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another range/efficiency discussion

Discussion in 'Roadster: Technical' started by dpeilow, Aug 10, 2008.

  1. dpeilow

    dpeilow Moderator

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    Can someone explain what is being shown here pls? Is it either:

    1) 73 miles from the 5kWh just put in (way too much?) or;
    2) 73 miles in total from the recharged battery (too small?).
     
  2. TEG

    TEG TMC Moderator

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    My guess:

    Someone just put in 5kWh of charge in 3 hours and 53 minutes from a standard US household outlet. The 73 miles is projected range expected from the what charge is in the pack now. Charge in the pack should be 5kWh plus whatever was in the pack before charging started. If you do 73/220*52 you get about 17kWh, so I would guess that the pack had about 12kWh before they started charging.
     
  3. deenko

    deenko Member

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    The 73 miles is the expected range. It is calculated on the battery level of charge and the drivers previous recent driving habits. So, since the battery looks like it is nearly fully charged, the last driver was driving really hard.
     
  4. vfx

    vfx Well-Known Member

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    #4 vfx, Aug 10, 2008
    Last edited: Aug 10, 2008
    Really?!?

    So to sum it up.
    The upper left says, "Done Charging" and below it says that it had charged for 3 hours and 53 minutes. The graphic shows that the green bars are almost all the way to the right looking like the batteries are about 97 percent 'topped off'.

    The bottom right says the car was plugged into a standard 120 volt edison wall plug putting out 12 amps. (which we could see the crude converter box on the floor in the other pictures)

    And the maximum amount of mileage the car will go is 73 miles? This is much lower than any worst-case-senario ever published.
     
  5. deenko

    deenko Member

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    First of all, the car is in standard mode, so the range is not going to give you the absolute max that the batteries are able to do. Second, who says this is an absolute thing. It is based on previous driving. Like any trip computer, you can always make it look like you are not going to get any kind of good mileage out of it. Take any car, reset the trip computer, look at the mpg or distance to empty, and floor it. the computer will tell you that you will get 2 miles a gallon. This is no different.
     
  6. dpeilow

    dpeilow Moderator

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    I was hoping it was not this, but I can't think of another explaination for what the screen is showing - given that the graph is near full.
     
  7. deenko

    deenko Member

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    In what way can you not understand that it is a trip computer. It uses your previous driving to make an estimate on your driving range. A lead foot results in a low estimated range.
     
  8. dpeilow

    dpeilow Moderator

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    I the way that for it to be that low, the previous driver had to have a pretty heavy lead foot...

    I understand exactly what you are saying - what I was hoping was that it was not possible to get it that low under any circumstances. Unfortunately it appears that it is.
     
  9. malcolm

    malcolm Active Member

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    #9 malcolm, Aug 11, 2008
    Last edited by a moderator: Mar 13, 2016
    Thrash anything and the mileage plummets

     
  10. WarpedOne

    WarpedOne Supreme Premier

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    Do the math.

    53kWH of available energy at max power output gives you less than 20 minutes of running time. At max speed of 120mph that means 40 miles of range. If you are only doing 60mph, you've driven 20 miles. 76 miles is plenty in comparison :D
     
  11. dpeilow

    dpeilow Moderator

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    The EPA sticker in F16 shows 33kWh/100 miles on the highway and 32 around town.


    [​IMG]


    Have I misunderstood? That means 160.6 miles from the 53kWh battery.
     
  12. graham

    graham Active Member

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    Ouch! When I saw the sticker before I saw your comment that was my thought and the number I came up with as well. :-(
     
  13. stopcrazypp

    stopcrazypp Well-Known Member

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    #13 stopcrazypp, Aug 13, 2008
    Last edited: Aug 13, 2008
    Let's not forget that the sticker also includes the charging losses. That 33kWh/100miles highway, 32kWh/100miles town, doesn't vary from the 0.327 kWh/mi highway, 0.316kWh/mi town, figures we have been given in the past, which includes charging/battery inefficiencies.

    Here is the relevant quote:
    "From our latest testing, the results for city/highway cycles were range of 231/224 mi and electricity use of 0.316/0.327 kWh/mi respectively."

    http://www.teslamotorsclub.com/tesla-roadster/1280-mpg-equivalent.html

    This gives a weighted range of 227.85 miles combined.

    The pack size is 52.8kWh. Given the 227.85 miles combined range and .321kWh/mi figure, it takes 73.1kWh from the plug to fill up. Charging/battery efficiency is then 72.2%. I would assume that is using the 3.5 hour charge, which requires battery cooling to work: thus the low efficiency.

    Another side point is there is no range rating on the sticker; I would imagine that is quite important for EVs.
     
  14. dpeilow

    dpeilow Moderator

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    That clarifies things. Thanks.
     
  15. Joseph

    Joseph Member

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    Tesla used to say that charging the Roadster was ~85% (if my memory is correct) Then later on their blog the editor said it was around 70%. This kind of jumping back and forth between numbers is a bit alarming, but I'm glad to see that the results from the EPA validate Tesla's (blog editor's) claim.
     
  16. SteveF

    SteveF Member

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    This all raises a question for me. If this has been addressed earlier somewhere, I trust one of you will point me to that post.

    If charging the battery at 220V to get a 3.5 hour charge is less efficient, since it requires battery cooling, then it seems obvious that mode should only be used when you really need a quick charge. Most nights my car will be sitting in the garage for 12 hours from the time I get home to the time I leave for work the next day. Can I set the charger to "slow speed"? Then how does this play versus electricity rates that I believe are lower in the middle of the night, but perhaps higher during other portions of my typical 12 hour window?

    In other words, how do I figure out the best way to charge my Roadster if I want to find the least costly/most efficient method?

    Thanks.
     
  17. vfx

    vfx Well-Known Member

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    This would probably to also need to figure in battery replacement cost VS the few hours of "expensive rate" charging over 5 years.

    In my neighborhood the low rate KW kicks in at 9PM you still might get in a slow charge depending on if you have fully drained the battery and what time you leave for work.

    Don't forget that EV charge rates are cheaper in some areas too.
     
  18. dpeilow

    dpeilow Moderator

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    The charger should include a degree of intelligence, so that if there is a power outage in the night and there is still time to charge the car when it was restored, it varies the current so that you have a full battery in time for the commute.
     
  19. Kevin Harney

    Kevin Harney Active Member

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    That sounds GREAT!! Slowest charge possible to be fully charged by 8:00 AM or what ever time you input.
     
  20. graham

    graham Active Member

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    It is exactly this type of idea that makes me want to be able to remotely control the Tesla via the USB port. My remote home automation computer already has this kind of logic built into it, and could easily poke the car to turning on/off or varying the rate of charge based on external conditions.

    I hope that they either allow me access to the USB protocols, or that John Carmack publishes his work using it...
     

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