edatoakrun
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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 11:59 am

As discussed in the thread below, it now appears that if the model 3's new batteries are improved over previous generations, it is not in
having achieved a very significant improvement in energy density.

Ok I think I have to be the first to say this, so please brace yourself:

If the base Model 3 really has 50 kWh, as stated in the article, the cells are worse than the 18650s.

... the cells probably would have a worse gravimetric energy density, too.

Now add in slower charging and less performance and either the new cell format is just worse than the 18650s, or the pack has more than 50kWh total capacity.

https://teslamotorsclub.com/tmc/threads ... ils.96792/

Earlier statement from TSLA:

Tesla Model 3’s battery will be 30% more energy dense than the Model S’ original pack

Tesla CTO JB Straubel:
...when we went from the Roadster to the Model S, they have improved by about 40% and when we were designing the Model 3, they were about another 30% better...

https://electrek.co/2016/11/14/tesla-mo ... y-model-s/

edatoakrun wrote:Just in case anyone might be interested in the actual thread topic...

Tesla Model 3: Exclusive first look at Tesla’s new battery pack architecture

...The standard 50 kWh Model 3 battery pack is made of 2,976 of those cells in groups of 31 cells per “brick”. The bricks go into 4 separate modules (2 modules of 23 bricks and 2 modules of 25 bricks).

That pack is going into production later this year. Currently, Tesla is producing a 74 kWh ‘long range’ battery pack, which consists of 4416 cells in groups of 46 cells per brick and the same brick distribution in the 4 modules...

https://electrek.co/2017/08/24/tesla-mo ... hitecture/
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lpickup
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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 1:00 pm

edatoakrun wrote:As discussed in the thread below, it now appears that if the model 3's new batteries are improved over previous generations, it is not in
having achieved a very significant improvement in energy density.

Ok I think I have to be the first to say this, so please brace yourself:

If the base Model 3 really has 50 kWh, as stated in the article, the cells are worse than the 18650s.

... the cells probably would have a worse gravimetric energy density, too.

Now add in slower charging and less performance and either the new cell format is just worse than the 18650s, or the pack has more than 50kWh total capacity.

https://teslamotorsclub.com/tmc/threads ... ils.96792/

Earlier statement from TSLA:

Tesla Model 3’s battery will be 30% more energy dense than the Model S’ original pack

Tesla CTO JB Straubel:
...when we went from the Roadster to the Model S, they have improved by about 40% and when we were designing the Model 3, they were about another 30% better...


Those two statements are not necessarily mutually exclusive.

The first statement says that the energy density of the 2170 cells themselves is not as high as the latest 18650 cells.

The second statement says that the energy density of the Model 3 battery pack is greater than the Model S original pack.

If you read on in the linked thread, you'll see that it goes on to explain that there is more energy in the 2170 cell, but taking into account the volume increase, the 2170 cell is actually less energy dense than the 18650 cell.

But then you have to consider efficiencies by using larger cell form factors at the pack level. You may gain back some of that lost density.

And add to THAT that it's not necessarily clear that when JB was talking about the 30% energy density improvement that he wasn't talking about the specific energy density (Wh/kg, not Wh/l). In fact, he probably was since the context of the whole article you linked was on the weight and how the COST of the Model 3 battery was expected to be lower because in volume, the weight of an object tends to define the cost of an object. So now we're not even talking apples and apples. The first argument is clearly talking of Wh/l since all they did was divide the size of the pack by the number of cells to get a per cell Wh capacity and then compare that to the same calculation for the Model S.

So the net is, yes, on a volumetric basis, the Model 3 battery is not as dense as the Model S/X (not surprising, since you can only fit a 75kWh pack in a Model 3 vs a 100kWh in a Model S, despite the fact that the footprint of the S is not 33% larger than the 3). But the COST is significantly less, because as JB was explaining, the cost is driven more by the specific energy (Wh/kg).
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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 3:39 pm

Another issue is that the percentage of the pack taken up by structure, cooling and other Balance of Pack items will be greater in a smaller pack than a larger one, because volume increases more rapidly than surface area. So, it's entirely possible that even if a smaller pack uses cells with higher energy densities, the densities of the pack may still be lower than a larger pack using less energy dense cells which has to devote a smaller percentage of its space to BoP items.

I think the % of Model 3 customers who'll care approximates zero.
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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 5:03 pm

GRA wrote:Another issue is that the percentage of the pack taken up by structure, cooling and other Balance of Pack items will be greater in a smaller pack than a larger one, because volume increases more rapidly than surface area. So, it's entirely possible that even if a smaller pack uses cells with higher energy densities, the densities of the pack may still be lower than a larger pack using less energy dense cells which has to devote a smaller percentage of its space to BoP items.

I think the % of Model 3 customers who'll care approximates zero.

