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Electric motor wear and tear

Discussion in 'Technical' started by DFiveK2, May 9, 2015.

  1. DFiveK2

    DFiveK2 Member

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    I'm wondering if "mileage" is the best way to measure the condition of a used tesla vehicle. In ICE cars mileage is good indicator of the condition of the overall vehicle due to the various parts affected by the usage of a combustion engine over time.

    With less moving parts and less consumables/replaceable parts in the tesla... Wouldn't battery cycle measurements be a better indicator than mileage to determine the value of a used tesla? Or total power used... If I hammer the accel over and over but don't drive far.... Wouldn't that be worse? Or if I drove really fast all the time....

    Maybe this has already been discussed. If not I'd like to hear what people think.
     
  2. David99

    David99 Active Member

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    Yes the motor is really not a concern in an EV when it comes to aging. The battery is probably the most important part. It's the most expensive part and determines the car's rage which is so far the most limiting aspect of an EV. Nissan allows you to see the battery aging using the dots and I think it's easy to read a more accurate number from the car's computer. Tesla really doesn't want us to have a simple way to measure battery aging. Sure we can use the displayed range at a full charge but it's just an estimate. It's not a measure for battery condition.
    I've seen a service screen on the Model S that showed the actual capacity in kWh. It's only visible to service centers, though.
    Since every EV has a different way to show battery capacity, it would really be helpful to have a unified and standard method that shows the battery aging process.
     
  3. kennybobby

    kennybobby Member

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    i agree with you D5K2, the number of charge cycles is a good measure of battery life--there is a curve on the panasonic cells that shows the capacity loss versus number of cycles, it seems that nearly all the battery manufacturers show that same sort of curve.

    i would guess that tm has that info stored somewhere in memory. Apple's macbook will display number of cycles on the battery when you click the apple About this mac/system report/hardware/power. kb
     
  4. David99

    David99 Active Member

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    The problem with cycles is that we hardly do full cycles. We charge every night but for the most part the battery is not empty and we don't charge 100%. Often we just top off. The typical battery test of running cycles which is used to determine battery aging isn't how the battery of an EV is used.
    There are also several other factors that contribute to battery aging just as much. Temperature for example plays a big roles. Aggressive driving style, how low or high you discharge or charge the battery each time. How high the state of charge is when the car is resting. Instead of keeping track of all these things, it would be much easier to have a full cycle capacity test that shows how much energy a battery can hold and deliver. In the end it doesn't really matter what caused the capacity reduction (aging of the battery), what matters is how much usable capacity is left.
     
  5. mhpr262

    mhpr262 Member

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    I very much doubt that it really showed the capacity. It is simply not possible to determine the actual capacity of a Li battery without doing a 100%-0% discharge. And once you have done that you won't know the capacity either, because you will have lowered it considerably by putting it through such a hard discharge cycle.
     
  6. jaguar36

    jaguar36 Member

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    Mileage is a reasonably good approximation of battery health, at least as good an approximation as mileage on an ICE is anyway. An ICE can run at constant revs at reasonable temps for an extremely long time. Its the changing load and the changing temperature that really ages a ICE. Just like those variables effect a ICEs actual life, so does the charging amount, temperature and style of the battery effect its life. In general though, I think mileage, as well as 90% charge amount is a reasonable measure of the health of the battery and what sort of longevity it has had.
     
  7. ScepticMatt

    ScepticMatt Member

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    Heat has also a strong effect on battery lifetime. A Model S battery in Tromsø, Norway will last a lot longer than one in Phoenix, Arizona - active cooling system notwithstanding.
     
  8. jbcarioca

    jbcarioca Active Member

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    All this is obviously true. There is a big "however" though that nobody seems to be thinking about in this thread. Li-ion battery pack behaviour varies enormously with chemistry, manufacturing techniques, assembly techniques and equalisation, as well as all the other factors being discussed here. From both unofficial and official sources we know that Tesla cells, batteris and packs are all materially different than any others being produced. We also know that material changes are being made in several crucial areas both by Tesla and by Panasonic.

    So, anything we say about battery life in our cars cannot be a simple extension of other li-ion performance, nor even of prior Tesla history. Our tesla packs are now probably good for eight years and about 100,000 miles, more or less, with 80% or more capacity at the end. Will any precise measurement of residual capacity be available? No! The deterioration curves of lithium chemistries all seem to have been remarkably consistent; an initial sharp capacity drop (often pre-performed prior to customer delivery) followed by quite long stability with gradual drop, then a sharp drop commencing just prior to failure. The problems are dual; First, precise in-service capacity measurement cannot be made without harming cell service life, so various algorithms are used to estimate capacity. Second, effective service life has been increasing rapidly for nearly all lithium chemistries, but each improvement also introduces new question about service longevity. All anybody knows is that it is improving, and for Tesla probably more than most others.
    Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive - Chemistry of Materials (ACS Publications) is just one recent example of published developments
    Theoretically we might guess that the 90kWh packs might have shorter life because they have introduced at least some silicon in the anodes, increasing capacity but also challenging shorter anode life. There is plentiful published research on this subject, and additives of various types are reducing the negatives:wink: It seems Tesla/Panasonic are well advanced in solving these problems and may well have some substantial further improvements in service life, energy density and manufacturing cost reduction coming within the next year or two.

    We need not be much preoccupied as users, IMHO.
     
  9. qwk

    qwk Model S P2681

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    It did show KWH remaining and the state of charge, but it was in developer mode. The regular service mode in the current firmware does not show it, only CAC. Although both are only accurate, when the pack is balanced and calibrated.
     
  10. tom66

    tom66 Member

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    I think total usage hours would be the best measurement.

    This would tell you how many hours the battery has been discharged in total due to motor usage.

    Most motors are rated in hours operation (or MTBF.) A 10,000 hour motor travelling at 55mph would achieve over 550,000 miles.
     

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