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Loosing charge when connected to the shore power

Discussion in 'Model S: Battery & Charging' started by Rogard, Apr 1, 2017.

  1. Rogard

    Rogard New Member

    Joined:
    Feb 5, 2017
    Messages:
    4
    Location:
    Redmond, WA
    I left my new Model S60 charging in the garage overnight and in the morning it was 88/90.
    TeslaFi raw logs show that it was charging in the evening and reached 90/90 at about midnight. After that the state was changed to charge completed and by the 7am the battery lost 2%.

    I would expect that when the car is plugged in, the battery charge should stay constant.
    Am I missing something?

    Thank you,
    Rogard
     
  2. jdw

    jdw Supporting Member

    Joined:
    Jun 1, 2015
    Messages:
    259
    Location:
    Montreal, Canada
    #2 jdw, Apr 1, 2017
    Last edited: Apr 1, 2017
    Congratulations on your new car!

    First, the Tesla battery is around 400VDC and you are charging from ~220-240VAC so there is charger/inverter in your car. It would be both unsafe and wasteful to leave the charger/inverter and the HV battery energized all the time, so the car charges to your set point and then disconnects the charger and battery. If you left your car for a few days and the battery level dropped 2-3%, it will re-engage the charger and top off the car to your set level.

    The loss in charge you saw is nicknamed “vampire drain” and happens because to some degree the car is always on (computers, LTE, possible cooling/heating, 12V battery charging etc). This can be managed in the car somewhat using the energy settings “Always Connected” and “Save Energy” settings.

    With “Save Energy” off and “Always Connected” on, the car will rarely sleep and will use more power when parked as a result. The upside is that the car will be immediately responsive via the app or when you get in. With them enabled, there may be a delay while things wake up when you use the app or first open the door in the morning.

    If you use Teslafi, without setting up the sleep preferences, it will override these settings and prevent the car from sleeping at all as it “pings” the car every minute. If the car never sleeps, it will use a lot of power just sitting there overnight, as you have seen.

    You can minimise overnight loss by:

    1) Setting the car to both save energy and to not be always connected
    2) Setting Teslafi to allow both sleep and deep sleep, during times when you do not normally use the car, say from 8PM to 6AM
    3) Use the timed charge so that your car finishes charging say an hour before you leave in the morning.

    Point 3 doesn’t change the amount of loss, but it minimises the time the car is at a higer state of charge, warms the battery and ensures you are fully charged when you leave. Other than being ready for an emergency, there is no upside to charging the car and letting it sit.

    You can easily monitor whether or not your car is sleeping using Teslafi - once it is properly configured, opening it will not wake the car up and you will be able to see both sleep and idle time.

    As a bonus of letting the car sleep, you cycle the 12V battery less and save energy.
     
    • Informative x 1
  3. Rogard

    Rogard New Member

    Joined:
    Feb 5, 2017
    Messages:
    4
    Location:
    Redmond, WA
    Thank you very much for the detailed explanation! Makes total sense.
     

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