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Thoughts on cold weather battery technology / regen capacity...

Discussion in 'Model S: Battery & Charging' started by patn, Mar 24, 2014.

  1. patn

    patn Member

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    So, in cold weather the car uses energy to heat battery to mitigate the loss of the regenerative braking capacity while the battery is cold. So the car's heating algorithm has to weigh the cost of heating the battery to a certain temperature in a certain time vs. the likelihood that we'll be driving long enough to recoup and exceed the cost, etc.

    I'm sure Tesla has thought about this *way* more than any of us but - Given that regen capacity is limited because the battery is too cold to accept the charge rate, it feels like there should be an opportunity to use excess generation capacity to heat the battery... Now, I am guessing that it's not easy. I mean, you probably can't just dump 60kW into a point heat source intermittently... So it would have to be distributed across the full battery pack somehow... and maybe that adds too much complexity or extra weight... Still, I wonder if this could be integrated into the cells in the future. Has anyone ever heard them talk about this topic? It must drive the engineers crazy to not harness that power :)

    As for the software, I also wonder how much it would help if the car had a hint about where we are going... traffic / speed and approximate length of time to destination.


    thanks,
    Pat
     
  2. VolkerP

    VolkerP EU Model S P-37

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    They apparently have thought about that. The pack heater comes on only after driving a few miles - that is, the car assumes not just a driveway shuffle.
    As for regen limited to way below 60kW: The pack heater is an electric heating element in the coolant loop. IIRC It draws 6kW (10kW with the cold weather package). Upping that to 60kW demands bigger piping and more water flow (heavier pumps). I think engineers had to strike a cost/weight/efficiency compromise here.
     
  3. neroden

    neroden Happy Model S Owner

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    I think this is a mistake. How often *do* people driveway-shuffle anyway?

    There really should be a way to make the pack heater kick in before you start *driving*. And don't tell me to use the mobile app. I want to be able to punch a button on the touchscreen!
     
  4. digitaltim

    digitaltim Sig737 VIN628

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    If you are plugged in, "preheat" the battery and car by starting a range charge 30' prior to leaving - works great for me - car is warm, toasty and not regen or power limited.
     
  5. qwk

    qwk Model S P2681

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    Or schedule the charge so it is finishes charging just before departure. This is much simpler than elaborate hardware.
     
  6. digitaltim

    digitaltim Sig737 VIN628

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    Exactly...I just tend to like the xtra range...and no worries on battery impact (from my perspective) since I only range charge when I expect to drive it shortly thereafter.
     
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    At least once every day.
     
  8. ThosEM

    ThosEM Space Weatherman

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    Regenerative heating came up in a comment on my article in greencarreports.com. It's a brilliant idea to make sure that regenerative power is always going somewhere, and if not into the battery, then into the HVAC system where it can be put to use in warming the battery so it can accept regenerative power. Even a fraction of the maximum 60 kW regenerative power would be useful and hasten the warming of the battery so that the energy can be recaptured.

    A significant other benefit would be the addition of regenerative braking action so that it is never completely lost just because the battery is cold and cannot accept it. If the battery is cold, the power should be going into warming it. I find that when the battery is really cold, the regen power is limited to zero, and the car coasts as if it had no braking at all. Therefore, power is currently being wasted that could be put to use.

    Tesla, why didn't you think of this?
     

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