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Degredation of battery?

Discussion in 'Model X: Battery & Charging' started by volkerbradley, Sep 11, 2016.

  1. volkerbradley

    volkerbradley Member

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    My car is a P90D. On evtripping.com, where I can see some of my vehicle logs, I see that on my battery I have 71.4 kWh remaining at 89% charge.
    upload_2016-9-11_2-55-52.png
    Since 89% of a 90 kWh battery is 80.1 kWh, why is there such a difference?
     
  2. dhrivnak

    dhrivnak Active Member

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    Because Tesla, as most manufacturers lock out part of the capacity for longer life. For example the new Roadster battery is branded as 80KWh but only about 71 is usable. I think it would have been much clearer to report usable capacity. The Volt is one of the worst allowing you to only use 10.4KWh of a 18KWh pack.
     
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  3. No2DinosaurFuel

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    Please read up on how tesla rates their higher capacity cars. Your 90D only has 85-86kwh total. Factor in the reserve, you are looking at only 80-81KWh usable. So adjust your 100% charge to be around 81KWH. 89% of 81KWh is around the 71.4KWh so everything makes sense to me.
     
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  4. volkerbradley

    volkerbradley Member

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    Thank you.
     
  5. digicool

    digicool Member

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    #5 digicool, Sep 29, 2016
    Last edited: Sep 29, 2016
    Can you highlight any threads that discuss this specifically? I recently ran the car from 100% to 2% and got 199.5 miles. The car averaged 357Wh/mile for this run and if I say the remaining 2% will yield another 5 miles (rated range), I am looking at 204 miles at 357 Wh/mile. That is like 73kWh total usable capacity which seems to off for a 90D.

    Around here, some 75D owners are reporting 200 miles range. I wonder the "high capacity" batteries on the 90D are not delivering to the design expectations. I have a service appointment coming up next week and one of the items I plan to dig deep is this reduced range out of the 90D.

    *Edit*: As for the driving conditions for my test run:
    1. Start at 100% on Sunday 11AM, drive 120 miles. 55 miles on Monday and 25 miles on Tuesday.
    2. Weather was in 70 to 80F all three days during driving
    3. 2 to 4 adults for about 150 miles and no heavy cargo
    4. AC on and set at 73F but the whether was so good AC probably did not run much
    5. Over 150 miles were highway at 60 mph avg speed.
     
  6. Jeff N

    Jeff N Active Member

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    You are mixing model years. The original 2011 Volt allowed 10.4 kWh out of 16 kWh (65%). The 2016-2017 Volt allows 14.0 kWh out of 18.4 kWh (76%).

    Plugin hybrids generally need to preserve more lower-end state of charge than all-electric cars because they keep using the battery to assist in driving for potentially long periods of time together with using a gas engine.
     
  7. No2DinosaurFuel

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    Here is the thread you should read. It's long, but if you look at what wk057 posted, it is helpful. Most other ones are speculations and/or supporters or detractors of the practices.

    Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

    Keep in mind a couple of things that might be happening:
    1) You are losing battery capacity overnight. You should turn on energy saver to reduce vampire drain

    2) You do have more weight in the car with the additional passenger so your efficiency will go down

    3) You need to recalibrate the battery if you really want to know the true range. Usually you have to charge to 100% leave it for a while to balance and then drain to low capacity like 5% and repeat a few times if possible to get an accurate measure.

    4) It is possible your battery have higher degradation rate compare to the expected. In this case, I would contact the SC for more details. But I would do 3) with just maybe 1 other adult or less and see where your range settles.
     
  8. Rocky_H

    Rocky_H Member

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    That is not a test run if you are spanning it across multiple trips on multiple days, because it does not log the energy used when the vehicle is not in Drive. So all of your vampire loss overnight is not accounted for in the watt hours per mile calculation. You can only try to take a measurement on this from one long continuous drive.
     
  9. digicool

    digicool Member

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    Thanks for the link, I will read.

    Fair point. From my measurements and also confirmed by several others at TMC, the vampire drain amounts to about 50W. In my test run of 60hrs, that should account for about 3kWh. That still leaves quite a few kWh unexplained.

    So I did run the battery down to 4% and then fully charged it 3 days before my "test run". Not too surprisingly, even though the charge limit was set to 100% (I know, it was not at some point near 100% but at the rightmost edge of the slider), the car stopped at 96% and claimed that the battery was full. Right then I knew there was some calibration issue going on. After this, I drove around for 3 days and decided to charge up again to 100%. This time it did hit 100% full and that is when I decided to do the test run.

    So I will give it a few days and try the 100% to 2% test again to see if the balancing and recalibration had anything to do with it.
     
  10. AndyW

    AndyW Member

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    I have been using Testlafi data logger for a while and have found that in order to achieve 100% efficiency (miles driven equal to rated miles reduced), you have to be driving at 317 Wh/mi efficiency as indicated by the trip meter. I can achieve that when using autopilot on freeway at 70miles speed. Other times, you always get lower efficiency.

    The rated mile line on the car (90D) seems to be sitting at 330 Wh/mi which is highly misleading. To add a bit more confusion, if you derive Rated Wh/mi from Kwh added and range added data after each charge, the constant is about 325Wh/mi.

    As for the usage battery capacity on 90D, if you use the Kwh added data after each charging and factor that into 100%, I have been getting around 83Kwh very consistently.
     
  11. dhrivnak

    dhrivnak Active Member

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    We were both wrong as the 2015 model I have is a 17.1 KWh pack but we only get to use 10.4 of the total pack size.
     
  12. Jeff N

    Jeff N Active Member

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    Nope. The 2015 does have a 17.1 kWh pack but 11.2 kWh is usable. You can see this on the following GM graphic comparing the 2015 Volt with the 2016 Volt (ignore the fact that they swapped the model year car photos....):

    image.png
     

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