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limited regen down a steep grade or an issue?

Discussion in 'Model S' started by fasteddie7, May 16, 2017.

  1. fasteddie7

    fasteddie7 Member

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    This is the first time i've experienced this and i wondered if it is normal. I live near a very mountainous area. My wife, son, and myself traveled up the mountain to a nice restaurant for dinner. On the way back down, it is a relatively steep grade. I had 201 miles out of 259 on my 75D. After a few minutes coming down the mountain, I was at 206 and suddenly I saw the yellow dotted line for limited regen. I was nowhere near a full battery, so is this heat related or is there an actual issue? Ambient temperature was 80 degrees Fahrenheit. Screenshot 2017-05-16 at 8.03.09 PM.png
     
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  2. gavine

    gavine Petrol Head turned EV Enthusiast

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    As far as I know, the only times that regen is limited is either when thenpack is at a very high state of charge, or if the pack is too cold. It doesn't sound like that's the case with you so perhaps an issue? Maybe a bad coolant temperature sensor is telling the BMS that the pack is cold? Hopefully someone else has a better solution/explanation.
     
  3. whitex

    whitex Active Member

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    When I drove through the mountains last year on cross USA trip, I did notice intermittent power and regen limitations that I never see in everyday driving. I figure mountain terrain driving is a bit hard on the battery so maybe sometimes it reaches some thermal thresholds limiting the performance.
     
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  4. NC70D

    NC70D Member

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    I experience regent limits coming down from my mountain house every time...every season/temperature. Annoying? Yes. But, I do not think it is a concern.
     
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  5. Mediocrates

    Mediocrates Member

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    I don't think that would be characterized as "nowhere near" full. You're at about 80% charge and regen can reach up to, what, about 60kw? I don't know if you've ever tried using a supercharger at 80% charge on a 75D...can it accept 60kw at that state of charge?
     
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  6. icefree

    icefree Member

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    So when going down hill and the regen is limited (for whatever reason), how do you slow down without using the brakes? You obviously can't downshift, which is the way I reduce my speed in my ICE cars without riding the brakes.

    I've also heard that the regen is limited when the SOC is high. I assume it means there reduced braking effect. If this is the case, couldn't there be a circuit that just dumps the generated electricity so it can maintain the braking level?
     
  7. chillaban

    chillaban Active Member

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    Use the brakes. Modern brake pads are designed to expel excess heat in the form of heated dust particles. They make your rims look like crap but they prevent your brakes from burning up down a mountain pass the way they used to in the good old days.
     
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  8. JPUConn

    JPUConn Member

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    Did you have range mode on? Curious, as this could minimize battery cooling and with the right condition cause the battery to get too hot and require some cooling off before allowing higher regen
     
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  9. Ulmo

    Ulmo Active Member

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    #9 Ulmo, May 18, 2017
    Last edited: May 18, 2017
    This makes the most sense. I have experienced similar things. It's hard to really define; it's just a general stress issue in my experience, and as with you, it was always in non-urban driving. I think the smaller 75 battery has less "sink" to absorb issues; the higher range batteries (85, 100) probably have less of these issues, however, the newer chemistry batteries (90, presumably 100, and presumably all batteries now including my 75) did introduce some limitations.

    For instance, I have little idea if the relatively hot (from my usual experience) 80º was a factor in fasteddie7's "general stress" as I most ignorantly put it. Using my ignorance and imagination combined, it's easy for me to imagine a part of the battery heating up beyond threshold limitations without it being easy for the system to cool it off given the ambient temperature, even while other parts of the battery might be just fine. Or, the chemical reaction going on in the cells might have been very particular to that terrain signature that require a very particular fractal response of some sort (as maximum threshold usability), and trying to describe that in any sort of simple way would be foolish; that's all coming from my ignorant imagination. Such as, the terrain signature could cause very particular chemical layerings (at least from an information perspective) in the reactions and chemicals that need particular counterresponses to properly process for further use; since I'm not a chemist, I'm almost certain to be abundantly wrong (or alternatively exactly right and there's no easy way for them to know how to quickly counterbalance the phenomena). I wonder if purpose designed and built quantum AI computers could learn and figure it out, eventually riding along with every Lithium Ion (or other) battery system, eeking out just that much more performance.
    I did not know that. I suspected something better was going on with them, though. That's great!
     
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  10. Barry

    Barry Member

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    I regularly drive an interstate with steep grades (I-70 in Colorado). Even with limited regen, it's enough to keep the speed in check at highway speeds. If I need to tap the brake from time to time, it's no big deal.

    If had occasions where the power graph pops up on the IC with an exclamation point, indicating that regen maxed out at 60KW, but have never had it limited further than that. If it's cold soaked, or the SOC is very high, those areother issues.
     
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  11. whitex

    whitex Active Member

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    The mountain driving I was referring to was last year was in a P85DL and outside temperature was between 50-60. The power exclamations would usually show up for few seconds at a time, most often after hard acceleration (say driving uphill at steady speed, then need to pass someone to floor it - car accelerates - then a few seconds later the exclamation shows up, sometimes with dotted lines on power or regen side, but often without. Another few seconds later, gone.). I was driving in a spirited fashion btw, enjoying the car's power and handling. Part of that trip was through Montana where the only thing limiting my speed was the distance between superchargers - fun drive, beautiful scenery too :)
     
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  12. ucmndd

    ucmndd Member

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    Same. I can predict it with great accuracy now.
     
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