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Don't skip Superchargers on long trips

Discussion in 'Model S: Battery & Charging' started by David99, May 17, 2016.

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  1. David99

    David99 Active Member

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    #1 David99, May 17, 2016
    Last edited by a moderator: May 20, 2016
    The discussion about what is better comes up a lot here. On road trips, is it faster to charge more and skip a Supercharger, or stop at each Supercharger and just charge as much as you need?

    The simple answer is: It's almost always faster overall to use every Supercharger than trying to skip where you can. Sounds counter intuitive because adding more stops slows you down. Yes it does and going off the freeway to a Supercharger and back adds extra driving time. But since we are talking about an EV charging the necessary energy for a given distance does not change. One way or another you need to charge that amount of energy to make your trip.

    The tricky and unique part about Superchargers is that their charging speed depends a lot on how full the battery is. An empty battery can be charged very fast, an almost full battery can only be charged at a slower rate. That's just the nature of how batteries work these days. The difference can become quite significant. When you try to skip a Supercharger and plan for a longer leg to make it to the next one, you have to charge your battery to a higher level. This means your average charge rate is slower. In other words, to charge from zero miles 250 miles in one session takes much longer than charging twice from zero miles to 125 miles. You can read more about that here. This example assumes the Superchargers are about 100 miles apart of each other on your route. That's roughly the case at this time when doing cross country road trips.

    To show this a little better in an example I made up a route in EVTripplanner.com.

    We start somewhere in Los Angeles and go passed Denver. On the route you see three white Superchargers that we are skipping: Las Vegas, Richfield and Grand Junction. On the lower left side you can see total drive time, total charge time and total time for the trip. Now let's add the Richfield Supercharger and see what happens.


    The total drive time got a little longer because it takes time to get to the extra Supercharger. But the total charge time went down by a lot. So we added a few minutes driving, but we save more charging. Now let's add the Grand Junction Supercharger.


    Again, the drive time got a little longer. We added 7 minutes to get off the freeway and back on. But we also saved 20 minutes on charging time. Adding these two Supercharger stops shortened the trip by 26 minutes! But now let's look at the Las Vegas Supercharger. That one is only 46 miles after Primm where we are stopping and charging already. What happens when the distance between Superchargers is less than 50 miles?


    The gain in charge time is eaten up by the added drive time. Overall it added 1 minute. Let's say it's a wash. We can stop there and charge or we can skip it, it makes no difference in terms of time.

    Looking at a typical road trip example, it shows that skipping Superchargers is most likely not going to get you to your destination faster. It will actually slow you down. When distances between Superchargers are very small, then it makes little difference one way or another.

    OK what about weather? How does that play in. If you have bad weather, rain, snow or strong head winds, basically things that require more energy, the favor goes even more towards stopping at each Supercharger because you are trying to add more energy into the battery charging it near 100% where the charge rate becomes slower and slower.

    So much for the bare numbers and optimizing your trip for speed. Reality often looks different. There is nothing wrong taking a longer break while eating for example. Then you would of course charge longer and might have plenty of energy to skip a Supercharger. You might have kids in your car that are sleeping. Each time you stop they wake up! Definitely charge longer and drive longer! :)
     
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  2. KJD

    KJD Member

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    Nice write up David. What speed are you using on the freeway ?
     
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  3. deonb

    deonb Active Member

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    The title is incorrect based on the content - specifically this statement:

    "When you try to skip a Supercharger and plan for a longer leg to make it to the next one, you have to charge your battery to a higher level."

    What happens if your battery is already at a higher level as a result of an opportunity charge? E.g. in the first example, let's say you had some family in Beaver and you visit them for a 90 minute lunch while it's charging. When you leave, the cost is already sunk - stopping at Richfield only makes the overall trip slower.

    A more apt title would be: Don't wait for a higher charge in order to skip the next Supercharger.

    I must say, based on all my Supercharger trips, I'm very seldom really waiting for a Supercharger. Maybe 15% of the time. Most of the time by the time I get back from whatever I was doing, I have more charge than I need. And a lot of those times I have enough extra to even skip one.

