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The 12 Volt Battery

Discussion in 'Roadster: Technical' started by smorgasbord, Jun 14, 2012.

  1. smorgasbord

    smorgasbord Active Member

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    There are a couple discussions dancing around the 12 volt system in Roadsters:
    http://www.teslamotorsclub.com/showthread.php/4849-12-volt-accessories
    http://www.teslamotorsclub.com/showthread.php/4560-Voluntary-fix-offered-for-Roadster-models-2-0-and-2-5?highlight=12+volt+battery

    However, I couldn't find a lot of specifics on the 12 volt battery.

    1) Is it just an AGM battery?

    2) How/when is it charged?

    3) Can anyone categorically state which systems it drives and/or acts as a buffer on?

    4) Has anyone had it fail? If so, what happens?
     
  2. dsm363

    dsm363 Roadster + Sig Model S

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    I can answer the last one. Mine went out recently (got car Dec 2010). Am waiting for it to get replaced. I have to use physical key to open my door.
     
  3. markwj

    markwj Moderator, Asia Pacific

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    It is a little lead-acid motorcycle-style 12V battery.

    It is kept topped-up by the main ESS.

    It drives the car's emergency systems. Things like brake lights, hazard warnings, alarm system, etc.

    If it fails, VDS will give a warning and car must be manually unlocked.

    I've no idea if car can be driven if it has failed. Some reports say yes, but it may depends on the degree of failure - 0V is obviously a failure, but what about 1V, 5V or 10V?
     
  4. ggr

    ggr Roadster R80 537, SigS P85 29

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    Yes. I'm on my third, as of last week. Everything works fine once you actually turn on the car (since that uses the main battery).
     
  5. Doug_G

    Doug_G Lead Moderator

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    Here's what the battery looks like:

    photo.JPG
     
  6. markwj

    markwj Moderator, Asia Pacific

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    By the way, I can personally attest that the other way round doesn't work - if the main ESS goes out and little 12V is fine, brake lights work but car can't be driven :)
     
  7. NigelM

    NigelM Recovering Member

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    Tesla replaced mine as part of the annual service. AFAIK there was nothing wrong with the old one, it was only 1 year old.
     
  8. smorgasbord

    smorgasbord Active Member

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    Is it kept topped-up even when the car is off? Like sitting around for a few months? Or, only when the car is plugged in?
     
  9. W.Petefish

    W.Petefish Active Member

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    I'm wondering if the 12v battery could be moved to the trunk. I think that might be easier to replace and it could be made bigger so that it doesn't need to be replaced as often. Only downside would be, you'd lose some trunk space.
     
  10. DRM

    DRM Roadster #619

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    Just had mine replaced yesterday; it went out last week. The key fob didn't work, but rather than using the manual key i was told to open the charge-port door -- it engages the high-voltage system which then provides 12v. It was a bit wierd opening the charge port door b/f the keyfob would work but wasn't really a problem. The car otherwise operates as normal. The battery itself is a smallish motorcycle-sized battery.
    //dan.
     
  11. NigelM

    NigelM Recovering Member

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    ^ Isn't opening the charge port door just waking the car up? In that case it would also be possible to open the car still with OVMS, circumventing any 12v battery issue?
     
  12. vfx

    vfx Well-Known Member

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    My first thought is they did a firmware change.
     
  13. markwj

    markwj Moderator, Asia Pacific

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    Aw, crap, mine just went 'fault' this morning.

    Car still operates just fine - just getting a warning every time I get in to it.
     
  14. dsm363

    dsm363 Roadster + Sig Model S

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    Can you unlock the doors with the key fob? Mine finally got fixed.
     
  15. markwj

    markwj Moderator, Asia Pacific

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    Haven't tried - I've been using OVMS to lock/unlock as I know that works even without a 12V battery working :)

    I'm told that the car tries to use the 12V battery to unlock the doors, but if there is insufficient power then the car issues the alert to the VDS then wakes up the main ESS and 12V converter (hear the little coolant circulation pump working) and uses that to power the door unlock. Opening charge port door, or just pressing door handle, does the same thing - but may take a second or two to wake up. Pretty much aligns with everything I learned doing OVMS.
     
  16. tetsuos

    tetsuos HK #488 (2.5)

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    Mine failed recently. Unlocking the doors with the fob took a few extra presses (and smaller range), and following unlock, the door handles did not release the door latch until the car had booted up (around 5-10 seconds after unlock).
     
  17. markwj

    markwj Moderator, Asia Pacific

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    Simon's also.

    Seems like these things have a 12-to-18 month lifetime.
     
  18. dsm363

    dsm363 Roadster + Sig Model S

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    Yeah. I'm wondering if Tesla should just replace them with the annual service or find something longer lasting.
     
  19. Doug_G

    Doug_G Lead Moderator

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    Mine is at 24 months... no problems yet. Will probably die when the weather gets cold. In my experience these types of batteries under moderate usage last a few years.
     
  20. Tesla 940

    Tesla 940 Member

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    +1 - I'm at 2 years since delivery. But then again I don't use the car that often. Service will be in about 2 weeks.

    How difficult is it to access the battery? The picture is good - I just don't know how much it took to access it.
     

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