AndyH
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Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 8:30 am

EVDRIVER wrote:People thought the pack was 24kwh and would use 80% and go 100 miles, I knew that was not possible nor did I believe any auto maker would cycle batteries 95-100% DOD. This explains the the 24 KWH usable. 80% DOD at about 30 kwh is 24 kwh


Some people didn't. ;)
May 8th: http://www.mynissanleaf.com/viewtopic.php?p=2568#p2568
May 9th: http://www.mynissanleaf.com/viewtopic.php?p=2670#p2670
May 11th: http://www.mynissanleaf.com/viewtopic.php?p=2770#p2770

My guestimate from May is that the cells are about 40Ah each for a 27kWh pack. I think they're actually larger than that - and we have one member that held a cell and seemed to think it was a similar size to a 50Ah cell.

What we know:
The pack has 48 modules of 4 cells (192 cells total)
Nominal cell voltage is 3.6V

AESC's battery page says their EV battery is made from 33Ah cells. We don't know for sure that the Leaf will use 33Ah cells.

Mark Perry reported in DC that the consumer state of charge range was the 'middle' 80% from 10% to 90% charged.

Pack capacity is cell capacity times nominal voltage times number of cells.

An example using an AESC standard 33Ah cell in a Leaf pack:

33Ah * 3.6V * 192 = 22,809.6Wh or 22.8kWh

This is smaller capacity than even the Leaf's reported 24kWh consumer capacity. This suggests the cells must be larger. As already reported, we need a 30kWh pack to get 24kWh of usable energy at 80%.

Working backward:
30,000Wh / 192 / 3.6V = 43.4Ah

The cells need to be at least 43Ah each to give a 24kWh pack when new. But if the cells are 50Ah, we'd start with a pack that could provide up to 34,560Ah when new...and that would give some 'extra capacity' that could be used later in the pack's life. I'd use 50Ah cells if it was important to maintain a minimum drive range at end of pack life...

One last pack indicator - technically 'hearsay' but also from Perry in DC - the suggestion that total pack size is 32kWh: http://www.mynissanleaf.com/viewtopic.php?p=17255#p17255

A 32kWh pack size means we need 46.3Ah cells.

I'm feeling pretty good about 46-50Ah cells for a total pack capacity between 31.7kWh and 34.5kWh

Andy

indyflick
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Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 9:01 am

Excellent analysis and summary Andy. Your analysis makes a lot of sense from a technical perspective. I also believe from a marketing perspective they would also want some head room in the pack. No customer is going to be upset because their car can go too far. I think the thing we need to careful with is that some of the analysis was on pre-production vehicles. The production pack could have slightly different specs and no doubt they are tweaking the battery management software/firmware based on empirical data collected from the vehicles in the field.

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garygid
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Joined: Wed Apr 21, 2010 8:10 am
Delivery Date: 29 Mar 2011
Leaf Number: 000855
Location: Laguna Hills, Orange Co, CA

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 9:39 am

Do we have ANY info yet on how, when, or how often Battery Cell balancing will be done?

We assume, if it exists at all, that it must be some form of "top" balancing, right? ... Because many (most) will "never" drive until their LEAF's battery is "empty".
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
PU: SDG&E
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle

kmp647
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Delivery Date: 11 Nov 2011
Location: Northern Virginia

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 9:45 am

There is no doubt that the Leaf monitors and balances all the cells in the pack.

No mfr would build a 192 cell pack and put it into consumer use without active balancing
and cell monitering. Otherwise a fire might result, or at least cell/pack failure.

the tolerances and action of this BMS are less important as long as they have been programmed correctly.


Technicians will be able to pull up battery health and the system will likely flag poor performaing or out of balance cells for replacment

No doubt a "check battery" light exist as a signal dealer service is required.

Hopefully we wont see it much except when the ign is first turned on!
2012 SL Leaf
order 07/28/2011
took delivery 11/11/11
47,000 miles 10 bars 211 gids
Turned back into Nissan 12/31/14 @ 50,000 miles
BMW i3 rex 24 month lease
2017 BMW X540e phev
Tesla model 3 reservation

indyflick
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Joined: Fri Jul 09, 2010 8:18 am

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 10:17 am

When I look at the photo and diagram AndyH posted, it occurs to me that Nissan may have an interesting pack maintenance strategy. So the rear seat is over the controller on the far right. Look at the rear floor area of the pack. Do you see what I see? There is actually room for four additional modules, two on each side. Or, instead what if some of the 48 modules in the pack are actually blanks? Point being that when necessary, the strategy could be you take your LEAF to a Nissan authorized dealership for a pack "tune up". What they actually do is add modules (to either the available space in the rear or by replacing blank modules) the battery management senses the additional capacity, automatically recalibrates, self tests, and you are on your way. The customer is happy and the dealership is very happy. Just throwing some wild ass speculation out there for ya to chew on. Hey we need something to do while we wait for delivery, right?

AndyH wrote:I seriously doubt there's a fan inside the battery box. Nissan shows in their documents that the battery box is completely sealed.

Image

Image

LEAFfan
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Leaf Number: 1855
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Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 10:31 am

"While we wait for delivery"? How about while the rest of us wait to order. ;)

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garygid
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Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 10:52 am

No room for 2 more modules on either side wilhout RISING the rear-passenger foot-space floor level.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
PU: SDG&E
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle

indyflick
Posts: 505
Joined: Fri Jul 09, 2010 8:18 am

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 11:21 am

garygid wrote:No room for 2 more modules on either side wilhout RISING the rear-passenger foot-space floor level.
I'm not so sure. Look at the photo below. Also, what if the actual production model appears with a flat rear floor?


Image

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evnow
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Leaf Number: 303
Location: Seattle, WA

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 11:26 am

indyflick wrote:I'm not so sure. Look at the photo below. Also, what if the actual production model appears with a flat rear floor?


They can't make any changes here without affecting rear headroom etc. So, won't happen ...
1st Leaf : 2/28/2011 to 5/6/2013
2nd Leaf : 5/4/2013 to 3/21/2017
Volt : 3/25/2017 to 5/25/2018
Model 3 : 5/10/2018 to ?

indyflick
Posts: 505
Joined: Fri Jul 09, 2010 8:18 am

Re: Battery Design and Engineering Issues

Tue Sep 21, 2010 11:42 am

evnow wrote:
indyflick wrote:I'm not so sure. Look at the photo below. Also, what if the actual production model appears with a flat rear floor?


They can't make any changes here without affecting rear headroom etc. So, won't happen ...
Rear seat mounts above the controller, that height wouldn't need to change. Also, there's a "hump" in the rear floor already with flap that provides rapid access to the SD/SW. A flat rear floor would bring your knees up a bit, but not raise the rear seat.

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