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12V Aux battery

Discussion in 'Roadster' started by heychubs, May 12, 2016.

  1. heychubs

    heychubs Member

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    For those in the SJ/Bay Area CA who have purchased this battery for their Roadster, where did you buy it? I want to change mine out this weekend, and am looking for a place I can just go pick one up. Thanks!
     
  2. heychubs

    heychubs Member

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    So the batteries are pretty easy to find in any motorcycle shop. I purchased this battery from GP Sports in Santa Clara. $80. Looking ahead though, I think I will just go the eBay route (as a member here suggested) since the battery needs to be replaced every two or so years. They go for about $20 on eBay. I've attached a picture of the old and new battery, part number: YTX9-BS.

    battery.JPG
     
  3. MileHighMotoring

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    You can also find good motorcycle batteries at anyplace that sells automotive batteries, $39 at Walmart, or Sears, or auto parts stores, etc.
     
  4. ViviV

    ViviV Member

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    Four days ago with much appreciated help from @markwj I was able to set up OVMS on my Roadster (Thank you Mark!). I will post the details of that in a separate post on the OVMS thread. Today, I just got this alert!!! about 12V battery critical (11.3V, ref - 13.0V). The main battery is at 85% with 160 miles ideal range. The outside temperature is 31 F (cold and windy, brrrrr). The car had been parked for 2.5 hours when I got the alert. Annual service at Tesla was done 2 months ago.
    QUESTIONS: Should I ignore this? Should I be concerned? Without OVMS would I even know this? Is it possible that OVMS vampire drain has caused this? I see above that this battery is supposed to be replaced every 2 years -- is this true? If yes, why didn't Tesla suggest this? Thank you in advance. I love this Tesla and Roadster community.
    PS- I enjoyed meeting @Botbldr45 and his wife in Sedona over Thanksgiving and seeing all the cool modifications he has made to his car!

    upload_2016-12-15_12-54-4.jpeg
     
  5. MLAUTO

    MLAUTO Member

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    Thats a good indication that your battery is almost done. 2.5 hours in the cold shouldn't drop the voltage to 11.3v. The battery only charges when the car is on, so unless Tesla checked it after sitting awhile, they wouldn't find anything wrong. It was also a lot warmer 2 months ago.
     
    • Like x 1
  6. markwj

    markwj Moderator, Asia Pacific

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    That measurement is of the 12V line powering the OVMS module. In the roadster, that is powered from the main pack and nothing to do with the little 12V lead acid battery. Also nothing to do with vampire drain (the OVMS vampire drain (to maintain cellular connectivity) of about 1W is not going to have much impact on a 53kWh pack (I think that works out about 6 years) - really insignificant compared to the drain from the VMS and other battery management systems.

    Looking at the logs for your car, it looks normal. For roadster 2.x, I normally see 13.x on that measurement, and 11.x often when the car is sleeping. The calculated reference voltage on your car is 13.0, which sounds about right.

    I think you just had one unusually low dip in voltage (to 11.3V). It recovered back to 11.7V a few minutes later. The car was just sitting there, seemingly plugged in to the EVSE, but with the charge having completed 12 hours earlier.

    If it happens a lot, perhaps worth looking at more deeply, but if just a one-off I wouldn't worry about it.
     
    • Informative x 1
  7. gregd

    gregd Member

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    Mmmm, main pack, really? When the car is on (key in, turned past Acc to On), or charging, then yes. The 12v side will be driven by the DC-DC converter from the high voltage side. But when it's off, the main contactors are not engaged, so I believe the only source of 12 volts is the little 12v battery on the 2.x cars (which her Sig says she has), even if the car is plugged in. So, I think MLAUTO is more likely correct, and that the 12v battery is likely a bit weak.

    You should get a real alert on the VDS with enough warning to get to the Service Center for a replacement, so I agree to monitor things and see what happens. Just don't be surprised when it comes.
     
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  8. ViviV

    ViviV Member

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    Thank you for the responses, yes it is a 2.0. I will monitor (and I guess so will OVMS). Since the car itself did not alert me with a VDS alert, if this single OVMS alert is predictive of near future issues, then it shows the value of the OVMS monitoring. Its kind of like molecular screening tests for early detection of cancer.
    I have another question--let's say I do need to replace it. Can I trust this to my local NTB (National Tire & Battery) store (they put on my winter tires last month so they have worked with the Roadster) or would it be most prudent to take it to Tesla Service Center (about 1 hour away from me)?
     
  9. markwj

    markwj Moderator, Asia Pacific

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    From my understanding, in 2.x cars the little 12V battery only powers emergency systems (hazard warning lights, rear brake lights, etc). Main 12V is still provided by the converter in the ESS, even if contactors are disengaged. The contactors only affect the high voltage side.

    I once started up my car. Foot on the brake, turned the key. A big pop as the main fuse in the ESS went. Everything went off (VDS, instrumentation, etc), including OVMS. The only thing still running was the brake lights (visible as a bright red glow on the wall behind the car).
     
  10. MLAUTO

    MLAUTO Member

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    The standby power (12v from the dc/dc converter inside the ESS) runs to both the switchback and the VMS, as does the 12v from the aux battery. The lines are separate from each other so it depends where the OVMS gets its 12v reading from. I would think 11.3v for the standby power would be low as well, since the standby converter is fed from full pack voltage, and is always powered even when the car is asleep.
     
  11. MLAUTO

    MLAUTO Member

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    Replacing the 12v battery is really simple so I wouldn't worry about a third party doing it, although you will probably have to show them where it is located at.
     
  12. ViviV

    ViviV Member

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    Thank you @MLAUTO .....I believe it is located behind the right front wheel? is that correct?
     
  13. gregd

    gregd Member

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    Also make sure they know how / where to jack up the front of the car to remove the tire. Really bad thing will happen if they don't do it right.
     
  14. gregd

    gregd Member

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    Ha. Learned something new today, thanks!

    So, if there's always 12v power from the ESS's converter, wouldn't that keep the 12v battery at a float charge level? Or does the Roadster cycle / recharge the 12v battery periodically? There's a long thread on the Model S side of the forum about the apparently poor charge management of the MS 12v battery, leading to battery failure every year or two. We also seem to have a history of battery failure, so now I'm puzzled as to why...

    Whenever I measure mine (I had the Service Center bring a set of wires to a PowerPole connector up top when they replaced mine 18 mos ago), it's always been at a constant healthy 13.7v. Yet, the Nav system in the dash shows a varying voltage level from the high 11's to low 12's, and it was my first clue (perhaps only coincidentally) that the 12v battery was failing. I think it was showing about 11.8 or so at the time, not that it's a highly calibrated instrument. But the Nav system is only on when the car is on (Acc or fully On), so the DC-DC would be fully engaged there too.

    Perplexed...
     
  15. MLAUTO

    MLAUTO Member

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    I don't think the 12v ESS converter and the 12v battery are ever connected, as the 12v battery is charged by the APS through the switchpack. The internal switchpack circuits are still a mystery to me, as I have yet to have one fail. All the power circuits (standby, APS and 12v bat) are connected to the switchpack, so which power supply gets connected to what and when only Tesla knows.
     

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