    If you're constantly waiting for a charge to complete, get a kid. Or a dog. Or both - you'll never wait for a Supercharger again!
     
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  4. David99

    David99 Active Member

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    EVTripplanner doesn't set a certain speed, rather it goes off what Google maps says as the average speed cars are going on a specific road. Then you enter a 'speed multiplier' to adjust your own speed. The default is actually pretty close to what I would drive. When I plan I put in 1.05 or 1.1 as a multiplier when I know it's at night and I can go faster without traffic.
     
  5. David99

    David99 Active Member

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    Out of my 74k miles I drove about 40k doing very long road trips. I love driving, but man when you are on a 2k miles stopping to charge does get old quickly. You just want to get on the road again. But I admit, those cases are not the norm.
    Regarding the opportunity charge, totally agreed. If you are doing something anyways, it makes a lot of sense to charge the entire time as much as you can. I also agree, doing the trip in as little time as possible isn't always what you want. Making the trip fun and enjoyable and seeing interesting things on the way are often more important than saving 40 min.
     
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  6. deonb

    deonb Active Member

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    It does. I don't really mind the act of stopping or the time it takes so much as the locations that Tesla has for some/most of the Superchargers.

    Put some in national and state parks and the experience would be very different from today. But even a highway rest area would be much preferable to a parking lot of a Golden Corral.
     
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  7. AWDtsla

    AWDtsla Active Member

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    The evtripplanner charge times are suspect. It's making assumptions about how much reserve to keep, for example. The difference between at 30 and a 60 mile buffer when you're nearly full is a huge difference a supercharge time. Also not being able to set starting charge is kind of annoying.
     
  8. JohnQ

    JohnQ Active Member

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    Yup, the key is riding the bottom of the pack as much as possible. Most of my road trips are south through Newark, DE which is 185 miles from my house. I arrive there with 20 miles left and then charge enough to have 20 miles at the next charger. Rinse and repeat. The problem is always locations where it takes a while to get to the charger ... Macedonia, OH. Or lot's of traffic like Cranberry, PA.
     
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  9. David99

    David99 Active Member

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    I think it assumes you arrive at aprox 15% battery which is a reasonable value.
     
  10. AWDtsla

    AWDtsla Active Member

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    It's reasonable, but not for all conditions. Nice clear spring or fall day could go less. Winter with windy weather and possibility of snow or rain, go more, maybe 25%.

    Also I should add without support for 75/90 packs evtripplanner will make you wait for charging more than you would have to.
     
  11. brianman

    brianman Burrito Founder

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    Point of clarification:
    Where "bottom of the pack" is the UI 'bottom' of "1 rated mile and above", not "below 0% in the UI".

    Regularly "riding in the negatives" (in the UI) is quite risky.
     
  12. bxr140

    bxr140 Member

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    To clarify, the original assertion is a suggestion and not a rule. In the real world, it probably applies to a very small percentage of actual tesla road trips.

    For those who missed it, the OP was challenged on this very subject in another thread, and instead of responding to the challenges started this new thread that, unfortunately, does not accurately describe the whole picture.

    The truth is that it depends a whole bunch on a number of variables, and if you apply the 'stop at every charger' plan to every road trip you take, MOST of those trips will take longer than had you applied a little more in depth logic.

    Some reasons why it doesn't always make sense to stop at every charger:
    1. Starting a road trip at 100% will often allow you to skip the first charger.
    2. In charger dense regions you can waste more getting to/from an additional charger than you would charging for those same few minutes at the previous station. This will become ESPECIALLY true as charger density increases on major routes around the country.
    3. If you're on a heavily traveled route where pairing (or even lines) are probable, you could end up net-positive by charging up more and skipping a high risk station.
    4. Similar to #2, if your daily destination (with charging) is reasonably just beyond the next station, you could be better off charging up more and the second to last station and heading straight to your destination.
    5. If you're taking a longer break for whatever reason (sit down meal, cleaning up your kid's puke, etc) and get enough to skip the next charger, do it.
     
