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keeping it plugged in

Discussion in 'Model S: Battery & Charging' started by California Roll, Mar 24, 2016.

  1. California Roll

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    For a number of reasons I often do not charge overnight when I park my Model S 90D in my garage. Tesla recommends to have the car "always plugged in when not in use". But does it mean *plugged in AND charging*? Is it ok to cancel charging after plugging in overnight? I know if you plug in and cancel charging, there is still the vampire drain, as I loose 1-2% of battery charge overnight.

    So, what's happening when the car is plugged in, but charging is cancelled? Is the onboard electronics maintained by the battery or the external power?
     
  2. Ohms Andwatts

    Ohms Andwatts Unknown Member

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    The car charges to whatever point you determined was appropriate. At that point, it stops charging. It doesn't start charging again until the battery has drained something more than it will in a day. If the car sits for a long time, keeping it plugged in just ensures the battery doesn't drain too far. It is better to just let it do its thing. You aren't wasting electricity and you are not doing damage to the battery; You are actually protecting it.
     
    • Like x 1
  3. California Roll

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    Thanks, but what if you plug in but immediately CANCEL charging (while leaving the car plugged in). Will on board electronics and battery maintenance be powered by the battery pack, 12V battery, or the external power? Judging from the vampire drain that is still there, it is probably the 12 V battery - still a design flow. I'd much rather it used the grid than the 12 V battery
     
  4. Ohms Andwatts

    Ohms Andwatts Unknown Member

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    There is another thread discussing this issue and it seems there is some disagreement. Each battery has its own purpose and feeds the electrics assigned to it. My understanding was that the primary battery charges the 12v. But like everything people "know" this could be wrong. If true, the wall charger is only for the main battery. And when plugged in, I imagine it would serve the needs of the car for battery maintenance, whether you had canceled charging or not.

    The primary battery will suffer some loss each day of 2 to 12 miles range but typically about 3. It doesn't matter if it is plugged in or not. You can always cancel charging, but when the battery discharges to some amount related to the last charge setting, the charger will automatically turn on. You would have to cancel charging again but I haven't done that so I don't know if you would be doing this constantly. And if you did, eventually the battery would discharge to some very low state. I imagine Tesla will not allow you to cancel charging if the battery gets dangerously low, but I don't know that for sure and can't imagine anyone doing this. But that isn't the point of your question.

    Maybe this is too much rambling and you still don't have an adequate answer.
     
  5. BertL

    BertL Active Member

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    To the OP's question, it appears my MS battery does not (generally) draw from my HPWC just because it's plugged-in.
    • My MS will loose range during the day between the time the last scheduled charge finishes and the next one starts even if plugged-in to my HPWC.
    • I have also started a manual charge session and cancelled it, and I still loose range after that while the car is parked and plugged-in but not charging.
    • If I plug my MS into my HPWC after arriving home, when HVAC and other systems have gone off, but the headlights are still on for a minute, my HPWC does not provide power to my MS during that time (the HPWC Ceylon eye does not move).
    • If I open the door and my Tesla turns on HVAC and other systems, my HPWC begins providing power to the MS (the HPWC Ceylon eye begins to move). The HPWC turns off when the lights and HVAC/etc go out.
    • If I turn on HVAC via my Tesla App while my MS is otherwise OFF, plugged-in, but not charging, my HPWC will start providing power to the MS (the HPWC Ceylon eye begins to move). The HPWC turns off after turning off the HVAC. While I've not experienced it first hand, I extrapolate from that should my MS ever need to turn on HVAC to heat/cool the battery while I'm plugged-in because of extreme external temps, MS is smart enough to then also use external power for that purpose when it's plugged-in.
    Given those personal experiences, IMHO MS uses it's internal batteries most of the time when plugged-in but not charging to cover what most of us call "vampire loss". I see no reason why canceling a charge just because I was plugged-in causes any damage to anything.

    IMHO Tesla suggests you keep MS plugged-in because it's easy and provides MS the most opportunities to sustain the charge you intended, no matter what circumstances arrise or how long it may be until you want to take your MS out for it's next drive. MS is really quite "smart" with it's battery management -- more so that I could consistently be. As such, I have elected to not over-think it, allow MS to deal with all this, and doubt you should be concerned.

    I have my S90D set to 90% default charging. I plug it into my HPWC every time I arrive home and don't have any additional errands planned for the day. My MS tops-off charging as required beginning at midnight each day when my TOU rates are lowest. If I don't drive my MS for a couple of days, MS allows the available range to drop by a few miles and tends to then top-off again only after rated range has dropped a total of 7-8 miles. Easy ...and I have time to worry about other things. ;)
    Good luck with your own decision.
     
  6. mikeash

    mikeash Active Member

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    When plugged in but not charging or otherwise active, the wall power is disconnected and the car is electrically no different than if it was sitting unplugged. If you have an HPWC, you can verify this by standing near your car when it's plugged in and idle and turning on climate control. As the car starts to draw power from the wall, you'll hear the relays in the HPWC click to start the flow of current. That of course means that the relays weren't closed before, so the car wasn't electrically connected to the outside world.

