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Vampire drain while plugged in?

Discussion in 'Model 3: Battery & Charging' started by Sparky4life, Aug 13, 2018.

  1. Sparky4life

    Sparky4life Member

    Joined:
    Jul 20, 2018
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    Location:
    San Jose, CA
    I have a j1779 charger (240v, 30A) and I keep my Model 3 plugged in overnight with charging scheduled to start at 11pm every night. My understanding is that the car will not pull power from the battery if it's plugged in, is that correct?

    According to TeslaFi, last night:

    - Charging finished (limit set to 70%) at 12:21 am
    - Idle between 12:21am and 2:25am and LOST 0.85 miles
    - Sleep between 2:25am and 5:27am, NO range lost
    - Idle between 5:27am and 6:32am (when I went to work), LOST 0.85 miles

    Saturday night:

    - Idle between 2:04am and 6:00am, LOST 4.22 miles

    The car doesn't seem to use any power when sleeping, but loses almost 1 mph when idle, even when plugged in. I've only had the car for two weeks so I'm not sure whether it's related to an update. I've been updated once, from 24.11 to 28.2 but I've seen this both before and after the update.
     
  2. Uncle Paul

    Uncle Paul Active Member

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    Canyon Lake,CA
    Plugging in goes directly to the battery. When the battery is full the charging stops.

    The vampire drain will happen even when plugged in. Only when your main battery drops below a certain amount will the plugged in vehicle again take a charge.
     
  3. scottm

    scottm Version 9 software sufferer

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    Does anybody know the "certain amount" drop for a model 3 that would cause it to retrigger a top-up charge cycle?
     
  4. TexasEV

    TexasEV Well-Known Member

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    It’s 3% in the Model S and X. There’s no reason to think the Model 3 would be programmed differently, but I haven’t tested it.
     
    • Helpful x 1
  5. JNB11

    JNB11 Member

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    North Las Vegas
    Before going on a vacation to New Zealand earlier this year, I left my M3 plugged in with a 59% SOC and the charging threshold set to 50%. I’m not using any aftermarket apps and the garage temperature never went below 50 F. I checked the car several times during my vacation and noticed the SOC dropped significantly every time even though the owner’s manual states:

    Whenever Model 3 is plugged in but not actively charging, it draws energy from the wall outlet instead of using energy stored in the Battery. For example, if you are sitting in Model 3 and using the touch screen while parked and plugged in, Model 3 draws energy from the wall outlet instead of the Battery.

    If I understand the manual correctly, there shouldn’t be any vampire loss when plugged in yet the battery went from 59% to 42% over a three week period. Is this a problem Tesla is addressing or will I have to live with it even though the manual says this shouldn’t happen?
     
  6. AlanSubie4Life

    AlanSubie4Life Active Member

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    For their specific example, Tesla is correct. If there is sufficient load on the charger, it will go ahead and close the contactors, and draw power from the wall, as well as either charge or not charge (by matching voltage out of the charger to the HV battery voltage presumably) the HV battery, depending on your charge level target.
    The exact logic you would have to experiment with; I don’t know exactly - but the charging screen in the car will tell you. If the car draw is low enough and it decides you’re not in the car, it will just have the UMC de-energize the shore power.

    When Tesla says “draws energy” in above context, they are not referring to vampire drain. They are referring to loads that are an order of magnitude larger (at least 300-400 watts).
    But, in general when parked, the car will allow the battery to discharge a bit over time with the absurd vampire drain, and then recharge all at once starting a few % below the charge target - I think because it means the charger will operate at decent efficiency (higher load). Better to operate at high efficiency and high output over a short time than very low efficiency and low output all the time...

    As to why yours did not charge after it dropped below 50% (or 47%) - I don’t know. Are you using a Tesla-brand EVSE? (UMC/Wall connector). I wonder whether the EVSE did not get the memo that it was time to charge again? I could see logic in an EVSE that might prevent another charge cycle from occurring without a “re-plugin”, if it were not expecting a leaky Tesla (vampire is a proprietary Tesla feature) . However, never heard of that issue before...
     
  7. JNB11

    JNB11 Member

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    Shortly after I purchased my M3, I started using a Kill-O-Watt meter to monitor energy consumption when the car was plugged in. Even when sitting for a couple days in a warm garage the vampire loss was about four miles a day and the meter showed negligible power usage (.02KWh). The manual specifically states the car will draw power from the wall and not the battery when it is plugged in. There are no caveats to this statement, i.e. the power draw must be at a certain level, etc. From what the manual states, there should be no vampire loss when the car is plugged in. Aftermarket products and applications are not an issue, I’m using the portable EVSE supplied with the car.
     
  8. AlanSubie4Life

    AlanSubie4Life Active Member

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    That is correct. However, you have to read between the lines - they mean “significant energy” - that’s when the on-board charger will turn on and start supplying the car. This aligns with your experience of course.

    Regarding vampire loss: obviously doesn’t really matter if you are plugged in or not - vampire losses whether they are reflected in a loss of range or not, always exist, whether plugged in or not. Sure it won’t impact range much if you are plugged in with your desired charge level, but that is kind of inconsequential - other than the important point that if it trickle charged from the wall you could save cycles on the HV and 12V, but that is not what it does (for efficiency reasons presumably).

    Two quotes:

    This is as close as Tesla gets to describing the behavior (the periodic topping up to prevent 0% battery).

    Yes, this could definitely be misread and there are no caveats, other than the specific example.

    Overall it is incompletely and ambiguously described, I agree.
     

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