 4.0 
to 4.01 volt!  It was about three weeks before I had them install, So I 
connected them all in parallel which acted like one big cell at 4.0 volts which 
kept them equalized. 

 

When I was running a military battery shop, we use this same method for the Ni 
Cad aircraft cells. 

 

I am using the Orion BMS which you can see the data from there manual at 
OrionBMS.com 

 

Roland 

 

  


- Original Message - 

From: Lee Hart via EVmailto:ev@lists.evdl.org 

To: Electric Vehicle Discussion Listmailto:ev@lists.evdl.org 

Sent: Thursday, June 18, 2015 9:46 AM

Subject: Re: [EVDL] Bicycle battery



David Nelson via EV wrote:
 That is a reason I don't use a cell level BMS. With a cell level BMS
 like the miniBMS there is a constant drain on the cells running the
 BMS boards and it is nearly impossible to make sure that each board
 uses the _exact_ same current regardless of voltage in the cell.
 Furthermore, boards like the miniBMS expect that you will balance at
 the end of every charge and last I saw, that balance voltage was at
 3.6V or so which is over the theoretical 100% SOC level for LiFePO4
 cells which leads to potential overcharging of the cells on every
 charge cycle. If you stop charging without the balancing taking place
 and/or let the pack sit for extended periods of time then the
 different current draw of each board working 24/7 introduces an
 imbalance in the SOC of the cells in the pack.

Yes, this is a problem in the BMS market. Like quack medicine, it's full 
of customers worried about a problem that they don't understand very 
well. So there are marketeers only too happy to throw together some 
piece of junk that purports to solve it. It doesn't have to actually 
work -- it only needs to *sound* like it works, to separate the customer 
from his money.

So some BMS work -- and some don't. The bad ones are so bad that they 
give the whoel BMS market a bad name.

I've written about this over and over... check my old posts. It mostly 
seems to be of no avail, so I won't repeat myself again. Anything I say 
is overwhelmed by the noise of the internet.
-- 
The greatest pleasure in life is to create something that wasn't
there before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, 
www.sunrise-ev.comhttp://www.sunrise-ev.com/
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Re: [EVDL] Bicycle battery

I would be very surprised if DeWalt does not have a BMS on their Lithium packs,
all power tool packs with Lithium that I have opened always come with a BMS
which both checks every cell and turns off any current flow above max and
under min voltage levels.

I agree that if you let LiFePO4 sit at 3.6V for a while, you are over-charging
because you chose the wrong voltage level for your BMS, how is that the fault
of the circuit? It is a design error.
If you want to properly shunt LiFePO4 cells you should do so while keeping them
at about 3.4V since there is almost no capacity above that voltage anyway.
Oh and shunting should be a relatively short process: burn away the differences
(the delta in the small self-discharge between cells) and as soon as all cells
are at shunting level, the charging is disconnected and all cells can float to
their resting voltage.

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
proprietary information of Proxim Wireless Corporation.  If you received this 
message in error, please delete it and notify the sender.  Any unauthorized 
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-Original Message-
From: Paul Dove [mailto:dov...@bellsouth.net] 
Sent: Thursday, June 18, 2015 6:28 PM
To: Cor van de Water; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

I did not say it was impossible. As long as you stay below the open circuit 
voltage it's possible. However, if you hold the voltage at 3.6 for LiFePO4 
while shunting the current you will still be charging the cell. In essence all 
you are doing is modifying the charge procedure and loosing track of actual 
charge time. CC CV charging dictates holding the voltage and tapering the 
current which is not achieved in this scenario. 

I said its unnecessary. I am not really concerned about what engineers are 
doing in commercial products it's clear from the laptop fires the airplane 
fires the car fires etc. that there is still a lot of false beliefs about these 
cells.

I know dewalt bottom balances their battery and has no cell BMS  

Sent from my iPad

 On Jun 18, 2015, at 1:43 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Paul,
 How familiar are you with electronics?
 My wife's eBike has a nice pack with a built-in BMS that simply starts 
 shunting current above a certain voltage and presumably (but I can't 
 verify) also reduces charging current, so you can take care that the 
 shunting cells are receiving zero current and no longer rise in 
 voltage. The trick is to find a good voltage at which your BMS will 
 protect the cells.
 That pack is very nicely top-balanced and I expect that many more BMSs 
 that you are not even aware of in daily appliances such as power tools 
 will all top-balance.
 
 Regards,
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and 
 proprietary information of Proxim Wireless Corporation.  If you received this 
 message in error, please delete it and notify the sender.  Any unauthorized 
 use, disclosure, distribution, or copying of any part of this message is 
 prohibited.
 
 
 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove via 
 EV
 Sent: Thursday, June 18, 2015 9:40 AM
 To: Lee Hart; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery
 
 No one has convinced me that top balancing is even possible much less that a 
 BMS can achieve this.
 If you hold a cell above the Open circuit voltage you are charging it 
 even if you are trying to shunt the current with a Mosfet
 
  From: Lee Hart via EV ev@lists.evdl.org
 To: Electric Vehicle Discussion List ev@lists.evdl.org
 Sent: Thursday, June 18, 2015 10:46 AM
 Subject: Re: [EVDL] Bicycle battery
 
 David Nelson via EV wrote:
 That is a reason I don't use a cell level BMS. With a cell level BMS 
 like the miniBMS there is a constant drain on the cells running the 
 BMS boards and it is nearly impossible to make sure that each board 
 uses the _exact_ same current regardless of voltage in the cell.
 Furthermore, boards like the miniBMS expect that you will balance at 
 the end of every charge and last I saw, that balance voltage was at 
 3.6V or so which is over the theoretical 100% SOC level for LiFePO4 
 cells which leads to potential overcharging of the cells on every 
 charge cycle. If you stop charging without the balancing taking place 
 and/or let the pack sit for extended periods of time then the 
 different current draw of each board working 24/7 introduces an 
 imbalance in the SOC of the cells

Re: [EVDL] Bicycle battery

2015-06-18 Thread Michael Ross via EV

A question for Paul DOve,

Whence came your evidence of self discharging in Li ion cells?

