TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Charging completed, battery drain

Discussion in 'Model 3: Battery & Charging' started by scfreed, Jul 30, 2018.

  1. scfreed

    scfreed New Member

    Joined:
    Jun 3, 2017
    Messages:
    3
    Location:
    Syracuse, NY
    Newbie question here. If I have the car plugged in but I am not charging, should the battery still drain, or should it pull power from the wall for things such as the cabin overheat protection?

    I plugged in at work this morning and set the charge limit to 60% (for the purposes of this test). It charged up to 186 miles and said charging complete (it finished by 10am). By the time I came out to the car at the end of the day, the car range was at 182 miles, but the car was still plugged in. So it 1) didn't seem to pull power from the wall, and 2) didn't start charging again after it drained the battery a few miles.

    Is this normal?

    (Side note: a few days ago I was connected to a charger that caused it to keep starting and stopping charging, so I wanted to make sure the behavior above wasn't caused by some type of damage from the apparently intermittent charger).
     
  2. Uncle Paul

    Uncle Paul Active Member

    Joined:
    Nov 1, 2013
    Messages:
    1,755
    Location:
    Canyon Lake,CA
    Tesla will run accessories off the battery pack. It will not recharge the pack until a certain amount of power is needed. Don't want to be charging and discarging all the time as there are only a finite number of cycles the batteries will endure.

    No worries though. From time to time your batteries will recharge to the specified level. Pretty good system.
     
  3. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    725
    Location:
    Beaverton, OR
    I am pretty sure my Tesla Model 3 is using "shore power" for whatever it can rather than the battery.

    When I fire up the AC before I leave the house in the AM I can see it draw varying amounts of current from my house using my Sense Monitor app. It is not enough current for battery charging, and it clearly looks like a variable speed unit ramping up and down as needed.

    So I think while the car is in standby it is on battery, but it will kick the EVSE back on when it needs to boost charge or to run something like AC. Not sure about cabin overheat protection, etc... But I assume that would all be shore power.
     
    • Disagree x 1
  4. Tozz

    Tozz Active Member

    Joined:
    Jan 10, 2018
    Messages:
    1,058
    Location:
    Tynaarlo
    Not completely true, but not completely false either. Tesla's charge to the set percentage (or range) and then the charger is disconnected. When the SoC drops to a certain level (i believe it was 5% below set level) the car starts charging again.

    So it is completely normal that the car will have 1 or 2 percent lower charge after a day or two after it has charged, even while power is still connected to the car. If you leave it for a week or so it will charge back up to your set level.

    Exceptions are AC and heating. Those run off shore power when it is available. I don't know about cabin overheat protection.

    So: Onboard systems such as the displays/computer are running off the battery. Big power users such as AC and heating use shore power.
     
  5. Tozz

    Tozz Active Member

    Joined:
    Jan 10, 2018
    Messages:
    1,058
    Location:
    Tynaarlo
    This is not true.

    It is true that a battery has a finite number of cycles. However, it is not true that every switch between charge and discharge counts as a cycle. If you charge from eg. 89% to 90% that does not count as a full cycle. Cycles are usually seen as going from 0% to 100% or somewhere close to that.

    Trickle charge isn't using up a cycle every "trickle". If you drive from 55% SoC to 50% SoC and then charge back to 55% you did not waste a charge cycle.

    Li-Ion cells are perfectly fine with a float charge, but Tesla doesn't do that for reasons unknown to me. Could be power consumption, as the on-board computers remain on while charging, and thus a float charge could very well be using more energy than required, as the computers keep running.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC