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Limited Regen, temperature or capacity?

Discussion in 'Model X: Battery & Charging' started by Gwgan, Apr 5, 2017.

  1. Gwgan

    Gwgan Almost a wagon

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    Maine
    I'd like to leave the house with 100% charge and no thermal regen limit for the first leg of a trip. Usually there is some regen limit due to battery temperature when I get going from the 45°F garage after charging to 80% to 90% up util departure. I saw this thread PSA: Significantly reduce range charge time with max battery power and did notice that I could reduce the time to regain full regen by using Max Battery Power for a few minutes while still on shore power. It doesn't seem possible for non-ludicrous easter-egg'd cars to show if regen is limited by battery temperature or by the reduced capacity to regen when at 100% charge. Is there some percentage I could charge to before the capacity limit begins to appear? Perhaps I could charge to that target, warm the battery, then finish charging to 100%.
     
  2. vandacca

    vandacca ReActive Member

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    If I understood your request correctly, the answer is you cannot have 100% battery and the ability to use Regen.

    Regen puts energy back into the battery, so if your battery is 100%, there is no room for those regen electrons. You can't over-fill the battery. You have to obey the laws of physics.
     
  3. Gwgan

    Gwgan Almost a wagon

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    Not quite. I know I'll be starting my trip without regen. What I want to get to is the point where the regen limit is only related to capacity and not temperature but from conditions that would usually be too cold for full regen without some shore power heating. Let's say I charge to 100% but the battery is still too cold for full regen. When I start driving, energy will be spent to heat the pack but my only indicator, other than the high consumption, is the regen limit on the dash which is the result of both thermal and capacity restrictions.
    At what percent charge does the capacity start to limit regen? If I stop charging before that, heat the pack, then resume charging, I might be able to set out with a full and warm pack instead of a full and cold pack.
     
  4. vandacca

    vandacca ReActive Member

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    Ah, now I understand. Not sure I can help, as I don't even believe that it's possible to pre-warm the battery. I have tried for 3 months to pre-warm the battery by turning on the climate and/or pre-charge the battery prior to leaving. Never noticed much of an improvement (maybe it's been too cold?). I've always left with limited regen due to cold (not capacity).
     
  5. Rocky_H

    Rocky_H Active Member

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    I get your question. If your battery is totally full, you will start getting some regen back when you've gone just 2 or 3 miles, so it does seem to be at 99.some% that it will start to free up a little room to store regen energy.

    As to how to do this best? Charging the battery seems to be the best and most direct method of warming it up to remove the temperature limit on regen. So what many people do is set their overnight charge limit to about 90 or 95%. When you get up in the morning, go ahead and push that slider all the way up to full and get it charging again. During that hour or so when you are showering and packing up to get ready to leave, it will be warming up the battery with that charging and removing most of the regen limit. Also that way you're not wasting any energy, since you will be using that range you're charging anyway, and the byproduct heat is still retained when you're ready to leave.
     
  6. Gwgan

    Gwgan Almost a wagon

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    As an experiment I used Max Battery Power to warm the battery then charged to 99%. At 95% there waa no regen limit, then it went faster than I expected so I missed a measure but there was some limit at 99%. Like you said, the limit was gone pretty quickly and was all gone by the time the charge was 98%.
     
  7. Pwdr Extreme

    Pwdr Extreme Member

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    Nov 30, 2016
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    Bozeman, MT
    It's pretty easy to calculate how long it will take to charge your battery to whatever level you want and set the charge time start accordingly so the car has reached the set state of charge about the time you are ready to leave, thus you are leaving with a warm battery avoiding the limited regen.

    Here in Montana it barely went above the teens for max temperature this winter and I found the above method to work quite well. My car charges at 32mph (HPWC @48 amps). I know that my standard 90% is 233 miles and my 100% is 260 miles, so it's pretty easy to work backwards and figure how many hours I need to charge to reach that level. I'd take that time, toss on an extra 15 minutes and back it off from my usual 8am leaving time. Always had full regen immediately upon leaving. I do have my car parked in a garage that was generally around 40 degrees, so I'm sure that makes a difference. If you are parking yours outside, turning on your climate control from your phone app will also heat your battery, so you can do that a half hour or so before leaving, (keep it mind the cabin heater will cut your charging speed, mine would generally drop to about 15mph charging)

    In answer to your 100% charge vs. regen question, usually after about 10 miles of driving I will have full regen capability when leaving at 100%
     

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