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No Supercharging for 40Kwh :(

Discussion in 'Model S: Battery & Charging' started by fairlycool, Dec 20, 2011.

  1. stopcrazypp

    stopcrazypp Well-Known Member

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    #181 stopcrazypp, Dec 26, 2011
    Last edited: Dec 26, 2011
    The cell density of the NCR18650A (in 85kWh pack) is (note I'm using prismatic volume so not cylindrical):
    3.6V*3.1Ah / 45.5g = 0.245 Wh/g
    3.6V*3.1Ah / (18.6mm*18.6mm*65.2mm) = 0.495mWh/(mm^3)
    http://industrial.panasonic.com/www-cgi/jvcr13pz.cgi?E+BA+3+ACA4001+NCR18650A+7+WW

    The cell density of the SCiB is:
    2.4V*4.2Ah / 155g = 0.065 Wh/g
    2.4V*4.2Ah / (62mm*95mm*13mm) = 0.132mWh/(mm^3)
    http://www.toshiba.com/ind/data/tag_files/SCiB_Brochure_5383.pdf

    So SCiB pack of the same capacity would be 3.79x cell weight and 3.75x cell volume of the NCR18650A, so even a 40kWh SCiB pack with have about 1.8x the cell weight/volume of the 85kWh pack. The SCiB does save some weight/volume from not requiring liquid cooling, but I doubt the cooling system used by Tesla takes up half the volume and weight of the 85kWh pack.

    In general, I'm guessing a A123 cell (like the APR18650) is a better match. It keeps the same form factor and is better than the SCiB cells in density (A123 pack of same capacity would be 2.63x weight, 2.88x volume vs NCR18650A):
    3.3V*1.1Ah / 39g = 0.093 Wh/g
    3.3V*1.1Ah / (18mm*18mm*65mm) = 0.172/(mm^3)
    http://www.a123rc.com/goods-102-Nano-Phosphate+LiFePO4+Original+A123+APR+18650+M1A+Cell.html

    And what's this talk about 1C? There's no doubt the 40kWh pack can charge at 1C safely (40kW), since the 85kWh pack can charge at that rate (there's some slight chemistry differences, but in general lithium cobalt 18650s are cycle tested from 0.5-1.0C charging rate, so 1C shouldn't be an issue for most cells). I thought this was already established in previous discussions.

    The argument was over whether it can safely charge at 90kW ("supercharger" speeds); that's 2.25C. I'm pretty sure even if that can be safely done, it's going to severely effect the life because that's twice the charging rate of the cycle test. And even that 1C rate only gives the 40kWh pack 80k miles life (corresponding to the typical 500 full cycles * 160 miles); Tesla gets the other 20k miles (125 full cycles more) by treating the pack better than the cycle test does.
     
  2. dpeilow

    dpeilow Moderator

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    Well, all we have to go on is the Roadster ESS. If you calculate the cell mass vs pack mass for that, it is roughly half.


    Actually go and look at the charge curves in the Panasonic datasheets. They are not 1C for those larger capacity cells, more like 1/3. The Sanyo was the only one I came across that really shows 1C.

    Agree the A123s look interesting, even if you do need 11,000 to reach 40kWh.


    No, most people are saying they'd be happy with 1C (to get the same 80% in 45 minutes or close to it). It seems to be the "300 milers" who are steering the argument towards 90kW all the time.

    And this is the straw man, because it assumes the owner fast charges every time - rather than the reality of a few times a year in the vast majority of cases.
     
  3. Norbert

    Norbert TSLA will win

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    #183 Norbert, Dec 26, 2011
    Last edited: Dec 26, 2011
    At least according to these specs: A123 @Mavizen ,
    the numbers of A123's "prismatic pouch cell", AMP20, look better on paper:

    Converted to the units you use above:
    0.131 Wh/g
    0.246 mWh/(mm^3)

    Using your numbers for the NCR18650A, it would be 1.88x weight and 2.02x volume for the same capacity. And 0.88x the weight and 0.94x the volume for a 40 kWh pack, compared to the 85 kWh pack using NCR18650A. So it might fit.

    With apparently *much* higher charging power possible (not sure which of those numbers to use, though). Apparently "only" a question of cost. ;) However, not sure if these calculations are correct...
     