I have the other impression entirely - that there is no mechanism by which
self discharge is even possible.

If cells are mismatched in a pack there can be an accumulation of drift
relative to other cells in a pack (which can cause problems), parallele
cells will equilibrate among themselves (why you want them to be closely
matched) BMS and other electrical/electronic equipment can produce a
parasitic load across a pack, but a charged cell sitting alone on a shelf
does not lose charge. It's capacity can decrease so that subsequent
performance is less good, but there is no self discharge.

Mike

On Thu, Jun 18, 2015 at 10:59 PM, Cor van de Water via EV ev@lists.evdl.org
 wrote:

 Paul,

 I presume you never ride in a car, because Ford's Pinto was a bomb on
 wheels and unsafe at any speed.

 Your line of reasoning does not warrant a serious response and I have
 given many reasons why a BMS
 is a good thing - I like to discuss based on arguments and data, not on
 lore and incidents.

 BTW, last I heard the root cause of the dreamliner fires is still unknown,
 there is suspicion
 about the quality of the batteries, similar to what caused laptop
 batteries to catch fire
 due to impurities embedded in the cells and trigger thermal runaway.
 I have helped to investigate a fire in a converted EV with Lithium-Ion
 prismatic cells
 that I suspect (but it was never conclusively proven) was caused by
 manufacturing defects.
 There was no BMS on that pack and it was not being charged, still it
 caught fire just sitting.
 One thing that I found was that what appeared to be a hotspot also showed
 severely deformed
 (folded crooked as if they were rammed into the prismatic case) cell
 plates (the original
 pouches that are contained in a bundle inside the prismatic cell) in one
 of the cells.
 But you can't say they used a BMS so that caused the fire. If you have a
 source
 that proves that it was in fact the BMS causing the fire then I would be
 interested in a link.
 Here is what I have:

 http://arstechnica.com/business/2013/02/investigation-reveals-cause-of-battery-fire-on-boeing-787-dreamliner/
 https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems

 http://www.ifsecglobal.com/dreamliner-lithium-battery-fire-cause-still-unknown/

 Regards,

 Cor van de Water
 Chief Scientist
 Proxim Wireless

 office +1 408 383 7626 Skype: cor_van_de_water
 XoIP   +31 87 784 1130 private: cvandewater.info
 www.proxim.com


 This email message (including any attachments) contains confidential and
 proprietary information of Proxim Wireless Corporation.  If you received
 this message in error, please delete it and notify the sender.  Any
 unauthorized use, disclosure, distribution, or copying of any part of this
 message is prohibited.


 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV
 Sent: Thursday, June 18, 2015 6:31 PM
 To: EVDL Administrator; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery

 Even Boeing burned up dream liners with a BMS.

 Got any other argument besides everyone is doing it?



 Sent from my iPad

  On Jun 18, 2015, at 2:02 PM, EVDL Administrator via EV 
 ev@lists.evdl.org wrote:
 
  On 18 Jun 2015 at 11:43, Cor van de Water via EV wrote:
 
  That pack is very nicely top-balanced and I expect that many more
  BMSs that you are not even aware of in daily appliances such as power
  tools will all top-balance.
 
  One more time.  There is a really good reason that the only place you
  find aversion to BMSes is among EV hobbyists.
 
  Real world electronics manufacturers -- the ones who build millions of
  laptops, mobile phones, power tools and yes, commercial EVs -- know
  that you don't sell a product with a lithium battery unless it has
  ample smarts to protect the battery, the user, and the manufacturer.
 
  Trust me, these guys have bean counters looking over their shoulders.
  They wouldn't be using BMSes if they weren't necessary.  BMSes protect
  the battery from early failure, the user from hazard to life and limb,
  and the manufacturer from the lawyers!
 
  David Roden - Akron, Ohio, USA
  EVDL Administrator
 
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL
  Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = =
  = = = = = = = = = = = = =
  Note: mail sent to evpost and etpost addresses will not reach me.
  To send a private message, please obtain my email address from the
  webpage http://www.evdl.org/help/ .
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Re: [EVDL] Bicycle battery

Paul, the 29.6V is not the max charge voltage of the pack. It is the nominal 
voltage:
8 x 3.7V (these were Cobalt cells) = 29.6V
So the max 32V on the bus is actually only 4V per cell and that means that they 
keep those cells
below max charge voltage of 4.2V
So, it was not possible that the battery was over-charged, unless a cell 
shorted and the 32V
was applied to 7 cells in series instead of 8!

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
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message in error, please delete it and notify the sender.  Any unauthorized 
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prohibited.


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV
Sent: Thursday, June 18, 2015 8:21 PM
To: Cor van de Water via EV
Subject: Re: [EVDL] Bicycle battery

We already covered how to tell is a cell has internal defects. You drain the 
cell to 2.5 volts and then if the cell voltage rises it's good if it keeps 
falling don't use it. I did think this up This is what NASA does. I read it in 
one of their presentations. I can dig it up if you like. 

As for the Dreamliner I followed that carefully. My favorite chart that they 
presented to the FAA said 
- the only thing that causes lithium battery fires is overchargeing
- we can find no evidence we are over charging 
- therefore the cause of the fire is unknown

One of those statements has to be wrong. And the fire was the evidence of 
overcharging.

The open circuit voltage of their battery was 29.6 volts. The system voltage 
was 32 volts. They were charging the cells the whole time the APU was running 
and wondering why it burned.

As for laptops they were overcharging as well. The paper I read the designer 
claimed that leaving a small amount of current flowing or trickle charge as 
they call it would not hurt lithium batteries. 

