Tesla Model S Battery Degradation

Discussion in 'General' started by Carcus, Apr 4, 2017.

  1. Carcus

    Carcus Well-Known Member

    2019.16.x rambling speculation (all based off of internet forum lurking):

    Looks like in 'some' of the Model S 85 kwh vehicles there is a problem with a module. (there are 16 modules in a pack, 6 bricks in a module, 74 cells in a brick (pack is 96s74p).

    In order to preserve the module (and thus, the pack) . . Tesla is issuing software updates that limit the pack .. those limitations include:
    - lower pack capacity -- i.e. lower max cell voltage (thus pack voltage) (i.e. maybe 4.1v/cell instead of 4.2v/cell)
    - lower supercharger speeds
    - less brake regen
    - less acceleration

    Also appears that the 'bad' (or getting bad) modules cannot be feasibly replaced. (too hard to find matching modules to keep the repaired pack balanced, plus it's beyond the scope of the SCs.)

    So I wonder if Tesla could develop a fix that would "clip" the bad module ... but this would probably be a fair amount of work, .. possibly have to change out some of the BMS(?) and, of course, would result in a pack that will not perfom like when new (i.e. .... it had 16 modules in series, repaired would only have 15 -- lower max pack voltage, less acceleration, lower range) ** add -- I would think this is along the lines of a recall, and might involve some sort of payout to the affected owners as well,.. the way it stands the software route is just buried in the category of ""normal"" degradation.

    /can't find much about why a module would be singled out as bad ... perhaps it has a hot spot .. extra resistance due to circuitry, .. bad cooling ...I dunno(?)
    // no idea how widespread the problem is, how many vehicles are affected

    ///take all of the above with a huge cup of salt (lurking has its limitations),..
     
    Last edited: Sep 5, 2019
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  2. Carcus

    Carcus Well-Known Member

    IF the above speculation is true (or even somewhat true) ,... then I would think Tesla wants to limp these cars across the finish line (end of the warranty period (8 years)). After that, I think they'll want these bad module ridden packs either repaired (the clip solution)-- possible(?) , or off the road -- more likely, . as soon as possible. They've got the software control to make that happen. If Tesla doesn't want your vehicle on the road, they'll get it off.
     
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  3. Carcus

    Carcus Well-Known Member

    So, .. based off of what a knowledgeable guy has posted in another forum (and he is very/intentionally vague). ....

    It looks like Tesla can "clip" a module or two out of a pack. (i.e turn a 85 pack with a delinquent module or two into a refurbed 70 or 75 pack).

    Also, having watched a video on Model s pack dissassembly, I'm not so sure Tesla will ever go into the sealed section (where the cells/modules are) until the pack is done being in a vehicle. So they may have the "rearrangement hardware up in the "penthouse", "fusebox" or whatever they call that section in the model S. ... So it may not be a ton of work to "clip" a module or two, .. maybe they could handle that at a SC,... very little information that I can find out there on this subject. And who knows if a de-rated (70,75) pack could stay in a 85 car, ..can all power electronics handle that?
     
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  4. Carcus

    Carcus Well-Known Member

    Europe: VW e-up -- 32 kWh, , 0% to 80% in an hour, $24,500.**
    China: Ford Escape (Territory) -- 49 kWh, 20% to 80% in 40 minutes, $27,800.

    imo -- These two are priced to sell in volume, if they're actually available, ...
    /capable of producing a more practical spla$h than the model 3, .. we may be viewing (from afar) the first wave of "car 2.0"

    ** edit/add -- videos are out now on the e-up, ... it is a pretty bare bones city car (0 to 60 in about 12 seconds, top speed of 81 mph, hard plastic everywhere, no mirror on the visor, phone app handles the cars info, no battery thermal management (?), etc...) so less of a car than I was expecting
     
    Last edited: Sep 16, 2019 at 5:09 PM
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  5. Carcus

    Carcus Well-Known Member

    WAG: --(wild guess)

    I see from watching the Shanghai fire that the parked car starts smoking from the front. Looks like right behind where the front motor would be on the "D" car (dual motor, .. if it was a dual motor).

    Maybe a front module is getting uneven heating, especially during a lot of stop and go traffic (motor is hot from acceleration and regen). Owner parks car and then heat soak from the front motor starts to really warm up one end of a specific module (the one (or two) in closest physical proximity to the front motor). Over time this gets the module quite a bit out of balance. The hot (and now higher voltage) cells start to feed into the cool cells, .. a thermal runaway ensues. ????

    /it appears uneven temperature distribution throughout a pack (or module) is a pretty bad thing ... but I don't really know much about it.
    // add -- the cells have built in vents which should prevent an explosion, but I have read that if the temperature is right (high) the off gasses can mix with oxygen and start a fire --- so maybe there was a combustible mix in the front two module section, after the car was parked -- a heat soak ensues (from the front motor?) which brings the mix up to a combustible temperature ??
     
