TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Optimum Supercharger driving speed

Discussion in 'Model S: Battery & Charging' started by Brass Guy, Mar 6, 2015.

  1. Brass Guy

    Brass Guy Member

    Joined:
    Jan 5, 2014
    Messages:
    505
    Location:
    Stoughton, MA
    In an attempt to find the optimum driving speeds between superchargers for the minimum total charge + drive time, I did some number crunching.
    Using the Supercharger Table found here Tesla Model S - Supercharger Table for charge times and EVTripPlanner for rated miles used and drive times at different speeds, I plotted the total time for different distances. What did surprise me was that even with shorter distances, there's still an optimum speed below the car's maximum speed.

    The data is not very accurate; since the Supercharger Table is rounded to 10 miles and even minutes, and EVTripPlanner is rounded to the nearest minute. Near the optimum, the difference in time with 5mph increments is negligible. I was still able to demonstrate that the charge time curve does indeed overtake the drive time curve. All the curves for different distances look similar, and the optimum drive speed seems to change very near linear with the distance.

    It's easy to map routes in EVTripPlanner between superchargers, so I tried to choose superchargers at different distances with little elevation change, near highway ramps, using all the default settings except using the Model S85 with 19" wheels. Since the topic is optimizing time, I decided to assume we just arrived at the first supercharger with 0 miles (presumably from a previous supercharger stop) and are charging just enough to get to the next supercharger at our desired speed with 0 miles left again. I plugged values into the speed multiplier until I got even multiples of 5mph on the highway segment in the "steps" tab, and I used the entire trip drive time.

    Here is the longest distance I tried, between FL Port St. Lucie and St. Augustine. It looks like 80mph is the fastest you can drive and make it, and only with a brand new battery. If you have any degradation symptoms (real or "balance" issues), a lower speed will have to be used to avoid the last long minutes of supercharging before departure.
    image011.gif
    Even at 200 miles, the time difference between 75mph and 80mph is only 10 minutes. That cost 22 rated miles at the top of the battery, which adds about 17 minutes charging time.

    Here is a more typical distance, between FL Port Orange and Port St. Lucie:
    image009.gif

    And another typical distance, between FL Lake City and Ocala:
    image006.gif

    Here is the shortest distance I tried, between CT Darien N and Milford N:
    image002.gif

    Disclosure: I did tweak some of the minutes by a few 10ths to smooth out some of the curves, but none more than a half minute.

    Using the 85 vs 60 supercharge video Bjorn posted, I compared the charging rate with the Supercharger table and found that the table is a bit optimistic to that video; so even though the table is rather old I can conclude it was constructed with times from a 120kW charger and non-A battery pack. (Maxed at 114kW)

    I also tried to make a similar table for the 60kWh battery using that video, but in the video he only charges to 80% so there's not enough data there to do many iterations or very high speeds. Again the resolution is just too low to establish optimum speeds within 5mph, but for the 3 distances I tried (28.8mi, 63.4mi, 80.8 mi) the optimum drive speed seems to be in the range of 80-90mph; slower than in the 85kWh as expected.

    The results clearly show that there is no one optimum driving speed for minimum total time.
     
    • Like x 1
  2. BerTX

    BerTX Member

    Joined:
    May 2, 2014
    Messages:
    635
    Location:
    Texas/Washington
    Wow, thanks! That's a lot of good work!

    I get something a little different take on this info than some will here. I see that driving between typical Superchargers in Texas, where the speed limits are typically 75 mph, I will only save 2 minutes by driving 80 mph. But, if traffic is moving at 80-85 mph (as it typically does), I can go along with it and still be good range-wise.

    Thus range-anxiety, time-anxiety, keeping-up-with-traffic anxiety and speeding-ticket-anxiety are all eliminated.
     
    • Informative x 1
  3. Brass Guy

    Brass Guy Member

    Joined:
    Jan 5, 2014
    Messages:
    505
    Location:
    Stoughton, MA
    Yes, any time savings will really be minimal.
    Over longer distances, like on the 136 mile graph, you can save 5 minutes by driving 85 instead of 75 - for and hour and 40 minutes without slowing!
     
  4. ThosEM

    ThosEM Space Weatherman

    Joined:
    Dec 13, 2013
    Messages:
    610
    Location:
    Annapolis, MD
  5. brucet999

    brucet999 Active Member

    Joined:
    Mar 12, 2015
    Messages:
    1,302
    Location:
    Huntington Beach, CA
    My take on what you have painstakingly charted is that at 75mph (about the most I want to drive) the net speed, factoring in charging time, is about 65mph. over any distance.
     