Sent from my iPad

 On Jun 18, 2015, at 9:59 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
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Re: [EVDL] Bicycle battery

We already covered how to tell is a cell has internal defects. You drain the
cell to 2.5 volts and then if the cell voltage rises it's good if it keeps
falling don't use it. I did think this up This is what NASA does. I read it in
one of their presentations. I can dig it up if you like.

As for the Dreamliner I followed that carefully. My favorite chart that they
presented to the FAA said
- the only thing that causes lithium battery fires is overchargeing
- we can find no evidence we are over charging
- therefore the cause of the fire is unknown

One of those statements has to be wrong. And the fire was the evidence of
overcharging.

The open circuit voltage of their battery was 29.6 volts. The system voltage
was 32 volts. They were charging the cells the whole time the APU was running
and wondering why it burned.

As for laptops they were overcharging as well. The paper I read the designer
claimed that leaving a small amount of current flowing or trickle charge as
they call it would not hurt lithium batteries.

Sent from my iPad

On Jun 18, 2015, at 9:59 PM, Cor van de Water via EV ev@lists.evdl.org
wrote:

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Re: [EVDL] Bicycle battery

I have Lithium cells (CALB 180Ah) sitting in my garage since 1.5 years
and have measured their self-discharge and plotted it in an Excel spreadsheet.
I can *see* their self-discharge.
I can *see* effect from ambient temperature on the change in self-discharge 
rate over time
I can *see* the differences of up to a factor 2 in amount of self-discharge 
between cells
that were initially charged to exact same state of charge (charged in parallel, 
then left
for many days connected together in parallel, then disconnected all cells from 
each other
and with every cell unconnected to anything, take a measurement with a DVM once 
every few days
for a couple months.) If you did this, you would be able to tell as well.

Besides - the resident Lithium expert on this forum (who has helped to setup a
Lithium-Ion cell factory) tells us that there is self-discharge,
so I am seriously wondering why you continue to argue that self-discharge does 
not exist???

As for failures without BMS:
Yes, I have helped investigate a burned-down conversion that did not have BMS.
It is likely that in that case, a manufacturing defect in the cell was the root 
cause
because the fire started at a moment that the pack was not connected: not 
charging, not discharging,
just sitting there.
There is a small chance that it was something that fell *on* the pack but since 
nobody was present
at the time that the fire started, that is unlikely. I discovered that there 
was an anomaly in the
layout (folded layers of some of the pouch cells inside the prismatic case) 
that is the likely
start of the problem - a workmanship problem. But also that was never proven 
just like the
fire with the Dreamliner which was never pinpointed to a root cause.

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
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message in error, please delete it and notify the sender.  Any unauthorized 
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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV
Sent: Thursday, June 18, 2015 8:23 PM
To: Michael Ross; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

I agree with that. 

Sent from my iPad

 On Jun 18, 2015, at 10:12 PM, Michael Ross via EV ev@lists.evdl.org wrote:
 
 A question for Paul DOve,
 
 Whence came your evidence of self discharging in Li ion cells?
 
 I have the other impression entirely - that there is no mechanism by 
 which self discharge is even possible.
 
 If cells are mismatched in a pack there can be an accumulation of 
 drift relative to other cells in a pack (which can cause problems), 
 parallele cells will equilibrate among themselves (why you want them 
 to be closely
 matched) BMS and other electrical/electronic equipment can produce a 
 parasitic load across a pack, but a charged cell sitting alone on a 
 shelf does not lose charge. It's capacity can decrease so that 
 subsequent performance is less good, but there is no self discharge.
 
 Mike
 
 On Thu, Jun 18, 2015 at 10:59 PM, Cor van de Water via EV 
 ev@lists.evdl.org
 wrote:
 
 Paul,
 
 I presume you never ride in a car, because Ford's Pinto was a bomb on 
 wheels and unsafe at any speed.
 
 Your line of reasoning does not warrant a serious response and I have 
 given many reasons why a BMS is a good thing - I like to discuss 
 based on arguments and data, not on lore and incidents.
 
 BTW, last I heard the root cause of the dreamliner fires is still 
 unknown, there is suspicion about the quality of the batteries, 
 similar to what caused laptop batteries to catch fire due to 
 impurities embedded in the cells and trigger thermal runaway.
 I have helped to investigate a fire in a converted EV with 
 Lithium-Ion prismatic cells that I suspect (but it was never 
 conclusively proven) was caused by manufacturing defects.
 There was no BMS on that pack and it was not being charged, still it 
 caught fire just sitting.
 One thing that I found was that what appeared to be a hotspot also 
 showed severely deformed (folded crooked as if they were rammed into 
 the prismatic case) cell plates (the original pouches that are 
 contained in a bundle inside the prismatic cell) in one of the cells.
 But you can't say they used a BMS so that caused the fire. If you 
 have a source that proves that it was in fact the BMS causing the 
 fire then I would be interested in a link.
 Here is what I have:
 
 http://arstechnica.com/business/2013/02/investigation-reveals-cause-o
 f-battery-fire-on-boeing-787-dreamliner/
 https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems
 
 http://www.ifsecglobal.com/dreamliner-lithium-battery-fire-cause-stil
 l-unknown/
 
 Regards

Re: [EVDL] Bicycle battery

I agree with that. 

Sent from my iPad

 On Jun 18, 2015, at 10:12 PM, Michael Ross via EV ev@lists.evdl.org wrote:
 
 A question for Paul DOve,
 
 Whence came your evidence of self discharging in Li ion cells?
 
 I have the other impression entirely - that there is no mechanism by which
 self discharge is even possible.
 
 If cells are mismatched in a pack there can be an accumulation of drift
 relative to other cells in a pack (which can cause problems), parallele
 cells will equilibrate among themselves (why you want them to be closely
 matched) BMS and other electrical/electronic equipment can produce a
 parasitic load across a pack, but a charged cell sitting alone on a shelf
 does not lose charge. It's capacity can decrease so that subsequent
 performance is less good, but there is no self discharge.
 
