# [EVDL] leaf battery balancing



## EVDL List (Jul 27, 2007)

I think the LiMn cells that Nissan uses have a steeper charge curve than the
LiFePO4, so there are more pronounced voltage changes at lower SOC. I doubt
Nissan ever charges to 100% since even with LiFePO4 balancing can be done
below that. It might be necessary to occasionally charge to higher than 80%
for full balancing, I don't know what Nissan recommends regarding that, but
obviously they feel 80% is the way to go for longer life.




> Peri Hartman wrote:
> >
> > Hi. Does anyone know what the Leaf does for battery balancing. My guess is
> > that at the end of the charge cycle, the charger "tops off" the cells to
> ...


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## EVDL List (Jul 27, 2007)

They do recommend charging to 80%. I haven't seen anything any the manuals
about battery balancing, but I certainly expect they have addressed it. 

So, you're saying that, depending on the chemistry, it might be possible to
balance at 80%?

Peri 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of AMPhibian
Sent: 26 June, 2011 8:44 AM
To: [email protected]
Subject: Re: [EVDL] leaf battery balancing

I think the LiMn cells that Nissan uses have a steeper charge curve than the
LiFePO4, so there are more pronounced voltage changes at lower SOC. I doubt
Nissan ever charges to 100% since even with LiFePO4 balancing can be done
below that. It might be necessary to occasionally charge to higher than 80%
for full balancing, I don't know what Nissan recommends regarding that, but
obviously they feel 80% is the way to go for longer life.




> Peri Hartman wrote:
> >
> > Hi. Does anyone know what the Leaf does for battery balancing. My
> > guess is that at the end of the charge cycle, the charger "tops off"
> ...


----------



## EVDL List (Jul 27, 2007)

Yes, quite a few people run without a BMS. Most, however, balance
their pack at the start either by charging every cell to something
like 3.6V (or just parallel the whole set and charge to 3.6-4V and
hold it there for a while) or by discharging the cells to 2.8-3V open
circuit voltage.

Given the voltages you listed for the cells before you started you
probably killed one of the cells due to over charging given that one
was at 3.3V while the others were at 3.1-3.2V. That is potentially a
big SOC difference. That is if these are LiFePO4 cells you are using.

If your son likes to run it until the pack is nearly dead I would
recommend you bottom balance the pack so it will go flat all at once
and not have three cells drive the 4th into a reverse voltage
situation.

On Sun, Jun 26, 2011 at 11:28 AM, Douglas A. Stansfield


> <[email protected]> wrote:
> > I am wondering about this subject as well. Recently, I took 8, 40Ah li=
> thium
> > cells and converted over a small motorcycle for my son and didn't use a B=
> ...


----------



## EVDL List (Jul 27, 2007)

> Douglas A. Stansfield wrote:
> > I am wondering about this subject as well. Recently, I took 8, 40Ah lithium
> > cells and converted over a small motorcycle for my son and didn't use a BMS.
> > All the cells were off of each other by 1 to 2 tenths of a percent. 3.1,
> ...


----------



## EVDL List (Jul 27, 2007)

> Douglas A. Stansfield wrote:
> 
> > I am wondering about this subject as well. Recently, I took 8, 40Ah lithium
> > cells and converted over a small motorcycle for my son and didn't use a BMS.
> ...


----------



## EVDL List (Jul 27, 2007)

Corbin, David and Willie,

Thanks. The cells have been going strong for a month now in the 24v tiny
cycle. He isn't really driving the cells to death each trip but does spend
some time on it and likes it a lot.

Still seems like the pack is balanced all on its own after this long. I'm
not sure if it was the 3.3v one that died. It may or may not have. I
wasn't keeping that close attention to it. These are only $55 to $60
cells, not $230 cells. Shame to lose one but since my wife got the bike
with a gas motor for $10 from a garage sale it was worth the fun building it
with my son. He enjoyed building it with me and now has a great bike to
ride on.

Happy EVing everyone!


Sincerely;


Douglas A. Stansfield
Vice President, www.ECEDRA.com 
President, Trans Atlantic Electric Conversions LLC
www.TransAtlanticElectricConversions.com 
President, NJ Electric Auto Association
Member, Board of Directors, Electric Auto Association




-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of corbin dunn
Sent: Sunday, June 26, 2011 7:29 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] leaf battery balancing




> Douglas A. Stansfield wrote:
> 
> > I am wondering about this subject as well. Recently, I took 8, 40Ah
> > lithium cells and converted over a small motorcycle for my son and didn't
> ...


----------



## EVDL List (Jul 27, 2007)

To really check the balance measure each individual cell voltage just
before the charger shuts off while the current is really low. If the
cell voltage is much over 3.625v I would recommend you discharge the
top one a little bit. Also, if you can turn down the ending voltage a
little to protect the cells from over charging. Over charging can
cause a very hot fire. Did you watch the short video Steve posted a
while ago?