    I think Tesla's advice to stay plugged in is just for the long term, so the car can maintain the battery's charge against the vampire drain by recharging every couple of days. It also saves some energy and battery use when you pre-heat or pre-cool the car by doing that directly from wall power.

    As usual, the best advice here is just to not worry about it. The battery management systems in the car are sophisticated and will take care of things.

    I'm curious why you often don't charge overnight in your garage, when it sounds like you have the equipment to do so. If you can fix whatever's behind that, it'll be nicer. It's great to just be able to plug in when you get home and not have to think about anything.
     
  7. Rocky_H

    Rocky_H Member

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    I'm not the original poster you were asking, but the question and the logic applies to me as well. Most days we do less than 10 or 20 miles of driving. So even though it's 5 or 10 seconds, it's still just not needed every single day, so it's wasted time, so I don't bother sometimes. The car rarely goes under 100 rated miles on it, and we usually plug it in every other day or whenever it looks like it's getting into the low 100's. However, the exception to this is that we have pretty extreme temperatures in summer and winter. We'll get several degrees over 100 and a few degrees below 0, so in those seasons, I will try to remember to plug it in every day, so it can manage what it wants to keep its battery temperature good.
     
  8. TexasEV

    TexasEV Active Member

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    Keeping it plugged in also allows you to preheat and precool using shore power.
     
  9. Rocky_H

    Rocky_H Member

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    Yeah, I know, but I never preheat or precool from inside my garage, where the temperature stays mild.
     
  10. pedriscoll

    pedriscoll True Blue Tesla Fan

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    I think it is just easier to plug it in every time I park in the garage. Always have "full tank" in the morning. Also if I have to take an unexpected trip in the evening I know I will have the range to do it. The car is smart enough to manage the battery and I prefer not to have to think about it.
     
  11. mikeash

    mikeash Active Member

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    That makes sense to me, I sometimes do similar on a smaller scale, not bothering to plug in if I come home early and know I'll be going back out later. But the original poster specifically said they plug in but often cancel charging, so something else must be going on.
     
  12. California Roll

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    The only thing that is going on has to do with the annoying Southern California Edison rate structure and difficulties in changing it, and that I mostly charge at work. When I get back home, there is little or actually no need to charge, but I still do want to keep the car plugged in overnight (because Tesla clearly says "plug in if not in use"). Tesla does not say "always charge if not in use". I was making an attempt to decipher the difference.

    I could always reset charging limit by moving it up or down by 10% or so, but that is too much hassle and it is much easier to just to press "cancel charging" as it pops up as soon as you plug in.

    I really would not want to excessively cycle the 12 V battery (power is continuously needed for main pack maintenance and onboard electronics), and was hoping that keeping the car plugged in but not charging would achieve that.
     
  13. DCGOO

    DCGOO Member

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    The 12V battery is charged from the main pack whether it is plugged in or not. So there is no effect on the 12V battery cycling.

    Personally, I always plug in whenever the car is in the garage. We have no TOU rates here, and pay less than 6¢ per KWH (actually there is a TOU Plan available, but its use case is not compelling at all).
     
  14. CHG-ON

    CHG-ON Still in love after all these miles

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    I've learned to plug it in every time I come home because if I don't, there is that rare occasion that I don't and actually need the charge that I forgot to do. It's just easier that way for me. It doesn't hurt the battery, as it might with others, like cell phones, etc. And Tesla says to do so. Who am I to argue with the Great Elon?!
     
  15. mikeash

    mikeash Active Member

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    That makes a lot of sense. If this annoying rate structure involves high rates at certain times of day, you can set the car to charge when it's cheap. If it just involves paying a lot no matter what, then I'd just not bother plugging in unless you're going to be gone for a while.
     
  16. kyalami

    kyalami Member

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    I plug in every night whether or not I need to because I know of at least one instance where someone came into my driveway and disconnected my charge cable at the outlet and tried to steal it. They could not because it was "locked" to the car.
     
  17. Branzo90D

    Branzo90D Salt and Pepper

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    I'd have to agree with this. To me, the biggest issue is having it charge at night, when power rates are at their lowest, not whether it might only need a few miles of range. If I forget to plug it in after a particularly long range drive, that is a disaster for me, as I then might have to wait several hours for charging at higher electric rates to even be able to make it to the nearest SpC.
     
  18. brkaus

    brkaus Member

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    To the best of my knowledge, based on previous threads here and a less clear exchange with tesla support.

    The external charger will only charge the high voltage battery. There is no path to trickle the 12v system.

    When the 12v gets low, the contactors close and it is charged through the DC to DC convertor from the high voltage pack.

    Also the reason that some here suggest putting a battery maintainer/trickle charger in the 12v system.

    Of course, specs are always changing.
     

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