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Info: When Balancing Occurs, and Pack Maintenance

Discussion in 'Model S: Battery & Charging' started by Todd Burch, Feb 12, 2016.

  1. Soolim

    Soolim Member

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    I edited my response and hopefully it answers your question.
     
  2. Electroman

    Electroman Well-Known Member

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    So storage SoC as 50% and daily driving SoC as 90% is that good practice ?

    Or are you suggesting that even daily driving SoC should be less than 90%, if you only need say around 70 miles of range per day ?
     
  3. Ampster

    Ampster Member

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    If that is addressed to me, yes. There is already a cushion built into Tesla's number, but everything I have read says you will shorten life if you contantly keep your battery full. My question to @apacheguy was rhetorical, hoping that he would clarify his statement. The great thing about a Tesla is you can set a percentage and that is what I intend to do with mine. I will charge it to 100% before any journey that I will need the full range.
     
  4. zwede

    zwede 2013 P85+

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    I guess you could do it the same way the service center does it: Open the windows and run the heater on max.
     
  5. Quantum`

    Quantum` Member

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    #65 Quantum`, Feb 14, 2016
    Last edited: Feb 14, 2016
    Please read my post more carefully.

    The idea is not to run it flat so you know the capacity... when you hit zero miles it won't go any lower, but you still have capacity. The only way the BMS can know the actual capacity of the pack, is to calibrate it by running the pack flat and then charging to 100%.

    The theory is that ostensibly at 93% balancing starts. Some modules may be at full charge then, and some will not. So the BMS starts bleeding down those which are higher, and charging up those which are lower. Eventually all the modules will be close to the same voltage and all will be practically fully-charged. That is full capacity.

    And you can see that if balancing were done when the car is not charging, it would impair range. That would be senseless.

    Some have suggested that, instead of using bleed resistors to drain off higher packs (just venting that energy as waste heat), that those higher modules should be diverted to a resistive element in the coolant loop when the weather is cold. I think it's a fantastic idea, but suspect that Tesla hasn't done it because that would drop the module voltage way too quickly, and also the voltage to the element would be quite variable depending on how many modules were diverted to it.

    Good idea. Everyone should calibrate their system say, once a year (birthday?) after you're pretty sure you have the pack balanced. (This is where individual module voltage readings would be very handy) You might end up with a few more miles than you thought. Heck if most here have been charging only to 90%, you're surely out of balance, so just fixing that might gain you a few miles.

    The car was designed to be charged to 100%. No theorizing is stronger than Tesla's silence on the issue.
     
  6. David99

    David99 Active Member

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    Keeping the car plugged in doesn't do anything special. Many people people have monitored their power draw from the grid. The Model S does not draw power from the grid other than while charging or when pre-heating/cooling. There is no other time the car draws power from the grid to do anything else. So there is no indication that balancing or anything else only happens when the car is plugged in.
    The reason Tesla recommends to keep it plugged in whenever possible is for other reasons.
     
  7. Canuck

    Canuck Well-Known Member

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    The car says "Trip" after 90% and Tesla recommends not to charge in the "Trip" range unless going on a trip and that extra range is needed. In fact, on the app you even get a pop up warning when going above 90%. I don't see this as silence on Tesla's part. I see it as Tesla actively telling us not to go above 90% unless needed.
     
  8. Ampster

    Ampster Member

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    Actually that quote was by @quantum. I agree with your statement that Tesla is implying not to go above 90% unless needed.
     
  9. Quantum`

    Quantum` Member

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    "Tesla recommends"? Reference please.

    If you never charge above 90% your pack will always be out of balance. Take it or leave it.
     
  10. wk057

    wk057 Senior Tinkerer

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    This is false. The car has a max delta it will allow the pack to slide down from the user's set point before it will bump the pack back up to that point automatically. For example, in the extreme cold, the pack power will be used to keep the pack warm. Once the pack drains by a set amount (which has changed in various firmwares, so I don't know what exactly that number is today) the car will correct this by charging the pack back to the set point (at the scheduled time, if applicable). So if you leave the car sitting for an indefinitely period of time it will certainly always use grid power to keep the pack topped off.

    Balancing only INITIATES when the car is plugged in and charging. It will continue to balance, however, long after this even if the car is not plugged in.

    - - - Updated - - -

    Also false. While never charging past 90% will cause the pack to never trigger the active balancing circuits, it doesn't mean the pack will "always be out of balance." Again, and I think this is very very important for people to understand: In all likelihood your pack is NOT actually out of balance anyway! All this talk about balancing ends up being confusing because of the capacity estimate calibration errors that people keep referring to as "out of balance," which just is not true in the vast majority of cases.

