Lithium LiFePO4 charging question

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Lithium LiFePO4 charging question

Theoldcars@aol.com
Hello David
 
You can speculate on voltage at top of charge as your assuming or  accept
it is the reduced range in capacity that has been shown to increase  cycle
life. This is why the reduced capacity percentage out of a  cell is
recommended by manufacturers for maximum cycle life.
 
In 2007 I bought from A123 almost 100,000 dollars in cells  when A123 were
not selling to the public. I have been following LiFePo4  with a lot of
interest for many years.  What I am seeing is the same data  then applies today.
Even today's Nissan Leaf has an OEM recommendation  of charging to 80% SOC.
Obviously Nissan wanted as many as possible to charge to  80% because they
have that setting built into the Leaf. The owners  manual states if you
don't need the range to use 80% SOC setting.
 
It is the limits of a cell where the most degradation will occur. It is a  
mistake to assume because the voltage curve does not change at top of  
charge your still causing the least amount of impact. Your only  considering
voltage and overlooking capacity itself does impact cycle  life.
 
I normally would not push the issue but until a manufacturer states  
otherwise it is best not to assume based on voltage. Your going to have better  
results since your not deep discharging your pack. All conditions being the
same  your results would most likely be even further improved if you stay out
of the  top 20% of the SOC.
 
With NiMH batteries the same 40 to 80% SOC greatly increases cycle  life as
well. A totally different chemistry but it is interesting to note a  
reduced range of capacity has the same results. Far greater cycle life.
 
Don Blazer
 
 
 
In a message dated 9/29/2012 12:01:38 A.M. Pacific Daylight Time,  
[hidden email] writes:

Message:  16
Date: Fri, 28 Sep 2012 21:02:44 -0700
From: David Nelson  <[hidden email]>
Subject: Re: [EVDL] Lithium LiFePO4 charging  question
To: Electric Vehicle Discussion List  <[hidden email]>
Message-ID:
<CALxN3-g_XdNT0PWjpvPuBhDTdwOqgUh7xy94AZ0Q=[hidden email]>
Content-Type:  text/plain; charset=ISO-8859-1

Given that the voltage curve is really  flat all the way to 95-98% I
doubt that you will see much benefit staying  below 95%. According to a
NASA study I read all lithium cells last longer  if they are not kept
at 100% SOC but if they are charged just before they  are needed. I
have gone to only charging every few days depending on need  and then
only starting the charge cycle where it will finish just before  I
leave in the morning. I charge to 98-99% SOC so my cells never  sit
long in that SOC range. I also generally recharge when my pack  is
around the 50% SOC point. Unfortunately it will take me several  more
years to know how the pack does with this type of  treatment.

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Re: Lithium LiFePO4 charging question

Cruisin
Don, I believe the Leaf restricts the charge to 80%, only when charging at level 3 due to the high charging rate.
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Re: Lithium LiFePO4 charging question

David Nelson-5
In reply to this post by Theoldcars@aol.com
Note that I did NOT say that there would be NO benefit staying below
95% I said that there wouldn't be much benefit. The rate of
electrolyte break down is faster at higher potentials in the cell.
Staying out of or low in the upper voltage knee of a LiFePO4 cell will
extend its life: cycle and calendar. Whether the trade off in a
LiFePO4 cell to not use the upper 15-20% of the SOC range and have
shorter vehicle range or to use that region and have a longer range is
something to be considered. Do not forget that there are basically two
life factors to consider, cycle life is only one of them. Also, I was
responding only with respect to LiFePO4 cells not LiMn cells like used
in the LEAF. While they are similar they are not identical.

If you have data showing what happens to calendar life and cycle life
when using different SOC ranges then please let us know what you are
seeing. Increasing the cycle life of a LiMn cell by 100 cycles is a
significant improvement but increasing the cycle life of a LiFePO4
cell by 100 cycles is not nearly as significant given the
significantly greater numbers of cycles LiFePO4 is projected to have
over LiMn.

In the case of my 200Ah LiFePO4 pack, it has only delivered a little
over 32,000Ah since January 2010. At that rate the calendar life will
be a more significant factor. A few cycles shorter will be lost in the
noise.

