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100 KW Saltwater Misadventure

Discussion in 'Model S' started by Haxster, Mar 4, 2017.

  1. Haxster

    Haxster Member

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    So here's a scary scenario:

    On your way to an unplanned plop in the ocean, your Tesla's battery pack is ruptured when you go over the guard rail. The rail that's supposed to keep you and your car between the highway and the water...but doesn't.

    So now there's like 400 V and 100 KW of energy seeing conductive salt water as an easy path to something potentially very unpleasant for the car and anyone in it.

    Are there design safeguards for this situation?
     
  2. Maximapolak

    Maximapolak Member

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    Yes. Don't drive crazy by saltwater.
     
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  3. Haxster

    Haxster Member

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    Or to paraphrase a line from the movie "Butch Cassidy and the Sundance Kid" when they were about to jump off of a cliff into the water (and Sundance said that he couldn't swim, Butch said, "Don't worry about swimming. The impact will probably kill you"
     
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  4. McRat

    McRat Active Member

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    I'm going to guess the cold water and relatively low conductivity of salt water would just drain the battery dead.
    Grab a LiPoly pack and throw it in salt water and see what happens. Thermal runaway requires high temps, and the water stops that.

    But it would be MUCH cheaper to destroy a Tesla than what this idiot did:

     
  5. McRat

    McRat Active Member

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    PS - IIRC that was insurance fraud.
     
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  6. f-stop

    f-stop Member

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    As you burst through the guard rail and are flying through the air on your way down (in cinematic slow motion, of course), perhaps it's a perfect opportunity to enable 007 submarine mode...
     
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  7. Ames

    Ames Member

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    I would say Tesla has superior safeguards in place than an ICE vehicle that is about to land in the bone dry drought stricken undergrowth after it had its fuel tank ruptured...I personally think a guardrail is less likely to rupture the Tesla battery with its ballistics grade aluminium underbody shield.
     
  8. stopcrazypp

    stopcrazypp Well-Known Member

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    I think in that case you have other more pressing things to worry about, like how to get out of the car without being trapped:


    Another thing is to consider the current path. The high voltage battery is insulated from the car body. This is different from the low voltage systems which ground using the chassis.

    Details here:
    "DC circuits have current flow that complete a loop circuit from one battery terminal to the other terminal. It follows the path of least resistance to complete the circuit back to itself. That means if the battery becomes submerged the current will not flow from the “+” terminal, out into the water, through you, back out into the water and back to the “–” terminal. It will not, for the same reason, cause the body of the vehicle to become electrically charged. The battery will short internally."
    The following link is a resource for rescue divers about high voltage batteries in vehicles, and is a good read if you want to learn more:
    New Vehicle Technology Awareness for Public Safety Divers

    Thus electrocution risk is actually quite low in this case. Fire risk is actually higher, but if you are submerged in a large body of water, that prevents that from happening.

    This is a different case from live electrical connections (where there is a connection to a power supply and there might be a grounding path through the water). And in this case, salt water is actually safer than fresh water because the current will conduct around you (given much high conductivity of salt water) rather than through you. However, if you touch the metal part that is radiating current, then you might still get electrocuted.
    [​IMG]
    Electric Shock Drowning (ESD) Explained - Seaworthy Magazine - BoatUS
     
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  9. anonim1979

    anonim1979 Member

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    Water shorts battery/cells
    Individual fuses blow up.
    Nothing happens. No explosions.
    Michael Bay is disappointed.

     
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  10. Haxster

    Haxster Member

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    Nice video. But I don't think that salt water has anywhere near the conductivity of #1 wire...or the amount of current that the inverter draws without blowing any fuses.

    I'm still not convinced that "surviving" passengers in a a Tesla in salt water won't be at risk of electrocution or maybe burns from some really hot water.

    And keep in mind that even with a fully intact battery, there is still (non-water-sealed?) high voltage in the car.

    Maybe there are electrical paths (designed in or ad hoc) between strategic high voltage terminals and chassis ground that will discharge the battery in salt water in a relatively safe manner. Maybe.
     
  11. anonim1979

    anonim1979 Member

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    Nothig will happen.
    There will be no shocks, there will be no "hot water". Etc.

    Trust me I'm an engineer! :)
    (No seriously)

    And here's official firefighter study, just in case there is a need for confirming that sun shines ;)
     
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  12. Skysurfer

    Skysurfer Member

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    The second there is a short or issue with the 12v system the high voltage contactors will open, isolating any high voltage to the sealed pack connector.
     
  13. anonim1979

    anonim1979 Member

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    (Sorry, video starts from beginning instead of selected time)
    "Electric shock potential"
    9:00
     
  14. stopcrazypp

    stopcrazypp Well-Known Member

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    #14 stopcrazypp, Mar 5, 2017
    Last edited: Mar 5, 2017
    I'm not sure if you read my link, but the high voltage (HV) battery is insulated from the rest of the vehicle. As others point out, if there is an issue with the 12v, the contactors will open and then the battery pack will be completely disconnected. The HV battery pack is not grounded to the chassis or earth ground (unlike the 12V systems you may be used to).

    All the electrical connections in the cabin would be low voltage (powered by 12V battery or DC-DC converter). The current path must travel from positive to negative terminal of the HV pack through you before it can electrocute you.

    I'm not seeing how there will be a viable current path that will go through a human even in a salt water situation. If there is a path through the chassis, it would likely go directly through the chassis.

    Edit: The video linked below is a very good example. At around 9 minutes in, the firefighters used a direct stream right close to the car with a HV battery. There was no electrical shock because the battery does not have an earth ground. If they did the same where there is live power with an earth ground, they would have been electrocuted, but this is not the case with a vehicle battery.
     
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  15. DougH

    DougH Active Member

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