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12V issue and "isolation"

Discussion in 'Model S: Battery & Charging' started by cpa, Nov 28, 2015.

  1. cpa

    cpa Member

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    Well, I got the dread "12V error warning" earlier today as I got back into my car to return home from the grocery store. It cautioned me that my car may not restart. It took a few moments, but I was able to put the shift lever in drive, and I made it home.

    I telephoned roadside assistance, and they told me that Seaside Service Center would be contacting me no later than Monday.

    The service manager from Seaside called me about 45 minutes later. I inquired if the ranger could just come to Fresno when convenient next week to replace the 12V. He indicated that after he pulled my logs that there was a more serious (but not horrible) issue with "battery isolation." He apologized that he was not as familiar with the logs as the technicians are, but he felt that it had something to do with the battery heater.

    (I told him that I thought something may be a little off, as the notification that I receive upon completion of charging would indicate that the battery was at 202RM, but when I would enter the car a few hours later, the rated miles were always down to around 192-194.) That seemed highly odd, as the lows here are not that terribly low (probably 45 degrees in the garage.)

    So, the S85 will be picked up Wednesday morning and hauled to Monterey/Seaside.

    Finally, what is interesting is that the return e*mail address refers to [email protected] However, apparently that address has not been created formally, as when I replied to the calendar appointment to thank them for prompt service, it was returned. (And yes, I just used the blue underlined link in the email that Tesla generated to me.)

    Has anyone else experienced this sort of issue with the battery heater?
     
  2. apacheguy

    apacheguy Sig 255, VIN 320

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    No. Please keep us posted on the resolution.
     
  3. Ingineer

    Ingineer Electrical Engineer

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    To my knowledge, there is is no way a high-voltage isolation fault can be traced to a particular component automatically be the car.

    If the car detects an isolation fault, it may refuse to close the main contactor. If that happens, the DC-DC converter will not be powered and the car will issue the 12v system warning. Apparently the isolation fault must have cleared and the BMS finally closed it's contactors, otherwise you wouldn't have been able to drive.

    For those that don't know, the high-voltage system is totally isolated from the chassis, and the BMS is constantly checking for leakage current to/from the high voltage system and the chassis. In the event the leakage current exceeds a certain threshold, it will indicate a fault and may lock out high-voltage power on start up. This is done for safety.

    If the battery heater did have an insulation fault there is no real way for the car to know , and it would be up to the technicians to locate the fault by disconnecting parts of the system and measuring it until the find the leak.
     
  4. apacheguy

    apacheguy Sig 255, VIN 320

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    What electrical input does the BMS take to determine whether HV is escaping to the chassis?
     
  5. Ingineer

    Ingineer Electrical Engineer

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    I'm not (yet) sure exactly how Tesla does it, but it will involve checking resistance from each side of the pack to chassis and looking for leakage. The Prius did this with a square wave alternating between pack plus/minus and watching for current flow over a set threshold. I think the Tesla system also does some kind of a pre-closure check as well. This is all done inside the pack's sealed housing, so in the event of a fault, no high-voltage will come out of the pack.

    It works almost like a GFCI (RCD) does on AC power.
     
  6. cpa

    cpa Member

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    Thanks for your explanation! I will update this thread as I receive information from service.
     
  7. cpa

    cpa Member

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    Here is the description per the invoice from Tesla Service:

    Concern: Customer states Alert appeared: "Car Needs Service, Car May Not Restart", car
    can restart.
    Pay Type: Warranty
    Corrections: Vehicle Alerts General Diagnosis
    Pulled vehicle logs and found alerts for internally faulty battery coolant heater. Replace
    coolant heater and re-check.
    Corrections: Coolant Heater - Electric - Battery - 2nd Generation
    Removed and replaced electric battery coolant heater. Verified no alerts present at this
    time and vehicle is operating optimally.
    Part Quantity
    ELECTRIC BATTERY HEATER - RWD AND
    DUAL MOTOR (1038901-00-G)
    1
    ETHYLENE GLYCOL COOLANT - 50/50 MIX
    - 1 gallon (1029320-00-A)
    1
    Parts Replaced or Added
    0.00
    RONC9714000352

    Apparently the battery heater was not operating properly from time-to-time. This conclusion was derived from the diagnostics that service received on my car. The way that I understood the service technician was that this error message is rather general instead of specific. Any sort of issue that concerns the main pack generates this sort of warning, as there could be much more serious problems which would cause the car to shut down permanently.
     
  8. apacheguy

    apacheguy Sig 255, VIN 320

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    I did not know there was a separate battery heating module.
     
  9. Kalud

    Kalud Member

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    Montreal, QC
    Yes, Battery heater (coolant), Battery chiller (shared with cabin) acting on coolant, and cabin air heater.

    Temp Screen 5.12.JPG
     
  10. Ingineer

    Ingineer Electrical Engineer

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    batt heater.jpg

    5.6kW no less!
     
  11. sillydriver

    sillydriver Member

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    Kalud, what an interesting screen! I would love to be able to see battery temperature and the like. How do you get into diagnostic mode?
     
  12. apacheguy

    apacheguy Sig 255, VIN 320

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    See here, but don't get your hopes up:

    Hacking v7
     
  13. GoBlue88

    GoBlue88 Member

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    Just had this same thing happen to me only with the more drastic consequence in that the car would not drive. Story related here: Battery coolant heater failure
     
  14. Atebit

    Atebit Member

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    Same thing happened to me while charging at the Glen Allen SC last May. Tesla had to flatbed the car back to NC and gave me a loaner car to continue our trip to PA & back to NC again. Bad timing all around :)
     
  15. GoBlue88

    GoBlue88 Member

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    Have you had any related issues since they replaced the coolant heater unit? I'm hoping this doesn't happen again.
     

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