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Battery 101: 40 000 cycles with Panasonic 18650 cells?

Discussion in 'Technical' started by slyastro, Jan 22, 2016.

  1. slyastro

    slyastro Member

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    Electrical Engineer, Frank Boucher, just wrote an interesting and easy to understand technical article about Panasonic NCR18650B Cells.

    He also explains why a EV battery pack will be good for much more than 500 cycles, but up to 40 000 cycles (by keeping the pack between 30% and 70% SOC).

    That means that with a 85 kWh Model S, you could drive 100 miles per day per cycle and drive 4 000 000 MILES!!

    I think we should keep it for reference for all those EV sceptics that think that the battery will be due for replacement after 2 years!

    Ok, he kept it simple for the «mass» non technical reader. Your input about batteries physical characteristics would be appreciated.

    LET'S TALK ABOUT THE PANASONIC NCR18650B

    BatterieLi-ionNCR18650B-525x340.jpg
     
  2. nwdiver

    nwdiver Active Member

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    The thing that makes this a bit more complicated is the 'balancing' issue. I have little doubt that shallow cycling the battery between ~30-70% increases longevity but it also decreases usable capacity since the cells become more unbalanced if you don't do a full range charge. My max range charge is down to ~226 miles but I claw about 10 miles back on road trips due to frequent >90% charges.
     
  3. CHG-ON

    CHG-ON Still in love after all these miles

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    Very helpful. Now I fully understand it.

    Thanks for posting this.
     
  4. mkjayakumar

    mkjayakumar Active Member

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    I didnt see any link on that first post.
     
  5. omgwtfbyobbq

    omgwtfbyobbq Member

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    I don't see a link either, but it's probably from this SAFT chart or something similar.

    SAFT.png

    It's probably accurate assuming the batteries are always at ~75F and are charged/discharged non-stop, but IRL, there will be losses in capacity due to aging that also reduce capacity. The lifespan of most packs will probably be pretty good, but probably not 40000 cycles at 40% dod good.
     
  6. mguw

    mguw Member

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    Why shouldn't it balance? On my rc helicopter batteries I can charge to 50% with balancing. It is what we call storage mode.
     
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  7. slyastro

    slyastro Member

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  8. jdbob

    jdbob Member

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    I don't think it needs to charge fully to balance the cells. This isn't for a Tesla but a PHEV but I'm guessing the method of balancing is the same:

    "Individual cells can deviate over the life of the high voltage battery. The purpose of cell balancing is to equalize theindividual cell charges. By balancing the cells the high voltage battery maintains top efficiency. The BECMcontinuously monitors individual battery cell voltages and will perform balancing automatically only when required.When balancing is performed BECM discharges individual cells with the highest voltage to match the remainingcells."

    I don't see any reason why the battery control module in the Tesla couldn't discharge individual cells, no matter the state of charge of the entire pack.
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    I think people are talking about links to the data that supports 40k cycles at 30-70% SOC cycling for those particular cells. The blog linked only shows the generic datasheet which does not support that claim.
     
  10. scottf200

    scottf200 Active Member

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    #10 scottf200, Jan 23, 2016
    Last edited: Jan 23, 2016
    I did appreciate the article overall. Thanks.


    This is an extremely misleading statement. I think with the Tesla pack this occurs regularly in cold weather and I've read it in many threads. HOWEVER, I've never read that happening to normal Volt users ... even those that park outside. May happen in GM extreme testing. I have a 2011 Volt that I've left outside in the open parking lot for 9-10 hr workday in some of Chicago's coldest day and the regen felt the same as on warm days.
    Early Volts are also from 22% to 87%.
     
  11. Johann Koeber

    Johann Koeber Member

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    Very interesting information.

    Also keep in mind that recuperation does charge the battery - somewhat. This happens all the time. I think the way I drive it gets a little charge about every minute or so. LOTS of cycling the battery. But each charge is just very small, usually less than 1 %, even 0.2 %.

    So now I feel sure, these frequent but small charges will not hurt the battery in any significant way.

    On another note: My Lexus 450h GS hybrid car has gone 200,000 miles without any noticable battery degradation. The battery is a completely different tech (I think NiCd), but seems the same reason it does not degrade.
     