    Just drive your car, charge as much as you need to get where you're going, and let the car do its thing. Simple as that.
     
    • Informative x 1
  11. Canuck

    Canuck Well-Known Member

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    Press the battery icon in your car. Note the "Trip" area that starts after 90%. The "Daily Driving" range is lower than 90%. Why does Tesla want you below 90% unless on a trip? Because lithium ion batteries degrade less when they are not fully charged:

    http://powerelectronics.com/site-files/powerelectronics.com/files/archive/powerelectronics.com/portable_power_management/battery_charger_ics/804PET22li-ion-battery-life.pdf

    Now, why doesn't Tesla tell spell it right out, like you want them to? That's because when a car has different charge levels the EPA averages the two levels. This was done on the 2011-2012 Leaf and the 2012-2014 RAV4 EV, to name a couple of examples. Nissan removed the 80% charge option in response, and sacrificed battery health for higher EPA numbers.

    So Tesla is being extra careful not to fall into that trap. In fact, I just slid the slider on my phone to 100% to read Telsa warning, and I note it is now gone! My phone is Android so I don't know if it's gone on Apple too. I used to slide it 100% a lot just before leaving to my cabin (before they put a Supecharger in Hope)and I constantly got that warning, and for good reason too. However, Tesla probably removed it to avoid an EPA hit on range.
     
  12. wk057

    wk057 Senior Tinkerer

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    Now it only gives you the warning if you leave the car set at > 90% for several charge sessions. It'll pop up with the warning message letting you know that you shouldn't do this regularly (don't know the exact warning). Probably works out so that the EPA didn't see it. lol.
     
  13. mspohr

    mspohr Well-Known Member

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    We don't know this is true. There is no official word from Tesla. They have only said they recommend daily charging up to 90%.
    What we do have is speculation based on a lot of intensive detective work. We have some indication that looks like the pack balancing when charged to 93% but that could be an incorrect inference. The pack could be balancing at other times or it might be doing something different at 93%. In the absence of something official from Tesla, I would be cautious about regularly going over Tesla's recommendation of 90% max for regular charging (and also of draining the pack).
     
  14. jerry33

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

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    That's how my Model S has worked for the past three years. It's not new. (Unless I'm miss understanding)
     
  15. wk057

    wk057 Senior Tinkerer

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    On the app or the car, when I first got my P85 (firmware 5.x) it would always pop a warning when setting above 90%. Now it only does if you leave it there a while.
     
  16. Quantum`

    Quantum` Member

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    Fine. You'll live with an unbalanced pack. Sorry but I really don't care.
     
  17. PaulusdB

    PaulusdB Mayor Gnomus Vintage Limb

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    All this battery balancing stuff has a lot of similarities to hard disc (de)fragmentation to me.
    Even down to the hypnotising graphic representation!
     
  18. jerry33

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

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    On the car. It's always popped up if I charge over 90% three times in a row. As far as I know this has been the case since 4.1 (the first version I ran).
    I've never seen it on the App (iPhone), but I haven't range charged recently (last October was the last time).

    - - - Updated - - -

    I can assure you that disk fragmentation is real, but it's only a problem if your disk is close to being full (over 85% used). I had several production servers that regularly needed defragmentation or they would practically stop working.
     
  19. qwk

    qwk Model S P2681

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    I can now confirm this to be false. My last max charge was a couple months ago, followed by partial charges to less than 90%. Last Friday the car was set to max charge, BUT unplugged at 232 Rated miles and driven right away. 232 rated is more than 90%, but less than 93% SOC. One more partial charge from 180 rated to 209 over the weekend, then it sat until today. Service screen confirmed the battery is perfectly balanced(like a new car would read). It's safe to say that the BMS takes care of the pack so you don't have to worry about it, and that there is a ton of estimation drift that goes on with rated range.
     
  20. garygid

    garygid Member

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    The initiation of brick (what I meant when I used "cell" to mean 74 cells in parallel, effectively
    one "cell") equalization DURING charging might indeed wait until 93% SoC, but that does not
    mean that equalization is not attempted at other times, like when parked.

    If 93% is the ONLY time that equalization is initiated, then my S85 has never been equalized.

    When I get a working copy of TM-Spy, I will be able to monitor "cell" (brick) voltages better.

    Bleeding down the highest bricks while driving does not reduce your Range,
    since it is the lowest voltage "cells" that will stop the car.

    Likewise, it is the highest voltage bricks that will STOP a "full" charging,
    so those bricks will not get overly damaged.
     

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