 Mike
 
 On Thu, Jun 18, 2015 at 10:59 PM, Cor van de Water via EV ev@lists.evdl.org
 wrote:
 
 Paul,
 
 I presume you never ride in a car, because Ford's Pinto was a bomb on
 wheels and unsafe at any speed.
 
 Your line of reasoning does not warrant a serious response and I have
 given many reasons why a BMS
 is a good thing - I like to discuss based on arguments and data, not on
 lore and incidents.
 
 BTW, last I heard the root cause of the dreamliner fires is still unknown,
 there is suspicion
 about the quality of the batteries, similar to what caused laptop
 batteries to catch fire
 due to impurities embedded in the cells and trigger thermal runaway.
 I have helped to investigate a fire in a converted EV with Lithium-Ion
 prismatic cells
 that I suspect (but it was never conclusively proven) was caused by
 manufacturing defects.
 There was no BMS on that pack and it was not being charged, still it
 caught fire just sitting.
 One thing that I found was that what appeared to be a hotspot also showed
 severely deformed
 (folded crooked as if they were rammed into the prismatic case) cell
 plates (the original
 pouches that are contained in a bundle inside the prismatic cell) in one
 of the cells.
 But you can't say they used a BMS so that caused the fire. If you have a
 source
 that proves that it was in fact the BMS causing the fire then I would be
 interested in a link.
 Here is what I have:
 
 http://arstechnica.com/business/2013/02/investigation-reveals-cause-of-battery-fire-on-boeing-787-dreamliner/
 https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems
 
 http://www.ifsecglobal.com/dreamliner-lithium-battery-fire-cause-still-unknown/
 
 Regards,
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626 Skype: cor_van_de_water
 XoIP   +31 87 784 1130 private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and
 proprietary information of Proxim Wireless Corporation.  If you received
 this message in error, please delete it and notify the sender.  Any
 unauthorized use, disclosure, distribution, or copying of any part of this
 message is prohibited.
 
 
 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV
 Sent: Thursday, June 18, 2015 6:31 PM
 To: EVDL Administrator; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery
 
 Even Boeing burned up dream liners with a BMS.
 
 Got any other argument besides everyone is doing it?
 
 
 
 Sent from my iPad
 
 On Jun 18, 2015, at 2:02 PM, EVDL Administrator via EV 
 ev@lists.evdl.org wrote:
 
 On 18 Jun 2015 at 11:43, Cor van de Water via EV wrote:
 
 That pack is very nicely top-balanced and I expect that many more
 BMSs that you are not even aware of in daily appliances such as power
 tools will all top-balance.
 
 One more time.  There is a really good reason that the only place you
 find aversion to BMSes is among EV hobbyists.
 
 Real world electronics manufacturers -- the ones who build millions of
 laptops, mobile phones, power tools and yes, commercial EVs -- know
 that you don't sell a product with a lithium battery unless it has
 ample smarts to protect the battery, the user, and the manufacturer.
 
 Trust me, these guys have bean counters looking over their shoulders.
 They wouldn't be using BMSes if they weren't necessary.  BMSes protect
 the battery from early failure, the user from hazard to life and limb,
 and the manufacturer from the lawyers!
 
 David Roden - Akron, Ohio, USA
 EVDL Administrator
 
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL
 Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = =
 = = = = = = = = = = = = =
 Note: mail sent to evpost and etpost addresses will not reach me.
 To send a private message, please obtain my email address from the
 webpage http://www.evdl.org/help/ .
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 For EV

Re: [EVDL] Bicycle battery

I did not say it was impossible. As long as you stay below the open circuit
voltage it's possible. However, if you hold the voltage at 3.6 for LiFePO4
while shunting the current you will still be charging the cell. In essence all
you are doing is modifying the charge procedure and loosing track of actual
charge time. CC CV charging dictates holding the voltage and tapering the
current which is not achieved in this scenario.

I said its unnecessary. I am not really concerned about what engineers are
doing in commercial products it's clear from the laptop fires the airplane
fires the car fires etc. that there is still a lot of false beliefs about these
cells.

I know dewalt bottom balances their battery and has no cell BMS

Sent from my iPad

On Jun 18, 2015, at 1:43 PM, Cor van de Water via EV ev@lists.evdl.org
wrote:

Paul,
How familiar are you with electronics?
My wife's eBike has a nice pack with a built-in BMS
that simply starts shunting current above a certain voltage
and presumably (but I can't verify) also reduces charging current,
so you can take care that the shunting cells are receiving zero current
and no longer rise in voltage. The trick is to find a good voltage at
which your BMS will protect the cells.
That pack is very nicely top-balanced and I expect that many more BMSs
that you are not even aware of in daily appliances such as power tools
will all top-balance.

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626Skype: cor_van_de_water
XoIP +31 87 784 1130private: cvandewater.info
www.proxim.com

This email message (including any attachments) contains confidential and
proprietary information of Proxim Wireless Corporation. If you received this
message in error, please delete it and notify the sender. Any unauthorized
use, disclosure, distribution, or copying of any part of this message is
prohibited.

-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove via EV
Sent: Thursday, June 18, 2015 9:40 AM
To: Lee Hart; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

No one has convinced me that top balancing is even possible much less that a
BMS can achieve this.
If you hold a cell above the Open circuit voltage you are charging it even if
you are trying to shunt the current with a Mosfet

From: Lee Hart via EV ev@lists.evdl.org
To: Electric Vehicle Discussion List ev@lists.evdl.org
Sent: Thursday, June 18, 2015 10:46 AM
Subject: Re: [EVDL] Bicycle battery

David Nelson via EV wrote:
That is a reason I don't use a cell level BMS. With a cell level BMS
like the miniBMS there is a constant drain on the cells running the
BMS boards and it is nearly impossible to make sure that each board
uses the _exact_ same current regardless of voltage in the cell.
Furthermore, boards like the miniBMS expect that you will balance at
the end of every charge and last I saw, that balance voltage was at
3.6V or so which is over the theoretical 100% SOC level for LiFePO4
cells which leads to potential overcharging of the cells on every
charge cycle. If you stop charging without the balancing taking place
and/or let the pack sit for extended periods of time then the
different current draw of each board working 24/7 introduces an
imbalance in the SOC of the cells in the pack.

