Gavin
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 10:02 am

Well Tesla's needs to be complex...the batteries they use have been shown to catch fire if too hot.

But the Volt chemistry is similar to the LEAF I thought...and that chemistry and packing does not have the same fire risk...

So you could state, "I know why the Tesla needs advanced cooling, and I know why the LEAF doesn't need advanced cooling, but why does the Volt use Advanced cooling? It adds weight and complexity to the system."

Gavin

JasonT
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 10:41 am

Gavin wrote:... but why does the Volt use Advanced cooling? It adds weight and complexity to the system.
Ah, but so does having an ICE system and all that goes with it. GM just can't help themselves in adding weight and complexity.

Sorry couldn't help myself. :)

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evnow
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 11:17 am

Gavin wrote:So you could state, "I know why the Tesla needs advanced cooling, and I know why the LEAF doesn't need advanced cooling, but why does the Volt use Advanced cooling? It adds weight and complexity to the system."


While the chemistries are same, remember GM doesn't have much experience with Li batteries. They source theirs from LG - so I guess they weren't sure how it will behave and have heavily over engineered Volt. They not only liquid cool the battery, their DOD is only 50%. This has cost them complexity, weight, extra battery cost and the middle seat at the back (Volt seat is divided at the back and can only seat 2, not 3).

Infact at one time Lutz was saying they will factor a replacement battery in their price. But once it became known that it was not needed - the general perception was that Volt won't be priced at $40K. One of the reasons there is a general revolt about its price in gm-volt.
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garygid
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 11:20 am

I think there are no fans inside the LEAF's battery pack. People have suggested that there could, might, or should be, but that is all.

EDIT: Oops (see posts below), one report stated that there will be a fan inside to better distribute the heat. That is quite possible, however I do not know if that is the "final word" on battery-box fans, ... and a fan would use extra energy.

With sufficient conduction inside the pack to the outside wall, fans are not necessary.

Every module in the pack has at least one side directly adjacent to the pack's outer box. The mechanism that holds the modules in place probably conducts heat to the box's bottom "skin". Apparently the box's top is removable, to allow modules to be removed and replaced.
Last edited by garygid on Fri Aug 06, 2010 12:43 pm, edited 1 time in total.
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evnow
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 11:26 am

garygid wrote:I think there are no fans inside the LEAF's battery pack. People have suggested that there could, might, or should be, but that is all.


From the article I linked earlier ...

Instead, Nissan has opted to use only an internal fan that circulates the air within the sealed pack to evenly distribute the heat, which escapes by passive radiation through the pack’s external case.


http://www.wired.com/autopia/2010/01/ni ... z0vqrgIoxT
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jkirkebo
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 12:14 pm

Nissans battery is probably the best solution for a small car with 100 mile range. But you can't use those modules for a battery that will power a large car for 300 miles, it would weigh at least 2000 pounds.

Teslas technology enables them to build such a battery with a weight of ~1200 pounds which is acceptable in a large car like the Model S.

I'd say around 40-45kWh of battery capacity is the point where Teslas battery starts to make more sense than Nissans.

AndyH
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 12:31 pm

Sorry guys - the Wired article is just wrong. There are no fans inside the box (there's no room and there's no benefit). There aren't any air ducts and there's no cabin air moving through the battery box.

We have some excellent high resolution battery box pictures now from various drive events. But the place to start is the October '09 Nissan 'slide show' http://www.absoluteefficiency.com/LEAF/NissanLeaf_Oct09.pdf

Page 24 shows how well the battery box is sealed. Not only is the battery box sealed well enough to withstand high pressure spray and dunking, but NISSAN also shows that the battery box is watertight when immersed in an ice water bath. The box is sealed well enough to resist water intake even when there's lower pressure inside the box.

The battery boxes on display have only four areas where items pass into the box. There's the disconnect plug on the top, and the three 'holes' in the front - two for the high-voltage connections and the third likely for the BMS communications to the car.

Image

Andy

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garygid
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 12:53 pm

This fan, if it exists, would be inside the box and just move air around inside the box. There would be no in/out holes or ducting required.

But, I also suspect there will be no fan included in the production battery box, because the heat generated is already spread fairly evenly throughout the box, with each module generating essentially the same amount of heat. So, the benefits of using an internal fan might be too minimal.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
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evnow
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 12:55 pm

jkirkebo wrote:Teslas technology enables them to build such a battery with a weight of ~1200 pounds which is acceptable in a large car like the Model S.


Prismatic batteries are better than cylindrical batteries (just simple math) in terms of volume.

Model S will apparently use new chemistry - that is why Tesla has been quoting 1200 pounds. Similar chemistry that is coming in gen 2 of Leaf will have about double the capacity for the same weight.

The reason why Tesla started using cylindrical was because
- cells can be sourced from a large number of vendors
- there was no prismatic battery vendor available

But the cons are
- Not as safe in LiMn that everyone else is using
- Needs complex BMS, liquid cooling etc
- Difficult to manufacture in volume because of 6000 cells that need to be soldiered

Here is a good reference : http://pubs.its.ucdavis.edu/download_pdf.php?id=1292

EVS24 : Stavanger, Norway, May 13 - 16, 2009
Performance Characteristics of Lithium-ion Batteries of Various Chemistries for Plug-in Hybrid Vehicles
Andrew Burke, Marshall Miller
University of California-Davis, Institute of Transportation Studies, California


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LEAFguy
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Re: Musk says Leaf battery primitive.

Fri Aug 06, 2010 1:35 pm

AndyH wrote:We have some excellent high resolution battery box pictures now from various drive events. But the place to start is the October '09 Nissan 'slide show' http://www.absoluteefficiency.com/LEAF/NissanLeaf_Oct09.pdfAndy


AndyH, thanks for the link to that Oct 09 pdf document. I had not seen that before, and it answered a significant number of questions that I had.

Regarding the wired article referenced earlier, I think this is the sentence that tripped some of us up:

The key engineering trade-off Nissan has made is opting not to include active thermal management, where the temperature of the pack is controlled by an HVAC system similar to what cools the passenger cabin on a hot day. The bold emphasis is mine.

Read More http://www.wired.com/autopia/2010/01/ni ... z0vrMUYnG5

While they state "similar to", it is easy to see how it could be mis-read by some. But... they provide no source of their statement that temperature is controlled by an HVAC system. This just seems to be in error. It would appear, based on this entire discussion, that there truly is no active management system (which is what Mr. Perry has stated all along).

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