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Tesla Battery Generations

Discussion in 'Battery Discussion' started by wdolson, Jun 12, 2016.

  1. wdolson

    wdolson Active Member

    Jul 24, 2015
    Clark Co, WA
    With evidence the 100 KWh battery pack will be available soon I did some calculations. Tesla hasn't been completely open about their batteries, but we know some things.

    The 100 KWh battery pack will be the 3rd generation of Model S/X batteries. The 1st generation has been studied in depth, but I don't see where anyone has taken apart a second generation pack (70/90).

    What we do know is Tesla makes a small pack and a large pack. The advertised capacities are as follows:

    1st gen
    Small - 60 (some early ones limited to 40 with software)
    Large - 85

    2nd gen
    Small - 70
    Large - 90

    3rd gen
    Small - 75? (software limited to 70 and most recently 60)
    Large - 100

    I'm assuming the battery pack layout is the same for the 2nd and 3rd gen as it was for the 1st gen, but I don't think anyone knows for sure. The packs are organized with a number of modules, each made up of individual cells. The small pack module has 384 cells and the large pack 444. The small pack is organized into 6 cells in series by 64 in parallel. The large pack is 6 cells in series by 74 in parallel.

    The small pack has 14 modules and the large pack 16. The small pack has 5376 cells and the large pack 7104. The large pack has 32% more capacity than the small pack just based on the number of cells.

    The individual cells in the 1st gen was the Panasonic 18650B of which Panasonic sells several sub-marks. The nominal voltage is 3.7V per cell with a max voltage at 100% charge of 4.15V. 3.7V is used for all KWh calculations. 4.15V is only at max charge and it quickly declines, staying between 3.6 and 3.8V over most of its discharge.

    We have pretty solid data from wk057 and others on the 1st gen packs and the actual size of the large pack was less than advertised.

    The current capacity of the cells is as follows:

    1st gen - 3.1 Ah
    2nd gen - 3.5 Ah (my best guess)
    3rd gen - 3.9 Ah (again my guess)

    This results are in the following chart:


    I'm guessing the nominal voltage is the same. That is established by the electrochemical potential between the materials used in the anode and cathode and if that hasn't changed much, the voltage should be the same.

    We know the 1st gen packs were really 61 KWh and 81 KWh, making the 85 KWh packs a bit of false advertising. By experimentation I found that a 3.5 Ah cell would give you a 69.6 KWh and 92 KWh pack for the second generation which is very close to the advertised capacities for the 2nd gen packs available for most of the last year.

    A 3rd gen battery of 3.9 Ah would give you packs of 77.6 KWh and 102.5 KWh. This argues that the new 75 KWh pack is really the new battery chemistry. To further the possibility if you look at the capacity of the Powerwall, it's advertised at 6.4 KWh, which is the rating for one large pack module with 3.9 Ah batteries.

    It is possible the 75 KWh battery is the 2nd gen battery with 15 modules instead of 14, but that would increase the voltage of the pack and might mess up some of the energy algorithms in firmware, though that can be adjusted in software. If the 75 pack is 15 modules of 2nd gen batteries, it would have a capacity of 74.6 KWh.

    This assumes the 2nd and 3rd gen packs have the same number of cells and the same module arrangement as the 1st gen packs. It's quite possible Tesla has redesigned the pack arrangement too. We won't know until someone takes apart a 2nd gen pack.

    If the current 75 pack is using the 3rd gen cells, it does raise the question why we haven't seen the 100 KWh pack yet. It may be the supply of 3rd gen batteries is limited right now and they only have enough to support the smaller packs. As Panasonic can supply more 3rd gen cells, the larger pack will go to 100 KWh. Bad news for people like me who just bought a car, but that's the way it all shakes out.
    • Informative x 2
  2. Saghost

    Saghost Well-Known Member

    Oct 9, 2013
    Although it hasn't been proven to my knowledge, the conventional wisdom on the forum is that the 70 and 75 kWh packs have the same 74 parallel modules that the 85 and 90 have, rather than the reduced modules of the 60.

    This would change a lot of your math...
  3. wdolson

    wdolson Active Member

    Jul 24, 2015
    Clark Co, WA
    Interesting possibility. If that's the case, the 70 would be using 1st gen cells and the 75 second gen cells. The math works for the 1st gen cells, it comes out to 71.2 KWh if you use 14 modules of 444 batteries. However if you use 14 modules of 444 batteries for the 2nd gen cells, you get 80.5 KWh. Even lowering the Ah of the 2nd gen battery to 3.4 Ah get a 90 pack with 89.4 KWh (which is possible), and a 75 KWh pack with 78.2 KWh. I would still think they would round up the 78 to 80 in that case.

    The 70 KWh battery pack was introduced in April 2015 and the 90 KWh in July 2015. The two being introduced so close together makes it more likely both are using the same generation of batteries and we're in the middle of another similar evolution now. The 100 could be coming out next month if the same pattern holds, which knowing Tesla, it probably won't.
    • Informative x 1

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