# Re: [EVDL] leaf cell monitoring (long review on my jeep progress)



## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Just want to double check. This is the first I've heard the the Leaf does
not monitor at the cell level. Certainly there's no user accessible
monitoring among all the stupid gages they've provided. But I'm surprised
if there isn't something accessible through some other service-only
interface.

Peri

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Martin WINLOW
Sent: 11 April, 2012 12:55 AM
To: David Ladd; Electric Vehicle Discussion List
Subject: Re: [EVDL] long review on my jeep progress

David,

I do not profess to be an 'expert' on LiFePo4 (if there is such a thing) but
the point I am making is that without some means of seeing what is going on
at the cell level, anything could be happening. Your statements about IR
are correct as far as I know - I am rather puzzled at the wide variation in
IR in your cells. Perhaps this is normal for CALBs.. or were they
previously used in different packs i.e., not all new and sourced all
together?

If you know you have weak cells then cell level monitoring (molly-coddling)
is all the more important if you are going to get the most out of them.

You may not be reversing them but even if you are pulling them down to a
volt or whatever, this will stress them quite badly and shorten their life
considerably (apparently). The good news is that even if you are killing
off the weak cells, it won't necessarily affect the good ones. So your
decision about whether or not to replace them may be taken out of your
hands.

I know some people will say "Well, Teslas and Leafs don't monitor at cell
level so why should I?" Whilst true, they have alternative means to deal
with failing cells and they are, I am sure, all well matched in the first
place.

Any sort of logging IMO is good.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk




> David Ladd wrote:
> 
> > if I were reversing a cell, isn't that fatal? My cells bounce right back
> after a hard pull, I think I'm just sagging them down. I have one cell with
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Just so happens that we had a Leaf owners meet up today at Koons
Nissan in Falls Church, VA. The Leaf mechanic there (Gregg, a great
guy) had some extra time, so came in and talked with us and answered
questions. The battery printout that the owners get at the yearly
service does not give information on individual cells, just the pack
in general. However, the Leaf does monitor each cell (he called them
modules), and if there is a problem, it will tell him exactly which
cell has a problem. Then, he will drop the pack and replace the
offending cell with a new one, calibrate it so it plays nice with the
existing cells, and the Leaf will be on its way.

Dave




> Peri Hartman <[email protected]> wrote:
> > Just want to double check. This is the first I've heard the the Leaf d=
> oes
> > not monitor at the cell level. Certainly there's no user accessible
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

That's great news! It's what I was hoping for, but how would one know
otherwise?

I'm wondering what other info might have come out of the mechanic. Like, =

- visibility issues; any design changes coming?
- any way to tweak regen to be stronger?
- any way to monitor when brakes are being used vs regen?
- any way to monitor kwh remaining?

Peri

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Dave Davidson
Sent: 14 April, 2012 4:22 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] leaf cell monitoring (long review on my jeep progress)

Just so happens that we had a Leaf owners meet up today at Koons Nissan in
Falls Church, VA. The Leaf mechanic there (Gregg, a great
guy) had some extra time, so came in and talked with us and answered
questions. The battery printout that the owners get at the yearly service
does not give information on individual cells, just the pack in general.
However, the Leaf does monitor each cell (he called them modules), and if
there is a problem, it will tell him exactly which cell has a problem.
Then, he will drop the pack and replace the offending cell with a new one,
calibrate it so it plays nice with the existing cells, and the Leaf will be
on its way.

Dave




> Peri Hartman <[email protected]> wrote:
> > Just want to double check. This is the first I've heard the the Leaf =
> 
> > does not monitor at the cell level. Certainly there's no user =
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

He didn't seem to think he can change much, at least with the training he's
had so far. I specifically asked about disabling the creep mode, but he
indicated it's fixed.

Dave


> "Peri Hartman" <[email protected]> wrote:
> >
> > That's great news! It's what I was hoping for, but how would one know
> > otherwise?
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Tesla also monitors at the cell level, always have.




> Peri Hartman <[email protected]> wrote:
> > Just want to double check. This is the first I've heard the the Leaf d=
> oes
> > not monitor at the cell level. Certainly there's no user accessible
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Hi Dave, If the mechanic said 'modules' I interpret that as a collection of cells, not one cell on its own, which is what I thought I had read somewhere. If you get the chance can you get him to confirm this either way, please?

Regards, MW.




> Dave Davidson wrote:
> 
> > Just so happens that we had a Leaf owners meet up today at Koons
> > Nissan in Falls Church, VA. The Leaf mechanic there (Gregg, a great
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Hi,

I would be grateful if you could give a link to where I can read about this.

I was under the impression, again from what I have read somewhere, that the Tesla Roadster (at least) does not have individual cell monitoring but relies on the built-in, over-heat cutout device on each cell to disconnect a cell if it over-heats for any reason.

It seems highly unlikely that it would be cost effective to monitor all 6381 cells individually!

