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Model S regenerative braking at temps under 40F (4C)

Discussion in 'Model S: Battery & Charging' started by EdA, Apr 12, 2012.

  1. EdA

    EdA Model S P-2540

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    I had the good fortune of meeting user cinergi at the Boston Model S showing back on February.
    He gave me a ride in his Roadster (thanks again!) and I (sadly) recently discovered his blog
    (Fearless Bit) and came across this entry:

    Regenerative braking shuts off entirely when the battery pack goes below 40F (4C). It does this because charging the batteries below freezing damages them. Unfortunately, this alters the intrinsic behavior of the car. Suddenly instead of slowing down when you lift off the accelerator, you simply coast. You must quickly re-train yourself to use the brake pedal (and lose out on the range benefits of regenerative braking).

    I am suspecting that this will hold true for the Model S, correct?

    Thanks,
    /Ed
     
  2. bolosky

    bolosky Member

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    Most likely. However, the Roadster will warm its battery enough that it won't have this problem if it's left plugged in and not in storage mode, so in practice it's really not much of an issue.

    The time when no regen happens more often is when you charge in range mode, which fills the battery up enough that it can't accept any more charge. It is really quite disconcerting to have the car not react the way you're used to, even though there's a big warning light in the middle of the dash telling you what's up.
     
  3. Doug_G

    Doug_G Lead Moderator

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    Beg to differ, it can happen. I've had my Roadster do that after sitting in the parking lot at work all day. The very first time it was a little alarming even though I saw the light. It really rolls without regen. Once I knew what to expect it was no big deal.
     
  4. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    Interesting behavior with the Roadster! Not that I'd ever see such temps in my neck of the woods but, I wonder if such change in regen behavior would be palatable for the average, less-informed, more 'mainstream' Model S buyer?! In general, Model S's regen will not feel as prominent going by several past quotes so, maybe, it'd not be so jarring...
     
  5. BYT_P1837

    BYT_P1837 Member

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    We have dipped in the 30's or even lower in the past year a few times here in the Bay Area gg so it can effect us.
     
  6. SByer

    SByer '08 #383

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    30's won't do it. There's a lot of thermal mass in the battery. It's a bit colder where Doug is.

    But, it's a good idea to 'practice'. Throw the car into neutral at some point when you'd normally let regen take over. I think it will be far less noticeable in the S.
     
  7. hcsharp

    hcsharp Active Member

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    Why? I love the regen in the Roadster and I hope they make it as strong or stronger in the S.
     
  8. Doug_G

    Doug_G Lead Moderator

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    At certain times of the year, yes, just a wee bit.

    The temperature has to be well below freezing for this to happen - it takes time to cool down the thermal mass of the battery.

    That said, the process can be accelerated if it's very windy; anything that's warmer than the ambient temperature is subject to "wind chill".
     
  9. SByer

    SByer '08 #383

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    I hope it's stronger in the S, and even stronger in the Roadster 3.0, too. I just don't think it will be :-(.
     
  10. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    Tesla folks said around the October factory event that the regen will not be felt as prominently, when compared to the current Roadster, because of the mass of the Model S as that's a factor that goes into the rate-of-regen equation and there's a max rate for the battery packs?!
     
  11. hcsharp

    hcsharp Active Member

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    That would be true with the 40 and 60 kwh batteries but it doesn't reconcile with the facts for the 85kwh battery. The roadster weighs 2700+ lbs with a 53 kwh battery. Model S weighs north of 4000 lbs with 85 kwh battery. That's a better kwh per unit of mass ratio than the Roadster. So in theory the 85kwh Model S should be capable of stronger regen than the Roadster. Further, the newer generation high density cells in the 85 kwh battery are capable of higher C rates while charging, allowing even stronger regen. All this is assuming the ESS voltage output is similar to the Roadster (375v nominal).
     
  12. jerry33

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

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    A particular battery pack can only take so much current at one time. I wonder if this changes the amount of regen possible if you have twin chargers?

    One of the problems with the Prius is that you have to fiddle with your foot to eliminate, or at least reduce, the regeneration (this is tricky to do in the 2004-2009 and much easier to do in the 2001-2003. I have no experience in the 2010+ ) Because regeneration (at least in the Prius) only captures 30% to 50% of the kinetic energy available (and my guess is that it's usually closer to 30%) driving to get a lot of regeneration reduces efficiency compared to gliding.

    It would be nice if the car was smart enough to switch between regeneration and gliding depending upon which one was more efficient. I think this could be done based on vehicle inclination (and perhaps deceleration rate as well). Usually you want regeneration when going down hills, you don't want it on the flats or going up hills. My guess is that an intelligent regeneration system could add at least 10% or 15% to the range by cutting off the regeneration when it's less efficient.
     
  13. hcsharp

    hcsharp Active Member

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    The chargers are not used for regen.

    Stop by and I'll let you drive my car because you will understand better how the system is implemented by Tesla using one-pedal driving. You can effectively control whether you are gliding or regen braking by how far you press the pedal so it works more efficiently than a computer could ever guess. Also, the inclination has little to do with whether or not you need braking. The vast majority of times that I need to slow down are on flat terrain and I sure as heck wouldn't want the computer to decide to coast just when I need to brake. But it's a mute point because with Tesla you always have complete control over regen or coasting.
     

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