Yes, this is a problem in the BMS market. Like quack medicine, it's full of
customers worried about a problem that they don't understand very well. So
there are marketeers only too happy to throw together some piece of junk that
purports to solve it. It doesn't have to actually work -- it only needs to
*sound* like it works, to separate the customer from his money.

So some BMS work -- and some don't. The bad ones are so bad that they give
the whoel BMS market a bad name.

I've written about this over and over... check my old posts. It mostly seems
to be of no avail, so I won't repeat myself again. Anything I say is
overwhelmed by the noise of the internet.
--
The greatest pleasure in life is to create something that wasn't there
before. -- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___
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Re: [EVDL] Bicycle battery

Even Boeing burned up dream liners with a BMS.

Got any other argument besides everyone is doing it?



Sent from my iPad

 On Jun 18, 2015, at 2:02 PM, EVDL Administrator via EV ev@lists.evdl.org 
 wrote:
 
 On 18 Jun 2015 at 11:43, Cor van de Water via EV wrote:
 
 That pack is very nicely top-balanced and I expect that many more BMSs
 that you are not even aware of in daily appliances such as power tools
 will all top-balance.
 
 One more time.  There is a really good reason that the only place you find 
 aversion to BMSes is among EV hobbyists.  
 
 Real world electronics manufacturers -- the ones who build millions of 
 laptops, mobile phones, power tools and yes, commercial EVs -- know that you 
 don't sell a product with a lithium battery unless it has ample smarts to 
 protect the battery, the user, and the manufacturer.  
 
 Trust me, these guys have bean counters looking over their shoulders.  They 
 wouldn't be using BMSes if they weren't necessary.  BMSes protect the 
 battery from early failure, the user from hazard to life and limb, and the 
 manufacturer from the lawyers!
 
 David Roden - Akron, Ohio, USA
 EVDL Administrator
 
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 EVDL Information: http://www.evdl.org/help/
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = 
 Note: mail sent to evpost and etpost addresses will not 
 reach me.  To send a private message, please obtain my 
 email address from the webpage http://www.evdl.org/help/ .
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 
 
 ___
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 For EV drag racing discussion, please use NEDRA 
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Re: [EVDL] Bicycle battery

Paul,

I presume you never ride in a car, because Ford's Pinto was a bomb on wheels 
and unsafe at any speed.

Your line of reasoning does not warrant a serious response and I have given 
many reasons why a BMS
is a good thing - I like to discuss based on arguments and data, not on lore 
and incidents.

BTW, last I heard the root cause of the dreamliner fires is still unknown, 
there is suspicion
about the quality of the batteries, similar to what caused laptop batteries to 
catch fire
due to impurities embedded in the cells and trigger thermal runaway.
I have helped to investigate a fire in a converted EV with Lithium-Ion 
prismatic cells
that I suspect (but it was never conclusively proven) was caused by 
manufacturing defects.
There was no BMS on that pack and it was not being charged, still it caught 
fire just sitting.
One thing that I found was that what appeared to be a hotspot also showed 
severely deformed
(folded crooked as if they were rammed into the prismatic case) cell plates 
(the original
pouches that are contained in a bundle inside the prismatic cell) in one of the 
cells.
But you can't say they used a BMS so that caused the fire. If you have a 
source
that proves that it was in fact the BMS causing the fire then I would be 
interested in a link.
Here is what I have: 
http://arstechnica.com/business/2013/02/investigation-reveals-cause-of-battery-fire-on-boeing-787-dreamliner/
https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems
http://www.ifsecglobal.com/dreamliner-lithium-battery-fire-cause-still-unknown/

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
proprietary information of Proxim Wireless Corporation.  If you received this 
message in error, please delete it and notify the sender.  Any unauthorized 
use, disclosure, distribution, or copying of any part of this message is 
prohibited.


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV
Sent: Thursday, June 18, 2015 6:31 PM
To: EVDL Administrator; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

Even Boeing burned up dream liners with a BMS.

Got any other argument besides everyone is doing it?



Sent from my iPad

 On Jun 18, 2015, at 2:02 PM, EVDL Administrator via EV ev@lists.evdl.org 
 wrote:
 
 On 18 Jun 2015 at 11:43, Cor van de Water via EV wrote:
 
 That pack is very nicely top-balanced and I expect that many more 
 BMSs that you are not even aware of in daily appliances such as power 
 tools will all top-balance.
 
 One more time.  There is a really good reason that the only place you 
 find aversion to BMSes is among EV hobbyists.
 
 Real world electronics manufacturers -- the ones who build millions of 
 laptops, mobile phones, power tools and yes, commercial EVs -- know 
 that you don't sell a product with a lithium battery unless it has 
 ample smarts to protect the battery, the user, and the manufacturer.
 
 Trust me, these guys have bean counters looking over their shoulders.  
 They wouldn't be using BMSes if they weren't necessary.  BMSes protect 
 the battery from early failure, the user from hazard to life and limb, 
 and the manufacturer from the lawyers!
 
 David Roden - Akron, Ohio, USA
 EVDL Administrator
 
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL 
 Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = 
 = = = = = = = = = = = = =
 Note: mail sent to evpost and etpost addresses will not reach me.  
 To send a private message, please obtain my email address from the 
 webpage http://www.evdl.org/help/ .
 = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 
 
 ___
 UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
 http://lists.evdl.org/listinfo.cgi/ev-evdl.org
 For EV drag racing discussion, please use NEDRA 
 (http://groups.yahoo.com/group/NEDRA)
 
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Re: [EVDL] Bicycle battery

We are not speaking of commercial products. At least I wasn't we are talking 
about our own conversion and the pros and cons of a BMS. 

