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Incorrect Regen Calculations

Discussion in 'Model S: Battery & Charging' started by Cottonwood, Nov 5, 2013.

  1. Cottonwood

    Cottonwood Roadster#433, Model S#S37

    Joined:
    Feb 27, 2009
    Messages:
    5,062
    Location:
    Colorado
    The Model S limits the regen in at least two situations:

    1. The battery is very full, like after a range charge. With a full battery, I never see the regen getting close to the orange limit line.
    2. The battery is cold. With a cool battery (no significant heat being added), the car will regen almost to the orange limit line.

    In most situations, because there are not any large electrical loads other than the need for motive power, setting the regen limit to the battery charge limit is correct.

    Heating a cold battery and the cabin is at least one major exception to that. When the battery and cabin are cold soaked to below 30˚ F. (-1˚ C.), I have seen heating powers on the order of 10 kW and charge limits of about 5 kW. This should set a regen limit of 15 kW, 5 kW for charging and 10 kW for heat. However, what I have seen is the display showing a charge limit of 5 kW and a battery use of 5 kW, meaning the regen was limited to 5 kW, and to get 10 kW for heat, the car was using another 5 kW from the battery! :eek: That is 10 kW of wasted regen!!!

    I had seen this same behavior last winter, but had forgotten about it until the cool weather started this Fall. I notice this a lot because the first 2 miles from my house goes down about 700 feet, but I am sure others see this during decelerations.

    Has anyone else noticed this?
     
  2. mknox

    mknox Well-Known Member

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    Have never completely charged to 100% so I can't comment on #1, but with #2 my regen seems to stop well short of the orange line. I thought this was odd the first few times I saw it. I was expecting the green regen indicator go right up to the dashed line and stop there, not well below it.
     
  3. Puyallup Bill

    Puyallup Bill Member

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    #1 - same here. #2 - I have not had limiting due to temperature - yet.
     
  4. cinergi

    cinergi Active Member

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    MA
    Yes, I reported this a long time ago for Model S.. and for the Roadster. Doubt they'll fix it :) Probably because the electrical load can be dynamic and would provide a much more dynamic regen experience.
     
  5. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Location:
    Colorado
    I beg to differ.

    Heating the battery and cabin are the only big electircal loads and are very predictable and can be changed slowly (are not dynamic) as each warms up. This is a very simple control problem.
     
  6. jvonbokel

    jvonbokel John VonBokel

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    853
    Location:
    Belleville (St Louis)
    I recently noticed this as well. The wasted regen is annoying, but not dangerous. What's dangerous is when the same error on the other end results in drawing more power from the battery than intended. I have seen my energy use exceed the limit line on multiple occasions. I now try to avoid that, but I wonder what damage I (and others) have potentially done to their batteries in these instances?
     

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