  4. Norbert

    Norbert TSLA will win

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    While only Tesla can tell us the specific reasons and details, I think it is a combination of several factors (such as the overall stress on a smaller pack), which caused Tesla to make this decision.

    People where hoping for Supercharging, but see the technical reason for limits around 1C. So they say 40 kW (or 35 kW due to the other stress factors) is better than 20 kW. Which of course it is.

    In the end, I think, this becomes more an argument in favor of a CHAdeMO adapter. But don't forget that the warranty for the 40 kWh pack is already reduced to 100K miles, perhaps without any DC charging capability at all.
     
  5. dpeilow

    dpeilow Moderator

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    I guess we now know why the new Rav4 EV won't have CHAdeMO.

    And probably why Mercedes switched the Smart ED to a different pack supplier for the new version with 22kW 3 phase charging.
     
  6. stopcrazypp

    stopcrazypp Well-Known Member

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    #186 stopcrazypp, Dec 26, 2011
    Last edited: Dec 26, 2011
    I figured you might say that. That's assuming all of the extra weight is from the liquid cooling system. I'm pretty sure the bulk of the weight is from interconnections, module enclosures, and the main enclosure. These elements will also be required by the SCiB pack (as well as the air cooling system, which replaces the liquid cooling system). You have to subtract all the overlapping elements to see the effect of only the liquid cooling system (minus the air cooling system on the SCiB pack). Given the cell weight is roughly half of pack weight, I'm pretty confident the liquid cooling system is less than half.
    It'll be more clear once we can get the pack density of the Fit EV vs the 300 mile Model S.

    Yes, in general the lowest capacity cells are charged at 1C (this is true of Panasonic's datasheets for lower capacity cells too), while the higher ones are charged at lower speeds (like 0.5, 0.7). But I don't take that necessarily as indication that higher capacity cells can't charge at that rate, but that may have more to do with the charging equipment (I notice they keep the charging current around ~1500-2000mA for the 18650s). Note: I'm looking at charging current/rate for the cycle test (not the charging characteristics graph).
    http://industrial.panasonic.com/www-data/pdf/ACI4000/ACI4000CE2.pdf

    I realize that, but I thought it was already established 1C is going to be fine for most cells.

    Actually, that is a fairly standard calculation for pack life (that I use personally even before Tesla ever said anything about the supercharger and that I also use for other manufacturers). That's the baseline life in miles (the only measured indication of pack life), which Tesla will have to do significantly better than in order to provide the 100k mile warranty.

    And in general, even if I was assuming quick charging (which I'm not); I think manufacturers tend to assume worse case in calculating warranty length (which minimizes the chance of warranty claims). As long as there is a possibility of the user relying solely on quick charging, Tesla has to account for that in the warranty to limit liability (or as I suggested, write a limit on quick charging into the warranty terms). Another warranty related factor is the fact that the 160 mile pack will have to quick charge roughly 2x to travel the same distance. Since the warranty is by miles, that means over the lifetime of the warranty, the 160 mile pack will have the potential to quick charge roughly 2x over the same miles.
     
  7. GDH

    GDH Banned

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    Why you can't supercharge a 40kWh battery:

    Why can't you supercharge the 40 kW battery?
     
  8. Oyvind.H

    Oyvind.H Member

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    Short version: Why can you fill a big bucket with your garden hose at full pressure, but not a regular coffee cup....

    Serious version: the superchargers put out so much current the 40kWh battery would probably be harmed if charged that quickly.
    With 90kWh charger the battery will theoretically fill up in one hour (charge rate 1C), but the 40kWh battery would refill in less than half an hour. That`s (most probably) too powerfull for the battery cells to receive.

    In comparison, the superchargers seem to charge the 85kWh at full speed from about 0-50% SOC, then slow down gradually until the battery is full. It`s the battery chemistry that limits the charging current.
     
  9. rolosrevenge

    rolosrevenge Dr. EVS

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    I still will never know why they didn't simply add identifying software which dials down the current to only a 40 kW charger when you plug in a 40 kWh pack. It would take the same time to get you on your way at least. Here's hoping they put a 20 kW AC charger at the locations to accommodate any 40 and non super charging 60 packs that may end up in desperate need of a charge.
     
