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Does the car feel slower when the charge is low?

Discussion in 'Model S: Battery & Charging' started by timk225, Feb 19, 2017.

  1. timk225

    timk225 Member

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    When you're driving your car, do you ever notice a difference in acceleration and performance when the charge is under 20%, as opposed to over 80%?

    I wonder if anyone has ever done timed testing of 0-60 speeds at a wide variety of battery charge levels.

    It doesn't matter in a gasoline car if it has 1% or 100% fuel, aside from the extra weight of the fuel, but I wonder how battery cars do with this.
     
  2. TexasEV

    TexasEV Well-Known Member

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    No, not until the charge is almost down to 0, which you shouldn't do intentionally.
     
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  3. andrewket

    andrewket Well-Known Member

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    Yes, the rate of acceleration will decrease as the pack voltage declines. All the 0-60 stats that you read are with the pack at near 100% SOC.

    It was most noticeable on a P85D pre-luducrious upgrade. The Ludi upgrade increased the maximum amperage that could be drawn off the pack, allowing maximum wattage to be drawn at lower SOCs and voltsge (watts = volts * amps).
     
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  4. evp

    evp Nerd

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    Here's nine 1/4 mile results in a row for a "classic" S85. The elapsed times drifted upwards, losing about 0.2 seconds, while the trap speed lost a little over 1MPH. The Charge column was largely computed, only the 191 and 164 were actually observed at the beginning and end of the day.

    Note that these nine launches each cost about 3 miles of range, including driving back to the start at 15MPH. I used regen for most of the deceleration.

    To answer the original question: no, the car didn't "feel" any slower. But it was indeed slower even after just 27 rated miles of discharge.

    Screen Shot 2017-02-19 at 10.11.39 AM.png
     
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  5. Andyw2100

    Andyw2100 Supporting Member

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    #5 Andyw2100, Feb 19, 2017
    Last edited: Feb 19, 2017
    This is completely and totally wrong. (Well except for the part about not intentionally letting your SOC get close to 0. That, of course, is correct.)

    There are threads with power output graphs at different SOCs and it is abundantly clear that SOC plays a huge role in available power. (If I can easily find one of those threads I'll come back and edit this post.)

    Edit--Here is a link to a post, and the graph in that post:

    Pack Performance and Launch Mode Limits

    LaunchLimit.jpg
     
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  6. TexasEV

    TexasEV Well-Known Member

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    The question was does the car feel slower. The car doesn't feel any different to me. I don't appreciate fractions of a second difference in acceleration in normal driving.
     
  7. Andyw2100

    Andyw2100 Supporting Member

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    I can't speak to what driving a 60 "feels" like, one way or the other.

    But as the chart shows, I can definitely feel the difference in power in my P85D, and I would expect most drivers of the performance versions can feel the differences shown in the graph. They are not insignificant.
     
  8. Andyw2100

    Andyw2100 Supporting Member

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    I love it when people like @WarpedOne disagree with informative posts. (Above.) No actual argument, of course. Just a cowardly click of a "disagree" button, that makes absolutely no sense.
     
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  9. Joelc

    Joelc Member

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    I don't drop below 30% often, but with around ~20% capacity remaining yesterday I immediately noticed a delayed acceleration from normal.
    Just felt 'sluggish' when accelerating from a complete stop. Not a big deal, but just enough to remind me charge soon. P85 BTW.
     
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  10. WarpedOne

    WarpedOne Supreme Premier

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    Max power vs. State of Chart chart posted above belongs in the BS category because Y axis starts with 310 kW and thus visually exaggerates the differences. It portrays the P85 max power at low SOC only at ~1/6 of the power at high SOC..

    Proper chart with same data that correctly plots the relationships is shown below.
    Yes, it contains a lot of blank space but that blank space allows one to correctly interpret the data.

