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Which is worse? 100% SOC or nearly empty?

Discussion in 'Model S: Battery & Charging' started by sorka, Jul 1, 2015.

  1. sorka

    sorka Active Member

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    Traveling this weekend from Merced, to clovis, and then to Atascadero. EV trip planner wants me to use Harris ranch but I want to bypass it and go straight to Atascadero down 41. EV Trip planner has me using 65 kWh for the entire trip to the Atascadero supercharger assuming a speed x of 1.1 and cabin temp of 70 on a 90 degree day.

    Should I charge to 100% and arrive with an estimated 10 kWh left which would be safest or should I charge to 95% and arrive with 5 kWh left? I'm inclined to do the former to have the extra buffer unless it's much worse for the battery to charge to 100% than for it to be almost empty. I've never charged to 100% before. Most I've been since after delivery is 90% and only once at that. The battery has spent the first 4500 miles between 35 and 85% except for that one time I charged to 90.

    Obviously if I charged to 100% it will literally be minutes before I leave. i.e. I'll charge and as soon as it hits 100% I'll drive off. I'll probably precondition the car first by driving it around the block to lower the viscosity of the reduction gear and run the AC while it's plugged int to get it as cold as possible inside.
     
  2. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Charging to 100% and then immediately leaving won't damage the pack. In fact, since you have never done it before, it will be beneficial because you'll give the pack an opportunity to balance. Beware, your car may charge upwards of an extra hour longer than the estimated time. This is when the pack is balancing. Let it finish.
     
  3. Max*

    Max* Autopilot != Autonomous

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    What happens if you don't?

    [I've never done a 100% charge yet, just curious]
     
  4. sorka

    sorka Active Member

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    If it truly needs to charge to 100% before it can balance, then I could see it being beneficial. I'm not at the point where I need to recalibrate. My 80% charge shows exactly the same rated miles as the day I got it.
     
  5. deonb

    deonb Active Member

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    Nothing bad at all.

    However, if you don't regularly do a range charge, it is just a good and rare opportunity that you can use to get the cells in balance and get your range calculations reset at the same time.


    If it's like 90+ degrees outside however, don't do it - just charge what you need.
     
  6. Panu

    Panu Member

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    You should charge to 100% because of the buffer. You should never hesitate to charge to 100% unless you do it all the time. In my understanding the balancing thing is pure speculation with no proof nor confirmation from Tesla.
     
  7. steph280

    steph280 Member

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    For our hobby we deal with lithium battery balancing constantly. Let me try to explain the effect of an unbalanced pack using a simplified scenario of 3 cells, assuming full capacity of 4 volts each cell.

    cell 1 and 2 are at 3.8 volts, while cell 3 is at 3.5 volts. To the charger it sees a 11.1v "pack", and it will try to charge it up to 12v.

    After some charging time, cell 1&2 are full at 4v, while cell 3 is still at 3.7v. Charger sees the pack as 11.7v and will continue to charge, eventhough cell 1&2 are already full.

    If there was no battery management system, cell 1&2 will continue to get charged and eventually lead to damage (or even fire). With battery management system, it will know to charge only cell 3 until all 3 cells have equal voltage (or balanced). But this balance process does not happen toward the end of charging process.

    So if you bypass this balancing process in the long term, cell 1 and 2 will get "used" more often through charge/discharge cycles. Every time a cell gets topped to full charge, it reduces its life to some extent. So eventually cell 1 and 2 will "age" quicker than cell 3.

    Of course Tesla charge system is a complete magic black box which nobody knows how it works. What I stated above are just common characteristics of multiple lithium cells being used in a battery pack. It may or may not apply to Tesla.
     
  8. AmpedRealtor

    AmpedRealtor Active Member

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    Poppycock! :) The battery pack is liquid cooled and the car maintains the temperature where it needs to be.
     
  9. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #9 FlasherZ, Jul 1, 2015
    Last edited: Jul 1, 2015
    I wouldn't worry about it and I'd probably start at 100% for the "insurance factor", unless my next stop were a supercharger where the bottom of the charge curve is much steeper than the top for my next stop.
     
  10. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Nothing bad, but you lose the benefit and opportunity to fully balance. But if you need to leave, don't hesitate to stop it.
     
  11. Ed Chan

    Ed Chan Member

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    While it's possible to do this, why not stop at Harris Ranch for a bathroom break and top off? Then you don't risk running out. It's not a major detour, I do it all the time going to/from Fresno...
     
  12. sorka

    sorka Active Member

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    It's 25 miles out of my way and it's too soon for bathroom break.
     
  13. David99

    David99 Active Member

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    I would recommend to charge higher and aim for a little more buffer at the end. You never know what happens during the drive and how much power you need. Going to a very low state of charge and still drawing significant power is more damaging than a 100% charge and then driving right away.
     
  14. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I charge to 100% whenever there's a possibility of not having enough. If you don't leave it sit for a long time (and I believe the definition of "a long time" is many hours to days) there's no harm done.
     
  15. sorka

    sorka Active Member

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    OK. I'll charge to 100% then. Should I reduce it from 80 amps to something lower near the end or will the MS taper itself or does it matter?
     
  16. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The Model S will taper the charge at the end. You don't have to do a thing. Note that 80 amps isn't much compared to a Supercharge, so you won't see the taper until near the very end.
     
  17. TexasEV

    TexasEV Active Member

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    No just leave it alone and let it finish. Let the battery management system manage the battery. It knows more than the collective wisdom of the group.
     
  18. JPWhite

    JPWhite Member

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    Agreed. When the LEAF first came out drivers claimed they 'rebalanced their packs' by charging to 100% and leaving it there for x number of hours. Neither Nissan nor Tesla have revealed how dynamic rebalancing is accomplished by the vehicle and there ceratinly is nota user procedure to invoke it. Add on meters have shown the LEAF pack continuously rebalances groups of cells as it drives/charges/sits still. My guess is Tesla do something similar.

    - - - Updated - - -

    Conventional wisdom says that more damage is done by running a battery very low on charge vs charging to 100%. I would choose 100% over running very low. You may also avoid a tow if you miscalculate slightly:)
     
  19. HankLloydRight

    HankLloydRight Fluxing

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    You can't even mess with the settings while supercharging. Just let it do its thing.

    Also, what's this about reducing the viscosity of the gear oil? I think you're over thinking it.
     
  20. UberEV1

    UberEV1 Member

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    Some evidence from other threads that beneficial battery balancing occurs at charge levels >90%, which implies the opportunity to balance the pack without having to go fully to 100%. Agree no verification from Tesla, but some of us did see range improve a few miles after several weeks of charging to 90% (vs. charging to lower levels). Maybe some day we'll really know. :confused:
     

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