  10. palmer_md

    palmer_md Member

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    The supercharger at 90kW on an S85 is about 150 miles in 30 minutes. For a 40kW charge it would be about 70 miles in 30 minutes. Given that they plan to put these about every 100-150 miles on the highway, a S40 could not make the distance from one to the next without a full charge. The charger will throttle back when above 50% SOC, so your talking about more than an hour charging the car. Lets say 1:20 for conversational purposes....I have no idea what a real value would be. So in a S40 you'd have to keep your speed down to 60mph to reach the next station, and it would take about 2 hours and then you'd have to wait 1:20 to charge up before heading to the next one. Because of this, the S40 is just not well suited to be used for long distance, which is the purpose of the supercharger network. I realize most people who are buying the S40 probably want it, and I'd want it also if I had ordered that car. On the other hand it makes sense for Tesla not to offer it because someone would order one and then try to make a long distance trip in it and find it is difficult and then they'd drive 75mph and not reach the next station. You know some reporter would do it just to make the car look bad. I'm sure this is the main reason it is not offered. I have to say I agree with the decision, even though (like I said) I'd like to have it offered on the 40 as well.

    Recap: The S40 is not well suited to long distance travel because you have to compromise both speed on the road and spend more time charging to make it viable. Tesla only wants to build "no compromise" vehicles, therefore opted to not allow the S40 supercharger network access.
     
  11. brianman

    brianman Burrito Founder

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    To me it seems fairly simple:
    Tesla has designated "supercharger" as "much faster than 20kW". According to Supercharger | Tesla Motors, they decided 90 kW is "much faster" than 20 kW.

    I think you're asking "but why can't they just drop that down to like 40 kW". Because a factor of 2 is not "super", it's just "double"? That's my read at least.
     
  12. GDH

    GDH Banned

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    Makes sense. For someone like me that does not do long trips the 40 is more than enough, however the longer charge time and the lack of charging stations around Portland is lame. I can do the 65 but 10K 70 more miles is out of my range with the added options. It also looks like they are discontinuing the 40 in Europe?, I wonder if they will do that in the US?
     
  13. RDoc

    RDoc S85D

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    I continue to hope that the reason it's discontinued in Europe and not available on the X is that they're dropping the 40 and adding a 120. :smile:
     
  14. GDH

    GDH Banned

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    Says the person that can afford a 120.
     
  15. Citizen-T

    Citizen-T Active Member

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    Why didn't they invest more time and money into building a system that would encourage their customers to spend less money on their products? The world may never know...
     
  16. doug

    doug Administrator / Head Moderator

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    Please do a search first. This topic is discussed at length here: No Supercharging for 40Kwh :(

    Also please choose thread titles more descriptive than "40". Will merge.
     
  17. Brian H

    Brian H Banned

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    Clogging the pipeline

    Since QC 40s would have to SC more often, and take longer (because of need to hit high SoC, etc.), they would potentially clog and monopolize some stations (near cities, e.g.). And even then could charge only enough to maybe limp to the next station -- or to the next city (since stations will mostly be inter-city, not intra-city).

    Feels like the wrong tool for the job.
     
  18. jcstp

    jcstp Active Member

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    Charging a leaf with 25kw takes 7 to 10 minutes longer (instead of 1h 30)
    http://www.americas.fujielectric.com/sites/default/files/DC%20Quick%20Charging%20-%20FEA%20Comparison%20Study%20%20%2825kW%20vs%20%2050kW%29%207-3-12.pdf page 4

    I think this shows that charging much faster for such "little" batterys is overrated and not necesary.
    That is why I think Tesla did not add supercharging to the 40Kw Battery

    Do you think waiting 1h30 iinstead of 1h40 is worth 500$ ? (price twin-charger 1500$, price for supercharging = 2000$ (+ 10000$ for 60kw battery) )
    Maybe instaid comme together with Tesla-owners and start installing HPC's!
     
  19. markb1

    markb1 Active Member

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    The problem is, with Tesla's announced supercharger rollout plan, superchargers will be far more common than public 90A HPWCs. But, yeah, if there were lots of places to take advantage of the dual chargers, supercharging wouldn't make much sense for 40kWh packs.
     
  20. Eeyago

    Eeyago Member

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    This question may have already been answered on the forum, so I apologize in advance since I'm unable to find it.
    Is it worth getting the twin chargers for the 40kWh if I don't plan to quick charge at home? Are there public chargers in the wild that we can take advantage of with the twin chargers?

    Phil
     

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