Double stacked battery pack

Tinker71

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I know it was mentioned in the reveal over 2 years ago that the CT3 would have a double stacked battery. I guessing they were planning on many battery day upgrades at the reveal but I doubt they built it all in. I am really struggling with the double stacked design for the following:

1.) There would be a 80mm void minimum in the CT1/2. Unless the floor pan was different, which would probably require different castings.
2.) The shear is transferred from the skin of the battery through the honeycomb matrix. If there is a stacked pack, there will be some sort of collector plate between stacks that will disrupt the shear transfer.
3.) Any movement between the sheets of batteries would be very problematic.
4.) I could see a spot repair on a single sheet of batteries. Double stacked = twice the problem.

I am guessing there is enough volume with a single sheet of batteries to get 500 miles of range with the CT3 or close to it. The other models will simply have more honeycomb material between batteries or possibly a different chemistry. It shouldn't be that difficult to model, but beyond my current capabilities.

I suppose it would be possible to stack sections or portions of the battery using more conventional modules near the axles, under the seats or in the dashboard. I think they already do that on the S to some degree.

In summary I think there will be a fairly standardized structural pack across the models with add on modules tucked here and there on the CT3. What do you think?
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Crissa

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1.) There would be a 80mm void minimum in the CT1/2. Unless the floor pan was different, which would probably require different castings.
The casting isn't the floor pan. But yes, we have no idea how they'd solve this. It may be the double pack extends down between the axles, and so there would be more empty space under the single-motor version.

2.) The shear is transferred from the skin of the battery through the honeycomb matrix. If there is a stacked pack, there will be some sort of collector plate between stacks that will disrupt the shear transfer.
This is true no matter whether there are stacked packs. I don't see it as an issue. If you took two piece of plywood and nailed them together, they wouldn't be less strong than a single piece.

3.) Any movement between the sheets of batteries would be very problematic.
True. But any movement between the battery pack and the cabin is also problematic.

4.) I could see a spot repair on a single sheet of batteries. Double stacked = twice the problem.
You can't spot repair a battery pack. Minute differences in he inherent voltage curve of the cells makes this a fool's errand unless you want to be hand-balancing the cells frequently.

-Crissa
 

Bigvbear

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Were assuming they will still go with the double stack pack. With the 4680 cells a single layer pack could do it.
 

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I know it was mentioned in the reveal over 2 years ago that the CT3 would have a double stacked battery.
Was that mentioned? or was it like the Vault T slots, something that people just speculated and spread?
 

Crissa

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Was that mentioned? or was it like the Vault T slots, something that people just speculated and spread?
One of the articles at release had a more detailed look inside, and they reported that the reason for the Tri-motor double range was in fact, a double-layer battery pack.

https://www.motortrend.com/cars/tesla/cybertruck/2021/tesla-cybertruck-electric-pickup-photos-info/
https://www.cybertruckownersclub.co...-vs-standard-equipment.2211/page-3#post-36662

We don't know the current plan, but Tesla's current battery is 70mm and 80mm is not twice that in size. So it's not 'double' because of the height.

I'm sure we'll find out when the Rivian is released.

-Crissa
 


rr6013

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I know it was mentioned in the reveal over 2 years ago that the CT3 would have a double stacked battery. I guessing they were planning on many battery day upgrades at the reveal but I doubt they built it all in. I am really struggling with the double stacked design for the following:

1.) There would be a 80mm void minimum in the CT1/2. Unless the floor pan was different, which would probably require different castings.
2.) The shear is transferred from the skin of the battery through the honeycomb matrix. If there is a stacked pack, there will be some sort of collector plate between stacks that will disrupt the shear transfer.
3.) Any movement between the sheets of batteries would be very problematic.
4.) I could see a spot repair on a single sheet of batteries. Double stacked = twice the problem.

I am guessing there is enough volume with a single sheet of batteries to get 500 miles of range with the CT3 or close to it. The other models will simply have more honeycomb material between batteries or possibly a different chemistry. It shouldn't be that difficult to model, but beyond my current capabilities.

I suppose it would be possible to stack sections or portions of the battery using more conventional modules near the axles, under the seats or in the dashboard. I think they already do that on the S to some degree.

In summary I think there will be a fairly standardized structural pack across the models with add on modules tucked here and there on the CT3. What do you think?
Once you asked about sheer, sheer transfer and castings the question belongs to Engineers who work for Tesla. If you want to know where to find clues instead of answers:

1) Casting more than one Part No. for Cybertruck? Tesla are efficiency minded engineers. Building molds, adding parts to inventory and production changeovers is inefficient. One mold, one casting and no casting changeover will support whatever is bonded at the end castings.

2) Sheer transfer will all be picked up at the battery box by its edge plane design, surface contact area and unitized dimensional cross section area of the battery box. Expect “dummy” layer of solid honeycomb fill where battery cells are not present.

3) Internal honeycomb will be responsible for battery movement by design. Torsional rigidity is the engineered property added into the battery box by use of the honeycomb battery cell matrix assembly.

4) Cell failure is repairable, however costly. Engineering design mitigates failure points through materials engineering, design and assembly processes. Multi-cell battery technology has been practiced since ever. Tesla are not in business to sell a dangerous product, combustible or explosive under any circumstances.

These components box, honeycomb and cells sandwiched into a matrix rigidity are Tesla‘s final answer to its exo-skeletal structure. Internally exist wire, components, fillers, cells and cooling that create complexities. Your concern may be one complexity. Solutions may vary but not the fundamental design. Design is not the real problem.
 

Crissa

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In the Aptera, the ultra-range does use a different shell than the normal-ranged models and loses some cargo space behind the front seats.

Since it's just a slightly higher panel, it's only a two-part difference.

I would assume the same for the Cybertruck; the extra battery impinges on some space somewhere, but since it's just a body part, no other parts would really be needed.

-Crissa
 
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Tinker71

Tinker71

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Casting more than one Part No. for Cybertruck? Tesla are efficiency minded engineers. Building molds, adding parts to inventory and production changeovers is inefficient. One mold, one casting and no casting changeover will support whatever is bonded at the end castings.
I agree 100% here. I have earlier hypothesized that the castings with be identical across the line. The CT1/CT2 rear gearbox may even be a dual motor layout albeit with different motors than the CT3. and there will some sort of cast blank will be used in the front of the CT1 so that most of the front suspension will be the same. This is precisely why the the basic structural pack will be the same volume across the line with more or less cells/more or less honeycomb/different chemistries.

I re-watched part of the battery day presentation and I wish I had the screen print to point out the area under the seats as potential for add on batteries. There is also a thread about space under the dash were the firewall would be in a ICE. These spaces might add up to 30Kwhrs of battery potential but might be just enough if Tesla can't fit all the juice for the CT3 in the standardized structural battery area. I suppose the areas under the seat and firewall could be continuous with the rest of the pack and could be "double stacked" in those areas but just can't envision that 90MM void (filled with honeycomb goo) in the CT1/2 across the entire pack.

Supposedly more details will come out this quarter and we can stop obsessing about things we have no control over this summer. :)
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