  6. Brass Guy

    Brass Guy Member

    Joined:
    Jan 5, 2014
    Messages:
    505
    Location:
    Stoughton, MA
    I tried that calculation, and came up with net speeds ranging from about 50 for the longest trip to about 55 for the rest.
    The main point to the exercise was to show that the distance affects the optimum speed. It also showed that the time you can save by driving like a maniac is minimal. If your usual cruise speed is 75, the most time you could save is 5 minutes off 85 minutes of drive+charge time by driving 95 on that 80 mile trip, and only if you run the bottom of the battery. It's just not worth it.
     
  7. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    2,048
    Location:
    Brea, Orange County
    Thanks for the work and presenting in a great way. This is indeed very helpful. It shows that driving too fast won't help as you need to charge to a higher state of charge where charging becomes slower. If Supercharging could be maintained at a higher rate to a higher state of charge (which will definitely come with newer batteries), the ideal drive speed would go up. But frankly we are already passed the legal limit.

    Once thing to consider is that you can't realistically drive 85 and run the battery down to zero. That's just asking for trouble. It's also not good for the battery to do that.

    One factor that is missing here is weather conditions. But they are actually easy to add in. Rain or snow will increase energy usage which requires longer charge times. So in bad weather the ideal speed would probably be a little lower than these.
     
  8. arijaycomet

    arijaycomet Member

    Joined:
    Dec 18, 2014
    Messages:
    365
    Location:
    Cleveland, Ohio
    This post comes at a perfect time, as I'm leaving in one hour for the Reach the Beach / Tesla Road Trip event. In total I'll be logging 1,000+ miles this weekend, stopping at no less than 5 different superchargers during those miles (some of them repeat, obviously, as I head back home). I've read up on these kinds of trips, though this is my personal first time going a long distance like this. I've done round-trip journeys with a single day-trip single supercharger, but never linking multiple ones together like this.

    One thing I've taken away here from your data, but also from what others have written, is that again for the most part the numbers seem to indicate a relatively minimal gain/loss going in either direction. There is a mental preconception that stopping more frequently is bad, but if that means charging in the mid-range "sweet spot" then you'll actually charge at a more optimal rate/speed, making those charging visits more effective (efficient?). This is my thought and approach, stop often, charge less.

    My route today will be interesting because every 140-miles (or LESS) I'll be passing a Supercharger (Cleveland, Ohio, to Salisbury, Maryland). That means that I really shouldn't have to ever stop to change very long. We are doing a layover in Baltimore MD, but I'll be there long enough on the L2 station I plan to visit (also free!) to recoup the loss going out of my way slightly. I plan to drive the car at 5-10 MPH over the posted limit (As I always do) and just enjoy driving. I'll be sure to charge ample to make it to the next charger, of course, but won't stay longer than needed beyond that (with some wiggle room for safety of traffic/weather conditions).

    Thanks for the post.. very neat to see this all graphed!
     
  9. MarcG

    MarcG Active Member

    Joined:
    Oct 29, 2014
    Messages:
    1,663
    Location:
    San Francisco
    How did your long trip go? Did you log any data for the rest of us to mull over?
     
  10. Cloxxki

    Cloxxki Member

    Joined:
    Aug 20, 2016
    Messages:
    269
    Location:
    Rotterdam
    I've seen a Bjorn video where he looked for the optimum cruising speed to get hte highest average speed (time). It was 160kph cruising for 120kph average. Newer Model S and even Roadsters may manage higher cruising speeds and/or shorter charging.
    I'd love to eventually see (or even build) interactive graphs to try and get a close-to-perfect advice for a given trip to the next SC. Factoring in weather, road surface and altitude. .

    It's nice to err on the side of speed, as you get to rest longer and drive less. Although the driving is the fun part, obviously.
     
  11. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    2,048
    Location:
    Brea, Orange County
    The new 90 battery charges faster to a higher state of charge. In other words, it just charges faster overall. That mean you can drive an even faster average saving time either in charging going a higher speed.
     
  12. Cloxxki

    Cloxxki Member

    Joined:
    Aug 20, 2016
    Messages:
    269
    Location:
    Rotterdam
    Right on.

    Now translating this to Model 3, it will with a decent size battery, and presuming the 2170 cells like quick charging, spend less energy doing a 160kph cruise and then less time charging back up what it lost. It's going to be pleasure to drive.

    Fast forwarding to a significantly larger pack for Model S, from the often tested real 90 (not the current update likely restricted 100), a 120kWh (+25%) would also lose much less state of charge between superchargers, and thus also much less time to charge back up. It may well already manage 130+kph average over long distances, including charge time. This makes EV travel more about traffic than range and infrastructure. If roads don't allow for 170-175kph cruising (even the Autobahn rarely does), we're left to follow traffic and try to not lose too much time charging versus refueling. On a much longer range and quicker charging, that might not be hard. Before long charging will add less time than refueling costs. No transaction with a card or line for the cashier, no waiting for the petrol, just chilling/eating around the car.
     

Share This Page