    Last edited: Sep 12, 2019
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  6. Carcus

    Carcus Well-Known Member

    continuing with the WAG, ..

    in this video you can see the front motor is in fairly close proximity to the aluminum structure and battery box. I believe there are aluminum stringers also in that battery box. In a stopped situation -- the radiant heat from the motor could be heating up that light weight aluminum fairly quickly. (something which might not show up too much in simulations, or where they were road testing)
     
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  7. Carcus

    Carcus Well-Known Member

    ... another forum lurking observation:

    There are a lot of A/C problems being reported over the past month or two (i.e. air conditioning being reduced, blowing hot air in the cabin, A/C running excessively while car is parked and unoccupied). -- many are associating this with software updates, but that is unknown.
    -- the cabin A/C also helps cool the battery, the system will prioritize the battery over the cabin
    -- I'm no sure where the condensor is, .. probably up front like most cars,... if it sits in stop and go traffic that heat might add heat to the front of the battery box .. could mean there are two sources of radiant heat for an unevenly cooking battery box in stop and crawl traffic (front motor on D models, A/C condensor on all models)

    so,.. it does kind of look like it 'could' be another instance of Tesla trying to baby the batteries at the expense of the owners (car's performance/comfort/usability)
     
    Last edited: Sep 10, 2019
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  8. Carcus

    Carcus Well-Known Member

    "
    Rationale
    Typically, the individual cells in a battery have somewhat different capacities and may be at different levels of state of charge (SOC). This is due to manufacturing variances, assembly variances (e.g., cells from one production run mixed with others), different histories experienced amongst the cells in a battery pack (e.g., charging/discharging, heat exposures, etc.) and must be accounted for to maximize life and service of the particular battery pack in use. Each battery cell will be, for these reasons, somewhat different and so every balancing circuit must be able to accommodate those differences. Without effective and appropriate balancing, discharging during use must stop when any cell first runs out of charge (even though other cells don't); this limits the energy that can be taken from and returned to the battery.
    ...........
    Lithium ion rechargeable battery cells are rather more sensitive to overcharging, overheating, improper charge levels during storage, and other forms of mistreatment, than most commonly used battery chemistries. The reason is that the various lithium battery chemistries are susceptible to chemical damage (e.g., cathode fouling, molecular breakdown, etc.) by only very slight overvoltages (i.e., millivolts) during charging, or more charging current than the internal chemistry can tolerate at this point in its charge/discharge cycle, and so on. Heat accelerates these unwanted, but so far inescapable, chemical reactions and overheating during charging amplifies those effects. Because lithium chemistries often permit flexible membrane structures, lithium cells can be deployed in flexible though sealed bags, which permits higher packing densities within a battery pack. Some of the breakdown products (usually of electrolyte chemicals or additives) outgas when mistreated; such cells will become 'puffy' and are very much on the way to failure. In sealed lithium ion cylinders, the same outgassing has caused rather large pressures (800+ psi has been reported); such cells can explode if not provided with a relief failure mechanism. Compounding the danger is that many lithium cell chemistries include hydrocarbon chemicals (the exact nature of which is typically proprietary) which are flammable. Not only is explosion a possibility with mistreated lithium cells, but even a non-explosive leak can cause a fire."

    https://en.wikipedia.org/wiki/Battery_balancing

    /add,.. from the schematic, a visual representation of a "safe zone" of an imbalanced pack (62% and 88% -- all cells green, 2% and 98% two cells red).... basically the need to stay away from high or low SOCs, aggressive software updates might show this as a "sudden loss of range"
     
    Last edited: Sep 10, 2019
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  9. Carcus

    Carcus Well-Known Member

    btw, .. the model 3 (apparantly) has an advanced/modified thermal management system .....

    (different cell chemistry (?), different cell size, blue goo, cooling ribbon glued, higher glycol pumping capacity, arrangement of cells, steel vs aluminum, etc....)
     
    Last edited: Sep 13, 2019
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  10. Carcus

    Carcus Well-Known Member

    So there's the lab, ... and then there's the real world. It is going to be interesting to see how the real world treats the Model S battery over the next few years, ... and then the model 3 the next several years after that. If the model S doesn't end up fairing so well ..(despite the promise of an improved model 3) ,... the transition to EVs could be a pretty slow process.**
     
    Last edited: Sep 16, 2019 at 5:20 PM
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  11. Carcus

    Carcus Well-Known Member

    **apparently, Tesla has been manipulating the range calculation*** (what almost everyone is using to determine their Tesla's battery degradation) with continual software updates, making it very difficult to judge anything about how any individual car or the fleet in general is doing in terms of battery health.

    *** when you charge to 90% or 100% the range meter will show a nice big number, but once you start driving that number falls rapidly (out of sync with wh/miles)

    /many P.O.'d owners on the forums, .. lots of talk about legal action
     
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