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6831 of these

Discussion in 'Roadster: Technical' started by NigelM, Sep 24, 2011.

  1. NigelM

    NigelM Recovering Member

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    I'm guessing that many of you have already seen one of these, but I searched and couldn't find a pic anywhere so figured I should just post one:

    attachment.php?attachmentid=2676&stc=1.jpg
    cell.jpg
     
  2. TEG

    TEG TMC Moderator

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    Compared to an AA:
    4864408854_507982d28d_b.jpg
     
  3. TEG

    TEG TMC Moderator

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    JB goes to Japan and gets them one at a time from Panasonic:
    ViewMedia?mgid=225194&vid=5&download=1.jpg
    (Just kidding!)
     
  4. TEG

    TEG TMC Moderator

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    It's the Batteries, Stupid!
    (from 2008)
     
  5. markwj

    markwj Moderator, Asia Pacific

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    I had to change the battery in my Tom Tom 910 gps and was pleased to discover it was an 18650. Easy and cheap to buy a replacement in the local electronics street.
     
  6. slcasner

    slcasner Member

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    Nigel, nice picture, but you should have put the other side of the scale near the cell! (65mm after all) :smile:

    I carry an old cell from a laptop with me so that I can show it to people when I say "6831 of these".
     
  7. S-2000 Roadster

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    So that's why the Roadster sells for $140,000!
     
  8. vfx

    vfx Well-Known Member

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    Yeah, and imagine how much time they waste taking a picture every handoff.
     
  9. smorgasbord

    smorgasbord Active Member

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    Using this math: 53000kWh/(6831*3.6v) I get 2.1 AmpHours per battery. Does anyone know what the ratings of the batteries actually used in the Roadster is - I haven't seen any 2.1mAh, just 2.2s.

    You can buy these 3.0 AH 18650s for $3.50 each in quantities of 2. Imagine the price when you're buying tens of hundreds of thousands. That would add 36% more range, or 333 miles for the Roadster.

    Here's a link to a Panasonic Data Sheet for the 3.0 Ah 18650s.

    Any chance Tesla would use something like these in a few years for Roadster replacement packs?

    (Sorry if this has been covered elsewhere, I did try searching, but it doesn't do so well with numbers)..
     
  10. qwk

    qwk Model S P2681

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    The roadster pack is 56 kwh....
     
  11. TEG

    TEG TMC Moderator

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    #12 TEG, Sep 25, 2011
    Last edited: Sep 25, 2011
    There has been a lot of discussion and speculation about the exact cells used in the roadster. I think it is likely that they are slightly 'derated' for longevity reasons. Also they are probably 'old technology' at this point. I suspect that the new cells in the 300 mile model S pack will be 'next generation' with higher energy density.
     
  12. TEG

    TEG TMC Moderator

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    It is hard to say what Tesla might offer in terms of future roadster replacement packs. Probably easiest to stick with what they know works as long as they are available, but one can always hope they offer an extended range pack someday. I bet it is feasible but at a cost of re-engineering and re-testing.
     
  13. dsm363

    dsm363 Roadster + Sig Model S

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    I don't know the exact specs but Tesla only gives the car access to a smaller amount of the battery capacity to help prolong battery life so it could be the 2.2s.

    I'm hoping Tesla provides updated packs at some point but nothing has been announced.
     
  14. TEG

    TEG TMC Moderator

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    Yeah - I think the best guess was 2200mah or 2400mah... Which isn't very dense by today's standards.

    Now, keep in mind that Tesla tested loads of cells, and found ones that they thought had the best balance of price / lifespan / energy density / power density / reliability / etc.
    Just because some other cells with more energy density are available doesn't guarantee that they would be a good fit for the Roadster application.

    Apparently the new cells for the Model S 300 mile range have been 'optimized' for use in an automotive application unlike the original Roadster pack which did the best it could with cells designed primarily for use in laptops.
     
  15. dadaleus

    dadaleus 4GETOIL P85#S70,FdrX,S85D

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    Peter Rawlinson specifically told me so at an S event at the Newport store. That was after they had said the first S's would have 240 mile packs, but then changed back to saying 300 mile packs. He said they weren't sure they could get the higher density batteries in time, but then got it worked out.
     
  16. S-2000 Roadster

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    53000 kWh would be 53000000 Wh. 2.1 mAh would be 0.0021 Ah.
    qwk has already pointed out that the first constant should be 56000 Wh. Based on information from other threads here, the batteries are charged to 4.1 V for standard mode and 4.15 V for range mode. That brings the performance down to 2.0 Ah or 2000 mAh. However, the Tesla Roadster battery is going to last significantly longer than if the same cells were used in the originally intended laptop, thanks to the advanced charging, cooling, and discharging technology.

    If Tesla Motors wanted to build a pure track car, where it doesn't matter if the battery pack were ruined after a day of racing, then I'm sure they could muster 3000 mAh from each cell. I just don't think the resulting technology would be very popular for normal drivers.
     
  17. bolosky

    bolosky Member

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    You can't just multiply like this, because as the batteries discharge the voltage drops. You need to find the voltage as a function of state of charge and then integrate over the whole range to find out how much energy you get from them.
     
  18. W.Petefish

    W.Petefish Active Member

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    I recently saw some of the 18650 cells that have a 2600mAh rating.
     
  19. stopcrazypp

    stopcrazypp Well-Known Member

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    #20 stopcrazypp, Oct 1, 2011
    Last edited: Oct 1, 2011
    Usually capacity for laptop cells are measured at nominal voltage, not at fully charged voltage. Like bolosky says, if you really want to be accurate, you would integrate the voltage over the state of charge, but the nominal voltage usually gives a good enough approximation.

    In a previous thread in last year, I already gave a pretty good guess as to the type of cells in the current roadster. I guess Sanyo UR18650A 3.6v 2250mah (min nominal capacity 2150mah), which works out to 52.87 kWh (2150 mah) to 55.33 kWh (2250mah) if you multiply it out for 6831 cells. That 52.87 rounds out to 53kWh nicely, 55.33 kWh is not quite 56kWh though. Anyways, the cells are likely around this range.

    http://www.teslamotorsclub.com/showthread.php/4549-What-will-be-the-price-difference-on-the-batteries-be?p=50104&viewfull=1#post50104

    Panasonic also makes 3.6v 2250mah cells:
    http://industrial.panasonic.com/www-cgi/jvcr21pz.cgi?E+BA+3+ACA4001+4++WW

    The next step up for them is 2900mah, so that is unlikely.

    Here's Sanyo's cells:
    http://battery.sanyo.com/en/product/lithium-ion/lithium-ion.html

    The next step up is 2600mah, which also is unlikely to me.
     

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