On Sat, Sep 29, 2012 at 10:41 AM,  <[hidden email]> wrote:

> Hello David
>
> You can speculate on voltage at top of charge as your assuming or  accept
> it is the reduced range in capacity that has been shown to increase  cycle
> life. This is why the reduced capacity percentage out of a  cell is
> recommended by manufacturers for maximum cycle life.
>
> In 2007 I bought from A123 almost 100,000 dollars in cells  when A123 were
> not selling to the public. I have been following LiFePo4  with a lot of
> interest for many years.  What I am seeing is the same data  then applies today.
> Even today's Nissan Leaf has an OEM recommendation  of charging to 80% SOC.
> Obviously Nissan wanted as many as possible to charge to  80% because they
> have that setting built into the Leaf. The owners  manual states if you
> don't need the range to use 80% SOC setting.
>
> It is the limits of a cell where the most degradation will occur. It is a
> mistake to assume because the voltage curve does not change at top of
> charge your still causing the least amount of impact. Your only  considering
> voltage and overlooking capacity itself does impact cycle  life.
>
> I normally would not push the issue but until a manufacturer states
> otherwise it is best not to assume based on voltage. Your going to have better
> results since your not deep discharging your pack. All conditions being the
> same  your results would most likely be even further improved if you stay out
> of the  top 20% of the SOC.
>
> With NiMH batteries the same 40 to 80% SOC greatly increases cycle  life as
> well. A totally different chemistry but it is interesting to note a
> reduced range of capacity has the same results. Far greater cycle life.
>
> Don Blazer
>
>
>
> In a message dated 9/29/2012 12:01:38 A.M. Pacific Daylight Time,
> [hidden email] writes:
>
> Message:  16
> Date: Fri, 28 Sep 2012 21:02:44 -0700
> From: David Nelson  <[hidden email]>
> Subject: Re: [EVDL] Lithium LiFePO4 charging  question
> To: Electric Vehicle Discussion List  <[hidden email]>
> Message-ID:
> <CALxN3-g_XdNT0PWjpvPuBhDTdwOqgUh7xy94AZ0Q=[hidden email]>
> Content-Type:  text/plain; charset=ISO-8859-1
>
> Given that the voltage curve is really  flat all the way to 95-98% I
> doubt that you will see much benefit staying  below 95%. According to a
> NASA study I read all lithium cells last longer  if they are not kept
> at 100% SOC but if they are charged just before they  are needed. I
> have gone to only charging every few days depending on need  and then
> only starting the charge cycle where it will finish just before  I
> leave in the morning. I charge to 98-99% SOC so my cells never  sit
> long in that SOC range. I also generally recharge when my pack  is
> around the 50% SOC point. Unfortunately it will take me several  more
> years to know how the pack does with this type of  treatment.
>
> -------------- next part --------------
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> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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--
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com
http://www.levforum.com

_______________________________________________
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| Please take those discussions elsewhere.  Thanks.
|
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| Multiple-address or CCed messages may be rejected.
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Re: Lithium LiFePO4 charging question

Mike Nickerson
Since I posted the original question, I feel some right to redirect the
conversation.  I have read responses saying that staying within the range of
40-80% SOC will lead to best life of the cells.  OK, makes sense.

Since I use 50% of the capacity on each trip, I can't stay within 40-80%.
The best I could do is 40-90% or 30-80% SOC.

Which of the two cases would be better for long life of the LiFePO4 cells?  

The difference in range is generally not important.  I only need 50% for the
drive home most of the time.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of David Nelson
> Sent: Sunday, September 30, 2012 12:10 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Lithium LiFePO4 charging question
>
> Note that I did NOT say that there would be NO benefit staying below 95% I
> said that there wouldn't be much benefit. The rate of electrolyte break
down
> is faster at higher potentials in the cell.
> Staying out of or low in the upper voltage knee of a LiFePO4 cell will
extend
> its life: cycle and calendar. Whether the trade off in a
> LiFePO4 cell to not use the upper 15-20% of the SOC range and have shorter
> vehicle range or to use that region and have a longer range is something
to
> be considered. Do not forget that there are basically two life factors to
> consider, cycle life is only one of them. Also, I was responding only with
> respect to LiFePO4 cells not LiMn cells like used in the LEAF. While they
are
> similar they are not identical.
>
> If you have data showing what happens to calendar life and cycle life when
> using different SOC ranges then please let us know what you are seeing.
> Increasing the cycle life of a LiMn cell by 100 cycles is a significant
> improvement but increasing the cycle life of a LiFePO4 cell by 100 cycles
is not
> nearly as significant given the significantly greater numbers of cycles
LiFePO4

