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NHTSA and lithium ion batteries

Discussion in 'Model S' started by aviators99, Nov 25, 2011.

  1. aviators99

    aviators99 Model S - R140

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  2. Robert.Boston

    Robert.Boston Model S VIN P01536

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  3. VolkerP

    VolkerP EU Model S P-37

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    Conclusion: If you crash your Volt into a pole or a tree, and roll over -- make sure you exit the vehicle within the next 6 hours
     
  4. Adm

    Adm Active Member

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    #4 Adm, Nov 28, 2011
    Last edited: Nov 28, 2011
    Actually, 1 car had no problems, 1 battery fire started after 7 days, 1 battery had sparks and smoke after it was turned over, but no word on open fire.
     
  5. VolkerP

    VolkerP EU Model S P-37

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    There were some questions back in 2006 why Tesla went with laptop cells, when most other traction battery packs used prismatic cells. Their answer was "safety", especially containing "thermal runaway events" (nice word for a fire sustained by the electric energy stored in the cells). Now there will be Li-Ion bashing, mostly regardless of pack architecture or a look on manufacturers historic log (Tesla: zero events).

    Or is there something in the records for Tesla?
     
  6. TEG

    TEG TMC Moderator

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    Umm... I think the reason was energy density and cost per kWh.
    Also, the "mass produced commodity item" (due to laptop and other common use) meant that they could chose from multiple suppliers, and little risk that they could get "locked out" or "price gouged" by one supplier.

    I think we heard a bunch about the safety aspect, not because they were trying to pick the "most safe" technology, but rather trying to show the world that they could devise a scheme to make the "not so inherently safe" cells "plenty safe" by adding multiple safety systems around them.
     
  7. JRP3

    JRP3 Hyperactive Member

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    Yes, the basic LiCo chemistry is probably the least safe lithium chemistry. Actually LiPoly is worse but so far no automakers are using those. The problem in the Volt case seems not to be the chemistry or the format but leaking coolant causing a short, possibly leading to a fire.
     
  8. Jeff N

    Jeff N Active Member

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    There has only been one out of many vehicle crash tests in which the Volt battery caught fire (3 weeks later).

    After the fire, NHTSA and GM tried to reproduce the crash test battery fire unsuccessfully. The Euro NCAP test has a similar pole side-impact test, I think, and they have not reported problems during their Volt tests. GM says their own internal Volt crash tests during development have not resulted in battery fires. It seems as if a single side crash test into a 10-inch steel pole at 20 mph caused battery damage that eventually led to the fire. The Volt received a five star occupant safety result from this side pole test as one part of the car's published overall 5 star score.

    Recently, NHTSA conducted several tests where they directly replicated the mechanical damage (rather than indirectly via a full pole crash test) seen in the pack that caught fire. After the replicated damage, a rollover was simulated by rotating the car containing the battery. It seems to be the combination of pack damage, broken coolant lines, and 180 degree rotation that triggered a delayed fire in one of the new test cases and a "spark and smoke" event in another test case (the third recent test case had no problems).

    The test simulates a post-crash rollover because there is a significant chance of this happening in an SUV or truck after a side impact. The chance of an actual rollover in a Volt is much smaller due to the weight and low center of gravity. This low chance of rollover is one of the many reasons why the Volt received excellent safety scores from NHTSA and EuroNCAP. The website informedforlife.org has rated the 2011 and 2012 Volt among the best 7% of cars and trucks for crash safety with a score of 44.

    http://www.informedforlife.org/demos/FCKeditor/UserFiles/File/MasterSCORE2012riskNov12.pdf
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    I think VolkerP's "their" is referring to the other manufacturers who use prismatic cells questioning the safety of laptop cells.
     
  10. VolkerP

    VolkerP EU Model S P-37

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    No, I refer to a statement by a Tesla engineer touting the overall safety of Tesla's ESS architecture. On the topic of "better cell safety of prismatic cells vs. laptop cells", he answered to ask the other manufacturers for crash / thermal runaway safety. He sounded pretty sure that the Tesla design would never encounter such a problem.