I wasn't lucky. My pack is the same voltage after charger to two decimal 
places. I simply look at the voltage when I unplug the charger. 

Only overcharging causes fires. And then not as likely with LiFePO4. We took a  
full cell and put 60 amps in it for three hours and all it did was vent and 
melt the plastic around the terminal. 

$125 cell was much cheaper than a BMS. I have had no issues since and it's been 
18 months now. The pack is the same voltage after every charge.

If I was using one of the other two types of cells maybe I would consider it 
but I doubt it. I would have to play with those cells some to see how they 
react.

I design electric circuits for a living and I trust the battery much more than 
the circuit. These batteries are very stable.

All the cars I have seen that burned had a BMS. I have heard of no one without 
a BMS burning down a car.

Sent from my iPad

 On Jun 18, 2015, at 2:58 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Paul,
 In your case, *you* were the BMS.
 But you were lucky that you noticed the lower end voltage and knew something 
 was off.
 You were lucky that the charger finished charging without cooking the other 
 cells to death
 You were lucky that the bad cell was a short and not a partial failure
 or you might not have detected it in time or faced a much more severe 
 situation than a shorted cell.
 Anyone less knowledgeable than you about your EV (and that would be 99+ 
 percent of all drivers)
 would not have caught this failure and continued until disaster, so your 
 vehicle can be used by you
 alone, because you are an essential part of that vehicle! (namely, the BMS)
 It looks like you just confirmed the thing that you tried to disprove...
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and 
 proprietary information of Proxim Wireless Corporation.  If you received this 
 message in error, please delete it and notify the sender.  Any unauthorized 
 use, disclosure, distribution, or copying of any part of this message is 
 prohibited.
 
 
 -Original Message-
 From: Paul Dove [mailto:dov...@bellsouth.net] 
 Sent: Thursday, June 18, 2015 11:13 AM
 To: Cor van de Water; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery
 
 I had this issue early on in my vehicle and at the end of charge my pack 
 voltage reflected this and I removed the bad cell. The cell was shorted but 
 the rest of the pack was fine. I have no cell monitoring.
 
 Pretty sure it was caused by a loose connection. That said, apart from 
 expense I have no problem with a BAttery Monitor that looks at every cell but 
 prismatic cells have multiple cells in them in parallel so you can't monitor 
 them individually.
 
 Still of the opinion it is an unnecessary expense.
 
 You haven't convinced me that cell discharge or drift between SOC is a real 
 issue. I cat see it ever being an issue. 
 
 Sent from my iPhone
 
 On Jun 18, 2015, at 12:44 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Paul,
 It is true that in series string the same *load* current goes through 
 all cells, but the principle of self-discharge is that it occurs 
 internal to the cell, so it is invisible to the outside world except 
 when you measure each cell (or blow them up due to overcharge or 
 under-discharge).
 I have actually measured cells and seen the self-discharge.
 As you say, it is a small effect in good cells.
 But still, there is about 1:2 difference in self-discharge between the 
 cells I monitor and the differences add up over time.
 It might not be a problem in the first year or even in the second.
 Then in the 3rd year you try to squeeze an 85 or 90% discharge from 
 the cells and boom - one reverses (or more) and it is destroyed and 
 you might only find out from the fireworks when you try to charge it the 
 next cycle or when you drive it.
 Oh BTW - one reason to monitor *all* and *every* cell is exactly the 
 issue with the infamous bottom-balancing without BMS approach:
 Some of the cells that I have were abused and too deeply discharged.
 Guess what happens? They become a resistor.
 Some are low resistance which is OK when they resemble a wire, 
 others are still in doubt whether they want to become a piece of wire or 
 rather a heating element.
 This has at least 2 disastrous effects if you do not detect this immediately:
 
 1. The pack voltage has dropped and each cell now gets a much higher 
 finish charging so you might have been charging conservatively with 
 all cells in the string, but with some cells removed, all the rest 
 is dividing up the difference and may easily be charged to destruction now!
 
 2

Re: [EVDL] Bicycle battery

Paul,
How familiar are you with electronics?
My wife's eBike has a nice pack with a built-in BMS
that simply starts shunting current above a certain voltage
and presumably (but I can't verify) also reduces charging current,
so you can take care that the shunting cells are receiving zero current
and no longer rise in voltage. The trick is to find a good voltage at
which your BMS will protect the cells.
That pack is very nicely top-balanced and I expect that many more BMSs
that you are not even aware of in daily appliances such as power tools
will all top-balance.

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
proprietary information of Proxim Wireless Corporation.  If you received this 
message in error, please delete it and notify the sender.  Any unauthorized 
use, disclosure, distribution, or copying of any part of this message is 
prohibited.


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove via EV
Sent: Thursday, June 18, 2015 9:40 AM
To: Lee Hart; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

No one has convinced me that top balancing is even possible much less that a 
BMS can achieve this.
If you hold a cell above the Open circuit voltage you are charging it even if 
you are trying to shunt the current with a Mosfet

  From: Lee Hart via EV ev@lists.evdl.org
 To: Electric Vehicle Discussion List ev@lists.evdl.org
 Sent: Thursday, June 18, 2015 10:46 AM
 Subject: Re: [EVDL] Bicycle battery
   
David Nelson via EV wrote:
 That is a reason I don't use a cell level BMS. With a cell level BMS 
 like the miniBMS there is a constant drain on the cells running the 
 BMS boards and it is nearly impossible to make sure that each board 
 uses the _exact_ same current regardless of voltage in the cell.
 Furthermore, boards like the miniBMS expect that you will balance at 
 the end of every charge and last I saw, that balance voltage was at 
 3.6V or so which is over the theoretical 100% SOC level for LiFePO4 
 cells which leads to potential overcharging of the cells on every 
 charge cycle. If you stop charging without the balancing taking place 
 and/or let the pack sit for extended periods of time then the 
 different current draw of each board working 24/7 introduces an 
 imbalance in the SOC of the cells in the pack.

