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12 volt battery

Discussion in 'Model S: Battery & Charging' started by MonkeyBC, Jun 11, 2016.

  1. MonkeyBC

    MonkeyBC Member

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    I have seen a few remarks regarding the 12 volt battery and if there is not enough power in that that the car will not "start". What else does the 12 volt supply? LED lights? Heating and AC? How does the 12 not battery charge? IS it thought the charing process or is there another form of generation as in an ICE car?

    Thanks very much in advance.

    Monkey
     
  2. MonkeyBC

    MonkeyBC Member

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    Guess nobody really know the answer to this. I am picking up my car on Thursday and try to find out .....I will keep you guys posted if I learn anything.
     
  3. spottyq

    spottyq Member

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    The 12V battery provides power for everything except resistive heat, the AC compressor and the motor(s) that drive the wheels.

    It is recharged from the main battery by a DC-DC converter when the car is on or as needed.

    When the battery reaches it's end of life, the car will try to notify you in advance. If it fails, you can jump-start the car like you would an ICE car. On the old MS design, the battery terminals are behind the nosecone. I don't know where they are in the new cars or in the X.

    There is a lot of information about it on the forums, just search.
     
  4. Brass Guy

    Brass Guy Member

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    The 12V system powers everything except the drive unit and heating elements, and maybe the AC compressor, I'm not sure. But definitely all the computer stuff, which is why you can't drive without that system.
    It fails to charge if there is a problem with the DC-DC converter system (converts the high voltage from the battery pack to charge the 12V and run 12V systems) or if the 12V battery weakens and needs to be replaced. The latter seems to be more common. A few have reported several bad 12V batteries, but I'm still on my original approaching 3 years, as well as others on the forum.

    (spottyq - I guess I still type slower.)
     
  5. Ingineer

    Ingineer Electrical Engineer

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    Yes, when the car is at rest, the high-voltage system is offline. During this period, the systems in the car are powered exclusively by the small AGM 12v battery. Because these systems draw a decent amount of power the little 12v is cycled often and works really hard. Several times a day the Gateway detects the 12v is getting low and brings the high-voltage system on line to charge it back up. You'll hear the contactors make the standard "Clunk Clack" noise when they close and then a while later you'll hear them go back offline with a single "thuck" noise. Whenever the HV system is online the car's DC-DC converter powers all 12v loads and also recharges the 12v battery.

    The powertrain, PTC cabin heater and A/C compressor is all high-voltage, everything else is 12v. This includes things like the HVAC fan, seat heaters, power steering, etc.

    If the gateway detects that the 12v isn't holding enough charge it will notify both you via way of a message on the IC and Tesla over the cellular connection. In severe cases the gateway will just keep the high-voltage system online constantly until you can replace the 12v.

    If the 12v does ever manage to go dead without the gateway noticing in time, the car will be unresponsive and will require a jump or an external charge. This is because there is no manual way to bring the HV system online without first having the 12v system powered.

    Because of the high duty-cycle, it seems most 12v batteries last only up to about 2 years or so. (There is plenty of variance based on driving patterns and ambient temperature though.)

    If you are not a daily driver and let your car sit unused for more than a few days at a time, you will likely see shorter 12v life. If this bothers you, there are things you can do:

    1. Set your charge power as low as possible so the charging takes as long as it can. While the car is charging, the HV system is online and the 12v battery is not being used. This adds life!

    2. Add in an external battery charger. I use and recommend this one: Amazon.com: CTEK (56-864) MUS 4.3 12 Volt Fully Automatic 8 Step Battery Charger: Automotive It has the best algorithm I have evaluated. It even does a better job than Tesla's on-board system of taking care of the 12v battery. It can stay connected indefinitely.

    3. If your car is going to be disused for over a month, charge the pack to around 70% (no higher) and then disconnect the 12v battery or make sure it's connected to an external charger with a proper algorithm that will not harm an AGM chemistry. (see above) DO NOT use a "dumb" 12v charger!
     
    • Informative x 4
  6. zambono

    zambono Member

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    I have the 3300 which states can be used with AGM
    Amazon.com: CTEK (56-158) MULTI US 3300 12 Volt Fully Automatic 4 step Battery Charger: Automotive
     
  7. Ingineer

    Ingineer Electrical Engineer

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    Yes, almost any of the CTEK units are fine, though the small 800 (or .8) sometimes has trouble keeping up.
     
    • Informative x 1

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