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Speed to Drive on a roadtrip

Discussion in 'Roadster' started by bolosky, Aug 14, 2009.

  1. bolosky

    bolosky Member

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    I've been thinking about richkae's drive from Menlo Park to Seattle, in part because I might want to do the same thing when my car's ready if my work schedule allows.

    So, I was wondering if you were going to drive a Roadster on a long road trip, how fast should you drive to maximize travel during the day. This isn't quite as simple a question as it sounds, since the efficiency of the Roadster varies with the speed, and you have to decide how to split the day between charging and driving. For efficiency numbers, look at the most recent engineering blog post on teslamotors.com (from December, 2008). They show a curve of range vs. speed, with the peak of about 410 miles per charge when travelling 15-20 miles per hour. However, you obviously wouldn't want to do a road trip at this speed, because it would take forever and you'd run out of travel time before you ran out of charge.

    So, imagine that your plan is that you start the trip fully charged, use up the whole of the charge during the day of travel (to be recharged while you sleep), and split the rest of the day between charging and driving in the correct ratio to leave you with an empty battery at bed time. How far do you go if you select different speeds?

    I took the graph from the engineering blog and eyeballed it into an excel table. From there, I figured the range and time to drain the battery. The remaining time in the driving day was spent running at the "effective speed" which is the speed that you accomplish when you factor in charging time as well as driving. This gives a range for each speed in the table (all multiples of 5mph from 5-85).

    The result is a spreadsheet that tells you for a given length of day and given time to full charge how far you get for each speed, and how many hours are spent driving (as opposed to charging). For instance, for a 16 hour driving day (and 6 hour full charge time using the 40 amp Eberhard charger), the optimal speed is 50, which gives a range of 516 miles with 10.3 hours of driving time and the rest spent charging. Going 85 gives you a range of 402 miles with only 4.7 hours driving and the rest charging, while conversely going 30 yields 442 miles with 14.7 hours of driving.

    For practical amounts of driving time and charge rates, the optimal speed seems to be around 50. This makes me think that it might make sense to do the drive up the Pacific Coast Highway rather than I-5. The lower speed will increase range nearly enough to compensate for the ~140 miles of extra distance. Plus, it seems like a much more fun drive than on the freeway the whole way.

    If anyone would like a copy of my spreadsheet, let me know and I'll send it to you. It's kind of interesting, since you can see the effect of different drive times/charge rates. (For instance, the 40 amp charger only adds 35 miles to the daily range, but increases the speed some, too. If there were 70 amp HPCs available wherever you'd like, you could do 593 [email protected] mph.)
     
  2. dpeilow

    dpeilow Moderator

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    ^ A bit late, but I think JB provided the excel spreadsheet that he got those graphs from as a link at the bottom of his blog.
     
  3. ChargeIt!

    ChargeIt! Member

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    No ... I think bolosky has a lot more going on here ... suggestion: put it on docs.google.com and give us a link ! Another Tesla Owners has done this ... let's compare spreadsheets ...
     
  4. bobw

    bobw Tesla Reader

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    When routeing a roadtrip, I think you should also consider the terrain. The stories so far, especially http://www.teslamotorsclub.com/tesla-roadster/3109-drive-menlo-park-seattle.html, and http://www.teslamotorsclub.com/tesla-roadster/2777-yosemite.html?highlight=yosemite seem to indicate that going up a steep hill really eats power. Regen on the downgrade doesn't nearly put it back. Also the downgrade may not come at a convenient point, or may not be on the route at all.

    That may be another advantage of the coastal route. I've driven a tiny part of the Oregon coast, Lincoln City to Newport. While I wouldn't call it level, it didn't have the huge grades.
     
  5. doug

    doug Administrator / Head Moderator

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  6. ra-san

    ra-san Member

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    On the owners forum there's a road tripping thread. Earl, who always had good information and analysis posts, went to the trouble of making a spreadsheet to do much of what the original poster was working on. Can find it here: http://spreadsheets.google.com/ccc?key=rvQANXff1VRqf4E5kPXhvqA

    I really don't think Earl would mind it being quoted here, so will risk pasting it in:
     
  7. SByer

    SByer '08 #383

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    Having done the entirety of CA 1 (in chunks, over my life), I highly recommend it. Especially if you can take time to stop at all the interesting places along the way. The Roadster is an ideal car for it, if you can find enough charging spots. We took 3 days to get up to Mendocino at one point, for an example - you know, classic road trip style!

    Even if you can't stop, it sure is a heck of a lot prettier than the inland route.
     
  8. bolosky

    bolosky Member

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    I think that the difference between what he did and what I did was that I assumed that you'd be sleeping and charging up at night, so you get one "free" battery worth for the day. This results in much higher speeds. I think that he was computing what I called the "effective speed," which is how fast you go when you need to include the time for the entire charge together with the travel time. So, he was getting speeds like 36 mph with the 40 amp charger, while I was getting 50.
     
  9. richkae

    richkae VIN587

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    #9 richkae, Aug 14, 2009
    Last edited: Aug 14, 2009
    When I do that drive again...

    ...I hope to do the drive up the coast.
    If I had, I would have enjoyed several advantages:
    - about 25 degrees cooler, which would have let me cruise farther on the same energy, and charge faster, and enjoy the stops more.
    When we stopped and it was 100+ degrees, we didnt want to do much outside.
    - slightly slower speed of driving would have extended range and reduced charge time ( it was annoying to be passed at 58-60 mph on I5 over and over )
    - prettier drive than I5

    But alas, I had done no significant planning other than I knew I had friends in Redding, and the HPC I found in Davis.

    Rich
     
  10. johnr

    johnr Member

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    @bolosky: I would be interested in getting a copy of your spreadsheet, but since I don't own a Roadster I'm sure I'd have to tweak the formula some for the model S or whatever EV I end up with.
     
  11. bolosky

    bolosky Member

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    Send me you email address by PM and I'll forward it to you (but not until Wednesday, it's at home and I'm on the road, alas without a Tesla since mine's still waiting for the Hethel holiday to end).

    You won't be able to use it for another car until you get a copy of the range-vs-speed curve for that car. I got the one for the Roadster from JB's engineering blog on teslamotors.com. Once you have it, you could just type it into the spreadsheet and it should work fine.
     
  12. doug

    doug Administrator / Head Moderator

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    I think you can also upload it here as an attachment.
     

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