    I'm sorry but I can't find the source for that, neither in my archives, nor in the Tesla blogs, nor in the web. Best cite I found is in Why is the "Tesla Roadster" electric vehicle fitted with commodity lithium-ion batteries? | E2A - ELECTRO-TO-AUTO FORUM. Might have been a youtube interview.

    Volker :confused:
     
  11. stopcrazypp

    stopcrazypp Well-Known Member

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    Here's what Tesla has on their battery pack; it might be in here:
    http://www.teslamotors.com/blog/bit-about-batteries
    http://webarchive.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf
    http://www.teslamotors.com/it_IT/node/3848

    The NREL has an article making a pretty detailed comparison of the safety aspects of cylindrical vs prismatic cells:
    http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/45779.pdf
     
  12. aviators99

    aviators99 Model S - R140

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    My big concern in all of this is how the media will portray it, and how the government is (over)reacting. That is why I mentioned conspiracy theorists. I know some have been saying that big oil lobbyists will find a way to ruin the EV again... If the government blows this out of proportion *and* then generalizes it to all EVs, we could have a problem.
     
  13. W.Petefish

    W.Petefish Active Member

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    You also need to take into account Tesla's safety measures that are integrated into the battery itself.

    And later on:

    So, they have taken most, if not all, of the potential problems into account when designing their packs.

    Source:
    http://webarchive.teslamotors.com/di...terySystem.pdf
     
  14. Dan5

    Dan5 Member

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  15. JRP3

    JRP3 Hyperactive Member

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    Just to be clear what has happened so far:
    So there have been 4 tests with two resulting fires, 1-3 weeks after the tests.
     
  16. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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  17. Jeff N

    Jeff N Active Member

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    Except for all the other crash tests done by NHTSA, EuroNCAP, and the insurance industry labs that didn't result in a fire.

    The original NHTSA test in May that resulted in the battery damage and eventual fire was a side impact pole test where the car is pushed to 20 mph so that the middle of the driver side front door slams into a vertical 10-inch steel pole. This test is being used for the first time in 2011 and only 20% of the cars from each manufacturer have to pass. By 2014 all cars have to pass. The Volt got 5 out of 5 stars on this specific test for occupant safety.

    After the fire in June, GM and NHTSA reportedly crashed multiple other Volts using the same test and were unable to reproduce the battery fire. Finally, in the November tests they directly damaged Volt battery packs in the same manner as the original battery that caught fire in June. With these 3 battery packs, 1 of them caught fire after a week.

    Part of the failure scenario may involve the simulated rollover that is part of the side impact pole test. SUVs and trucks have a significant chance of rollover in side impacts. The Volt has a low chance of rollover due to the low center of gravity from the battery. For example, the battery that sparked only did so after the pack was rotated 180 degrees as part of the test.

    When combining the crash test data from NHTSA and the insurance industry together with its relative weight, the website informedforlife.org gave the Volt a crash safety rating among the top 7% of all vehicles rated.
     
  18. vfx

    vfx Well-Known Member

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    I bet Tesla is looking at all this (and double checking their own sums) very carefully!
     
  19. JRP3

    JRP3 Hyperactive Member

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    Yeah I was thinking the same thing. With the S pack across the whole belly pan the side impact will certainly crush a bunch of cells and coolant lines.
     
  20. VolkerP

    VolkerP EU Model S P-37

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    I think the opposite is true. Here is my shot at things:

    Tesla designs all floor pan battery packs (Model S, X, Toyota RAV4 EV, Smart, Mercedes A-Class) to survive a pole side impact of 20-30 miles. Survive = contain the stored electric energy inside for hours post-crash.
    In the skateboard platform (Model S+X), the metal battery pack housing looks fairly rigid. It is contributing to passenger cell rigidity (ride+crash). The pole will not intrude the pack housing, just dent it.
    The other packs might not help in that task but protect themselves at the cost of overall vehicle structure integrity - e.g. they disassociate from the vehicle.
     

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