    Drop in max power is insignificant because of theese factors:
    - change in max power is in all cases less then 12%
    - duration when car releases maximum power is very short
    - max power is only released when the car is moving with a speed in right speed window
    - the accelerator pedal is floored

    So, the correct answer to the topic in question is: No, under normal driving the car does not feel slower.
    I don't know a single person that would describe hitting the accelerator to the floor as normal driving.

    Difference only shows in measurements of max available power when such spirited driving is called for.

    LaunchLimit.jpg
     
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  11. TexasEV

    TexasEV Well-Known Member

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    OK so the performance versions feel less "performancy" at lower states of charge. In my 60, and I suspect in non performance larger batteries as well, it's not something the average driver would notice under typical driving conditions.
     
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  12. Andyw2100

    Andyw2100 Supporting Member

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    Well, at least now we are having a discussion instead of just lobbing "disagrees."

    I did not create the chart, as I pointed out in the post. I was simply reposting the chart.

    Also the fact that the chart does not show the blank space that you showed in your chart does not make it BS. The numbers were all there. If someone is only looking at the chart visually, and not reading the numbers, that is a problem with how the chart is being interpreted and not a problem with the chart itself.



    12%? Are you mathematically challenged? On the P85D, the difference shown is about 353 to about 414. That's a difference of 61. 61/353= 17%.

    On the P90DL the difference is about 424 to about 510. 86/424=20%! And the low SOC on the P90DL was above 40% SOC. The numbers would be a lot worse at 20% SOC, which is what the OP was asking about.
     
  13. brianman

    brianman Burrito Founder

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    It gets especially punishing when you get down to < 50 rated miles and the limiters start kicking in (dashed lines in the UI give visible feedback of what's going on).
     
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  14. evp

    evp Nerd

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    Agreed. That's been my experience in my S85.
     
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  15. Rocky_H

    Rocky_H Active Member

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    Yeah, I'm going to throw in here. I see 9 different lines shown in that graph, and all of them are for some version or setting of a performance model. That's a significant detail with all of this generalizing going on. This is a fundamental condition of the original poster's question. The Performance inverter draws more current. I have heard a few people say that in their P versions, they did seem to feel the loss of some "kick" as the battery state of charge went down. With the S85 and S60 non performance versions, they just draw less current anyway, so most people don't notice any difference.

    Oh, and this was just a little humorous.
    Huh. It looked to me like the chart was showing numbers, not feelings.

    And regarding the percent number thing:
    Percent differences change depending on whether you're talking about an increase (divide by the smaller number) or decrease (divide by the larger number). Since the question was framed as a question of noticing a decrease of power as state of charge goes down, it should probably be more like 61.61 / 414 = 15%. That's obviously still bigger than 12%, but the power loss percentages should be a little lower than the numbers you're getting by calculating the percent increase.
     
  16. Andyw2100

    Andyw2100 Supporting Member

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    I think it was pretty obvious that what I was saying was that I could feel the large difference that the numbers on the chart represented.

    The original question was not clearly framed. And more importantly, I was responding to the following comment:

    "- change in max power is in all cases less then 12%"

    Change. Not reduction.

    And while we're at it, warpedone should have written "than", not "then." I simply repeated the error above. Unlike warpedone, I know better.
     
  17. Denarius

    Denarius Active Member

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    I notice a significant difference in my car once I've dropped below 50% SOC.
     
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  18. wcfinvader

    wcfinvader Member

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    Classic 85 here. We don't notice a significant difference until under 50 rated miles remaining. Power limit line is displayed is the only time we have noticeable reduction in power.
     
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  19. brianman

    brianman Burrito Founder

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    Ditto for me in P85, P85D and P85D. Haven't stressed P100D yet.
     
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  20. gavine

    gavine Petrol Head turned EV Enthusiast

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    It should be noted, for those to whom it is not generally understood, that Teslas will increase the amps to keep the wattage (power) consistent as the voltage in the pack drops with lower states of charge. It makes sense that the performance models are affected more because they are already maxing-out the amperage of the pack whereas the non-performance models are not. Therefore, the non-performance models will not be affected as much with the voltage drop in the pack.
     
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