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  #1  
Old 07-10-2012, 11:06 PM
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Default [EVDL] Lithium concerns

I have a brand new pack of 100 100ah Calb cells.
I am using the Lithiumate Pro BMS.
The cells have never been below 3.1V or above 3.6V.
They only have a few hundred miles on them.
When I take the lid off the pack I smell what must be electrolyte.
This can't be good.
Do I have a cell or cells with a bad vent seal or cracked case?
If that is the case, it will be very hard to find out which cell it is.
I'm pretty sure the cells aren't supposed to vent under normal use.

Thanks for any comments, Al

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  #2  
Old 07-10-2012, 11:35 PM
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Default Re: [EVDL] Lithium concerns

Sometimes the seal on the pole vents under pressure. Big issue is not
the smell but having it sucking humid air back in after the pressure
releases.

You can see the venting when logging the voltage behavior of the cell.
You need to have quite accurate system for good diagnosis but this is
why high-end BMS can detect most of the failure mechanisms before
anything happens. You'll have more than 10.000 miles left on the
venting cell still. No worries.

There must be a mechanical way to detect the venting cell. Hmm..
Smells like a cheap tester business here.

For now.. install a small ventilation device (computer blower, etc.)
to get the vapors out. You'll get head aches if you have to smell it
for too long periods of time.

-akkuJukka


http://www.google.com/profiles/jarviju#about


2012/7/11 Al <xxx@xxx.xxx>:
> I have a brand new pack of 100 100ah Calb cells.
> I am using the Lithiumate Pro BMS.
> The cells have never been below 3.1V or above 3.6V.
> They only have a few hundred miles on them.
> When I take the lid off the pack I smell what must be electrolyte.
> This can't be good.
> Do I have a cell or cells with a bad vent seal or cracked case?
> If that is the case, it will be very hard to find out which cell it is.
> I'm pretty sure the cells aren't supposed to vent under normal use.
>
> Thanks for any comments, Al
>
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  #3  
Old 07-11-2012, 12:55 AM
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Default Re: [EVDL] Lithium concerns

How long do you keep cells at 3.6V?
It may sound strange, but you may be overcharging
the cells by keeping them at 3.6V, because the
charging protocol is to charge them at a certain
current, for example 0.1C (which would be 10A in your case)
but I forget how much it exactly is - see the manufacturer
spec or search the archives, and as soon as the cell reaches
the 3.6V level you should stop charging it.
By keeping it at 3.6 a BMS will over-charge the cell.
It has been contemplated that you may want to lower the
BMS threshold voltage to around 3.45V and possibly you
are not overcharging them when you keep cells at that level.

I am not a Li specialist nor have I played a battery engineer
in a commercial, so do you own due diligence...

For me, the smell tells that at least some of the cells are
being overcharged, so I suggest to lower the (BMS) voltage
or the time they are at the 3.6V level as short as possible.

Search the archives for the full discussion and/or consult
a Li battery specialist.

Success,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Al
Sent: Tuesday, July 10, 2012 8:58 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] Lithium concerns

I have a brand new pack of 100 100ah Calb cells.
I am using the Lithiumate Pro BMS.
The cells have never been below 3.1V or above 3.6V.
They only have a few hundred miles on them.
When I take the lid off the pack I smell what must be electrolyte.
This can't be good.
Do I have a cell or cells with a bad vent seal or cracked case?
If that is the case, it will be very hard to find out which cell it is.
I'm pretty sure the cells aren't supposed to vent under normal use.

Thanks for any comments, Al

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  #4  
Old 07-11-2012, 09:15 AM
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Default Re: [EVDL] Lithium concerns

[quote]Cor van de Water wrote:

> It may sound strange, but you may be overcharging
> the cells by keeping them at 3.6V, because the
> charging protocol is to charge them at a certain
> current, for example 0.1C (which would be 10A in your case)
> but I forget how much it exactly is - see the manufacturer
> spec or search the archives, and as soon as the cell reaches
> the 3.6V level you should stop charging it.
> By keeping it at 3.6 a BMS will over-charge the cell.

This is incorrect. The typical charge protocol for lithium chemistries is a constant current/constant voltage regimen. This involves charging at a high rate until the voltage reaches a target level, then *holding* this level until the current drops below some minimum threshold. This threshold is generally on the order of 0.01CA.

