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Battery Capacity Down to 86.8% After 18,000 Miles

Discussion in 'Model X: Battery & Charging' started by gnuarm, May 7, 2019.

  1. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    Many here suggest the battery should be occasionally cycled between 100% charge and near 0% charge to keep the charge measurement calibrated. So I did that a couple of times. The first time the battery took a very long time to finish after it had reached 100%. It indicated around 8 kW charging rate and I switched to miles which read 276. It rose to 277 by the time the rate declined to 6 kW. The miles did not increase for another 20 or 30 minutes until it stopped charging with the rate down to 1 kW. I ran the battery down to around 3% before charging again to 100%. This time it reached 276 miles by the time it stopped charging and took a while, but not 30 minutes after reaching 100%.

    There were two charges to 90% since then. I have been thinking the trip numbers were a little off, showing too small usage of kW for the percentage of the battery being used. This is a P100D, so the kW/mile should be pretty close to 1.0. I took down numbers from the trip counters. From 91% charge to 3% charge reported as 73 kW used. That's 73kWh / (91%-3%) = 83 kWh on a fully charged battery. Repeating the measurement on the trip home, a shorter distance, I get 24.3 kWh / (90%-62%) = 86.8 kWh on a full charge.

    This has nothing to do with mileage. This is just measuring how many kWh the battery will hold. If this is already 15% off the original capacity, I can see why my range seems to suffer. The car is not even a year old with 18,000 miles. I typically charge to 90% but sometimes charge to 95%. Virtually every time I charge the car is driven at least 30 miles afterword before it is parked.
     
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  2. redgt

    redgt Member

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    i thought model x p100d was 289 epa range?

    12/289= 4.1% degradation
     
  3. mxnym

    mxnym Member

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    He said he was talking about kW and not miles. His assumption is the battery held 100 kW at 100% when new, and his numbers show it holding significantly less than that. @gnuarm I'm guessing you don't have similar measurements from when the vehicle was new? They would be the best way to compare actual degradation. Some degradation is normal, and actual real life capacity start point is debatable. From what I've read, degradation tapers off over time/miles, so you've possibly already seen the worst of it.

    ETA: It also matters if you drove the entire time or parked, the consumption when parked isn't counted, and there are lots of reports of vampire drain increasing with updates.
     
  4. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    There would have been time parked. Even if the kWh are not counted, they would show in the battery state, so I will take that into account as I watch this further. In the latter of the two measurements there would have only been two days of drain so factoring in 1% per day (which is what I typically see) brings it significantly closer to 100 kWh for a full charge. The previous measurement adjusted for 5% vampire is still pretty far out coming up to only 90 kWh on a full charge. I have the numbers recorded and will watch for more rapid drain this week.

    If the battery doesn't start at 100 kWh when new, how can they claim the starting range? That is supposed to be based on the EPA rated consumption and the battery capacity, no?
     
  5. MP3Mike

    MP3Mike Well-Known Member

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    The trip meter is not accurate for reporting kWhs, so it can't be used for degradation reporting.
     
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  6. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    Can you explain? Why would it not be accurate??? If it doesn't report accurate numbers, what is it for?
     
  7. MP3Mike

    MP3Mike Well-Known Member

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    Because it isn't. Part of the problem is that the kWh rating of a battery is normally rated at a very low draw. The faster you take the power out the fewer kWhs you get out of it. I'm just going to make some number up here, but if you are cruising on the freeway at 50 MPH you might get 90 kWhs out of the battery, while if you are going up a hill at 70 MPH you might only get 70 kWhs out of the battery.

    So the higher your Wh/mile rating the lower number of kWhs you will actually get out of the pack. (So an X will almost always get fewer kWhs out of the pack than an S will.)
     
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  8. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    But what you are saying is not that the trip reports are not accurate, but that the battery is not actually 100 kWh when used to drive the car. The issue is not that the kWh reading in the trip report isn't accurate, but that the kWh usage over the 100% range will be different depending on how the car is driven. So really, it's the percentage capacity number that is rather meaningless.

    People here try to say that we have the same range variations with ICE vehicles as with electric cars, but this is not really true. There is the issue of winter range reductions of up to 40%, then range is reduced if you want to keep warm or cool, range is lost from not driving the car, range is limited by trying to preserve the battery at the high and low end of capacity and now I find out that not only is range reduced at higher speeds because of higher drag, but the battery itself is noticeably less efficient.

    No, I'm sorry, but when I drove my truck for 20 years, I could get to within 10 miles of being out of fuel... consistently. I actually knew the true capacity of the fuel tank because on one occasion I ran out just as I reached the pumps. That's how consistent an ICE can be. Electric cars will not be accepted as everyday cars until the issues of charging are finally minimized to be at least close to those of ICE autos. They are going to need a LOT more charging stations and they need to be much more visible.

    I have a car with an alleged 289 mile range and I need to charge twice to drive that far because of all the issues of charging and range.
     