Yes, this is a problem in the BMS market. Like quack medicine, it's full of 
customers worried about a problem that they don't understand very well. So 
there are marketeers only too happy to throw together some piece of junk that 
purports to solve it. It doesn't have to actually work -- it only needs to 
*sound* like it works, to separate the customer from his money.

So some BMS work -- and some don't. The bad ones are so bad that they give the 
whoel BMS market a bad name.

I've written about this over and over... check my old posts. It mostly seems to 
be of no avail, so I won't repeat myself again. Anything I say is overwhelmed 
by the noise of the internet.
--
The greatest pleasure in life is to create something that wasn't there before. 
-- Roy Spence
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com 
___
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Re: [EVDL] Bicycle battery

2015-06-18 Thread EVDL Administrator via EV

On 18 Jun 2015 at 10:46, Lee Hart via EV wrote:

 I've written about this over and over... check my old posts. It mostly 
 seems to be of no avail, so I won't repeat myself again. Anything I say 
 is overwhelmed by the noise of the internet.

Lee Hart is one of the EVDL stalwarts. He's been here longer than I have, 
and that's over 20 years now. 

Lee is a true scientist, an electronic engineer.  He's thoughtful, 
deliberate, and focused.  He's not averse to recent developments, he just 
evaluates them carefully rather than jumping on the bandwagon that younger 
engineers often join.  He's not going to use a microprocessor where a relay 
works just fine.

Lee doesn't speak very loudly, but he has more years of engineering and EV 
design and building than most of the net's rambling loudmouths put together.

Lee beats any of them in battery research too.  I'm not talking about 
anecodotal it works for me so far stuff, I'm talking about actual rigorous 
testing.  You can get a taste for the battery work Lee does in his meager 
spare time here :

http://www.motherjones.com/environment/2008/05/charge-keep

Lee also has an extensive background in designing real world commercial 
products that MUST be safe and reliable and not catch fire.  

So pipe down for a minute, and LISTEN to Lee.  He's offering you wisdom. 
This is gold, freely given.  Don't let it pass you by.

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = 
Note: mail sent to evpost and etpost addresses will not 
reach me.  To send a private message, please obtain my 
email address from the webpage http://www.evdl.org/help/ .
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Re: [EVDL] Bicycle battery

I had this issue early on in my vehicle and at the end of charge my pack 
voltage reflected this and I removed the bad cell. The cell was shorted but the 
rest of the pack was fine. I have no cell monitoring.

Pretty sure it was caused by a loose connection. That said, apart from expense 
I have no problem with a BAttery Monitor that looks at every cell but prismatic 
cells have multiple cells in them in parallel so you can't monitor them 
individually.

Still of the opinion it is an unnecessary expense.

You haven't convinced me that cell discharge or drift between SOC is a real 
issue. I cat see it ever being an issue. 

Sent from my iPhone

 On Jun 18, 2015, at 12:44 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Paul,
 It is true that in series string the same *load* current goes through all 
 cells,
 but the principle of self-discharge is that it occurs internal to the cell, 
 so it is
 invisible to the outside world except when you measure each cell (or blow 
 them up
 due to overcharge or under-discharge).
 I have actually measured cells and seen the self-discharge.
 As you say, it is a small effect in good cells.
 But still, there is about 1:2 difference in self-discharge between the cells 
 I monitor
 and the differences add up over time.
 It might not be a problem in the first year or even in the second.
 Then in the 3rd year you try to squeeze an 85 or 90% discharge from the cells
 and boom - one reverses (or more) and it is destroyed and you might only find 
 out from the
 fireworks when you try to charge it the next cycle or when you drive it.
 Oh BTW - one reason to monitor *all* and *every* cell is exactly the issue 
 with
 the infamous bottom-balancing without BMS approach:
 Some of the cells that I have were abused and too deeply discharged.
 Guess what happens? They become a resistor.
 Some are low resistance which is OK when they resemble a wire, others are 
 still 
 in doubt whether they want to become a piece of wire or rather a heating 
 element.
 This has at least 2 disastrous effects if you do not detect this immediately:
 
 1. The pack voltage has dropped and each cell now gets a much higher finish 
 charging
 so you might have been charging conservatively with all cells in the string, 
 but with
 some cells removed, all the rest is dividing up the difference and may 
 easily be charged
 to destruction now!
 
 2. If charging does not harm the pack, what about discharging hundreds of 
 Amps through a
 resistor that is nicely embedded in the pack, insulated from the outside by 
 the cells
 around it? If it even drops 10V across it at hundreds of Amps, you now have a
 multi-kiloWatt heater inside your pack without much cooling. What do you 
 think will happen?
 
 Just some easy illustration of the *need* for a cell-level BMS, from practice 
 by measuring
 what happened to a used set of Lithiums (that indeed was run without BMS) and 
 I have been
 monitoring since taking it out of service. Learn from it or get your own 
 experience, your choice.
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and 
 proprietary information of Proxim Wireless Corporation.  If you received this 
 message in error, please delete it and notify the sender.  Any unauthorized 
 use, disclosure, distribution, or copying of any part of this message is 
 prohibited.
 