If the cell is not held at the voltage target until the current falls to a low level, then they will not be fully charged. As you note, some people prefer not to fully charge their cells.

Holding the cells at the voltage target for a long time may indeed overcharge the cells, but terminating charge immediately upon reaching the voltage target will, generally, undercharge them.

Cheers,

Roger.


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  #5  
Old 07-11-2012, 01:45 PM
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Default Re: [EVDL] Lithium concerns

Jack Rickard's chart: http://23.21.184.60/evtv-word-press/wp-content/upload=
s/2012/07/CAchargecurve.jpgshows going to 3.6V put 187 Ahr into a 180 Ahr c=
ell, and that continuing to hold 3.6V put in an addition 1.6% capacity (up =
to 190 Ahr). So yes, stopping at 3.6V does slightly undercharge, but not by=
much and that could be safer than trying to run right to the limit (Lithiu=
m is less tolerant of overcharge than lead).



________________________________
From: Roger Stockton <xxx@xxx.xxx>
To: Electric Vehicle Discussion List <xxx@xxx.xxx.edu> =

Sent: Wednesday, July 11, 2012 9:06 AM
Subject: Re: [EVDL] Lithium concerns
=

[quote]Cor van de Water wrote:

> It may sound strange, but you may be overcharging
> the cells by keeping them at 3.6V, because the
> charging protocol is to charge them at a certain
> current, for example 0.1C (which would be 10A in your case)
> but I forget how much it exactly is - see the manufacturer
> spec or search the archives, and as soon as the cell reaches
> the 3.6V level you should stop charging it.
> By keeping it at 3.6 a BMS will over-charge the cell.

This is incorrect. The typical charge protocol for lithium chemistries i=
s a constant current/constant voltage regimen. This involves charging at=
a high rate until the voltage reaches a target level, then *holding* this =
level until the current drops below some minimum threshold. This thresho=
ld is generally on the order of 0.01CA.

If the cell is not held at the voltage target until the current falls to a =
low level, then they will not be fully charged. As you note, some people=
prefer not to fully charge their cells.

Holding the cells at the voltage target for a long time may indeed overchar=
ge the cells, but terminating charge immediately upon reaching the voltage =
target will, generally, undercharge them.

Cheers,

Roger.


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  #6  
Old 07-11-2012, 03:05 PM
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Default Re: [EVDL] Lithium concerns

Well... Hysteresis is there and you can maintain the CV phase forever.
It will keep the cell at full.

We did single cell charger programs for large prismatic cells with
CC/CV curve in a way that when the LFP cell reaches 4.3V and current
less then 2A the charger goes to 'wait' -mode. Charger waits for few
minutes or longer (depends on the selected program) and sets the
voltage at the terminals as CV point. I_max was set to 1A. Then it
kept cell fully charged until it was removed from the charging system.
This is the way how we initiated cells after long transport.
Systematically all cells. (There were failsafes too to detect bad
cells)

Doing this (not exactly as described above but close) after few years
of operation it refreshens the cell. Regains capacity.

You can use the LiFePO4 cells nearly all the ways you can and they'll
provide the lifetime of the conversion.

-akkuJukka

http://www.google.com/profiles/jarviju#about


2012/7/11 David Dymaxion <xxx@xxx.xxx>:
> Jack Rickard's chart: http://23.21.184.60/evtv-word-press/wp-content/uploads/2012/07/CAchargecurve.jpgshows going to 3.6V put 187 Ahr into a 180 Ahr cell, and that continuing to hold 3.6V put in an addition 1.6% capacity (up to 190 Ahr). So yes, stopping at 3.6V does slightly undercharge, but not by much and that could be safer than trying to run right to the limit (Lithium is less tolerant of overcharge than lead).
>
>
>
> ________________________________
> From: Roger Stockton <xxx@xxx.xxx>
> To: Electric Vehicle Discussion List <xxx@xxx.xxx.edu>
> Sent: Wednesday, July 11, 2012 9:06 AM
> Subject: Re: [EVDL] Lithium concerns
>
[quote]> Cor van de Water wrote:
>
>> It may sound strange, but you may be overcharging
>> the cells by keeping them at 3.6V, because the
>> charging protocol is to charge them at a certain
>> current, for example 0.1C (which would be 10A in your case)
>> but I forget how much it exactly is - see the manufacturer
>> spec or search the archives, and as soon as the cell reaches
>> the 3.6V level you should stop charging it.
>> By keeping it at 3.6 a BMS will over-charge the cell.
>
> This is incorrect. The typical charge protocol for lithium chemistries is a constant current/constant voltage regimen. This involves charging at a high rate until the voltage reaches a target level, then *holding* this level until the current drops below some minimum threshold. This threshold is generally on the order of 0.01CA.
>
> If the cell is not held at the voltage target until the current falls to a low level, then they will not be fully charged. As you note, some people prefer not to fully charge their cells.
>
> Holding the cells at the voltage target for a long time may indeed overcharge the cells, but terminating charge immediately upon reaching the voltage target will, generally, undercharge them.
>
> Cheers,
>
> Roger.
>
>
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  #7  
Old 07-11-2012, 05:55 PM
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Default Re: [EVDL] Lithium concerns

