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Max charge 93%?

Discussion in 'Model S: Battery & Charging' started by ChooseGreen, Sep 20, 2019.

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  1. ChooseGreen

    ChooseGreen Member

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    Hello,

    I have searched around and tried a few things, but haven't had any success yet.

    I am a new owner of a 2014 S 60 (not the software locked one) (SW version 2019.32.2.1). Overall, I'm over the moon with the car. The previous owner treated the car like gold and it shows in both operation and appearance (Thanks)!

    I supercharged for the first time last night (only have 110 V at home as my HPWC is in the mail). I arrived at around 9% charge and I charged to 85% then came home and set it to charge to 100% overnight on my 110 V hoping to balance the cells.

    This morning, it said 'Charging complete' at 93%, 253 km rated range. My average in the week we have had it (~400 km) was 186 Wh/km though I don't think that matters as my understanding is that the range estimate is based off of 187 Wh/km no matter what.

    I tried unplugging both ends of the UMC, then plugging it back in, resetting the MCU but it still says 'Charging complete' at 93%. Note that I had Tesla do a battery health inspection before purchase and they confirmed that it is in line with all other S60s of that age for degradation.

    My main questions:
    -Are the cells able to balance themselves at 110V 12A?
    -Why did it stop at 93%?
    -Do I need to run it below 20% and charge back up fully a few more times for the computer to recalibrate the healthy extents of the battery?
    -If this is the new norm, should I now avoid charging to 90% as it is now considered a range charge if it is close to the maximum capability of the battery?

    Thanks for any help/advice/experience you are able to provide!
     
  2. MP3Mike

    MP3Mike Well-Known Member

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    The cells don't actually balance from charging, they balance as the higher cells are bled down to match the lower cells. So as long as the BMS wants to balance the pack it will.

    In the past the balancing didn't start until you charged to at least 93%, but I have heard that has changed and it can balance whenever it wants now.

    You should ask Tesla why it won't charge past 93%, it should.
     
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  3. ChooseGreen

    ChooseGreen Member

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    ...oh, and I noticed that when I left the supercharger at 85% SOC, there was a dotted line limiting regen which I thought was weird. It cleared within a minute or two of driving so I didn't think much of it at the time, but was that the battery capacity limiting the regen (couldn't have been temperature as the fans weren't running and it wasn't overly hot out.
     
  4. ewoodrick

    ewoodrick Well-Known Member

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    In my book, they absolutely balance as they charge. For an entire string to balance, i,e, charge to max, full voltage has to be applied. The "balancing" needs to occur because different cells have different internal resistances. This cause some batteries to charge faster than others. Balancing is just allowing all cells to come to a full charge. These batteries are in parallel sets of series connections. IT's the individual batteries in the series connection that need to be balanced and because they are in series, they can't charge each other.
     
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  5. ChooseGreen

    ChooseGreen Member

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    Interesting. Does that mean that I need the full 350V from the supercharger to balance the cells (60 kWh pack is 350V)?
     
  6. KokW

    KokW Member

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    Are you sure u didnt limit charging at 93%?
    U can change it between 50% - 100%. Maybe u didnt fully reached 100%...
     
  7. ChooseGreen

    ChooseGreen Member

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    I wish that were the case. Hopefully my image attachment works. You can see the charge limit bar at 100%.

    IMG-2241.jpg
     
  8. ewoodrick

    ewoodrick Well-Known Member

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    Well, aside from the fact that a Supercharge is the worse place to balance the cells, I think that the answer is yes.
    Balancing cells often takes well over an hour, best to do on slow chargers, plus, the batteries are going to be closer to ambient temperature, whereas a Supercharger is going to have the batteries pretty hot to begin with.

    I'm not privy to the exact max voltage that the pack needs. Is it really 350V or just somewhere near it, rounded off? I suspect that it's just close to it.
     
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  9. MP3Mike

    MP3Mike Well-Known Member

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    No. Balancing happens by the BMS connecting resistors to drain the higher voltage strings, and it is a very slow process.

    Balancing can't happen while charging unless you can bypass the higher voltage strings. (Otherwise you would overcharge the highest charged strings trying to bring up the lower voltage strings.)
     
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  10. MP3Mike

    MP3Mike Well-Known Member

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    No.
     
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  11. Electric700

    Electric700 Active Member

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    Tesla should definitely look at your car.