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  13. dgpcolorado

    dgpcolorado Member

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    Yes! Some of the ones I use are in hotel lots and not particularly interesting. All I really want is easy access restrooms and that would be the advantage of highway rest areas (plus picnic tables). One of my favorite locations is in Grand Junction where it is at a mall with dozens of stores and restaurants. And restrooms. Unlike the usual knock on malls — ICEing — that simply isn't a problem at the GJ location. One of the Supercharger Stations I am most looking forward to is Twin Falls ID. Talk about a terrific location!
     
  14. snellenr

    snellenr Member

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    We just finished a long trip (Harbor Springs, MI -> Houston, TX via Columbia, MO) and found that the onboard navigation had a tendency to schedule long charges to "skip" superchargers, but within a few miles of resuming the trip the "skipped" charger would be added back to the route. We were traveling at the speed limit - 70 mph in most cases -- and the "scheduled" charge at destination usually started out at around 15%. There was a bit of a crosswind, but not to the extent that it felt like the car was having to "battle" it...

    Examples included Cadillac -> St. Joseph (skipping Grand Rapids) and St. Joseph -> Normal (skipping Country Club Hills) - in both cases, the intermediate SCs were "un-skipped" within 15-20 miles after leaving the initial supercharger. After some shrugging and eye-rolling, we finally gave up and set the next supercharger in the nav at each supercharger (to help gauge how much charge we needed) and then switched nav to the final destination (to track progress) after we hit the road.
     
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  15. cantdecide

    cantdecide Member

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    Good analysis... it usually is faster to stop at almost all superchargers... when going on that route and most current routes, yes.
    However as superchargers get more dense this becomes much less true... and I would claim that where superchargers are already dense this isn't true.
    Even if every freeway exit had a supercharger, the optimal strategy is likely to be to drive until empty, then charge to ~50% each time (~130 miles).
    Driving from my home to Tahoe is 230 miles and goes directly past 7 superchargers. I'm not going to stop more than once unless I start empty.
    In NorCal the density is already there to mean you don't stop each time.

    Of course, I'm not optimizing for time anyway... (I understand the topic is purely about time taken)
    * I want to stop at a supercharger at a restaurant I like, and I'm not leaving after 20 minutes.
    * I would rather drive with autopilot for 10 minutes, and have a 10 minute extra walk at a supercharger (20 minutes total) than spend an extra 10 minutes driving in city traffic.
     
  16. swesson

    swesson Member

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    Agree! I found the same thing on my trip from Denver to Dallas and back.
     
  17. mmccord

    mmccord Member

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    Ah, you must have the rear-facing seats also. :)
     
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  18. Rocky_H

    Rocky_H Member

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    Apparently not everyone is as excited about this location as you are. Last summer, when the Twin Falls location had been picked, there was someone in that thread who was complaining about the location. Here were his comments:

    “Map shows it as 4.7 miles from I-84. Not too bad although I would have preferred something just off the freeway.”

    I pointed out that there was basically nothing right there at the highway exit, but he replied:

    “there's a truck stop next to a Days Inn (I stayed there in May) right off the freeway. Putting the Supercharger station there would have been more convenient, I think.”

    At least you are happy, even if that guy wasn’t. Oh, whoops, that was YOU! Glad to see you’re happy for that location now.:D

    Twin Falls, Idaho supercharger
     
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  19. dgpcolorado

    dgpcolorado Member

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    Yup. When I wrote that we hadn't pinned down the location yet and I thought it was farther into Twin Falls where the old visitor center seemed to be. Instead it turned out that they were building a new Visitor Center — my search for the old one showed it was farther south — next to the Snake River Canyon and the Supercharger Station was going to be there. So, the information changed and I changed my mind, especially after looking at Google Earth. My impression is that Twin Falls has been gradually expanding north toward the river, with the mall and motels and the like being well north of city center.

    So, not as far off I-84 as I believed. And, for my route, I now have to make Twin Falls my overnight stop because it is the closest city to halfway and a longer driving day than 600 miles just isn't practical in the Tesla the way was it was in my ICEV.
     
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  20. MichFin

    MichFin Member

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    I really look at each leg of the trip independently because some locations have easy access, good food and some are out of the way or with lousy shops to walk to. I stopped at the South Bend SC and it was 15 minutes off the highway... although they had great food choices. Sometimes you can't win :(
     

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