[quote]David Dymaxion wrote:

> Jack Rickard's chart: <http://23.21.184.60/evtv-word-press/wp-
> content/uploads/2012/07/CAchargecurve.jpg> shows going to 3.6V put 187 Ahr
> into a 180 Ahr cell, and that continuing to hold 3.6V put in an addition
> 1.6% capacity (up to 190 Ahr). So yes, stopping at 3.6V does slightly
> undercharge, but not by much and that could be safer than trying to run
> right to the limit (Lithium is less tolerant of overcharge than lead).

I don't follow Jack Rickard, so I apologise if he posted other charts for this test that I am unaware of, however, this chart is largely meaningless on its own.

The 180Ah cell was charged at 100A until 3.6V, then held there until the current tapered to 10A. 10A is not a normal charge termination level for a cell this size. 10A is about 5.5% of the rated capacity; a typical charge termination criteria might be 1-2% of the rated capacity: 1.8-3.6A. Obviously, more Ah would be returned to the cell during the CV phase if the CV phase were actually maintained to the proper point instead of being terminated arbitrarily early.

More importantly, it is not particularly relevant how many Ah are returned to the battery; what is more significant is the Ah that can be removed from the battery on the subsequent discharge. If terminating the charge at 3.6V and 10A yields 10Ah less than terminating it at 3.6V and 4A, then stopping at 10A has undercharged the cell. If stopping the charge at 3.6V and 2A doesn't yield any more capacity upon discharge than when charge is stopped at 4A, then continuing beyond 4A is probably overcharging the cell and would seem pointless. (Though Jukka may well point out that there is some benefit to the chemistry achieved by doing this at least once in a while ;^)

Information for the specific cell tested in this plot, CA180FI, is not readily available online, however, it does appear that the discharge capacity should be quite near to 200Ah (dependant upon discharge rate, of course), so it is quite possible that even the 190Ah returned in Jack's test did not fully recharge the cell.

Unfortunately, without knowing the discharge Ah before and after this charge cycle, it really isn't possible to determine just how near to fully charged the cell was when the charge was terminated.

Cheers,

Roger.


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  #8  
Old 07-11-2012, 10:05 PM
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Default Re: [EVDL] Lithium concerns

[quote] Roger Stockton <xxx@xxx.xxx> wrote:
> a typical charge termination criteria might be 1-2% of the rated capacity: 1.8-3.6A.

Roger,

You've made a similar statement before but the printed documentation
which came with my TS cells says 0.01-0.05C as the termination
current. 0.05C is therefore a perfectly appropriate termination
current to fully charge a cell.

Also, while the extra 10Ah put into the 180Ah cell doesn't necessarily
mean that it is or isn't available for subsequent discharge Jacks test
does show that there is very little to gain by holding the cell at
that voltage. Besides, if you can't put it in, you can't take it out.

FWIW, In my own rudimentary test on a TS-LFP100AHA cell charged to
3.451V ending at 476mA and then charged up to 3.650V ending at 420mA I
was only able to put 1.01Ah (1.0056Ah was my calculated measurement
but I don't think it is really that precise) into the cell. Even if
all of that became useable it is still barely 1% of the cell's
capacity. I've wondered how much of that is actually just the
capacitance of the cell.

--
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com

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  #9  
Old 07-11-2012, 11:35 PM
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Default [EVDL] Lithium concerns

I just opened up several boxes of CA180 cells and the tested capacity from
CALB was showing from 181Ah to 198Ah. This is a small sample but I was
surprised to see this much variation in capacity.

