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Fight Fire with Software

Discussion in 'Model S: Driving Dynamics' started by haid, Nov 11, 2013.

  1. haid

    haid Member

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    If we suppose that Tesla has the ability to charge and discharge individual cells, then perhaps there is a software mitigation strategy to a battery fire.

    Presumably a foreign object causes a short in the pack. This short generates heat, that overwhelms the temperature management in a few minutes (boil away the fluid?).

    What if the software chose to discharge the cells in a wide ring around the anomaly, into the rest of the pack. It could then try to discharge cells in successively smaller rings. The idea is to deny power to the vicinity of the problem. A fire line, of sorts. The shifting of the charge itself would generate heat, but it would be over a wider area (which would presumably be less likely to boil away the fluid). And then once the ring of discharged batteries is established, presumably it would limit the ability to spread beyond the initial point of battery damage.

    Even if the cells are individually charge/dischargable, I have no idea whether this theory would work in practice. It just seems worthy of investigation. After all, the earliest hard disks had to be perfect. But over time, manufacturers learned how to deal with failure. Modern HDs are in a constant state of failure and reconfiguration.
     
  2. Zzzz...

    Zzzz... Member

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    Problem is that electrolyte is a flammable fluid by itself, even if cell itself fully discharged.

    Plus they do not have control over individual cells, and I doubt they could discharge even a single row. But interesting idea nevertheless. I mean software could start to discharge some part of affected section.
     
  3. J1mbo

    J1mbo Member

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    I think the software monitors each unit, so should be possible to shut down a bad unit, maybe intentionally blowing thermal fuses to provide absolute electrical isolation from the rest of the pack.

    If you don't know exactly which cells are damaged (some may only have minor damage to casing), increasing the load on the unit by deliberately discharging it faster may cause more damage than good.

    Electrically isolating a damaged unit will lose more capacity than may be necessary, but IMO that would be preferable to shorting / fire.
     
  4. Raffy.Roma

    Raffy.Roma Active Member

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    To me this looks a good idea. Since the battery pack consists of several modules, when a module gets damaged it could be immediately switched off avoiding a fire to start. Is this too simple?
     
  5. ZombieLincoln666

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    As Zzzz said, the electrolyte is flammable so discharging doesn't help once the fire has started.

    In terms of preventing the ignition, it might be the case that it only takes one or a few cells to start an ignition, which would mean this wouldn't help. I would actually be surprised if Tesla doesn't already have some sort of fuse between the batteries to prevent them from dumping their current all at once.

    But if you could discharge these batteries to prevent ignition, the question is if you can even do that safely. That is a lot of current we're talking about.
     
  6. mknox

    mknox Well-Known Member

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    How about explosive bolts? If a fire is detected, the battery could be ejected kinda like the warp core on the Enterprise before it goes critical.:smile:
     
  7. Doug_G

    Doug_G Lead Moderator

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    Humorous. However it's probably much safer for the driver to stop the car and get out.
     
  8. evme

    evme Member

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    Shutting off that series is probably the best they can do with software.

    Though considering the main issue here is that the battery needs to be cooled, how about a small liquid nitrogen tube in each series that would freeze the cells in case of emergency?
     
  9. Lloyd

    Lloyd Active Member

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    I wrote to tesla and suggested that they use a non-flamable coolant for the battery. The flashpoint for ethylene glycol is in the range of an arcing battery. They could use a coolant that actually helps fight the fire. I could not find one on a quick search, but there may be one better than ethylene glycol for this use.
     
  10. ZombieLincoln666

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    I'm not sure liquid nitrogen would work because: Leidenfrost effect - Wikipedia, the free encyclopedia

    Also it might be impossible in general to stop a short from heating up since I would expect them to short at a very localized spot. Also because we are dealing with punctures, the coolant lines could also become damaged.
     
  11. Smop

    Smop Banned

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    They need another coolant loop filled with flame retardant, Phos-Chek comes to mind.
     
  12. Raffy.Roma

    Raffy.Roma Active Member

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    I was also thinking that in the case of the latest fire a long period passed passed between the crashing and the moment that the flames started. In fact the driver had two warning messsage by the onboard screen. Then he got out of the car and then other minutes passed before that the fire started. IMO this means that if the damaged module of the battery pack had been switched off immediately the driver could have had the chance to go home and then also to the Tesla service without having any fire.
     
  13. mknox

    mknox Well-Known Member

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    I'm no expert, but I don't believe that is correct. If I understand correctly, the battery is physically damaged and a short circuit occurs. This generates tremendous heat which fairly quickly causes a chemical fire involving the battery's component chemistry. With a physical short caused by damage, I don't thing there's anything to "turn off".
     
  14. ACDriveMotor

    ACDriveMotor Member

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    Lithium burns in the presence of air/water.
     
  15. Doug_G

    Doug_G Lead Moderator

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    This is something of a misconception, as far as battery technology is concerned. The lithium in the batteries is in the form of an oxide. The lithium is already oxidized. It also accounts for a mere 2% of the mass of the cell (or 1% of the pack mass) according to Elon.

    Regardless, the main issues are that there's a lot of energy stored in the battery in the form of chemical energy, and the electrolyte is flammable.
     
  16. haid

    haid Member

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    Maybe, this (or something similar) could be a design goal of the Gen3 battery pack. Some sort of individually addressable cells and/or circuit breakers. It would only be possible with a battery that consists of many cells, such as those Tesla designs. It could become another differentiator between Tesla and other manufacturers (who use a few large cells).
     

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