  12. Ampster

    Ampster Member

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    #12 Ampster, Jan 23, 2016
    Last edited: Jan 23, 2016
    It is a function of the settings on the balancing controller. Various RC chargers have different balancing settings. One of my RC chargers will pull down the highest cell even when there is no charge voltage. RC chargers have more settings than we get when charging a Tesla. The battery management system on one of my conversions lets me pick the voltage when I want the balancing to start. There is a body of thought that the Tesla charging/balancing process only balances at higher levels of SOC.
     
  13. docherf

    docherf Member

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    Great article. Thanks for the link
     
  14. ratsbew

    ratsbew Member

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    This is interesting, but going between 10 and 90% will (should) still net you 200,000+ miles of endurance while retaining sufficient capacity. I'd rather plan out how long I intend the vehicle to last and not artificially limit myself so it lasts a theoretical 4,000,000 miles.
     
  15. Lex

    Lex Member

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    True that, but it's not a bad thing to do the right thing as often as possible especially if it's not a big deal. But I agree, I use the car like Tesla designed and so far so good (ahem, well, full disclosure my MS's pack is getting brain surgery in the Mothership right now).

    As for battery management I actually had hoped some of the Tesla secret was keeping individual cells between this range (I previously heard 40-60 but 30-70 is a nicer) and/or resting certain cells... but that is just wasted mass this early, I guess.
     
  16. AZ Desert Driver

    AZ Desert Driver Genesis - The Beginning - MS60D in its nest

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    I'm not an electrical engineer, so forgive my neophyte question.
    1) Batteries should not drain below a floor of 20% - Seems like that could be defined as zero, and the 0-20% as "reserve" and take this question out of the drivers worry factor. That seems like an easy program for the brains at Tesla. Dumb-or smart?

    2) Batteries charge fast, then slow down when near full....To optimize supercharger time, could one fill a capacitor and let that continue to top- fill the battery while disconnected? Would incorporating this type of device help in the life of the battery cycling? Dumb-or smart?
     
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  17. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Just for reference, the article makes an assertion that the car uses NCR18650B cells. I don't believe that's ever been confirmed anywhere, and that they are cells made specifically for Tesla in the 18650 format with proprietary formulations.

    I may be wrong - so corrections welcomed if you have an authoritative source.

    It doesn't necessarily invalidate everything else in the article, but extrapolations based on the 18650B data sheets may not be correct. I personally believe that the Tesla packs should outlive even the 18650B standards, so it may be better in the end.
     
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  18. apacheguy

    apacheguy Sig 255, VIN 320

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    Okashira has posited that the cells are 18650BE based on his bench tests
     
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  19. jbcarioca

    jbcarioca Active Member

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    To be consistent we need to know what vintage the cells were since Tesla has had modifications in chemistry, the BMS, charging protocols and many other factors since the first Roadster until today. Anode design also changed quite significantly with the advent of 70-90 kWh packs. Just knowing a given cell was produced by Panasonic, that all have been 18650 format really tells little about longevity. Even bench tests are at best part of the story because the operative measurements need to be installed in an operating environment.

    Looking at the actual observations collected on EV battery lives it is safe to say all of them from every car builder, seem good to have longevity equal to or better than ice with less maintenance and equivalent power degradation.

    More than that is really speculation, isn't it? No matter how many individual cells may be tested...
     
  20. Lex

    Lex Member

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    I'm a nerd, so let me try :p

    Yes, Tesla's programming prevents you from damaging the pack. Car shuts down hardcore before that, you may even need a boost just to tow.

    But if you didn't charge as quickly as possible, perhaps permanent damage would start in .... x(x?) hours.

    Hmm, well let's see, capacitors are really just short-term energy storage "cells" that are good at buffering power so perhaps they could play a part in disconnected Supercharging one day, quickly pulling-in energy and then feeding it back out as quickly as possible either for propulsion or more charging....

    They do like to explode when they get old though :p And once they're depleted they would be dead weight. But I've typically been surprised to see how many capacitors find their way into circuits, and I have a feeling they're already there, for Supercharging possibly not in the car but in the SC charging stack.
     

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