The CA100 cells run fairly close to the SE100 between 108Ah to 112Ah

Don Blazer


In a message dated 7/11/2012 9:11:55 P.M. Pacific Daylight Time,
xxx@xxx.xxx.edu writes:

Information for the specific cell tested in this plot, CA180FI, is not
readily available online, however, it does appear that the discharge capacity
should be quite near to 200Ah (dependant upon discharge rate, of course), so
it is quite possible that even the 190Ah returned in Jack's test did not
fully recharge the cell.

Unfortunately, without knowing the discharge Ah before and after this
charge cycle, it really isn't possible to determine just how near to fully
charged the cell was when the charge was terminated.

Cheers,

Roger.

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  #10  
Old 07-11-2012, 11:45 PM
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Default Re: [EVDL] Lithium concerns

[quote]David Nelson wrote:

> You've made a similar statement before but the printed documentation
> which came with my TS cells says 0.01-0.05C as the termination
> current. 0.05C is therefore a perfectly appropriate termination
> current to fully charge a cell.

Any chance you could post a scan of this document online, or send me a copy by private email?

I can't lay my hands on a document specifying an end of charge criteria for Thundersky cells at the moment, but one I have handy for GAIA cells states I<= 0.01CA. LiFeBatt shows termination at 0.02CA; A123 shows 0.02CA (0.05A for a 2.3Ah cell).

Just because Thundersky printed 0.01-0.05CA in their literature doesn't make 0.05CA an appropriate termination to fully charge their cell, nevermind anyone else's. To be able to make that statement we'd need to cycle a cell to 100%DOD and see if we get the same capacity when charging is terminated at 0.05CA as a 0.01CA. Do you charge your cells to the charge voltage recommended in the Thundersky literature? Perhaps if you do, then 0.05CA might be an appropriate termination criteria. ;^>

> Also, while the extra 10Ah put into the 180Ah cell doesn't necessarily
> mean that it is or isn't available for subsequent discharge Jacks test
> does show that there is very little to gain by holding the cell at
> that voltage. Besides, if you can't put it in, you can't take it out.

Yes and no. Yes that if you can't put the energy in, you can't get it back out. No that Jack's test shows anything particularly meaningful. Looking more closely at his plot, not only do we not know how much energy was removed from the cell (and therefore the minimum that must be returned), but Jack's plot doesn't even start at 0Ah. Notice that the Ah axis starts at 104Ah; 190Ah has not been returned to the cell, instead, Jack has measured what he did put into the cell and has added that to what he thinks was still remaining in the cell at the start of charge. And, without data from a subsequent discharge we still don't know if the cell was fully charged or not.

> FWIW, In my own rudimentary test on a TS-LFP100AHA cell charged to
> 3.451V ending at 476mA and then charged up to 3.650V ending at 420mA I
> was only able to put 1.01Ah (1.0056Ah was my calculated measurement
> but I don't think it is really that precise) into the cell. Even if
> all of that became useable it is still barely 1% of the cell's
> capacity.

This is a totally different issue. You have demonstrated that little additional energy can be delivered to the cell by using a 3.65V charge voltage vs 3.451V charge voltage, provided that the CV level is held until the current is less than 0.005CA. This does not shed any light on how full the cell would be if charge were terminated immediately upon reaching the 3.451V or 3.65V target vs holding the CV level until the current tapers to a small fraction of the rated CA.

If you have the Thundersky manual, look at the plots showing the charge characteristics of the LFP cells (A-5, page 15 in my copy). It shows that charging at 0.5CA to 4.3V returns only about 70-75% of the capacity; the rest is returned during the CV phase while holding that voltage and letting the current taper off. These plots look calculated rather than measured to me, so I wouldn't put too much faith in the exact amount of capacity returned when the voltage target is reached, but the point is merely that the cell is *some amount* less than 100% charged when it reaches the voltage target, and terminating the charge immediately at this point will undercharge the cell by some amount.

The original statement I was correcting is that manufacturers recommend terminating the charge immediately upon reaching the voltage target and that continuing to charge at this voltage would overcharge the cells; this is *incorrect* - every cell manufacturer I have documentation for recommends a CC/CV profile, and while not all of them provide charge termination criteria for the CV phase, those that do largely specify the current falling below 0.01-0.02CA as indicative of having reached 100% state of charge.

Cheers,

Roger.


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