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When exactly is the 12v being charged?

Discussion in 'Model S: Battery & Charging' started by kishdude, Apr 4, 2013.

  1. kishdude

    kishdude P #130

    Joined:
    Jul 11, 2012
    Messages:
    136
    Location:
    Glendale AZ
    When I went to upgrade to the 4.3 update I got an error message saying that the update couldn't be done because the 12v was too low. Tesla service came out and replaced the 12v and everything is fine. Still weird that a 12v battery goes bad on a 4 month old car, but this got me wondering when exactly is the 12v charging? Here are some situations and what I think is happening. Anyone that knows for sure please correct this.

    1) driving - 12v is charging via DC to DC converter
    2) parked and main battery charging - 12v is charging
    3) parked and main battery is not charging but charge cable is plugged in - 12v is slowly draining
    4) parked and the charging cable is not plugged in - 12v is slowly draining
    4) parked and charge cable is not plugged in but car is "on" - this is a situation when you may be parked and waiting for someone and are sitting in the driver's seat so the car is on and the HVAC and all other systems are on. I'm assuming the 12v is charging here, but I'm not sure.
    5) parked and charge cable is not plugged in, but car is in accessory mode - this is the situation I'm most interested in in what is happening. I often when waiting for an extended time for someone will sit in the passenger seat of the car with the car not "on" but with screens and AC on and do some work on my laptop - sometimes for up to a couple of hours. Every 20 minutes or so the car turns off (ie screen go dark and the AC shuts off, but simply touching the screen brings everything back). I don't know what is happening to the 12v in this situation. Am I draining the 12v? Is it OK for me to use the car in this way? This is actually one of the great bonuses of this car - using it as a mobile office. Here is Arizona it is great to be able to run the AC in a car for extended periods without running the engine and releasing CO2 for a couple of hours.
     
  2. shokunin

    shokunin P85 & S40

    Joined:
    Feb 28, 2012
    Messages:
    960
    Location:
    Irvine, CA
    I would like to know as well. The 12V battery would not run your AC compressor, I don't think it has enough voltage or amperage to keep the AC running, but the touchscreens, stereo etc, could be running off the battery. The vampire losses we see throughout the day could be draining the battery faster than it can be recharged at night.

    It'd be nice if there was a dashboard or voltage meter on one of the screens that showed the 12v battery voltage and health. The car knew the voltage was low before allowing the upgrade. It should be able to warn us proactively and to recommend to charge the car longer (lower the amperage). I've started to lower the amperage so that the car doesn't recharge in just an hour and half (usually drive around 30 miles). Figured if it charged for 3-4 hours a night it should theoretically be plenty.
     
  3. Lloyd

    Lloyd Active Member

    Joined:
    Jan 12, 2011
    Messages:
    4,885
    Location:
    San Luis Obispo, CA
    We should be able to call up a vital statistics page

    12v Battery voltge
    12v Battery age
    Motor temperature
    Traction Battery temperature
    Amperage being used
    Miles since last service
    Miles since tire rotation

    Just to name a few...... I'm sure others can come up with more. Perhaps this is more appropriate in 'software wish list'
     
  4. kishdude

    kishdude P #130

    Joined:
    Jul 11, 2012
    Messages:
    136
    Location:
    Glendale AZ
    Or even better a live page that shows where energy is going - ie which components are using energy presently like heaters, ac, battery warmers, seats, etc.
     
  5. wycolo

    wycolo Active Member

    Joined:
    May 16, 2012
    Messages:
    2,425
    Location:
    WY
    Power Outlet turns OFF with car. I see 14.7v to as low as 13.7 here. Need to connect Bluetooth voltmeter directly to 12v battery. If not BT then whatever can send to a smartphone. Then an app to constantly record voltage and run 24 hour charts.

    But knowing the voltage while driving should provide enough confidence. If I start up the car and see only 12.6v or less I'd be concerned enough to use another car that day. I'd think a high quality gel battery might be indicated if the lead-acid ever needs replacing.
    --
     

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