The only practical matter here is heat dissipation aka charging speeds. I won't be surprised to learn that Tesla had to invest in more cooling for the 2170 cells or accept slower Supercharger speeds.

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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 5:16 pm

SageBrush wrote:The only practical matter here is heat dissipation aka charging speeds. I won't be surprised to learn that Tesla had to invest in more cooling for the 2170 cells or accept slower Supercharger speeds..


It may be that you can get a win-win here. From reading the other thread (and partly between the lines), it's possible that the 2170 cells have less specific energy density (volumetric), but possibly have a chemistry that requires less cooling. This is all speculation of course, but it's a possibility.
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SageBrush
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Re: Official Tesla Model 3 thread

Thu Aug 24, 2017 6:24 pm

lpickup wrote:
SageBrush wrote:The only practical matter here is heat dissipation aka charging speeds. I won't be surprised to learn that Tesla had to invest in more cooling for the 2170 cells or accept slower Supercharger speeds..


It may be that you can get a win-win here. From reading the other thread (and partly between the lines), it's possible that the 2170 cells have less specific energy density (volumetric), but possibly have a chemistry that requires less cooling. This is all speculation of course, but it's a possibility.

Possible but quite unlikely.

Everything points to Tesla using the same chemistry as the 1865 batteries but packaged as 2170. They get to package the cell more efficiently but the surface to volume decreases, leading to worse heat dissipation per cell.

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Re: Official Tesla Model 3 thread

Fri Aug 25, 2017 6:42 am

SageBrush wrote:Everything points to Tesla using the same chemistry as the 1865 batteries but packaged as 2170.


http://insideevs.com/tesla-2170-battery-cells-greater-power-comparable-cost/

However, all good things must come to an end. Tesla and Panasonic have now developed a new and improved type of cell, which will be used in the upcoming Model 3. The new 2170 cell, which is now being produced at the Gigafactory, is slightly larger – 21 mm by 70 mm. More importantly, it can store a lot more energy. According to Elon Musk, it’s “the highest energy density cell in the world, and also the cheapest.” The 2170 cell is around 50% larger by volume than the 18650, but it can deliver almost double the current (the 18650 delivers 3,000 mA, and the 2170 has been tested at 5,750-6,000 mA).


Same battery chemistry?

This battery change reduces the output impedance of the Tesla battery, which with 18650 cell was greater than
the Leaf's, i.e. per cell.

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Re: Official Tesla Model 3 thread

Fri Aug 25, 2017 7:19 am

lorenfb wrote:
SageBrush wrote:Everything points to Tesla using the same chemistry as the 1865 batteries but packaged as 2170.


http://insideevs.com/tesla-2170-battery-cells-greater-power-comparable-cost/

However, all good things must come to an end. Tesla and Panasonic have now developed a new and improved type of cell, which will be used in the upcoming Model 3. The new 2170 cell, which is now being produced at the Gigafactory, is slightly larger – 21 mm by 70 mm. More importantly, it can store a lot more energy. According to Elon Musk, it’s “the highest energy density cell in the world, and also the cheapest.” The 2170 cell is around 50% larger by volume than the 18650, but it can deliver almost double the current (the 18650 delivers 3,000 mA, and the 2170 has been tested at 5,750-6,000 mA).


Same battery chemistry?

The increased max amps is news to me -- thanks.
So I'll tentatively agree (out of general ignorance) that something in the chemistry has changed.

However, (IIRC -- I have to double check)
The peak power rates for 2170 cell packs are lower than 1865 for equivalent kWh pack sizes.
We can guess why that is, but the cell reduced surface area to volume is a given.
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lpickup
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Re: Official Tesla Model 3 thread

Fri Aug 25, 2017 7:43 am

SageBrush wrote:However, (IIRC -- I have to double check)
The peak power rates for 2170 cell packs are lower than 1865 for equivalent kWh pack sizes.
We can guess why that is, but the cell reduced surface area to volume is a given.


Yeah, different serial/parallel organizations would account for different peak power comparisons at the cell and the pack levels. This is not surprising, considering the 0-60 differences between 3 and S.
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Re: Official Tesla Model 3 thread

Fri Aug 25, 2017 7:57 am

lpickup wrote:
SageBrush wrote:However, (IIRC -- I have to double check)
The peak power rates for 2170 cell packs are lower than 1865 for equivalent kWh pack sizes.
We can guess why that is, but the cell reduced surface area to volume is a given.


Yeah, different serial/parallel organizations would account for different peak power comparisons at the cell and the pack levels. This is not surprising, considering the 0-60 differences between 3 and S.


0-60 is a result of the lower motor output of the PM motors and restrictions to separate the product offerings. The Model S 75 just got pushed a software update recently to shave 1 second off the 0-60.

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