 
 -Original Message-
 From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove via EV
 Sent: Thursday, June 18, 2015 9:57 AM
 To: Lee Hart; Electric Vehicle Discussion List
 Subject: Re: [EVDL] Bicycle battery
 
 Excerpt:In theory, all batteries are identical. If wired in series, you would 
 therefore expect them all to charge and discharge equally. But in practice, 
 there are differences. New batteries that are all the same brand, same model, 
 same date code (and without lemons or quality control defects) will still 
 have small differences. Each cell 's self-discharge rate, amphour capacity, 
 internal resistance, and charge/discharge efficiency will be slightly 
 different. This makes them drift to different states of charge. For example, 
 cells with a higher self-discharge rate run down faster just from sitting. 
 Cells with a lower amphour capacity get more deeply discharged on each cycle, 
 which lowers their efficiency (so they need a bit more current to fully 
 recharge). Cells with a higher internal resistance run a little hotter, which 
 affects their efficiency and self-discharge rate. These differences tend to 
 get larger over time. If not corrected, you can have a pack with some cells al
 most full, and some almost empty!
 Ok, here's the deal this is fiction. Self discharge is so low (milivolts over 
 years) as to be non-existant.Secondly, if they are in series then all current 
 passing through

Re: [EVDL] Bicycle battery

Paul,
In your case, *you* were the BMS.
But you were lucky that you noticed the lower end voltage and knew something 
was off.
You were lucky that the charger finished charging without cooking the other 
cells to death
You were lucky that the bad cell was a short and not a partial failure
or you might not have detected it in time or faced a much more severe situation 
than a shorted cell.
Anyone less knowledgeable than you about your EV (and that would be 99+ percent 
of all drivers)
would not have caught this failure and continued until disaster, so your 
vehicle can be used by you
alone, because you are an essential part of that vehicle! (namely, the BMS)
It looks like you just confirmed the thing that you tried to disprove...

Cor van de Water
Chief Scientist
Proxim Wireless

office +1 408 383 7626  Skype: cor_van_de_water
XoIP   +31 87 784 1130  private: cvandewater.info
www.proxim.com


This email message (including any attachments) contains confidential and 
proprietary information of Proxim Wireless Corporation.  If you received this 
message in error, please delete it and notify the sender.  Any unauthorized 
use, disclosure, distribution, or copying of any part of this message is 
prohibited.


-Original Message-
From: Paul Dove [mailto:dov...@bellsouth.net] 
Sent: Thursday, June 18, 2015 11:13 AM
To: Cor van de Water; Electric Vehicle Discussion List
Subject: Re: [EVDL] Bicycle battery

I had this issue early on in my vehicle and at the end of charge my pack 
voltage reflected this and I removed the bad cell. The cell was shorted but the 
rest of the pack was fine. I have no cell monitoring.

Pretty sure it was caused by a loose connection. That said, apart from expense 
I have no problem with a BAttery Monitor that looks at every cell but prismatic 
cells have multiple cells in them in parallel so you can't monitor them 
individually.

Still of the opinion it is an unnecessary expense.

You haven't convinced me that cell discharge or drift between SOC is a real 
issue. I cat see it ever being an issue. 

Sent from my iPhone

 On Jun 18, 2015, at 12:44 PM, Cor van de Water via EV ev@lists.evdl.org 
 wrote:
 
 Paul,
 It is true that in series string the same *load* current goes through 
 all cells, but the principle of self-discharge is that it occurs 
 internal to the cell, so it is invisible to the outside world except 
 when you measure each cell (or blow them up due to overcharge or 
 under-discharge).
 I have actually measured cells and seen the self-discharge.
 As you say, it is a small effect in good cells.
 But still, there is about 1:2 difference in self-discharge between the 
 cells I monitor and the differences add up over time.
 It might not be a problem in the first year or even in the second.
 Then in the 3rd year you try to squeeze an 85 or 90% discharge from 
 the cells and boom - one reverses (or more) and it is destroyed and 
 you might only find out from the fireworks when you try to charge it the next 
 cycle or when you drive it.
 Oh BTW - one reason to monitor *all* and *every* cell is exactly the 
 issue with the infamous bottom-balancing without BMS approach:
 Some of the cells that I have were abused and too deeply discharged.
 Guess what happens? They become a resistor.
 Some are low resistance which is OK when they resemble a wire, 
 others are still in doubt whether they want to become a piece of wire or 
 rather a heating element.
 This has at least 2 disastrous effects if you do not detect this immediately:
 
 1. The pack voltage has dropped and each cell now gets a much higher 
 finish charging so you might have been charging conservatively with 
 all cells in the string, but with some cells removed, all the rest 
 is dividing up the difference and may easily be charged to destruction now!
 
 2. If charging does not harm the pack, what about discharging hundreds 
 of Amps through a resistor that is nicely embedded in the pack, 
 insulated from the outside by the cells around it? If it even drops 
 10V across it at hundreds of Amps, you now have a multi-kiloWatt heater 
 inside your pack without much cooling. What do you think will happen?
 
 Just some easy illustration of the *need* for a cell-level BMS, from 
 practice by measuring what happened to a used set of Lithiums (that 
 indeed was run without BMS) and I have been monitoring since taking it out of 
 service. Learn from it or get your own experience, your choice.
 
 Cor van de Water
 Chief Scientist
 Proxim Wireless
 
 office +1 408 383 7626Skype: cor_van_de_water
 XoIP   +31 87 784 1130private: cvandewater.info
 www.proxim.com
 
 
 This email message (including any attachments) contains confidential and 
 proprietary information of Proxim Wireless Corporation.  If you received this 
 message in error, please delete it and notify the sender.  Any unauthorized 
 use, disclosure, distribution, or copying of any part of this message is 
 prohibited.
 
 
 -Original

Re: [EVDL] Bicycle battery

2015-06-18 Thread EVDL Administrator via EV

On 18 Jun 2015 at 11:43, Cor van de Water via EV wrote:

 That pack is very nicely top-balanced and I expect that many more BMSs
 that you are not even aware of in daily appliances such as power tools
 will all top-balance.

One more time.  There is a really good reason that the only place you find 
aversion to BMSes is among EV hobbyists.  

Real world electronics manufacturers -- the ones who build millions of 
laptops, mobile phones, power tools and yes, commercial EVs -- know that you 
don't sell a product with a lithium battery unless it has ample smarts to 
protect the battery, the user, and the manufacturer.  

Trust me, these guys have bean counters looking over their shoulders.  They 
wouldn't be using BMSes if they weren't necessary.  BMSes protect the 
battery from early failure, the user from hazard to life and limb, and the 
manufacturer from the lawyers!

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] Bicycle battery