    Charging to 100% on 120 V is probably not a good idea since the rate is slower, and the battery will be at a high state of charge for a long period of time. It's better to do this at a 240 V charging station or a Supercharger and drive immediately after the 100% charge completes. Normally, charging to 80 - 90% is better for the battery.
     
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  12. ChooseGreen

    ChooseGreen Member

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    Yes, agreed. I was trying to get to 100% because a) road trip and b) my understanding is that if the battery stays in the ideal range (40-60%) for a long period of time, the system that estimates battery capacity starts to lose a bit of accuracy. Considering that the 'new' EPA rated range of this vehicle was 335 km, I would expect around 300-320 fully charged at this age of the vehicle. If it is indeed 254 in summer-like conditions, my winter road trips will be challenging. It would also be approaching the 30% mark for a warranty battery.

    Digressing a bit, but yes I agree with you.
     
  13. ucmndd

    ucmndd Well-Known Member

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    I’ve had charging “complete” once or twice at ~97%, but never as low as 93.

    In my case, a couple subsequent discharges and charges fixed it - so I’d start there.
     
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  14. ChooseGreen

    ChooseGreen Member

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    Thanks for your input all.

    I happen to bump into a Tesla technician and got some interesting tidbits:
    • Yes, it is a balance thing
    • Yes, it can be addressed by discharging below 20% (10% if I'm feeling sassy)
    • The key that I missed is that after discharging, it is best to charge it to 100% *using 110V*
    I asked whether it would be okay to use 240V, but their suggestion was that the slower the charge, the more time each of the cells has a chance to balance. Luckily I have a 60 kWh battery so it will only take 2-3 days. He mentioned that someone else with a 100D had a similar issue recently and it took them ~5 days to trickle charge to full from nearly empty on 110V.

    I have a short road trip then have a service appointment for some other unrelated items so won't have a chance to do this for a few weeks, but will report back what the result is. I'm curious to see how many kWh go into the battery during that charge and what my resultant rated range at 100% is.
     
  15. Allistah

    Allistah Member

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    After doing a lot of reading, I think I'm going to change my charging practices up a bit. First off, I'm going to stretch out my charging as long as I can. We have a long commute every day so we start around 85% and end up around 35% or so. I'll figure out how slow I can go so that we will reach our set point by the time we leave in the morning (6am). I also think I'm going to set it to 95% for a couple days and see what impact that has on my range.

    Really interesting on the 100v charging method, I think you could easily dial that back in the car with 220v, just limit the current - which is what I'm going to do. Then maybe on the weekend, let it charge ultra slow and see if I can get it back up to 310. The more I read and experiment the more I learn. If I find anything interesting, I'll post back.
     
  16. tls

    tls Member

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    Oh, man. That explains a few things - like why I siddenly find myself having to charge midway to make a couple of my semi-regular trips that used to get me there with about 5% left.

    Your picture looks just like what I'm now seeing: after being left on my HPWC overnight with limit set to 100% my car says "charging complete" in the morning with just a little over 90% on. I thought I was imagining things...
     
  17. ChooseGreen

    ChooseGreen Member

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    Sorry to hear @tls . I haven’t got to the bottom of this yet. The Cole’s notes since I last posted: ran it down to 5% then charging fully uninterrupted on 110v: stopped charging at 96% but only 250km of rated range (3% higher than before but 4 km less rated range than before). Unfortunately I didn’t get a chance to observe how many kWh went in before the display reset (darn!). About a month later, I charged to 100% but starting at about 80% and I think it went to 98% and just over 260km rated range. Is my car slowly balancing itself every time I slow charge (we only have 110v available as our HPWC hasn’t been installed yet)? I don’t know. That’s why I haven’t followed up much on this post; not much to report yet.

    good luck!
     
  18. tls

    tls Member

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    It did it again this morning (indeed it has been doing it every morning, I think) and I took an app screenshot and scheduled a service appointment.

    Got the automated ack and about 5 minutes later, right as the folks at my designated service center should be starting their day...a second sms ack and...the car started very very slowly charging.

    Hmmmmm.
     
  19. Allistah

    Allistah Member

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    Let us know if it really went past 93%, where it stopped and if that was the intended Change to %.
     
  20. tls

    tls Member

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    It got to 97% then stopped and would not restart. Was tempted to call the SvC but this morning I have a 180 mile drive to work, so, no time to mess with it further.
     

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