  9. mxnym

    mxnym Member

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    My assumption is that there is a margin of error (like oft touted 3% for speedometers and 10% for calories). I believe there are thread(s) (possibly in this very forum) where the actual capacity of batteries when new is discussed and some vehicles have less than the stated capacity while others have more. I believe the information within was pulled from the BMS and should be accurate.
     
  10. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    That's fine if they have a tolerance, but how can they say every car has the same EPA range if the battery capacities aren't up to the stated 100 kWh?
     
  11. mxnym

    mxnym Member

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    Like the EPA rating for fuel economy, the EPA rating for electric range is based on testing several vehicles and averaging them together. If ICE vehicles and fuel batches were all identical, they wouldn't need to do that, and there would be no such precedent. However, as ICE vehicles and fuel batches clearly aren't identical, it's a bit of a stretch to expect electric vehicles and battery material lots to be identical.
     
  12. MP3Mike

    MP3Mike Well-Known Member

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    I would say that the difference is that they are measuring different things. You measure battery capacity at a specific draw, while the trip meter is measuring what you are actually using. But just like an ICE vehicle that some of the fuel is turned into heat vs. moving the vehicle, in a BEV heat is generated inside the battery as you use the energy and the trip meter doesn't count that. So there is energy use that the trip meter isn't counting.
     
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  13. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    That's not really the question. The EPA rating produces a consumption number. Multiply (or divide, whatever) with the kWh in the battery and that's what the car displays. This is not about the consumption number. This is about the kWh. If one battery has 101 kWh and another has 98 kWh to start, how can they apply the same consumption number to produce the EPA rated range number on the display?

    I've always wondered why they display miles and percent and not kWh. I think I know why now. But this leaves me wondering how many kWh I actually have in the battery and no good way to tell.
     
  14. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    Yes, I get that none of this is 100% efficient. But it never occurred to me there is no actual way to tell how many kWh are in the battery.

    Do me a favor and don't compare an EV to an ICE in this matter. When it comes to range and battery capacity the two are nothing alike. ICE is very predictable and reliable. The rule for EVs is to always be charging. Now I'm even more anxious about the Superchargers not even having started in Frederick, MD. Gaithersburg is a major PITA because of the heavily congested roads to get there and the congestion at the chargers. Haymarket is... well, Haymarket. Nothing to do for an hour but eat. Although I did stop in at my new insurance agent. I figured I'm going to be there charging... a LOT, so I might as well pick an agent that is maximally convenient. We did a review on the replacement cost of my houses and I was able to reduce the insurance amount. Yeah!
     
  15. gangzoom

    gangzoom Member

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    Did you ever do the same calculations when the battery was 'new'?

    For what its worth I've NEVER calculated more than 66kWh usable consistently from our 75D X since delivery based on the methods you are using. As you have also noticed there is a pretty big variation also between different runs, I've seen calculated/assumed figures based on this method range from under 58kWh to the one time when the numbers came out at 67kWh.

    I know 'technically' people have reported the 75D as having 71kWh usable, the 100D as 99kWH, I've just never seen it based on what the car reports.
     
  16. unpollo2

    unpollo2 Member

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    i lose 20 miles over a 24 hour period just sitting in my garage, that's from a x75
     
  17. rdskill

    rdskill Member

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    Doing business while charging is a great idea. I work during the week so charging after work means only places to eat open. Who knew that getting a Tesla could be fatting.
     
  18. mxnym

    mxnym Member

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    I'm not sure what you mean regarding the consumption number. I believe it is well documented that the "miles" display option in the IC can vary at 100%, and I'm not sure there is anywhere else to get a "consumption number" based on the EPA rating.

    Perhaps you're saying "an ICE always has an XX gallon tank while each EV has slightly different kWh battery," but given that the batteries are all produced the same way, kWh may be the wrong measurement to think about here (perhaps each car has XX pounds of lithium or whatever, and the variance in kWh is no different but less significant than the variance between summer and winter fuel).

    In either case, perhaps the closest you can come to kWh on your battery without third-party hardware or utilizing API access would be to switch to the "miles" display and do that math (at 100% charge, you would do the math against the rated distance, but at any other % charge, you would adjust the rated distance accordingly). Even then, you'd likely see variation from charge to charge and battery level to battery level. Charge to charge because cell balancing would change the reading. Battery level to battery level because the measurement isn't as simple as gallons (although arguably, one gallon of fuel could have a different amount of energy than the next and perhaps even at a different temperature).
     
  19. idoco

    idoco Member

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    This might answer the question (emphasis added).

    So I think your method of using the delta for the kWh from CID is probably inaccurate. A better way would be to use the rated miles reported @100% divided by the static consumption value to measure capacity/degradation.

    So in your case the 100% charge value indicates ~5% degradation:

    RM = 277, static rated miles for 342 Wh/RM
    277 miles * 342 Wh/RM = 94734 Wh
    100kWh - 94.734kWh = 5.266kWh

     
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  20. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    That certainly seems excessive. That's not much more than what you can put on using level 1 charging. I'm thinking something keeps your car on all the time. A kilowatt is actually a lot of energy in that a space heater in the US only draws 1.4 kW.
     

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