TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

12v Battery Died Before Main Battery??

Discussion in 'Model S: Battery & Charging' started by ImperialG, Nov 3, 2014.

  1. ImperialG

    ImperialG Member

    Joined:
    Mar 9, 2013
    Messages:
    48
    Location:
    --
    My 12v battery died and my car started to shut itself down last night while I was driving on a highway. Luckily I was able to roll into a parking lot and call Tesla HQ. They told me that somehow the 12v battery died before the main battery and they arranged a tow. The tow truck driver wasn't able to jump the battery after removing the nosecone, and he had to drag the car onto the tow truck from the rear. It was a terrible experience (especially after having my drive unit fail while driving on a major highway last month). This was actually the second 12V battery that I've had, since the first one was replaced in December 2013.

    Although the state of charge of the main battery was low (less than 15 rated miles), I didn't expect the 12v battery to fail first.

    Has this happened to anyone else?
     
  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

    Joined:
    Jul 12, 2012
    Messages:
    4,502
    Location:
    Maine
    Lots of 12V battery problems. Weren't very good, got better from same supplier but not good enough and now Tesla has gone with a different supplier. Don't know when supplier changed.
     
  3. glhs272

    glhs272 Unnamed plug faced villian

    Joined:
    Aug 21, 2013
    Messages:
    791
    Location:
    Burlington, WI
    This seems like an unusual failure. I would think that even if the battery was dying, that the DC to DC converter would keep things going while driving (like an alternator on an ICE car while the engine is running). Perhaps what is actually wrong is the DC to DC failed or the high voltage connection between the DC to DC inverter and battery failed.
     
  4. mspohr

    mspohr Active Member

    Joined:
    Jul 27, 2014
    Messages:
    1,800
    Location:
    California
    It may be that since your main battery was so low (less than 15 miles range) that the car stopped charging the 12v battery.
     
  5. TechPreacher

    TechPreacher Member

    Joined:
    Jul 18, 2014
    Messages:
    27
    Location:
    Zurich, Switzerland
    This is still one of the things that I find the strangest about Model S. You haul this huge battery that you keep in ship shape and charge everyday and it all still depends on a "black box" 12V battery that can die on you unexpectedly, especially if you don't use the car everyday... A constant problem I have had with all my ICEs.
     
  6. Zzzz...

    Zzzz... Member

    Joined:
    Aug 19, 2012
    Messages:
    867
    Location:
    East Asia/Canada
    Tesla could and should design "12V" battery from the cells it uses for the main pack. It would be even cheaper battery. More reliable. No heavy metals or acids. lighter weight. Big problem is to get component suppliers to certify hardware to operate in 12V-14.8V range instead of just 12V. It definitely doable, but due to very low production volume Tesla so far do not have leverage for such negotiations. Well, the components probably would not need to undergo physical design change, but unless they certified to operate at such voltage, Tesla could not put them into car for warranty/liability reasons.

    PS. Essentially each cell would need to be cycled between 3V-3.7V. Multiply by 4 and you get 12V-14.8V range
     
  7. Saghost

    Saghost Active Member

    Joined:
    Oct 9, 2013
    Messages:
    3,035
    Location:
    Delaware
    Keeping the high voltage power locked away until the computers are sure it is safe is an important safety feature, so you need some sort of low voltage battery system.

    Tesla certainly could make it a lithium pack instead of lead acid, but I'm not sure the cost and special handling concerns would be justified.

    It does seem like a disproportionate number of the stranded model s reports are related to problems with either the twelve volt battery or the dc dc converter driving it.
    Walter
     
  8. mknox

    mknox Well-Known Member

    Joined:
    Aug 7, 2012
    Messages:
    8,570
    Location:
    Toronto, ON
    Mine was changed proactively by Tesla. I had never received a warning or noticed any symptoms of failure myself.
     
  9. rdrcrmatt

    rdrcrmatt Member

    Joined:
    Jun 27, 2013
    Messages:
    551
    Location:
    Milwaukee

    I'm glad this was said.

    Tesla is using the 12v system (battery, computers, relays, etc) as a fail safe for the high voltage battery.

    If something goes horribly wrong, I'd prefer the 12v system to fail and open the relay for the main battery which cuts it off and then shuts the car down.
     
  10. spaceballs

    spaceballs Member

    Joined:
    Sep 17, 2013
    Messages:
    538
    Location:
    Sammamish
    I agreed with mspohr speculation.

    I think it's a combination with a bad 12v battery, and ESS battery wanting to not power the dc-dc converter (to save power).
     
  11. rdrcrmatt

    rdrcrmatt Member

    Joined:
    Jun 27, 2013
    Messages:
    551
    Location:
    Milwaukee

    I really wish we wouldn't speculate like that. I have heard no solid information that the DC-DC converter stops charging the 12V at a certain SoC of the main pack.
     
  12. wraithnot

    wraithnot Model S VIN #5785

    Joined:
    Dec 16, 2012
    Messages:
    475
    Location:
    SF Bay Area
    I've had two 12V failures in 2014 and both times it was something in the charging mechanism for the 12V battery that failed rather than the 12V battery itself. The first time it was a component in the main pack that failed (the high voltage interlock loop IIRC) and the second time it was some sort of intermittent contact elsewhere in the system (I only got that verbally from the technician). I definitely hope they install some sort of 12V backup system (either a second, smaller 12V battery or use the DC to DC convertor directly) so the car can keep driving until you can take it to the service center. Based on reports on this forum it seems like the most common ways a Model S will strand people is either a blowout (usually with the 21" wheels) or a 12V battery problem.
     
  13. spaceballs

    spaceballs Member

    Joined:
    Sep 17, 2013
    Messages:
    538
    Location:
    Sammamish
    Well if there was official documentation or operational guide for critical parts available to the public then the public woudn't have to guess when something happens.
     
  14. Saghost

    Saghost Active Member

    Joined:
    Oct 9, 2013
    Messages:
    3,035
    Location:
    Delaware
    I'm not that familiar with the guts of the Model S yet, but at least on the Volt a high voltage interlock failure isn't a component failure.

    The high voltage interlock circuit there is a low voltage circuit that the computers constantly monitor the connectivity of - with connectors that physically block access to the high voltage contacts, so that anyone touching the high voltage would have to disconnect the interlock circuit first.

    Since both companies are using the exact same nomenclature, I'm suspecting it's the same type of circuit, possibly mandated by some set of rules.

    If you're worried about 12V failures, one thing you could do is carry a small inverter/compressor/starter around with you, like I often do (early Volts had issues with discharging the 12V while parked, usually because the Bluetooth didn't shut down correctly. GM updated the software, but I was already in the habit of carrying it.)

    If you keep a socket for it pre-wired near where you store the box, you wouldn't need to mess with the jumper cables or taking off the nose piece.
    Walter
     
  15. wraithnot

    wraithnot Model S VIN #5785

    Joined:
    Dec 16, 2012
    Messages:
    475
    Location:
    SF Bay Area
    I've got another road trip coming up and I think I'll take your advice and bring along some sort of small 12 V source in the frunk and enough supplies to wire it to the terminals in the nose cone in case I have another issue with the 12V battery. And I thought my days of making duct-tape and wire fixes to cars in order to limp home were over when I got the Tesla :tongue:
     

Share This Page