Battery Design and Engineering Issues

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evnow said:
The problem with cold is not permanent damage (unlike extreme heat) - but lowered maximum capacity of the cells. IIRC, the BMS will think the cells are maxed out much before they actually are - leading to low charge and low range.

I wonder whether Nissan will have some kind of battery heating with their "Cold weather package".

The winterized package comes with battery heating. I remember reading that somewhere.
 
leaffan said:
Norway said:
leaffan said:
Nissan tested the LEAF near the North Pole...probably with the 'winterized package'. There was a photo of it on one of these threads, but I can't remember where it is.

In this one:

http://www.mynissanleaf.com/viewtopic.php?f=9&t=1030

Yeah! That's it! Thanks Norway! I wonder if they've printed their results after 6 years of testing there? Wouldn't that be great to hear that the batteries didn't lose any electrons by being heated? :)

Yes, that would make great reading.

And I guess they can claim the car is "polar bear proof", too! :mrgreen:
 
I spoke to the Leaf rep today after looking over the car. The Pack is about 30 kwh and usable is 24kwh which makes complete sense based on the range The extra is not a reserve or to be used over time as the pack ages to keep range constant it is just to prevent a low dod and harm to the pack as is usually the case. There are no changes to the range coming and no silly surprises.

Also, the motor and inverter are water cooled which we knew from day one and I checked every cooling line so let's put that one to rest as well.

The car weight is about 3540 as stated and the gross is far over 4000 lbs. It feels heavy.


The car looks very nice in person as well.
 
EVDRIVER said:
I spoke to the Leaf rep today after looking over the car. The Pack is about 30 kwh and usable is 24kwh which makes complete sense based on the range The extra is not a reserve or to be used over time as the pack ages to keep range constant it is just to prevent a low dod and harm to the pack as is usually the case. There are no changes to the range coming and no silly surprises.

Oh - finally some confirmation (?) about the pack size.

The car weight is about 3540 as stated and the gross is far over 4000 lbs. It feels heavy.

Any new info on why it might be that heavy ?
 
evnow said:
EVDRIVER said:
I spoke to the Leaf rep today after looking over the car. The Pack is about 30 kwh and usable is 24kwh which makes complete sense based on the range The extra is not a reserve or to be used over time as the pack ages to keep range constant it is just to prevent a low dod and harm to the pack as is usually the case. There are no changes to the range coming and no silly surprises.

Oh - finally some confirmation (?) about the pack size.

The car weight is about 3540 as stated and the gross is far over 4000 lbs. It feels heavy.

Any new info on why it might be that heavy ?


The rep does not know. I looked over all the components and like many 1st models of a new design it seems very bulky, many large radiators, casings, etc. I would also guess the pack box is very rigid steel and there is extra steel for safety, perhaps more sound proofing which is needed when you want and EV silent but can add up quickly. The pack may weigh a bit more than stated and may be mentioned as such or ambiguously to keep the actual size confidential until now. The build quality looks very nice in the motor bay.

I was not put off by anything in the car and silver looks very nice in person. The drive selector looks much smaller in person and the center space could have been used better with a different shift location IMO but it is still nice and "ICE" driver friendly.
 
garygid said:
WOW, I guess my 3520 pound entry weally DID win the "Guess the LEAF's Weight" contest!!! :)
(I am not always wrong.)


YOu have to wait for the official sticker, the curb was not listed but I asked only gross.
 
EVDRIVER said:
I spoke to the Leaf rep today after looking over the car. The Pack is about 30 kwh and usable is 24kwh which makes complete sense based on the range The extra is not a reserve or to be used over time as the pack ages to keep range constant it is just to prevent a low dod and harm to the pack as is usually the case. There are no changes to the range coming and no silly surprises.
I found a couple of articles which may have been the genesis of this chat. Plugincars was reporting Mark Perry said the LEAF would allow a 95% DOD. Mark Perry later denied he ever said that. That 95% DOD statement (or non-statement) spun a couple of other articles, LEAF’s 100 Mile Range; Can You Trust It? As well as, LEAF Depth of Discharge. Frankly, even if it were to have an extra 16 miles of range (80% DOD to 95% DOD), it wouldn't matter to me, I only need 50 miles range worst case anyways.
 
indyflick said:
EVDRIVER said:
I spoke to the Leaf rep today after looking over the car. The Pack is about 30 kwh and usable is 24kwh which makes complete sense based on the range The extra is not a reserve or to be used over time as the pack ages to keep range constant it is just to prevent a low dod and harm to the pack as is usually the case. There are no changes to the range coming and no silly surprises.
I found a couple of articles which may have been the genesis of this chat. Plugincars was reporting Mark Perry said the LEAF would allow a 95% DOD. Mark Perry later denied he ever said that. That 95% DOD statement (or non-statement) spun a couple of other articles, LEAF’s 100 Mile Range; Can You Trust It? As well as, LEAF Depth of Discharge. Frankly, even if it were to have an extra 16 miles of range (80% DOD to 95% DOD), it wouldn't matter to me, I only need 50 miles range worst case anyways.


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
 
EVDRIVER said:
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
 
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.
 
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".
 
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!
 
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 said:
I seriously doubt there's a fan inside the battery box. Nissan shows in their documents that the battery box is completely sealed.

Leaf_Pack.jpg


Leaf_pack2.jpg
 
garygid said:
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?


EXleafbatteries2(1).jpg
 
indyflick said:
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 ...
 
evnow said:
indyflick said:
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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