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2016 S60 RWD - Loss of range from battery pack fault or high vampire drain?

Discussion in 'Model S' started by brgr, Dec 7, 2018.

  1. brgr

    brgr Member

    Joined:
    Feb 9, 2017
    Messages:
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    Location:
    Los Angeles
    I have a Dec 2016 S60 RWD that I've been experiencing loss of range with.

    For reference, we have just over 17.5k miles. Lifetime Wh/mi is 321. All power saving modes are enabled (Always connected turned OFF, Energy Savings is turned ON). Note: I NEVER use the range prediction to look at battery State of Charge (SoC). It's an algorithm based on both battery capacity (which is in and of itself an algorithm) plus highly variable driving parameters). Battery capacity as a percentage should be a more reliable and stable method of tracking long term changes to the battery health itself. All data presented below is a mix of data reported by the vehicle itself via the displays and reported by TeslaFi. Data sources marked where applicable.

    The time I noticed loss of range coincided with the onset of summer in northern LA, so I attributed some of the loss to cabin overheat protection/battery cooling/etc. However, now that cooler "normal" weather has returned, I have not seen any improvement.

    As part of the Southern California wildfires, Tesla remotely and temporarily increased by S60 to an S75. I have data for both battery capacities.

    Example from November (while as an S75):

    Charge set to 90% limit - charge start 11/14 1:01AM @ 8% SoC. Charge complete 11/14 6:16AM @ 90% SoC. Charge added 55.06kWh. (From displays)

    Driving stats: 45 drive cycles, total mileage 130.5 miles. (TeslaFi) User interface reports 43.5kWh used for an efficiency of 333Wh/mi. (Car displays)

    Charge set to 90% limit: charge start 11/22 1:01am @ 11% SoC. (Car displays)

    The first discrepancy is in the amount of charge added versus the amount of charge used. For a 8%->90% charge, the battery added 55.06kWh. For a 90%->11% discharge, the battery used 43.5kWh. Delta: 11.56kWh for 3% battery delta, over 8 days. Rough average (not including 3% delta) of 1.445kWh per day of vampire drain. Seems high to me.

    Per wk057's analysis of the BMS, the starting usable capacity of an S60 is around 62.4kWh and an S75 is around 72.6kWh.

    Based on the numbers above for my drive plus the starting usable capacity (S75):

    Personal current battery capacity (charge) = 55.06kWh/(90% SoC - 8% SoC) = 67.15kWh

    This would equate to a roughly 7.5% battery degradation in 2 years/17.5k miles. Not terrible, but not great either.

    Personal current battery capacity (driven) = 43.5kWh/(90% SoC - 11% SoC) = 55.06kWh

    This would equate to a roughly 24.15% battery degradation in 2 years/17.5k miles, which is atrocious.

    Example from October with S60 (with fewer driving cycles):

    Charge set to 90% limit: charge start 10/7 1:13AM @ 58% SoC. Charge complete 10/7 2:54AM @ 90% SoC. Charge added 20.3kWh. (From displays). Interestingly, TeslaFi reports 18.8kWh used to add 20.3kWh, for an efficiency of 108.2%. I'll chalk this up to a TeslaFi error, but interesting nonetheless.

    Driving stats: 3 drive cycles, total mileage 105.44mi. (TeslaFi) User interface reports 31.9kWh used for an efficiency of 320Wh/mi. (Car displays).

    Charge set to 90% limit: charge start 10/8am @ 28%. (Car display).

    Same math as above: 58%->90% charge, the battery added 20.3kWh. For a 90%->28% discharge, the battery used 31.9kWh. 30% delta (58%-20%) equals 11.6kWh (abs(20.3-31.9)), scale to 100%, gives me 38.66kWh. Obviously something is amiss here.

    If we just look at the driven battery capacity: 31.9kWh/(90% SoC - 28% SoC) = 51.45kWh. Using the 62.4kWh from wk057, we get an expected degradation/vampire loss of 17.55%, which again, seems very high for 2 year battery degradation + 1 day of vampire.

    Now that the data is out of the way, I scheduled an appointment with my local service center for Monday, December 10th. I laid out the case above (but with less detail) and received a call from a service advisor that their techs were going to do remote battery diagnostics. I provided the dates above for the S75 case, and this is the response I received:

    "I am remotely diagnosing your concern at this time and wanted to follow up with my finding’s.

    I have run a remote battery health check of your pack, and found there to be no hardware issues currently flagged. I have also confirmed your pack has been successfully upgraded to 75kWh.

    What I have found, is your pack has a range calculation inaccuracy, which means the range displayed is not entirely accurate. This would explain why your consumption of 43.5kWh is equating to 79% of the packs available capacity. In fact this is a miscalculation of the packs consumed energy. Please note this inaccuracy does not affect the actual capacity of your pack nor the actual range your pack is capable of reaching.

    I have performed a battery degradation calculation using logs stored for your vehicle and have found the true degradation to be around 6.6% since the inception of your vehicle (Approximately 2yrs).

