Like I said before, even if you stack two Model 3 long-range battery into the new roadster, it would only get you to 160 kwh. And there is no way the new roadster has more than twice the space than the Model 3 to pack all those batteries. This fact alone STRONGLY suggests there is a new battery chemistry in new roadster with higher energy density per cubic volume/weight.
200 kWh Roadster Pack: How is Tesla Pulling This Off?
- Thread starter jackbowers
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- Batteries Roadster 2020
A couple of points:
1. 160 kWh is roughly sufficient for the performance specs stated by Tesla. The jump from 160 kWh to 200 kWh could be the expected improvement in energy density going from 2017 to 2020.
2. I don't think they've simply stacked two Model 3 packs. I think they've stacked Model 3 battery modules in some configuration in the car. They could have gone for eight 23s modules in two layers in the footprint plus two 25s modules on top of each other in the center channel, as an example. That would be roughly 195 kWh.
Continuing from external measurement thread.
If the internal pack cell area can be 83×47, that allows 5 m^2 in pack area for double stack. 200kWh of 3.6V, 4.75 Ah 2170 cells at 90% density takes 4.5 m^2. So it seems doable on current tech.
I measured about 48 between rear wheels (assume frame rail outside that point) and side wheel well to wheel well distance of 83-87 from video and 87-88 from render. So it seems possible with current tech.
I think you're missing the fact that the cost doesn't suggest there's some new experimental battery chemistry at play. If anything, the cost of the Roadster suggests the exact opposite, that they expect battery costs per kWh to be even lower by 2020 than they are today.
I'd love for that to be the case, because it means that it'd be possible to shove ~240kWh underneath my MX P100D, but nothing in the news suggests that level of advancement.
ecarfan
Well-Known Member
...a statement based purely on just what Musk said... not corroborated by anything we know about the current battery technology or any upcoming advances in cell chemistry
I'm inclined to believe Musk when he makes statements about what is. I take him with a grain of salt when he makes statements about when a new car model will be ready or when production will ramp up.
Several posters have offered plausible ways the prototype new Roadster could actually be carrying 200 kWh. No new battery technology seems needed, though advances could mean more storage space when the car goes into production.
Batteries have improved slowly over the years, and I see no reason not to expect them to continue to improve slowly.
My theory of new battery tech is based on BOTH costs and physical size/limitation. Not just cost.
Your theory where Tesla didn't use any new battery technology is just as unlikely, and even worse than my theory. You guys really think Tesla double stack Model 3 battery and cramp it into the new roadster?? The new roadster has a LOT less vertical height the designer can work with in the first place, and they need to double stack two battery to lower that vertical passenger space even further?? So the seat height clearance is just tall enough for a 15 years old kid??? Even if they did in some magical way and double stack the battery, it would only get u up to 150 or 160 kwh. NOT 200 kwh.
All of these are very strong engineering circumstantial evidence. Not some wild speculation and has no basis.
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We're just going to have to agree to disagree. The batteries are made up of modules, double stack doesn't have to mean there are exactly double the number of modules from the LR Model 3. From the videos I saw, the passenger's legs went almost straight forward and the seats looked reclined. I believe there's batteries packed into that chassis wherever there isn't space required for a body or a motor. That includes between the seats and under and behind the rear seats. Nobody says they have to be the same modules the Model 3 uses, more likely a battery built on top of the traditional tray, stacked upwards to fill every available cavity.
Sig72
Member
This sounds right. The current 100kwh S/X packs are still using the 18650 cells, and the 2170 cells are supposedly ~30% more efficient today. Give Tesla a few years and they will be able to find additional efficiencies. I think that double stacking 2170 cells will be doable. My guess is they will be stacked even higher below the rear seats (like a Bolt) just in front of the rear axle. I expect the rear seat of the new Roadster to be like that of a Porsche 911- pretty much useless. The expected range/pack size/efficiency is telling about the expected weight of the new Roadster too. I'm hoping that Tesla can match the Model S's drag coefficient (0.24), and they are predicting 620 miles of range out of 200kwh- indicating an expected efficiency of 323 wh/mi. A 100D today is rated for about 317 wh/mi. This indicates that either 1) the new Roadster is going to weigh 4500+ pounds or 2) it will be lighter, but with a higher Cd of drag. I'm hoping its the latter, as the car has a pretty serious rear diffuser and a small rear wing as well, both of which increase drag. The prototype was also wearing Michelin Pilot Sport Cup 2 325/30ZR21 rears and 295/35ZR20 fronts. This is a VERY sticky tire compound and even if Tesla pairs back that tire width for production, we're still looking at much more drag from the tire width (personally, with 7000+ lb/ft of torque, I want 325-section rears). Still, I have a hard believing that the car will be under 3800-3900 pounds, which means this will be more of a GT car than a featherweight sports car like the original 2800lb Roadster. Ballistically quick in a straight line, AWD, higher curb weight (plus more sound deadening that OG Roadster), likely higher center of gravity, and super long cruising range = GT car. This thing will corner like P100D (or P85D w/ + suspension), but not like a 911. Even if this will be a heavier hyper-GT and not a lightweight canyon carver, it still looks awesome and I can't wait to see final specs (and maybe own one).
P.S. @ecarfan we should go for a drive sometime, both in San Mateo
Sig72
Member
I'm also hoping that Tesla brings back the all carbon-fiber body panels in an effort to keep weight down
I think flathill means that the packs are modular like the s/x, but instead of having the cells vertically oriented, the cells are layered horizontally until they reach a height they want.
The difference would be which method is volumetrically more efficient in terms of packing cells.
The difference is the gas/fire vent path (safety)
Double stack can be made to work but blade config is safer
Lloyd
Well-Known Member
Brando
Active Member
18650 vs 2170
30% cheaper
47% more volume
right?
energy density of the cell vs of the module or pack - aren't they all slightly different?
energy density of 18650 vs 2170 - nearly identical if the chemistry is the same, right?
energy density of the module/packs vary depending cell/module/pack is used, right?
The battery parts are different, as in
Model S pack vs Model 3 pack
Model S module vs Model 3 Module
Model S cell 18650 vs Model 3 cell 2170
Thanks for pointing our any errors from above.
30% cheaper
47% more volume
right?
energy density of the cell vs of the module or pack - aren't they all slightly different?
energy density of 18650 vs 2170 - nearly identical if the chemistry is the same, right?
energy density of the module/packs vary depending cell/module/pack is used, right?
The battery parts are different, as in
Model S pack vs Model 3 pack
Model S module vs Model 3 Module
Model S cell 18650 vs Model 3 cell 2170
Thanks for pointing our any errors from above.
That depends on acceleration.
with a = 1.29 g
first foot takes 0.22 s
total 0 to 60 60 mph/(12.6552 m/s^2) = 2.12 s
Closer to 0.2 s than to 0.25 s
What's all this stuff about "rollout"? Does this mean that zero to sixty is not really zero to sixty? It's actually 1 or 2 mph (whatever the car can do in one foot) to sixty? Zero to sixty should start at zero. Otherwise they should say something like 3 mph to sixty, or whatever.
It's based on how you stage at a drag strip. Honestly, it doesn't matter to me which method they use, so long as everyone uses the same method. Or better yet, publish both values.
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