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Trip Navigation and charging buffer miles

Discussion in 'Model S: Battery & Charging' started by Sans Gas, Oct 6, 2015.

  1. Sans Gas

    Sans Gas Member

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    In going from point A to point B, X miles apart it appears necessary to have a range of X +n miles to proceed. What is this n buffer of range?
     
  2. JohnQ

    JohnQ Active Member

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    I would express it as n*X where n is a factor applied based on terrain, weather and driving speed. The faster you drive, the more energy you use. Headwind? More energy used at same speed over ground. Climbing mountains, same thing. Take a look at EV Trip Planner to get some examples of estimated energy usage for different speeds and terrain.

    Then you'll want to have some buffer range left when pulling into your destination just in case there are surprises. Just like you don't pull into a gas station on fumes.
     
  3. Zextraterrestrial

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    1.25X is usually enough if it isn't freezing or crazy windy and you semi-obey speed limits
     
  4. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    I prefer to use the Energy:Trip screen. Set your destination into the Nav, then pull up the Energy:Trip screen and look at the estimate for State of Charge (SoC) at your destination.

    This is very useful when charging for the next charger or the destination. The Energy:Trip estimator makes a reasonable estimate including terrain and typical speeds, but not current weather conditions. Given neutral conditions, I like to charge to a minimum 15% buffer at the destination. If weather looks tough (wind, temps, etc), I go up from there. Once you start driving, the energy estimator extrapolates from your energy usage over the last 10-20 miles and projects that on the rest of the trip. If I see the buffer at the destination go below 10% or so, I slow down or look for other charging options. If the estimate looks like I have the destination made without difficulty, I have no reservations about speeding up a little.

    In my 85, for round-number, in-my-head math, I use the approximation that 1% SoC is 2.5 rated miles.

    Enjoy your Tesla!
     
  5. Rodolfo Paiz

    Rodolfo Paiz P85 "Plug and Play"

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    As another point of view, when traveling with the family (car fully loaded with people and bags) in flat Florida, with heavy A/C use, my actual consumption is rather repeatably around 400 Wh/mile... roughly 1.4x actual miles. In order to plan conservatively, I plan to start the trip with no less than 1.5n + 30 miles of range. That means the longest I'll actually plan to travel with the family is about 150 miles, since 1.5 * 150 + 30 = 255.

    Could you plan on a smaller reserve? Sure, but it makes my wife nervous to think we could run out of charge. And the best way to make someone hate EV's is to make them nervous about running out of charge when they travel in one. Set your plan up so that you're never, ever nervous IMHO.
     
  6. artsci

    artsci Sponsor

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    I try to allow for a 20 percent buffer but it's not always possible. But whenever I have any concern I just draft a truck or large SUV. That always solves any concerns about reaching the next supercharger. It always works.
     
  7. Candleflame

    Candleflame Member

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    Is there any way to make the Model S display you range based on the speed/energy consumption over the last 5min or so as in ICE cars?
     
  8. JohnQ

    JohnQ Active Member

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    Yes. The Energy graph will allow you to project based on 5, 15 or 30 mile history.
     
  9. Candleflame

    Candleflame Member

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    oh, that explains why so many people have it up on their S dashboard.
     
  10. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Yes, but that graph is worthless in mountainous terrain. Take a look at this average usage over 30 miles and the projection.

    Zero Wh-mi.JPG
     
  11. joefee

    joefee Over 2 Million TMC page views

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    Day to day driving ...never worry about range. Trips, I add 50mi to the next supercharger distance.
     
  12. Electricfan

    Electricfan Member

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    I must me a risk taker compared to you. I'm ok with 40 - 45 buffer. Never less than that though.
     
  13. David99

    David99 Active Member

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    The trip energy graph does a decent job. Most of the time, you can trust it. With wind and weather, you have to be very careful! Especially wind has been tricky for some of my trips. I charged 20% extra and still had to slow down to make it!

    15-20% is a good buffer. If you have bad weather and want to go fast, use a little more. If adding 20% buffer means you have to charge to 100% it might be overall faster to charge only to 90%, use less buffer and drive a little more careful. The last 10% take a long time to charge. It eats up more time that slowing down 2-3 mph over the next leg.
     
  14. napabill

    napabill Active Member

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    #14 napabill, Oct 7, 2015
    Last edited: Oct 7, 2015
    The Energy:Trip screen has taken most of the guess work out of it. I used to charge to a 25% buffer, but now feel comfortable with a 15-18% buffer. The Energy:Trip graph makes it easy to see what your buffer will be to the end of the next leg.

    In the early days of my Tess (2012-2013) I remember a thread here that was seeing who get get the highest "projected" miles showing. Back then there was no limit, and coming down from Tahoe you could get projected ranges of 1,000 to 2,000 miles. Which would be true if the next 1,000 miles was downhill. It is now limited to 999 miles, still kind of silly.
     
  15. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Except in severe weather, just charge until the Energy->Trip screen's line is all green.
     
