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What kind of balancing is this??

Discussion in 'Model S: Battery & Charging' started by byeLT4, Sep 13, 2020.

  1. byeLT4

    byeLT4 Member

    Joined:
    Feb 16, 2017
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    663
    Location:
    Texas
    Backstory- New to me 2017 Model S with 100kW battery. Picked up in June. Recently had a 240V installed and had the time to fully charge and attempt to balance the pack. I've done what I feel like is tons of research to not have to ask these questions, but... apparently not enough so here I am....

    I drove the car down to 16% and parked in the garage. I wanted to go a little lower but it wasn't happening. Even stayed in the car a while with music and AC blasting but the percentage didn't change. Checked after supper and the car was now down to 11%??... Batteries cooled off? This drop for my car is not unusual. It doesn't always happen, but isn't uncommon for me. I checked the range left as I had never been this low, 34 miles. So I let the car sit for about 3 hours to hopefully sleep and get a good bottom starting point then plugged her in with 34 miles still showing.

    On the cell app I moved the charge limit to full and it estimated 309 miles. After about 20 hours at 20 amps the car said charging complete- range 278... The battery display on the phone didn't look full. I moved the charge limit slider back and forth but it never gave me the option to start charging again. I was messing with it for a minute or two, even closing the app and reopening but it wouldn't let me restart charging. Then I noticed my range, 282, then 283 and within less than a minute it was up to 285. The green showing the battery state of charge was climbing as well. I watched it climb for about five minutes and it settled at 302 and the battery display was showing full now. So it went from @92% to 100% without charging.

    I had always thought balancing would be a slow charge up to 100% but this has me scratching my head. Currently the car has sat overnight and has 84% with 13.x % used on our trip yesterday evening and I did leave the AC on for my wife while I ran in the store so the mystery 8% is still accounted for LOL! I'm sure the BMS has more tech than I can understand, but I'm just curious if anyone else has experienced this. Thanks for reading!



    tl;dr- car said full at 92% and stopped charging, then ghost charged to 100% within a few minutes.
     
  2. cookie99

    cookie99 Member

    Joined:
    Mar 14, 2016
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    California
    oo yea. that aint good. have you tried trickle charging the car using lvl1 charging? My new to me 2018 last year only wanted to charge to 98% before full, so i drained the battery completely to 0 miles left then trickle charged for 5 days and 100% it went.
     
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  3. Electric700

    Electric700 Active Member

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    I would make sure your software is current. If it is, you should schedule an appointment using the Tesla app and provide a detailed explanation.

    Regarding balancing, Tesla told me the cars always balance their batteries when charging so there's no need for you to charge to 100% just for this purpose. Try to charge normally to a maximum of 80 - 90%.

    I hope this helps. Congrats on your Tesla!
     
    • Helpful x 1
  4. P85_DA

    P85_DA Supporting Member

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    CA
    A lot of obsessiveness on balancing batteries here on the forum ;)..my experience I have owned three Tesla’s babied the first two batteries ..but that didn’t prevent Tesla from altering via “batterygate/chargergate” ...on my current vehicle with 100batt..I also babied the battery but on a software update last year my range dropped and I have never been able to get back ...now I drive ..down to lower levels supercharge as much as I want and just enjoy the vehicle ..the range has never changed since than ..my $.02 is just enjoy the vehicle you cannot control what Tesla will do with the BMS..nor does anyone really know other than Tesla :cool::p
     
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  5. PWlakewood

    PWlakewood Active Member

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    Its called a BMS for a reason.....let it do its job and just enjoy your car.
     
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  6. byeLT4

    byeLT4 Member

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    Oh... and I do so enjoy it... 6k miles in three and a half months and I think my favorite part is giving all my car buddies a ride and watching their reactions. Talk about priceless! :D

    I appreciate everyone's input and it is a lot easier to enjoy knowing that I have battery warranty through 2025. Just. In. Case...;)
     
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  7. tga

    tga Supporting Member

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    Music and A/C blasting uses very little power. If you want to run down the battery, open the windows and put the heat on high. The heater uses 6kw (peak).

    But to other's points, there's really no need to worry about balancing. The BMS will handle it itself. It doesn't need "help" with charges to >90% or discharges to <10%. All that may do is adjust the estimated range shown on the display, but it won't improve the actual range, just the estimation of the range remaining.

    And FWIW, strange bouncing around of the state of charge was my first symptom of battery failure. But I was jumping from 60%->80%->0%-60%.
     
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  8. tga

    tga Supporting Member

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    I should add, I don't think it's fair to call what happened to me a battery failure. Rather, I think it was a BMS failure; scans showed garbage data from 2 cell voltage sensors, but the total voltage of the series string was fine. The fix was the same (new pack), but I think the cells were fine. If the service center could open the pack and repair the BMS, I would have preferred that and kept my battery with <5% degradation, vs getting a reman with unknown history.
     

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