Regards, MW.




> Peter Gabrielsson wrote:
> 
> > Tesla also monitors at the cell level, always have.
> >
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Of course they're not monitoring all 6800 cells individually, they're
grouped into parallel bundles of 68cells so only 100 cell monitoring
channels are required.

Here's a picture of a leaf module, you can see that there are 4
parallel pouch cells inside each.
http://altenergyautos.blogspot.com/2010/05/nissan-leaf-battery-pack-cost-an=
d.html

I see a fair amount of automotive battery packs coming through our
test labs, I've never seen one without cell level monitoring.




On Sun, Apr 15, 2012 at 4:45 AM, Martin WINLOW <[email protected]> w=
rote:
> Hi,
>
> I would be grateful if you could give a link to where I can read about th=
is.
>
> I was under the impression, again from what I have read somewhere, that t=
he Tesla Roadster (at least) does not have individual cell monitoring but r=
elies on the built-in, over-heat cutout device on each cell to disconnect a=
cell if it over-heats for any reason.
>
> It seems highly unlikely that it would be cost effective to monitor all 6=
381 cells individually!
>
> Regards, MW.
>
>
>


> Peter Gabrielsson wrote:
> >
> >> Tesla also monitors at the cell level, always have.
> >>
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

>> On 15 Apr 2012, at 06:35, Peter Gabrielsson wrote..
>> Tesla also monitors at the cell level, always have.

Er=85 yes. Glad we agree on that then=85! MW



> Peter Gabrielsson wrote:
> 
> > Of course they're not monitoring all 6800 cells individually, they're
> > grouped into parallel bundles of 68cells so only 100 cell monitoring
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

So this is getting into semantics.

Monitoring at the cell level refers to monitoring every cell in a
series string, which, is also the topic of the discussion you replied
to when you implied that Tesla and the Leaf doesn't. It wasn't about
individually monitoring every cell in a parallel bundle, that is
nonsensical since they are all at the same voltage.





On Sun, Apr 15, 2012 at 9:18 AM, Martin WINLOW <[email protected]> w=
rote:
>>> On 15 Apr 2012, at 06:35, Peter Gabrielsson wrote..
>>> Tesla also monitors at the cell level, always have.
>
> Er=85 yes. Glad we agree on that then=85! MW
>
>


> Peter Gabrielsson wrote:
> >
> >> Of course they're not monitoring all 6800 cells individually, they're
> >> grouped into parallel bundles of 68cells so only 100 cell monitoring
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Peter,

I wasn't trying to be difficult=85 but I had forgotten the important point =
that, of course, 'modules' of cells connected in parallel will have the sam=
e potential and therefore are effectively being monitored at the 'cell leve=
l'. I was thinking too literally. Thank you for reminding me!

Regards, Martin.




> Peter Gabrielsson wrote:
> 
> > So this is getting into semantics.
> > =
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*



> Peter Gabrielsson wrote:
> > Monitoring at the cell level refers to monitoring every cell in a
> > series string, which, is also the topic of the discussion you replied
> > to when you implied that Tesla and the Leaf doesn't. It wasn't about
> ...


----------



## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

They don't have to know directly, they will find out due to the
reduced capacity and increased temperature that something is wrong.
Since the fuse is internal to the cell there is nothing else you can
do.

Presumably their pack has enough margin to safely operate with a few
failed cells.

Anyway, I don't work for Tesla so you may want to ask them.






> Lee Hart <[email protected]> wrote:
> > Peter Gabrielsson wrote:
> >> Monitoring at the cell level refers to monitoring every cell in a
> >> series string, which, is also the topic of the discussion you replied
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] leaf cell monitoring (long review on my jeep progress)*

Since they do monitor the voltage of each "macro" cell
(many cells in parallel) the ones where one or more
cells failed / blew their fuse have lower remaining
capacity, so the voltage will drop faster than others.
Since these are the laptop type Lithium-Ion cells, you can
see the cell SoC from the voltage, so a reduced capacity
means faster drop. Every commercial Li-Ion BMS that I have =

seen (as built-in to the laptop battery packs) detects
differences between the cell voltages and when they cross
a threshold (too much difference) an error flag is raised.
I am guessing that is what Tesla can do in their blades
as well.

Regards,

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] on behalf of Peter Gabrielsson
Sent: Tue 4/17/2012 9:42 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] leaf cell monitoring (long review on my jeep progress)
=

They don't have to know directly, they will find out due to the
reduced capacity and increased temperature that something is wrong.
Since the fuse is internal to the cell there is nothing else you can
do.

Presumably their pack has enough margin to safely operate with a few
failed cells.

Anyway, I don't work for Tesla so you may want to ask them.






> Lee Hart <[email protected]> wrote:
> > Peter Gabrielsson wrote:
> >> Monitoring at the cell level refers to monitoring every cell in a
> >> series string, which, is also the topic of the discussion you replied
> ...


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