On Sunday, June 26, 2011, Douglas A. Stansfield
<[email protected]> wrote:
> Corbin, David and Willie,
>
> Thanks. The cells have been going strong for a month now in the 24v ti=
ny
> cycle. He isn't really driving the cells to death each trip but does s=
pend
> some time on it and likes it a lot.
>
> Still seems like the pack is balanced all on its own after this long. =
I'm
> not sure if it was the 3.3v one that died. It may or may not have. I
> wasn't keeping that close attention to it. These are only $55 t=
o $60
> cells, not $230 cells. Shame to lose one but since my wife got the bike
> with a gas motor for $10 from a garage sale it was worth the fun building=
it
> with my son. He enjoyed building it with me and now has a great bike to
> ride on.
>
> Happy EVing everyone!
>
>
> Sincerely;
>
>
> Douglas A. Stansfield
> Vice President, www.ECEDRA.com
> President, Trans Atlantic Electric Conversions LLC
> www.TransAtlanticElectricConversions.com
> President, NJ Electric Auto Association
> Member, Board of Directors, Electric Auto Association
>
>
>
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On Beh=
alf
> Of corbin dunn
> Sent: Sunday, June 26, 2011 7:29 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] leaf battery balancing
>
>
>


> Douglas A. Stansfield wrote:
> >
> >> I am wondering about this subject as well. Recently, I took 8, 40Ah
> >> lithium cells and converted over a small motorcycle for my son and didn't
> ...


----------



## EVDL List (Jul 27, 2007)

David,

Thanks for the advice. No I didn't see any video post. I don't always get
a chance to read every post on the EVDL unfortunately but I do like to keep
up when I can. =


I just went out to the garage and looked to see what the voltages were on
the individual cells. Every single cell was at 3.3v. and the pack was at
26.4v and the charger is a 1.5 amp scooter charger up to 29v. or 3.6v per
cell. My son didn't ride the bike today so the charger had already shut off
prior to me checking the cells.

So far, beside the one cell not working, the rest seem to be doing very
well.

Thanks for the advice. I do appreciate it.


Sincerely;


Douglas A. Stansfield
Vice President, www.ECEDRA.com =

President, Trans Atlantic Electric Conversions LLC
www.TransAtlanticElectricConversions.com =

President, NJ Electric Auto Association
Member, Board of Directors, Electric Auto Association






-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of David Nelson
Sent: Sunday, June 26, 2011 11:10 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] leaf battery balancing

To really check the balance measure each individual cell voltage just before
the charger shuts off while the current is really low. If the cell voltage
is much over 3.625v I would recommend you discharge the top one a little
bit. Also, if you can turn down the ending voltage a little to protect the
cells from over charging. Over charging can cause a very hot fire. Did you
watch the short video Steve posted a while ago?

On Sunday, June 26, 2011, Douglas A. Stansfield
<[email protected]> wrote:
> Corbin, David and Willie,
>
> Thanks. The cells have been going strong for a month now in the 24v =

> tiny cycle. He isn't really driving the cells to death each trip but =

> does spend some time on it and likes it a lot.
>
> Still seems like the pack is balanced all on its own after this long. =

> I'm not sure if it was the 3.3v one that died. It may or may not =

> have. I wasn't keeping that close attention to it. These are=
only =

> $55 to $60 cells, not $230 cells. Shame to lose one but since my wife =

> got the bike with a gas motor for $10 from a garage sale it was worth =

> the fun building it with my son. He enjoyed building it with me and =

> now has a great bike to ride on.
>
> Happy EVing everyone!
>
>
> Sincerely;
>
>
> Douglas A. Stansfield
> Vice President, www.ECEDRA.com
> President, Trans Atlantic Electric Conversions LLC =

> www.TransAtlanticElectricConversions.com
> President, NJ Electric Auto Association Member, Board of Directors, =

> Electric Auto Association
>
>
>
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On =

> Behalf Of corbin dunn
> Sent: Sunday, June 26, 2011 7:29 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] leaf battery balancing
>
>
>


> Douglas A. Stansfield wrote:
> >
> >> I am wondering about this subject as well. Recently, I took 8, 40Ah =
> 
> ...


----------



## EVDL List (Jul 27, 2007)

I did a little bit of testing. I found that once bottom balanced, the cells 
would stay very close in Voltage without a BMS. I intentionally went past spec 
max current, and vented a couple of cells -- those cells did not stay in balance 
then! You can see the raw data on my web page, 
http://ExplodingDinosaurs.com/9electric/celltest .




