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A little spreadsheet trying to explain/conceptualize why things are the way they are

Discussion in 'Model 3' started by emir-t, Jul 30, 2017.

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  1. emir-t

    emir-t Member

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    Since the unveil I've heard so many people disappointed with;

    • Slow supercharging of the 3
    • Lower than expected performance values for the 3
    • Expensive options for the 3
    etc. etc.

    So trying to understand what they made with the 3 I plotted a spreadsheet explaining cells, pack architecture they used and supercharging speeds. We already know about the old S and X packs and their supercharging speeds. And last week we found out there were 4416 cells with the range version of the 3. Rest is all speculation but I think it makes sense. Correct me if I'm wrong or you have anything to add. I just love geeking out on technicalities like this. Here's the spreadsheet for your liking;


    Notes;
    [​IMG]
    • As you can see standard Model 3 will have a very low voltage pack. Whereas most packs have 400V and 75 pack has 350V right now. Standard Model 3 pack will have a 300V pack. Meaning the same amperage when charging and driving will yield less kW i.e. power.
    • That is why I think the spreadsheet shows the standard 3 to be slightly less efficient than the range one. I believe under acceleration packs will feed around 750-800Amps to the inverter. However because Tesla didn't want a slower than 6 sec. 0-60 car on the standard one they need more amps with standard due to less voltage. This might make it less efficient.
    • This also explains why they're coming out with the 400V pack first. More time to test the 300V system as it is the first time they're building something with this low voltage.
    • As for supercharging. You can see this past 4 years Tesla (up to 50%) had 1.05-1.1C supercharging with their chemistry. Figuring out the numbers from what we are given shows the same C rates for the 3. I would expect less since 2170, due to geometry, suffers from a less efficient heat dissepation. Yet apparently Tesla has made the pack cooling better with their new architecture, sustaining the same C rates. If anything they're pushing the standard pack to its limits. (I got the supercharging average power from various supercharging graph and videos I found online. They seem to check out.)
    • I'm so glad Tesla gave up on faux battery labeling. This has been discussed thoroughly but it is very clear old 85 and 90 packs are not 85 and 90. New 75, 100 packs give what they promised. Hell a 3 year old 85 can have the same capacity as a brand new 75 now even.
    • It astonishes me how much easier and cheaper pack building must have become with new cell geometry. ~2600 less needed for same capacity. For both terminals this means 5200 less holding or PCBs or whatever they're doing. Must have decreased the dead weight in pack as well.
    So to sum it all up I don't think Tesla is purposefully throttling Supercharging speed with the 3 to make S better value. If anything they're giving it their most. Also it will be very interesting if 75 indeed turns out to be more efficient than 55. OR 75 won't have 316 EPA but ~300 EPA. (Since they advertise standard to be 220mi EPA yet 310 mi non EPA for range pack)


    Thoughts?
     
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  2. emir-t

    emir-t Member

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    p.s. Only supercharging video for Model S 75 pack was the software limited 60 supercharging video of Bjorn. There the average power to 75's 50% (60s 62%) was 90kW. Hence highest C rate, closer to 1.2C. However I think this is due to it being a 75 pack software limited at the top. Since it will never reach true 100% (4.2V per cell open circuit voltage) Tesla is comfortable adding 0.1C more to its supercharging speed. I'm sure true 75s don't average 90kW to 50% right?
     
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  3. Jayc

    Jayc Member

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    It's a bit strange why, at a time when some supercharger stations are likely to be overwhelmed by an increase in demand due to Model 3, that Tesla has chosen to architect the battery pack to be lower in charge rate thereby slowing down Supercharger station throughput even further.

    My opinion: This car has been engineered from ground up with the next decade in mind. However, Tesla's marketing and finance, the same bunch who are dead scared of M3 cannibalising MS, is holding EM and Tesla engineering to ransom insisting that they software limit every feature that M3 has over MS.
     
  4. Matias

    Matias Active Member

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    What is your source for this?:)
     
  5. Matias

    Matias Active Member

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    I don't have the competence to evaluate your spreadsheet otherwise, but supercharger km/min should be miles/min.
     
  6. emir-t

    emir-t Member

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    Someone from the inside reported that 4416 cells were going to be used with the 3 in terms of geometry. However we know they made the whole gigafactory based on 2170 geometry and 4416 cell would be a pancake cell, rendering all of Tesla's experience with 100s of thousands of S-X invaluable. Just makes zero sense.

    Then, someone genious tested the idea that there can be 4416 cells. Math checks out incredibly well with capacity and range. It is in no way confirmed but would be more surprising if it was something different.

    My take is that Tesla didn't want to reinvent the wheel here. As you can see from the graph announced supercharging rates are exactly on par with rest of the fleet in terms of the stress cells are under. As I've said in OP if anything I would expect the rates to be less since heat dissepation inevatibly suffers with the new cells. I think Tesla wants to increase their presence, coverage and numbers by spreading Model S-X tech to masses. Advancements will come gradually during and after the Model 3 program. "S/X is good as it is, so spread it to masses and innovate on higher end as you become a large automaker in 2-3 years instead of a California startup." is their strategy imho.

    Your theory is certainly plausable since this is Tesla but it implies that the new cell chemistry is vastly different allowing up to 1.5C rates while charging and that it is software limited currently. I don't think they took the risk to vastly change cell chemistry with this volume vehicle and decided to not break something that works.

