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18650 cells with 5.8 Ah = 160 kWh battery

Discussion in 'Technical' started by David99, Nov 11, 2015.

  1. David99

    David99 Active Member

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    Just saw some 18650 cells that claim to have 5.8 Ah. The Model S cell has 3.1 Ah. If that cell I saw was legit, it would result in a 160 kWh batter for the Model S. Something can't be right here. Tesla would be be using them if they would be any good. I really haven't done much research on 18650 cells. What is the standard these days?
     
  2. hpjtv

    hpjtv Member

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    You'd need to provide a link to these cells you are stating. Most of the Chinese knock-offs state a higher capacity than they really are. They might also not be suitable for high drain applications.
     
  3. David99

    David99 Active Member

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    Yes often their capacity is overstated, but not by 100%. Here are some that even claim 6 Ah.
     
  4. stopcrazypp

    stopcrazypp Well-Known Member

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  5. wdolson

    wdolson Active Member

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    Counterfeits and exaggerated parts from China are a serious problem in many areas of industry. Alaska Airlines lost a 727 off Los Angeles due to counterfeit bolts from China around 2000. Integrated circuit suppliers are now having to check parts to make sure they aren't counterfeit. Counterfeit testers is now a growing industry.
     
  6. hpjtv

    hpjtv Member

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  7. MacroP

    MacroP Member

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    Yeah the interweb is full of fakes 18650 especially on Ebay which makes it hard for those not in the know. I've bought many fakes (on purpose) via Fleabay to test them (I have a Maynuo electronic load). Normally come in around 1000-1500mAh tops. Most still have the originally labeling or stamps underneath the new plastic shrink with the dodgy labeling. I then claim back from Ebay and leave the seller negative feedback :). The Ultrafires are a common fake.

    I get all my 18650s from Fasttech as they seem to be the cheapest online, have plenty of stock of all the majors and have pretty fast delivery to Australia where I live - if I pay the extra 2 bucks for express (otherwise free postage). I think they are Hong Kong based. They at least test all of their cells and give an honest capacity rating plus they have a review and discussion area for each product. Over the last few years I've been buying mostly Panasonic (now merged with Sanyo) but lately have been getting some quality LG cells which are around 75% of the cost of the Panasonic/Sanyo cells. Highest capacities on the market seem to be the Panasonic 3500mAh and the LG 3500mAh. I just got some new 3500 LGs the other days for some more cordless tool upgrades. Samsung also have a 3500mAh coming soon I believe. All of these are NCM chemistry.

    I have "18650 upgrade" OCD I think.:tongue:
     
  8. WarpedOne

    WarpedOne Supreme Premier

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    Can you please do some discharge charts of those cells at different C-loads?
    What is the weight, exact dimensions etc?

    Pretty please with sugar on top!
    :)
     
  9. Matias

    Matias Active Member

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    #9 Matias, Nov 12, 2015
    Last edited: Nov 12, 2015
    This has been discussed many times, but what is current consensus, what cells Teslas 85kWh pack has?

    Edit: OP said The Model S cell has 3.1 Ah. So using 3.5 Ah Tesla's pack would be 96 kWh?
     
  10. MacroP

    MacroP Member

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    Hi,

    Yep - these tests have been done already for you (and me). The LG MJ1s have been heavily tested by people on the webs hence why I have bought them myself. Google is your friend. 12-12.5Wh is doable from each cell on a 1C discharge. These are really energy dense cells but not really power dense. They get warm quickly when you pull 10Amps from them. The HG2s would be better for bit more power density. The HG2s are going in my Stihl cordless garden battery (10S3P).

    Here are the latest cells I received the other day. The specs are all there and accurate I've found in the past. Fasttech are really good with this normally.
    https://www.fasttech.com/products/2535100
    https://www.fasttech.com/products/2762804
     
  11. WarpedOne

    WarpedOne Supreme Premier

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    Not necessarily.

    'Transitioning' from Ah to Wh involves a thing called "nominal voltage".
    One can only measure voltage that changes during different SOC and C-loads, this number changes (drops) all the time from full to empty.
    Even full and empty are arbitrarily decided voltages where one decides to stop (charging and discharging) to limit degradation and/or prevent damage.

    How one determines what voltage he will call nominal is whole another story by itself.
    It is supposed to be the voltage, that multiplied by 'nominal' Ah would result in same 'nominal' Wh as would painstakingly summing together all different measured Voltage times measured current that one got by during discharge at some 'nominal' C-load, starting at some nominal 'high' voltage and stopping at some 'low' voltage.

    So, there is this plethora of variables that we do not know about, so we cannot speculate what kWh rating would such a pack get.
     
  12. MacroP

    MacroP Member

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    That's a good question. I'd certainly like to get my hands on a few Tesla cells for some bench-testing. When you start playing with batteries the mAh rating becomes somewhat arbitrary too. Watt-hour should be really used as this is the true energy capacity of the cell. No point having a really high mAh rating and then have with terrible voltage sag. Watt-hour gives better true reflection of capacity. Using the simple analogy of 7104 cells within the largest battery that gives pretty close to 12Wh for each cell (for the 85kWh battery) and 12.67Wh for the 90kWh unit. I don't know the nominal voltage but it is probably somewhere between 3.6 and 3.7 Volts but only Tesla knows this or I can work it out with my electronic load. Lets use 3.65V as a compromise. That gives us 3270mAh and 3470mAh respectively so in the ballpark of what people are expecting. I doubt the full capacity is used by Tesla.
     
  13. Matias

    Matias Active Member

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    Warped and Macro, thank you.
     
  14. WarpedOne

    WarpedOne Supreme Premier

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    I might add that I suspect 85kWh is the maximum energy one might get out of tesla's (2012) battery if he charged it to some crazy high voltage, just a bit before exploding, and then discharging it at crazy low current (milliamps) for crazy long time at some predetermined optimal temperature down to crazy low voltage, right into no-return zone, where permanent damage is already done and cells must not be charged anymore.
    Just pure experimental maximum, from one extreme to the other.

    They then looked at all the variables that affect degradation and performance to arrive at some ~77kWh usable capacity, with different safety margins etc. During production time they learned some additional details, cell chemistry improved a bit so they changed some safety margins and usable capacity for some tiny amount.

    There are reports that 90kWh battery contains the same number of same cells as 85kWh battery. It might, or it might not. It may behave differently when pushed to extremes.

    Oh, and just don't try to look at capacity through miles of rated range.
    That is whole another can of worms and magic and approximation.
     

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