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Optimize travel time = ...going as fast as possible?

Discussion in 'Model S: Battery & Charging' started by SuisseDriver, Aug 25, 2017.

  1. SuisseDriver

    SuisseDriver Member

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    Hello to all, there was a lot of discussion about the best charging / speed strategy in order to minimize the journey time.
    However, one of the graph posted on this post : Driving & Charging Time
    is pushing me to believe that indeed, the quicker you go, the faster your journey!

    Hear me out. I am living in Switzerland and traveling often in France or Germany where you can drive sometime quite fast.
    From the graphs in the link above, there are 2 conclusions :
    1. the optimum speed WHEN ARRIVING WITH THE SAME SOC to the next Supercharger is ~70-85MPH (120-135km/h)
    2. but, and this is a BIG but : going 90MPH and arriving at 0% or 10% (and charging back what was lost) is QUICKER overall than going 75MPH (the optimum above) and arriving with 20%-30% SOC

    My take on that is that, I do not expect having many cases where I would to a long trip where I would not stop for lunch / dinner (allowing a full charge) at least every 4-5 hours (400-500km).

    Then, with a S75D (the car I ordered), it may be faster overall to always target arriving with the minimum SOC to the next Supercharger (like 10% or less) and go as fast as possible (and/or permitted), and then take just enough to reach the 2nd Supercharger where the long charge will take place during lunch / dinner.

    Is my assumption / understanding correct?

    Then, it would mean that I could drive at 150km (~270W/km) and make 220-250km with 10% left, charge what I need to reach the next Supercharger for a full charge between 220-250km away (again driving at 150km/h) up to 300-320km away (if driving slower like 130 or 120km/h respectively), right?
     
  2. ShockOnT

    ShockOnT Quickish

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    That is pretty much correct, so long as you're supercharging, and you don't go crazy fast.
    Basically, driving at 150kph plus supercharging will get you there faster than either 100 or 200kph.

    This all assumes a long enough distance. Obviously on a short enough trip if you could skip charging completely by driving slightly slower then that would be better.
     
  3. SuisseDriver

    SuisseDriver Member

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    G
    Great. Thanks for the confirmation.

    Putting more though into that, I see all long journey here in Europe being a combination of 1 short and 1 long (with lunch / dinner) stop and repeating this cycle how many times you need.

    Considering that you could put the short pause (which is the pause where the time is really wasted, beside obviously allowing to stretch a little bit) before or after the long pause, I think that what is really important is what is the distance between the short pause and the one where you will stop longer for lunch / dinner and allowing a full charge.

    If this distance is bigger than 250-300km for a 75D (probably more than 350km for a 100D), then you become limited by the range and you cannot go at any speed you want, especially on winter and loaded because you may have to go 120 or lower on some of the portion to reach the next charger.
    This where things are becoming tricky.

    I have an example for a trip going from Swtizerland to Normandy in France. In one of the portion of the trip, I have the following choices, after a full charge stop to reach the final destination:
    • 150km (so SOC ~ 50%) - Supercharger a few minutes - 265km --> both distances are easy to get, at whatever decent speeds but I need to have enough margin for the 265km so should charge 90% or close to that so I may have to wait 20mn-30mn to go from 50% to 90% SOC on a S75D?
    • 300km - Supercharger - 118km (including Paris round road where you drive super slow -70km/h-) --> here, the stop can be very short as I do not need to take a lot of kW (25kW max) and I do not need to take to much margin. But the 300km are a stretch and may force me to restrain myself (120 or below). How long should I need if at SOC <10% to charge 25kW so ~35% on a 75D

    I do not know which scenario would be the best as I cannot find anywhere the real charging time of a S75D for the various SOC...
     
  4. Max*

    Max* Not Banned

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    I don't quiet follow your math.

    Your goal is to arrive at the next superchager with the minimum SOC you feel comfortable. Some people that's 20%, others it's 3%. It's your number, you aim for it.
    Your goal is to drive as fast as possible to get there with that small number.
    When you recharge for the next stop, you want to spend as little time at the supercharger is possible. So you charge until you can comfortably drive and arrive with your buffer (20%/3%/whatever).


    It seems that you're arguing that arriving with 20%, and then charging to a 0% buffer will save time. It will. But it's speed independent at that point.


    I've seen better graphs on TMC. The sweet spot for long distance trips is going about 75-80mph. More than that and your overall (charge + drive) time goes up a little due to the taper of the packs. For shorter trips, the faster you go the better off you are, as you don't need to charge as much at the SpC and stay below the taper.
     
  5. eschummer

    eschummer Member

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    Even if you knew the exact charging time the car takes, the real world charging time depends on a number of additional factors you have no control over, such as how many other cars are being charged at the same time, outside temperature, charger condition, etc.

    I basically plan out my route using ABRP (A Better Routeplanner), and then vary the speeds/charging times based on what real world conditions I run into. YMMV
     
  6. aesculus

    aesculus Still Trying to Figure this All Out

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    A few simple rules to minimize travel time:
    1. Never charge more than you need (your reserve) (see #3)
    2. Never drive faster than you can charge at
    3. Time spent doing something else (like a meal break) should not be included in your charge time - so keep charging
    4. Charge rates are often unpredictable - too many variables to guarantee a expected rate.
     
  7. Nosken

    Nosken Member

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    Years ago there was a post by a guy that drove SF > LA often. He calculated that the optimal balance of speed vs charge time was 75 MPH.
     
  8. Brass Guy

    Brass Guy Member

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    Optimal speed is determined by the distance between SC's. Farther apart, you end up charging more into the taper so need drive slower to avoid longer charge times.
    In general, 75-80 seems to be the sweet spot. +/- 5 or 10 mph seems to make a negligible difference, a few minutes.
    In this post I tried to demonstrate this: Optimum Supercharger driving speed
    It's a bit outdated, but I think in general it's sound.
     
  9. SuisseDriver

    SuisseDriver Member

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    I was maybe not clear enough. I have already seen those simulations that show the optimum speed to have the shortest trip.
    But in my case, i consider that once every 2 stops is a long one for lunch or dinner as i do not see myself driving with kids more than 500-600 and 5-6 hours without eating. Therefore, once every 2 stops, i do not need to consider the charging time.

    From the simulation i did with a Better Route Planner (that i did not know before and is terrific), it seems that charging at 50% SOC (up to 90%) can be as much as nearly twice as long as charging from 10% and could add nearly 20mn-25mn more charging time.
    It means that i can drive at 110-115km/h and still be quicker overall (plus waiting charging is no fun).
     

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