    While the chemistry rest of the automakers use are indeeed capable of faster charging, (My BMW i3 sustains +2C to 50% and more, Ioniq sustains 2,5C+) their energy density is much lower and their costs are much more expensive. I don't think they can close that gap and be competitive with Tesla in 3-4 years it'll take Tesla to up their charging speed chemistry. By then Tesla will become giant enough to not be dealt with, carving themselves a good spot in the industry. We'll see.

    Ah yes. Was making the excel to see for myself and test the idea in kms. Then decided to change the values to miles since this forum is mostly US. Didn't change the label. Calculations are correct with miles though.
     
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  7. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    #7 KarenRei, Jul 30, 2017
    Last edited: Jul 30, 2017
    Is the difference in Wh/mi confirmed? Where is that coming from?

    Ed: More to the point, the spec sheet seems to contradict it.

    Short range: 30 miles @ 240V*32A = 256Wh/mi
    Long range: 37 miles @ 240V*40A = 259Wh/mi

    Basically a rounding error between the two. Note that the above calc is a bit naive as rarely will a 240V*XA outlet actually deliver 240 volts and X amps. The voltage varies and is often a bit lower than nominal, and you generally can't hit the max amps. I don't know exactly how they're calculating this.
     
  8. R.S

    R.S Member

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    So the small battery version is less efficient than the big battery version? 248Wh/mile for the "55" and 234 for the "75" seems wrong.
     
  9. strykeroz

    strykeroz Member

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    If the M3 is software limited to force it to slot under the S/X then this isn't a bad thing imo. As all the platforms are continuously improved rather than being locked into a year model regime, we'll see incremental improvements over time - or, even before many of us see delivery. Aside from this the figures on supercharging overall are expected to change as the stations are upgraded.

    The future looks bright.
     
  10. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Yeah, software locks are nice that way. ;)

    I wouldn't expect software locks on the battery size at present (all signs point to the long range battery being literally higher capacity), but charge rates and motor performance, that's not unreasonable at all. Tesla doesn't know how they're going to wear, and doesn't want to warranty something that's going to come back and bite them.
     
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  11. Yggdrasill

    Yggdrasill Active Member

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    I'm still not buying that there are 4416 cells. It requires that Tesla has gone backwards with energy density for 21-70s, and I don't see any reason why they would do so.

    My expectations are more like:

    Long range version: 75.9 kWh total, 73.5 kWh available, 19.76 Wh/cell. 3840 cells, 96s40p. 8 modules with 12s40p. 355V nominal pack voltage.
    Base version: 53.1 kWh total, 51.1 kWh available, 19.76 Wh/cell. 2688 cells, 84s32p. 7 modules with 12s32p. 311V nominal pack voltage.
     
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  12. RubberToe

    RubberToe Supporting the greater good

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    Can you please summarize this with a single bullet on a Powerpoint, in case there are any upper management types trying to understand it?

    RT
     
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  13. jeremyz

    jeremyz Member

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    The EPA mileage tests don't include important driving elements like drag racing, burn outs or donuts. They're more like how a 95 year old drives a Buick. So, I don't think any reduced efficiencies (if they do exist) from pushing the battery/inverter/motor harder in the standard 3 would be reflected in the EPA rating.
     
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  14. emir-t

    emir-t Member

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    3300mAh from the new 90 pack 18650 becomes 4600mAh with only volumetric increase due to 2170.

    3% denser with a little more silicon in the anode would make 4700mAh. What more do you expect? I don't think Tesla is willing to take risks pushing the chemistry beyond what they already now. Once they settle Model 3 architecture and manufacturing they can push a new chemistry with new Model S-X redesigned Roadster packs, eventually finding its way to Model 3 after 2022.

    Also it makes too much sense that 4416 number is the number of cells. What else an it be??
     
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  15. Yggdrasill

    Yggdrasill Active Member

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    #15 Yggdrasill, Jul 30, 2017
    Last edited: Jul 30, 2017
    The current 18650 cells are ~12.4 Wh/cell. With a ~50% increase in usable volume for the 21-70s, that works out to 18.6 Wh.

    Tesla has also said that they expect improvements in chemistry with the Gigafactory. Going to 19.76 Wh would be a ~5.4% improvement. Probably not very risky. (Edit: Remember, the 90 pack started shipping mid-2015. So the current chemistry is two years old. They haven't managed a measly ~6% improvement in two years?)

    Incorrect intel.
     
  16. emir-t

    emir-t Member

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    Haha! Literally burst out a laughter!

    I meant even a cruuising power of 30kW needs much higher amperage for the small pack due to low voltage levels. You can get some limited Amp hours from a battery anyway. I don't know, just my .02$
     
  17. FlatSix911

    FlatSix911 918 Hybrid

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    Great analysis ... has the battery capacity of 55 and 75 kWh been confirmed?

     
  18. SageBrush

    SageBrush 2018: Drain the Sewer

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    Nice analysis; I think within 5% of actual with a high degree of probability.
    I don't see any errors -- but other available information like home charge rates give different consumption rates
     
  19. Zoomit

    Zoomit Member

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  20. SageBrush

    SageBrush 2018: Drain the Sewer

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