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Actual miles since last charge + rated miles left not adding up @ < 300wh/mi

Discussion in 'Model S: Battery & Charging' started by russman, Aug 20, 2014.

  1. russman

    russman Member

    Joined:
    Nov 12, 2013
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    Location:
    California
    Need a little help reconciling actual miles driven. So everyone talks about how much you can actually drive and how you drive affects the distance you can drive. I've been trying to understand what my real usage at various charge levels would be.

    I've heard all types of advice like give yourself 20% cushion and you can drive however you want. So if you want to go 100 miles, you can do that on 120 or more rated miles. Drive conservatively and in general, the MS has such a large battery, it doesn't matter, but on those days when I drive a lot, I'm noticing I'm not getting the actual mileage I was hoping for. The reason I say that is, my average after 8000+ miles is 335 wh/mi, but when I use the trip meter and look at Miles Drive since last charge no matter what the average wh/mi is at the time, it doesn't add up with the rated, even if the wh/mi is < 300wh/mi.

    My understanding is rated miles is based on driving @ 300wh/mi.

    Please help me reconcile this, as I start to do more and more longer trips this gap does give me a little "range" anxiety. Here are some samples from my trips:

    Charged to 80% = 210 rated, Since last charge meter shows 103.1 miles driven, 30.6 kWh used and an average energy of 296 Wh/mi, however my rated range remaining is 96. 96+103 = 199. That's 11 miles less than the rated that I started with and at 296 wh/mi, I should have slight better than rated miles, but instead I have 5% loss when driving below 300 wh/mi.

    Charge to 90% = 237 rated
    - 100 miles driven 32.6kwh used 326 wh/mi left me with 117 rated range left. (20 miles were lost giving an 8.4% waste, which could be because of driving > 300wh/mi)
    - additional 65 miles driven for a total of 165 miles using 55.9 kWh and average 339 wh/mi and left me with only 32 rated miles. This ended up with a 16.9% loss. Even if I applied the 16% loss to the last 32 miles, I would have only gotten 190 actual miles out of 90% charge, which is 20% loss of mileage from rated, even though at 165 it was 16.9%.

    Again, I'm not driving in the winter, I'm in nice neutral CA, I don't have the AC running. So in the most tempered climate, I'm not getting close to rated, even when I've driven <300wh/mi. The 339 wh/mi wasn't even a spirited drive, it was just a lot of freeway driving. The 296wh/mi was conservative driving and I still got less than rated.

    Gives me a little apprehension for longer trips. I'm sure it's unnecessary worry, but seems odd to me.

    Russ
     
  2. Zextraterrestrial

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    based on 28k miles of data - 268 Whr/mi matches rated range for the average of all my trips
    for just trips over 15mi - 260 Whr/mi = rated
     
  3. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Messages:
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    I think that you are driving a 60. In my P85, rated miles are closer to 290 Wh/mi. Also, remember that vampire miles and HVAC use when not ON, do not go into this accounting.

    For my P85, the approximate numbers for Rated Miles are:

    • 290 Wh/mi for DC out of the battery, driving.
    • 300 Wh/mi for DC into the battery, like on a Supercharger
    • 333 Wh/mi for AC into the battery, like from a UMC, an HPWC, or a J1772.
    Happy Accounting.
     
  4. rlang59

    rlang59 Member

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    My 60 is about 290 Wh/mi as well.
     
  5. Zextraterrestrial

    Joined:
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    Sure, if I am driving and trying to match rated on the energy meter it is at 290 Wh/mi

    but what I think I am saying is that the when your trip meter says you used 290Wh/mi you will have used more rated miles than how many miles you have actually driven.
     
  6. metafor

    metafor Member

    Joined:
    Aug 13, 2012
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    Location:
    Portland, OR
    What I've noticed is that since the last software update, the "rated miles" has changed. It used to be that maintaining ~290WHr/mile got me the rated range. However, now, it seems closer to 260WHr/mile. This is on a P85.

    What I do notice is that at 90% SoC, my rated miles went from 220-223 to 230. Now, that's about a ~3% inflation in rated miles so it couldn't account for all of the 10% reduction in energy efficiency required to get the rated miles. Something else must've changed. I noticed this significant difference after my last service. I took it in because the battery pack reported "charging reduced due to heat" or some such while supercharging. They had to replace the cooling pumps.
     
  7. Benjamin Brooks

    Joined:
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    Location:
    San Jose, California, United States
    Yes, this is absolutely correct, because the other non-drivetrain power loads on the battery (i.e. HVAC, consoles, accessories, etc) will have used up additional energy in the cells to make the rated miles remaining lower than "origination" rated miles minus miles driven @ 290wh/mi.
     
  8. wraithnot

    wraithnot Model S VIN #5785

    Joined:
    Dec 16, 2012
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    Location:
    SF Bay Area
    There may be some debate on the finer points, but here is my understanding of the situation:
    1) The Wh/mile calculation only considers energy used while the car is on- vampire drain while the car is parked will lower the range displayed by the car, but won't show up in the Wh/mile calculation
    2) The rated range is the distance a fully charged car goes before it stops, but the range meter will read zero a bit before the car actually stops so Tesla removes miles from the range reading a little faster than you would otherwise expect.

    People that have done more of this than I have seem to agree that an 85 kWh Tesla removes a mile of range from the display for every 290 Watt hours used. From the longest leg of a recent road trip to Seattle, I used 60.8 kWh of power and 217 miles of rated range which appears to be 1 mile of rated range for every 280 Watt hours which is pretty close to the accepted value (that leg of the trip was 171.4 actual miles, but I drove with the flow of traffic on I5 and had the air conditioner cranked all the way up and used 355 Wh/mile).

    If you're worried about making it your destination without needing a tow truck, my best advice would be to use evtripplanner.com ahead of time. With a speed Multiplier of 1.1, evtripplanner predicted I would use 224 rated miles on that leg of the trip which was pretty close to the actual 217 rated miles I used. It also looks like evtriplanner uses 288 Watt hours per rated mile.
     
  9. jerry33

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

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    Or better yet, plan more but shorter stops. If your trip requires eight hours of in-flight charging, it really doesn't matter to the total travel time if you have four two hour stops or two four hour stops (numbers picked for ease of calculation).
     

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