> is projected to have over LiMn.
>
> In the case of my 200Ah LiFePO4 pack, it has only delivered a little over
> 32,000Ah since January 2010. At that rate the calendar life will be a more
> significant factor. A few cycles shorter will be lost in the noise.
>
> On Sat, Sep 29, 2012 at 10:41 AM,  <[hidden email]> wrote:
> > Hello David
> >
> > You can speculate on voltage at top of charge as your assuming or
> > accept it is the reduced range in capacity that has been shown to
> > increase  cycle life. This is why the reduced capacity percentage out
> > of a  cell is recommended by manufacturers for maximum cycle life.
> >
> > In 2007 I bought from A123 almost 100,000 dollars in cells  when A123
> > were not selling to the public. I have been following LiFePo4  with a
> > lot of interest for many years.  What I am seeing is the same data  then
> applies today.
> > Even today's Nissan Leaf has an OEM recommendation  of charging to 80%
> SOC.
> > Obviously Nissan wanted as many as possible to charge to  80% because
> > they have that setting built into the Leaf. The owners  manual states
> > if you don't need the range to use 80% SOC setting.
> >
> > It is the limits of a cell where the most degradation will occur. It
> > is a mistake to assume because the voltage curve does not change at
> > top of charge your still causing the least amount of impact. Your only
> > considering voltage and overlooking capacity itself does impact cycle
life.

> >
> > I normally would not push the issue but until a manufacturer states
> > otherwise it is best not to assume based on voltage. Your going to
> > have better results since your not deep discharging your pack. All
> > conditions being the same  your results would most likely be even
> > further improved if you stay out of the  top 20% of the SOC.
> >
> > With NiMH batteries the same 40 to 80% SOC greatly increases cycle
> > life as well. A totally different chemistry but it is interesting to
> > note a reduced range of capacity has the same results. Far greater cycle
> life.
> >
> > Don Blazer
> >
> >
> >
> > In a message dated 9/29/2012 12:01:38 A.M. Pacific Daylight Time,
> > [hidden email] writes:
> >
> > Message:  16
> > Date: Fri, 28 Sep 2012 21:02:44 -0700
> > From: David Nelson  <[hidden email]>
> > Subject: Re: [EVDL] Lithium LiFePO4 charging  question
> > To: Electric Vehicle Discussion List  <[hidden email]>
> > Message-ID:
> > <CALxN3-
> g_XdNT0PWjpvPuBhDTdwOqgUh7xy94AZ0Q=[hidden email]>
> > Content-Type:  text/plain; charset=ISO-8859-1
> >
> > Given that the voltage curve is really  flat all the way to 95-98% I
> > doubt that you will see much benefit staying  below 95%. According to
> > a NASA study I read all lithium cells last longer  if they are not
> > kept at 100% SOC but if they are charged just before they  are needed.
> > I have gone to only charging every few days depending on need  and
> > then only starting the charge cycle where it will finish just before
> > I leave in the morning. I charge to 98-99% SOC so my cells never  sit
> > long in that SOC range. I also generally recharge when my pack  is
> > around the 50% SOC point. Unfortunately it will take me several  more
> > years to know how the pack does with this type of  treatment.
> >
> > -------------- next part -------------- An HTML attachment was
> > scrubbed...
> > URL:
> > http://lists.sjsu.edu/mailman/private/ev/attachments/20120929/b103e907
> > /attachment.html
> _______________________________________________
> > | Moratorium on drag racing discussion is in effect.
> > | Please take those discussions elsewhere.  Thanks.
> > |
> > | REPLYING: address your message to [hidden email] only.
> > | Multiple-address or CCed messages may be rejected.
> > | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > | OTHER HELP: http://evdl.org/help/
> > | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>
>
>
> --
> David D. Nelson
> http://evalbum.com/1328
> http://2003gizmo.blogspot.com
> http://www.levforum.com
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

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|
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Re: Lithium LiFePO4 charging question

David Nelson-5
Given that the cycle life is projected to be significantly higher with a
70% DOD as compared to an 80% DOD you may want to stay above 65% DOD to
give your self a little extra room at the bottom and also to account for
the pack capacity decreasing over time. So far no one has provided hard
evidence for LiFePO4 cells staying below 80% SOC. Unless you have an Ah
counter attached to your charger or you estimate time to 80-90% SOC on
charge and stop the charger you will likely find it easier to charge above
90% SOC where the voltage is climbing more rapidly to set your cutoff point
for charging. Again, unless someone has hard evidence for the life, both
calendar and cycle, being significantly longer by staying below 80% SOC you
may find it not worth the hassle.

