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Best supercharging road trip strategy?

Discussion in 'Model S: Battery & Charging' started by Jhall118, May 5, 2014.

  1. Jhall118

    Jhall118 Member

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    Hey guys, after trying to do the math, and being unable to convince myself one way or the other, I figured I would call upon the help of those that have traveled long distance using superchargers before. I am driving from Seattle, WA to Utah, and taking the long way through California because I can find zero HPWC in Idaho :(

    Is it faster to travel at the speed limit (say 65) to get to the next supercharger. Or is it faster to travel faster (at say 75), and then charge longer at a supercharger. I have the 85 kwh battery (performance with 19" wheels).

    Assume that you get 120kw at the supercharger. I am going through California on a road trip through the middle of the week/night (hoping to avoid the majority of the busy supercharger times), and was wondering which strategy to employ. Any opinions?
     
  2. PV_Dave

    PV_Dave Member

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    Between full power Superchargers (i.e. where you're not sharing a Supercharger, and thus you're able to pull 90kW or better), my understanding is that the quickest total trip duration is achieved when you go as fast as you can without:
    1) Running out of charge before you make it to the next Supercharger, or
    2) Getting into an accident, or
    3) Having an extra unplanned stop to speak with your local highway patrol officer.
     
  3. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    4) Wasting time charging at the Supercharger into the taper for more rated miles than you need to get to the next stop with margin (avoid #1 above). By putting all the correct numbers into EV Trip Planner and adding a 25% buffer, I have never gotten close to a #1 experience. Of course, add more percent buffer if you have a big headwind or the blizzard is coming.
     
  4. gene

    gene Active Member

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    I have always found it to be best if you always go downhill.:biggrin:
     
  5. bob_p

    bob_p Member

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    Because the charging rate is much faster when the battery is at a low charge, the extra energy consumed by driving at higher speeds should be recovered faster - and not penalize you on total time.

    It's important to monitor your energy consumption between chargers - and if your estimated range (I use mileage + 30% plus 30 miles) drops below the rated range, then back off the speed a little (5 MPH can have a large impact) and slow down to ensure you can safely reach the next charger.

    HOWEVER, if it requires charging above 80% while at a supercharger to reach the next charger - then you may save time by charging below 90% and driving a little slower - because the charging does start slowing down considerably as you approach 90-100%.
     
  6. Reed

    Reed Member

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    You are charging at anywhere between 200-400 mph. Unless you figured out how to disable the speed governor on your Tesla, it is always quicker to drive faster and charge longer.

    Have a safe trip and enjoy the free charge! :)
     
  7. Shumdit

    Shumdit Member

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    With Superchargers and assuming arriving with a low amount of range left (0-40 miles) the best strategy is to charge up to approx 80% and then move off to the next unit. That last 20% takes as long as the first 80% so it's wasted time as long as you know you have the range to make it to the next unit. You can drive at the higher speed because the reduction of range caused will be offset by the fact that the SC can recharge in less time than you saved by driving faster. If you don't have Superchargers for "refueling" this strategy will not apply nor will it apply if you arrive and find out you have to share your SC unit with another car and therefore your charging rate is less than it would otherwise be.
     
  8. David99

    David99 Active Member

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    Assume you travel 100 miles (which is the average leg between Superchargers).

    Going at 65 mph: drive time is 92 min, charge time is 17 min = 109 min total
    Going at 75 mph: drive time is 80 min, charge time is 24 min = 104 min total
    Going at 85 mph: drive time is 70 min, charge time is 30 min = 100 min total

    Driving faster you are using more energy to travel the same distance, hence the charge time is longer, but since the Superchargers are so fast the time lost in driving slow outweighs the extra time spent charging.

    You can also minimize the time spent at Superchargers when you arrive at them with as little in the battery as possible. The charge speed is highest when the battery is close to empty. The higher you charge, the slower it gets.
     
  9. brianman

    brianman Burrito Founder

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    5. The math changes when you leave your "last" supercharger. Unless you plan to park your car for 4+ (and probably 8+) hours at your destination, it's a good idea to be a bit more conservative on the last leg of your journey.
     
  10. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    If you need an L2 to make it to your destination. You want to leave the Supercharger when the charge rate at the Supercharger goes below the charge rate at the next L2 charger; at that point, it't faster to charge at the L2. Of course this assumes that you can make it... For an 85 heading to 240 Volt service, the time to move on is approximately when the Supercharger current goes below half of the L2 current ahead. See below for math.