________________________________
From: Douglas A. Stansfield <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Sun, June 26, 2011 12:28:42 PM
Subject: Re: [EVDL] leaf battery balancing

I am wondering about this subject as well. Recently, I took 8, 40Ah lithium
cells and converted over a small motorcycle for my son and didn't use a BMS.
All the cells were off of each other by 1 to 2 tenths of a percent. 3.1,
3.2, 3.3, 3.1 etc. I had an old 24v battery charger from some other kids
toy and hooked that up to charge the batteries. After two rides one battery
was dead so I swapped it out with another one. Then my son rode it every
day for two weeks. I decided to check the batteries after it was charged
the other day and all the cells were resting at 3.2v. They balanced
themselves? The charger brings the total pack voltage up to 29v or 3.6v
each. Seems to work really well. No serious issues at all. My son is
addicted to it and runs it everyday for at least 4 miles up and down my road
and then charges it back up. 

All this without a BMS. Anybody else try this approach with Lithium cells?
I'm interested to hear other peoples accounts.
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## EVDL List (Jul 27, 2007)

I expect that they will be monitoring the cells, not shunting them.
If they get too much out of whack, it may be that they require you
to come in for a battery pack service.


Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] 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: [email protected] [mailto:[email protected]] On
Behalf Of Peri Hartman
Sent: Sunday, June 26, 2011 8:16 AM
To: evdl
Subject: [EVDL] leaf battery balancing

Hi. Does anyone know what the Leaf does for battery balancing. My guess
is that at the end of the charge cycle, the charger "tops off" the cells
to ensure all have 100%.

Now, here's the correlary question. If you set the charger to stop at
80% - wise, accorging to Nissan, for prolonging battery life - how will
the cells ever get balanced?

I've also posted this on one of the leaf forums but they appear to have
very little traffic at this time, so I'm hoping the trusty EVDL comes
through!

Peri


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## EVDL List (Jul 27, 2007)

"As others have noted, 3.2v is the resting voltage of the cells, and that
indicates they are somewhere from 20% to 80% charged." This is incorrect. I
recorded voltage of each cell in my pack at end of discharge and after
charge for over 6 months. According to that data 3.3V is about 40 - 45%
SOC, 3.2V is about 20 - 25% SOC. The change in voltage of LiFePO4 cells with
Ah charge/discharge is not zero in the region between the exponential parts
of the curve at the two ends. I found that rest voltage recorded after the
cells have set for at least 3 hours correlates well with SOC and is
repeatable, though I think it varies a bit with temperature.

--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/leaf-battery-balancing-tp3626084p3627725.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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## EVDL List (Jul 27, 2007)

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## EVDL List (Jul 27, 2007)

He's talking about CALB LiFePO4 cells, very similar curve to TS cells.




> Lee Hart wrote:
> >
> > On 6/27/2011 8:32 AM, tomw wrote:
> >> "3.2v is the resting voltage... somewhere from 20% to 80% charged."
> ...


----------



## EVDL List (Jul 27, 2007)

Can't find the document at the moment but the LEAF actively balances the
cells, not just monitors them. I'd guess the cells are very closely
matched and need very little actual balancing.



> Cor van de Water wrote:
> >
> > I expect that they will be monitoring the cells, not shunting them.
> > If they get too much out of whack, it may be that they require you
> ...


----------



## EVDL List (Jul 27, 2007)

Here is a picture from the LEAF service manual
http://ingineerix.com/pic/?leaf-bms
Speculation on the LEAF forums is that
1. The cells are so closely matched that very little balancing happens and
there is enough safety margin in capacity that even if no balancing occurs
during the 80% charge it won't matter.
or 
2. LiMn has a steeper charge curve so balancing can occur even with the 80%
charge.
or
3. If charging only to 80% most of the time an occasional 100% charge might
be useful for balancing.
Take your pick, or mix and match.




> AMPhibian wrote:
> >
> > Can't find the document at the moment but the LEAF actively balances the
> > cells, not just monitors them. I'd guess the cells are very closely
> ...


----------



## EVDL List (Jul 27, 2007)

"He's talking about CALB LiFePO4 cells, very similar curve to TS cells." 
Yes. We all cavalierly describe most of the charge/discharge curve as
"flat" but of course it is not. Graphs of voltage vs time while charging
from cell log8 data show definite, though small, slope in this region, and
you can get a fairly good estimate of SOC from rest voltage if you wait long
enough and measure at least to 3 decimal places. A charge counter is of
course much better.

Thanks for the figure from the Leaf manual. So they use logic to turn on
their "shunts". You sure must spend a lot of time on the net JRP3. 

--
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## EVDL List (Jul 27, 2007)

> tomw wrote:
> >
> > You sure must spend a lot of time on the net JRP3.
> >
> ...


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