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Acceleration performance and State of Charge. Data anyone?

Discussion in 'Model S' started by TR5642, Aug 10, 2017.

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  1. TR5642

    TR5642 Member

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    In one of those 'long roadtrip random thoughts' exercises, I started to think about the parameters on the battery in various SOCs and how that might impact maximum output of the motor and thus acceleration.

    It would seem likely that as SOC drops and thus voltage drops on the pack, there would be less energy available to the motor at any given moment. However, this might be masked by controller tricks that keep amperage in a relatively constant range regardless.

    My perception (and I have not (yet) done the simple thing of collecting data from various SOCs), is that when the battery is in a high SOC, particularly right as it comes off the charger, the car has more oomph. And that as it gets toward the lower end of SOC it's a bit more 'leisurely'. But perceptions can easily be fooled by preconception.

    Does anybody have data and or formulae on output vs SOC?
     
  2. deonb

    deonb Supporting Member

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  3. xveys

    xveys Member

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    Today I was very low on charge right before a SuC (2-3%), and the acceleration while driving was very much reduced, almost to ICE response levels ;). This was durting normal driving, no 0-60 accelerations, and I wasn't accelerating to max power output either, which is of course also reduced (yellow lines). I pressed the pedal, and it was as if there was a lag. Indeed it seems that power to the motor is reduced at (very) low SoC.

    So no actual data, but the difference is very noticeable. I must imagine that with a performance model, the reduction in power, or response, must be even greater.
     
  4. Old Man Mike

    Old Man Mike Member

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  5. D.E.

    D.E. Member

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    #5 D.E., Aug 11, 2017
    Last edited: Aug 11, 2017
    I think with very low charge staes, the car goes into a reduced power mode to maximize remaining range. I've forgotten where I read it. There is one description from a person who drove until the car finally stopped. It was 16 miles or so past the 0 charge reading. It may have been in that description. I'll see if I can find more. It does make sense that there'd be a reduced power consumption mode as charge nears exhaustion, in the hopes the few extra miles of increased range would help one limp to the next charger.

    Did you notice any other signs of power conservation, climate system operating in a reduced mode, etc.?

    I'm 65 and we tend to keep cars for a long time, 20 years or so, so this is probably my last car. As such I'd like to wring out the greatest number of charge cycles. My understanding of Li Ion batteries is they last longest if one keeps the charge level as close to 50% as possible, so it'll provide more lifetime power cycling between 40-60% than it will between 5-95%. So I try not to run it down to 2-3%. I have a problem with mine in that when supercharging it blows right through my maximum charge setting.

    Anyway, I'll see if I can find what I read about the reduced output at extremely low charge levels. Electronically, I would expect the voltage regulating circuitry to adjust the lower voltage at low battery levels to whatever is the ideal for the car, and so if there is a low battery reduced consumption mode, then I'd think it would be electively done in software rather than simply being a function of a lower voltage battery state.
     
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  6. xveys

    xveys Member

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    When I had reached the SuC and plugged in the car, I got the notification that A/C power was reduced due to a low battery. Otherwise, nothing during the drive.
     
  7. TR5642

    TR5642 Member

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  8. TR5642

    TR5642 Member

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    Fascinating chart. Thanks

    Two things I noted

    1) that they don't all have the same curve. I wonder if that's an artifact of limited data points or other testing anomaly or something different about the different configurations.

    2) I've long joked to passengers who comment on how quick mine is that it is the slowest car Tesla makes (an S85). This chart really shows how true that is (particularly since it is below the lowest line) ;-)
     

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