    I do this every time I drive from Boulder to Pagosa. That trip has three segments, Boulder to Silverthorne Supercharger, Silverthorne to Salida 70 Amp J1772, and Salida to Pagosa. Because the Salida J is 70 Amps, I leave Silverthorne when the charging current goes below 35 Amps. At that point the charge rate is about 50 mph, but because the charge rate when I arrive is well above my driving speed on I-70, I go as fast as I want driving to Silverthorne. Because I only need a small charge in Salida to make it to Pagosa, and the total driving time is almost 5 hours, it turns out the tradeoff between driving driving slower/charging less and driving faster/charging more is a very soft or flat optimum. Even though it costs me a few minutes, I have found it is far more comfortable to drive with the traffic and take a few minutes more on the trip; this puts in Salida for about 1.5 hours. Besides the Salida J is at a very nice location in Salida with lots to do. I can greatly reduce the reserve that I keep on the Salida to Pagosa segment because there is a 70 Amp J in downtown Pagosa that is 20 rated miles before my house. If I cut it too close, I just stop in Pagosa for a few extra miles.

    Math:
    1. AC power must be multiplied by about 0.9 to compare with DC power because of the ~90% efficient AC charger.
    2. At the end stage of charge, the battery pack in an 85 is at about 400 Volts.
    3. Assume the AC charger is about 230 Volts.
    4. Define Supercharger Amps as SA and J1772 Amps as JA.
    5. 400*SA = 230*JA*0.9
    6. SA = 230/400*0.9*JA
    7. SA = 0.52*JA
    8. As I said, for an 85, when the Supercharger Amps are about half of the L2 Amps ahead, it's time to move on.
     
  11. David99

    David99 Active Member

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    The last leg can have all sorts of different requirements. For example I sometimes charge longer on my last SC because I don't have a charger at my destination and I want to make sure I have enough to make it back to the SC when I'm on my way back.
    If I do have a charger at my destination I only charge just as much as I need.
    If I'm not in a rush and I'm still eating or getting a coffee, I might just fill up longer on my last SC (provided no one else is waiting of course).
    But all of that is besides the original question which is about what driving speed is best for SC trips.
     
  12. joshuaeven

    joshuaeven Member

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    We are going to be making a trip from Portland to Disneyland this summer, with a stop over in SF. Before reading this thread I was assuming we should be driving slow and conservative to maximize charge between Superchargers. Now I see the light!
    Quick question- are there any legs that are spaced such that we should be more careful? I made a list of all the Superchargers we should be stopping at, but I don't have the actual distances between chargers anywhere. We have an 85, 19" wheels. Do I need to worry? Thanks!!
     
  13. David99

    David99 Active Member

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    Sounds like fun trip! Disneyland has 20 charging stations in their parking structure. Make sure you use the "Mikey and Friends" parking structure and tell the person in the booth that you want to charge your EV. They will give you a tag and redirect you to the charging stations.

    I would definitely give yourself a buffer when charging between Superchargers. How much you actually need depends on the speed you drive and elevation gain/loss. For example when I drive between the Supercharger in Buckeye and Quartzsite, the distance is just 100 miles, but with wind and going an average of over 80, I need about 150 miles of rated range. So I usually charge to 160 miles to have 10 miles of extra. That's an extreme example, though.
    You can use this website to figure out how much you need. EV Trip Planner
    It will assume realistic driving speed so you get a pretty good idea.
     
  14. DennisLevitt

    DennisLevitt Member

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    I just finished driving Los Angeles to New York, and I think it's definitely better to drive faster. Cruising in the fast lane with traffic feels a lot better than watching Nissan Sentra's fly by. Through most of the country, the superchargers are only about 150 miles apart, so charge to Daily Top (about 230 in an 85) and fly.

    As @Cottonwood suggested, when you start to charge, put your next destination into the Nav system and charge to 25% above that. If you're charging from about 50 miles Rated Range up to 200 miles rated range, it goes very fast. Often only 20-30 minutes.

    Through much of the Seattle -> Utah drive you will be going through a lot of elevation change. EVTripPlanner.com is very good at giving you the range miles needed.

    Don't be afraid of leaving the Supercharger Trail, as long as you plan it using something like Plugshare.com . We went Kingman -> Blanding, bypassing a number of superchargers and seeing incredible scenery in Monumental Valley.

    @Gene - It's even better if you can go downhill both ways :rolleyes:
     

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