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Does Ideal Km/Miles after standard mode charge actually mean anything

Discussion in 'Roadster: Technical' started by Doug_G, Jul 4, 2011.

  1. Doug_G

    Doug_G Lead Moderator

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    When I first got the car a year ago, after a standard mode charge it would show 299-300 km; occasionally 301 km.

    Almost a year later it was usually showing 299.

    Recently I gave the car a rather good workout. Couple of Range mode charges and a couple of days of "spirited" driving (mostly in Standard mode but some Performance). At one point the PEM caused a power limit, and immediately afterwards I noticed the PEM fan was getting noisy. I expect it will have to be replaced during the upcoming annual service (it just passed its first "birthday").

    Ever since that weekend it's been charging to 294 or 295 km.

    Does this lower range indication actually mean anything?
     
  2. cinergi

    cinergi Active Member

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    I noticed this at a smaller scale after aggressive performance mode driving (and not after any of my range mode activities). IM after std mode charge went from 188 to 185 and has slowly (weeks) crept back up to 187. This is morning-after-charge observation ... I do notice that immediately after a charge it's 188 but by morning it's now 187. It does feel like heat and perf mode do some damage ...

    Edit: I should add that I've had the car for 8 months and it was stable at 188 IM until the above.
     
  3. Doug_G

    Doug_G Lead Moderator

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    Okay maybe I'll see the same thing; it's only been a week since the aggressive driving.

    One thing I've noticed recently, when I've seen it finishing the charge (at home this always happens in the wee hours so I don't see it), is that it shows a higher number right after it finishes charging. But this number drops off, perhaps during the balancing that reportedly happens following a charge.

    Probably what is happening here is I have a modest imbalance, and it will settle out after a few weeks of more normal charge cycles. As I recall, the range is determined by the difference between the weakest string ("empties" first) and the strongest string ("fills" first).
     
  4. richkae

    richkae VIN587

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    Some battery expert should correct me if I am wrong, but:
    I don't know if the standard mode reported range really means that much.

    The only way for the computer to really know what "full" is is to to charge in range mode and try to fill it all the way up.
    When you charge in standard mode, the computer stops charging at some percentage of what it thinks full is.
    It also may stop when some portion of the battery pack ( sheet? brick? ) achieves a charge threshold, but when it reports the available energy it may need to report the minimum value from all the bricks/sheets.
    Charging in range mode may put more effort into balanacing the sheets/bricks than standard mode.

    So after several months of use, your total battery capacity may be reduced but you don't know if you have not charged in range mode.
     
  5. daniel

    daniel Active Member

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    Pardon me, but the differences reported above seem minor to me, given that these are estimates. We know that range is dependent on speed and driving style as well as traffic conditions. My new Roadster shows 188 miles ideal range after charging, which drops slightly over the course of a few hours. The car is drawing energy from the batteries while idle and won't charge again until the next day unless you tell it to. There is not a perfect match between ideal miles before and after a drive, and miles driven, but I find it to be surprisingly close.

    So, does "ideal miles" after a standard charge mean anything? Yes. It means the distance you can expect to get with whatever Tesla considers to be "normal" (sometimes I say "sane") driving. Drive it as the car was intended to be driven and you'll get less, which is why they give us the second estimate "as you've been driving the last 30 (or is it 40?) miles."
     
  6. smorgasbord

    smorgasbord Active Member

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    1 or 2 miles difference is less than 1% of the battery's total capacity (245 miles). Determining usable SOC (state of charge) in a lithium battery is difficult. For a detailed discussion, this seems to be a good article.

    Besides the usual temperature/age variations, the article claims that gas gauges in cars are only accurate to 5%, so that's considered good enough for EVs.
     
  7. Doug_G

    Doug_G Lead Moderator

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    Well, of course. What I was really getting at...
    • Is this number giving an indication of pack imbalance that will settle out?
    • Does this number provide any indication whatsoever of lifetime pack degradation?
    • Does it maybe mean nothing at all?
     
  8. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    #8 tennis_trs, Jul 5, 2011
    Last edited: Jul 5, 2011
    The number has reduced noticeably on mine. Average reading of about 188 IM after a completed standard mode charge when I first got my new Roadster. After about 23,400 miles and 22 months the average reading is about 173 IM after a completed standard mode charge.
    I'm not sure how accurate it is, but, if it is reasonably accurate, then it doesn't seem too bad for nearly 2-years/24K-miles.

    My completed range mode charge when new was about 240 IM. Now it's about 222 IM.
     
  9. donauker

    donauker Member

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    My take on the number is that it based on the calculated kWhr capacity of the pack.

    At 27 months and over 29,000 miles I am down to 165-167 IM per standard mode charge and around 212 IM per range mode.
     