On Sunday, September 30, 2012, Mike Nickerson wrote:

> Since I posted the original question, I feel some right to redirect the
> conversation.  I have read responses saying that staying within the range
> of
> 40-80% SOC will lead to best life of the cells.  OK, makes sense.
>
> Since I use 50% of the capacity on each trip, I can't stay within 40-80%.
> The best I could do is 40-90% or 30-80% SOC.
>
> Which of the two cases would be better for long life of the LiFePO4 cells?
>
> The difference in range is generally not important.  I only need 50% for
> the
> drive home most of the time.
>
> Mike
>
> > -----Original Message-----
> > From: [hidden email] [mailto:[hidden email]] On
> > Behalf Of David Nelson
> > Sent: Sunday, September 30, 2012 12:10 PM
> > To: Electric Vehicle Discussion List
> > Subject: Re: [EVDL] Lithium LiFePO4 charging question
> >
> > Note that I did NOT say that there would be NO benefit staying below 95%
> I
> > said that there wouldn't be much benefit. The rate of electrolyte break
> down
> > is faster at higher potentials in the cell.
> > Staying out of or low in the upper voltage knee of a LiFePO4 cell will
> extend
> > its life: cycle and calendar. Whether the trade off in a
> > LiFePO4 cell to not use the upper 15-20% of the SOC range and have
> shorter
> > vehicle range or to use that region and have a longer range is something
> to
> > be considered. Do not forget that there are basically two life factors to
> > consider, cycle life is only one of them. Also, I was responding only
> with
> > respect to LiFePO4 cells not LiMn cells like used in the LEAF. While they
> are
> > similar they are not identical.
> >
> > If you have data showing what happens to calendar life and cycle life
> when
> > using different SOC ranges then please let us know what you are seeing.
> > Increasing the cycle life of a LiMn cell by 100 cycles is a significant
> > improvement but increasing the cycle life of a LiFePO4 cell by 100 cycles
> is not
> > nearly as significant given the significantly greater numbers of cycles
> LiFePO4
> > is projected to have over LiMn.
> >
> > In the case of my 200Ah LiFePO4 pack, it has only delivered a little over
> > 32,000Ah since January 2010. At that rate the calendar life will be a
> more
> > significant factor. A few cycles shorter will be lost in the noise.
> >
> > On Sat, Sep 29, 2012 at 10:41 AM,  <[hidden email]> wrote:
> > > Hello David
> > >
> > > You can speculate on voltage at top of charge as your assuming or
> > > accept it is the reduced range in capacity that has been shown to
> > > increase  cycle life. This is why the reduced capacity percentage out
> > > of a  cell is recommended by manufacturers for maximum cycle life.
> > >
> > > In 2007 I bought from A123 almost 100,000 dollars in cells  when A123
> > > were not selling to the public. I have been following LiFePo4  with a
> > > lot of interest for many years.  What I am seeing is the same data
>  then
> > applies today.
> > > Even today's Nissan Leaf has an OEM recommendation  of charging to 80%
> > SOC.
> > > Obviously Nissan wanted as many as possible to charge to  80% because
> > > they have that setting built into the Leaf. The owners  manual states
> > > if you don't need the range to use 80% SOC setting.
> > >
> > > It is the limits of a cell where the most degradation will occur. It
> > > is a mistake to assume because the voltage curve does not change at
> > > top of charge your still causing the least amount of impact. Your only
> > > considering voltage and overlooking capacity itself does impact cycle
> life.
> > >
> > > I normally would not push the issue but until a manufacturer states
> > > otherwise it is best not to assume based on voltage. Your going to
> > > have better results since your not deep discharging your pack. All
> > > conditions being the same  your results would most likely be even
> > > further improved if you stay out of the  top 20% of the SOC.
> > >
> > > With NiMH batteries the same 40 to 80% SOC greatly increases cycle
> > > life as well. A totally different chemistry but it is interesting to
> > > note a reduced range of capacity has the same results. Far greater
> cycle
> > life.
> > >
> > > Don Blazer
> > >
> > >
> > >
> > > In a message dated 9/29/2012 12:01:38 A.M. Pacific Daylight Time,
> > > [hidden email] writes:
> > >
> > > Message:  16
> > > Date: Fri, 28 Sep 2012 21:02:44 -0700
> > > From: David Nelson  <[hidden email]>
> > > Subject: Re: [EVDL] Lithium LiFePO4 charging  question
>


--
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com
http://www.levforum.com
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Re: Lithium LiFePO4 charging question

David Nelson-5
I see that Don's response with data from his memory some how got
disconnected from this thread. There is some data for you. What ever you
do, keep the best data you can on your pack so that someday we will have
some real world data to work with or just confuse things even more. :)

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