  16. Rodolfo Paiz

    Rodolfo Paiz P85 "Plug and Play"

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    We've already been stuck behind an accident on the Florida Turnpike and sat there for 90 minutes, sucking down A/C and running down the battery (slowly, but for 90 minutes). Y'all leave little to no reserve if you're comfortable with that... I'm no longer comfortable with that. :)
     
  17. David99

    David99 Active Member

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    True, but if you go by that logic, you would always have to charge to 100%. Getting stuck behind an accident, then road blocked, so you have to take a detour, all while a storm blows against you and ... :) Well you get the point. There is always an unforeseeable case where any buffer would not be enough.
     
  18. Electricfan

    Electricfan Member

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    You left us hanging there! What happened? Did you make it? How much did you have left when you got home or to the next SC?
     
  19. MyJoule

    MyJoule Member

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    For day to day driving in the home region- just charge to 90% in your garage and just drive it.

    For Supercharger trips based upon my actual experience with two times arriving at Superchargers that were off line: Enough to skip to the next supercharger. That is my new plan- while I've never been stranded, in my two long trips one from AZ to Indiana and one from AZ to CA I've experienced two supercharger stations not working. The first was in May, 2015 and Perry, OK was within it's first few weeks of operation. I had been warned it might not be on line due to a utility transformer issue, so I charged extra in Weatherford, but unfortunately the weather conditions used some extra range so I was screwed. I arrived at Perry with 86 miles range and had 92 miles to go to Wichita, Luckily there is an RV park that let me charge for an hour about 56miles north of Perry. The second trip was in September 2015 and I arrived in El Centro to find all stations down. Utility issue, and I was the first to report it to Tesla. Had 76 miles range needed to make it to Yuma, and had 82 miles range showing, so we cut the speed to 60MPH and made it to Yuma with plenty of range to spare, but based upon my personally experience I have about a 5% chance of the supercharger station being off line, so I will charge enough to be able to skip a supercharger, then stop at each one anyway. At least of the foreseeable future that is my plan.
     
  20. Rodolfo Paiz

    Rodolfo Paiz P85 "Plug and Play"

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    EV adoption took a step back in our family that day, because it showed my wife that you still need to "manage" your energy with significantly more care than in an ICE and it scares her a little bit. We were going from Miami to Orlando, and the plan was to charge at the Fort Drum Service Plaza on the Turnpike (160 miles). A full charge (255 rated) had been whittled down to 245 miles by stopping for a few supplies... but you'd think that 245 rated miles was enough to go 160 real miles without a problem.

    Due to Turnpike speeds (limit is 70, most traffic is 75), A/C use, some rain, and heavy loading (four people plus bags), we were using about 420 Wh/mile. It looked like we'd arrive in Fort Drum with 18 rated miles left, about 7% charge, so I started slowing down (not what the family wanted to see, but hey) until projected reserve increased to 12%... and then we reached the back of the line. We sat in that line, gradually inching forward, for about 90 minutes by which time projected reserve was down to 5% (IIRC). I bailed at the first available exit and diverted to Port St. Lucie which was 40 miles closer but about 10 minutes off our track.

    We were never close to actually running out of energy, but we did make arrive in Port St. Lucie with 50 miles of rated range, meaning we'd used 207 rated to drive roughly 140 real miles. That's a nearly 50% increase in consumption over rated miles... and though that happens in an ICE as well, you have to be more mathematically aware to really notice it. The significantly longer range of a gas tank hides that additional consumption if one isn't paying attention and doing the math.

    And to my wife's eyes, it showed that EV's (even Teslas) have made marvelous advances (her words) but are not yet to the point where she feels comfortable switching. In particular, she's of the drive-til-you-get-there mindset and would far prefer to go from Miami to Orlando (230 miles) non-stop... and on either I-95 or the Turnpike, driving 62mph to make it non-stop makes you a nuisance, even a danger to others, on the highway. One more ICE for her while the technology continues to improve. I'll happily do the math, take the extra care, and switch to Model X. :D

    I will add, though: I'd love to see a setting on the Trip screen where you select whether the consumption forecast is based on past history as it does now, or on some particular value you select. I'd set that sucker to 420 Wh/mile, aim for a 10% reserve, and be a happy camper.

    - - - Updated - - -

    No, there's no flaw in the logic, it's just that you are highlighting the undesirable result of extrapolating to the extreme. Stating that it's not reasonable to do something that I am not doing, is to make a true but completely irrelevant statement.

    Of course there is always the possibility that something else could go wrong and your strategy will not work. But risk management is not about driving the risk of failure to zero (can't be done anyway), but about reducing the probability (or mitigating the consequences) of an undesirable outcome to an acceptable level. Adding additional buffer reduces the probability that foreseeable risks will cause negative consequences for you. How much buffer to add, and how far to reduce the perceived probability of a negative outcome, is a personal choice. So I repeat: y'all go ahead and use small buffers if you like. I'm not comfortable with that.
     

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