  10. daniel

    daniel Active Member

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    I would call 1% insignificant. I'd call 8% (down to 173 from 188) significant. My understanding is that "battery lifetime" is generally used to mean the time it takes for a battery to degrade to 80% of its original capacity. I'd think that a decline of 8% in 2 years is a lot. It would suggest a "lifetime" of 5 years, compared to the seven years Tesla has recently suggested. OTOH, for many people even a 50% decline would still be adequate. For others, a 10% decline would render the car unable to perform as needed.

    For myself, 100 miles in a day is a LOT. I've done it twice in my first few days, but only because I took the car out for a purposeless jaunt in the country. If I want 125 miles of range, that's roughly half the range of a new Roadster. There will come a time when to get that range I'll have to charge in Range mode and then drive in Standard, and presumably degradation will speed up, but the car will still be useful for a few more years before I need a new pack.

    If 4% per year is the norm, that's still over 10 years. (One of the reasons I think I'd have been less happy with a Leaf is that it has too little buffer for battery degradation.)
     
  11. S-2000 Roadster

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    Some 2008 Roadster 1.5 owner(s) who call the Seattle Tesla Store home still have completely undegraded battery performance after all this time. I don't yet know what their secret is, but it might be possible to stretch these batteries for decades. Tesla started with conservative estimates of the longevity, but there are owners with 100,000 miles who still have full capacity. Tesla increased the promise to 7 year after learning that the battery last longer than originally predicted. I hope we'll eventually get more details on all of this.
     
  12. Doug_G

    Doug_G Lead Moderator

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    I wonder if they keep capacity "in reserve", so you don't see the loss at first?
     
  13. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    #13 tennis_trs, Jul 5, 2011
    Last edited: Jul 6, 2011
    They've never had any "promise" about battery life, have they? All I've seen is, from the current Roadster specs page:
    "Expected Battery Life Seven-years or 100,000 miles"
    With no definition of "Expected Battery Life".

    Hopefully if there really are any freak cases of longevity, Tesla can learn what's making them last longer to maybe tweak firmware to try to increase the life of other customers' batteries.
     
  14. S-2000 Roadster

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    Well, I should point out that what I wrote is based on hearsay. Come to think of it, I believe I actually heard that some owners are "approaching" 100,000 miles without any signs of degradation, which isn't exactly the same as showing 100,000 on the odometer with full range.
     
  15. donauker

    donauker Member

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    I would say that I would certainly like to hear some direct evidence of this claim.

    There was a firmware update last year that sent the IM on charge completion into pretty rapid decline over a multi-month period as it began to better evaluate the true remaining pack capacity.

    At 27 months and 29,000 miles I am down about 12%. With only another 8% to go to that stated 80% after 7 years the decline really better slow down!

    And this is with a battery pack that has led a rather protected life. I have only ever done one performance mode charge to completion and have rarely used performance mode driving. I have fairly regularly cooled my battery pack after hot day use and have never used the lower range mode reserve.
     
  16. tdevince

    tdevince Member

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    I thought they set the life at 70% capacity, not 80%.
     
  17. donauker

    donauker Member

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    I'm not sure if there is an officially stated value. I have seen posts stating 80% and others have said 70%.
     
  18. Todd Burch

    Todd Burch Electron Pilot

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    I thought I read not too long ago that the Tesla owner with the most mileage--or kilometer-age, depending on where you're from :)--recently hit 100,000 km--or 100.000 km, depending on where you're from ;)--not miles.
     
  19. Doug_G

    Doug_G Lead Moderator

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    Correct. I'm not sure about the original Roadster quote, but they're still saying that for the Model S.

    Model S | Frequently Asked Questions | Tesla Motors

     
  20. Doug_G

    Doug_G Lead Moderator

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    Okay, I think I mostly understand why "Ideal Km" number varies each morning.

    When the car just finishes charging, it usually shows 301 km. This number slowly goes down over a period of hours. In the winter time, when it is dead cold in storage mode, the range number changes less than 1 km a day. At much higher temperatures (and in Standard mode) the car must be consuming extra power.

    I caught it last night running its cooling system when I hadn't prodded it, so apparently it periodically stirs the pot in hot weather. Also I suppose battery balancing activity after charging would consume some power. Add to this the variable delay between end of charge and me showing up to drive, and that probably explains all the variation.

    The other day my Ranger said my battery was in unusually good shape for a 1 year old. Down only 0.5. I imagine the Ideal Range number will eventually start going down as the battery ages.

    What all this doesn't explain is yesterday, when it showed 298 km when I got in the car. I backed ten feet out of the garage and stopped, and it showed 296 km. HVAC wasn't even on. Go figure.
     

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