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12 Volt Battery Failure

Discussion in 'Model S: Battery & Charging' started by Blathering1, Mar 5, 2015.

  1. Blathering1

    Blathering1 Remember

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    About 5 weeks into the cars life, I experienced the '12 volt battery too low to start your vehicle'. Routine, around town driving. Charged the night prior.

    I thought we were past the 12 volt battery challenges on relatively new batteries. Are folks still seeing this issue pop up?

    I haven't had my cone off on the new car--- is there any extra space in there that you could fit a small backup 12vDC battery?
     
  2. wraithnot

    wraithnot Model S VIN #5785

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    I've had two 12v warning messages since I've owned the car and neither was caused by the 12v battery itself. The first time the solution was to replace the entire 85 kWh battery pack so I assume it was a contactor failure. The second time I was told it was some sort of loose connection in the 12v charging circuitry. A backup battery or larger capacity 12v battery might have allowed me to get to service center without a flatbed tow truck, but it wouldn't have fixed the underlying problem. A warning as soon as the 12v was no longer charging properly and some sort of state of charge indicator for the 12v battery would have been more useful than a backup battery since there currently is no way to know how far you could drive on a backup 12v battery if the 12v charging mechanism has failed.
     
  3. Blathering1

    Blathering1 Remember

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    Wraithnot: Agree, that the car would need service. Depending on distance from the nearest SC, getting the car running may be a useful step just to get home, etc..

    Do we know when the aux battery gets charged? I have heard the contactors fire (main pack coming on line) when the car is not plugged in.

    I saw this in the Roadster forum--cycle the charge port door to get the main pack online. Is there a way to manually get the main pack to start charging the 12 V aux battery in a similar fashion? I would think the car could effectively monitor the 12V SOC and offer a charge from the main pack as needed.

     
  4. wycolo

    wycolo Active Member

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    One would assume the dc-dc converter would be prodded more than once by independent or redundant circuits. If not perhaps safety concerns prevent TM from implementing this.

    You can easily monitor the 12v circuit with a plug-in voltmeter into the 'cigar' outlet. Well, not that easily as you have to lean forward a bit to see it; a short extension cord could fix that. Much better would be to add an under voltage alarm to this voltmeter so it would signal @12.4v and give you plenty of time to park somewhere and contact TM.

    The old MS did not have any warning messages like you have seen. Did you require road service?
    --
     
  5. saladman

    saladman Member

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    Instead of a spare battery, has anybody just added shore power terminal plugs behind the nosecone? Common on small aircraft, they let you plug in a battery booster, start the engine while staying clear of the props, and then unplug cleanly once you're ready to be on your way.

    BMW had this in the 90s too I think.
     
  6. apacheguy

    apacheguy Sig 255, VIN 320

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    Even if the 12 V is shot, the DC-DC converter should fire up and let you be on your way. Unless it's completely dead in which case you wouldn't even be able to get into the car. Don't understand how the 12 V can become a problem if it's backed by a main pack.
     
  7. Blathering1

    Blathering1 Remember

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    Service

    Road Service was needed and they were on hand remarkably quickly with a loaner. The car still functioned, mirrors unfolds, lights on, etc, just wouldn't start (and go into drive). I wonder what a volt meter would have reported.

    Once the car is in drive, I don't think a low 12V battery would have a problem as the main battery would be online, and perhaps charging the aux battery.
     
  8. wycolo

    wycolo Active Member

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    #8 wycolo, Mar 7, 2015
    Last edited: Mar 8, 2015
    > Unless it's completely dead in which case you wouldn't even be able to get into the car. [apacheguy]

    On its last legs the door handles are extended and the windows rolled down a few inches (on a warmish day). So you then can open the front doors by pulling on the handles, for a while at least.

    And you can pull the cable to open Frunk.
    --
     

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