    We are constantly evolving the algorithm for range calculation to avoid inaccuracies like this and it should get better with future firmware updates.

    If you have any further questions, please don’t hesitate to reach out."

    Correct me if I am reading this wrong, but what they are saying is that there is an range calculation inaccuracy (despite me never having said that I use the range calculation, only battery percentage), but then they mention that there is a miscalculation of the packs consumed energy, which seems like a major flaw to me. They note that this does not impact actual capacity or actual range, yet in my experience, it does impact one or both of those parameters. A true battery degradation of 6.6% sounds reasonable, so that part is fine. And then they say that this should get better in a future firmware update, which (me being an engineer) is what we say when we have no intention of actually fixing it, but customer service needs something to tell a customer.

    Expanding on my note above about the actual impact on either the actual capacity or range: we are limited to charging based off what the battery pack is reporting. If the battery pack reports 11%, it believes it only has 11% capacity left, and the firmware begins to provide notifications that charging is required. On the flip side, the charge circuitry also controls how much charge can be added to the battery, especially when the charge limit is set to 90%, which is a function of the built in fuel gauge. So if there is a fault in the fuel gauge, or in the calculation of the "packs consumed energy" as noted by Tesla, then there is a very real impact to at least the actual range the pack is capable of reaching. The pack itself may be fine, but the fuel gauge may not be.

    I responded back with the above concerns and they responded that they have escalated it for a 2nd look.

    TMC hive mind: Is there something I am missing here? Do I have an error in my analysis calculations? Or is vampire drain greatly increased with recent software updates?

    Happy to answer any questions! Thanks!
     
  2. ucmndd

    ucmndd Active Member

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    Location:
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    10,000 words above and not a single mention of the displayed rated range at 100% SoC, which is really the only somewhat consistent measure available to you regarding what the car thinks the current battery capacity is.

    You will drive yourself crazy trying to make sense of consumption ratings, kwh in vs kwh out, etc etc. The car's estimates of that seem to be wildly inaccurate. You would be well served to drop this line of reasoning ASAP as there's little to no sense to be made of it.

    To give you a reference point, my Dec 2016 S75 with 65,000 miles shows a rated range of 228 miles at 100% charge.
     
  3. brgr

    brgr Member

    Joined:
    Feb 9, 2017
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    Location:
    Los Angeles
    Appreciate your insight, but rated range is an obfuscated measure of physical battery parameters. I design and integrate battery management systems for consumer/medical/automotive products for a living, so I'm only interested in physical battery parameters or fuel gauge measurements. If the rated range at 100% says you can go 228 miles, but you only get 150, what good is the rated range?

    You are correct in that I have not charged to 100%, but I have also not drained the battery to 0%. It's been well established by Tesla, the Tesla community, and all suppliers of batteries that charging to 100% should only be done for long range trips (of which I have none to share) and that the battery should never be left at or near 100% SoC. Besides, I (normally) have an S60, so charging to 100% could be done without harm to the battery pack, but Tesla has conveniently (or inconveniently, based on my current desire to get to the bottom of this) temporarily increased the pack capacity to an S75. The algorithm in the fuel gauge should be well tuned for both the battery chemistry and well as the discharge curves under various loads, not to mention accounting for battery degradation. These features are available in consumer electronics, so there is no reason to believe that a company who's entire product portfolio is based around a batteries would not have done their design due diligence.
     
  4. animorph

    animorph Active Member

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    Scottsdale, AZ
    I didn't read through the whole OP because it seemed like just another post trying to reconcile battery size/rated miles/trip efficiency/charging energy.

    This might be one help:
    Car’s energy consumption (lack of) accuracy

    I expect the car's charge added should come close to reconciling with the battery capacity.

    Per the link above, you will find that the faster you withdraw energy from the battery, the less you get out of it.
     
  5. animorph

    animorph Active Member

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    Location:
    Scottsdale, AZ
    Rated range is every bit as valid as the battery percentage display, if not more. Both are estimates of battery energy. Rated range simply displays it as battery energy divided by a constant that depends on your car model. That constant is determined by the car's EPA mileage ratings only, not your driving, and does not change over the life of the car.

    I'm actually a little leery of the percent reading. If the battery degradation has reached 50% for example, the percent gauge still says 100% if the battery if full, right? However, the Rated Miles should indicate only about half of what you had when the car was new. How is that useful?
     
  6. brgr

    brgr Member

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    Location:
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    I'm not trying to reconcile rated anything, only battery percentage vs usage.

    Yes, energy added will be greater than energy out for driving, as it's known that other system loads are not shown in that screen. I'm looking at charge vs driven to determine a combination of battery degradation + vampire drain. I'm losing kWh per day to one or the other, and the question is whether the loss I am experiencing is due to a hardware fault (Tesla says the battery pack itself is fine, so the fuel gauge then) with a how the battery is measuring power out, how the system is managing power, or something else.
     
  7. brgr

    brgr Member

    Joined:
    Feb 9, 2017
    Messages:
    9
    Location:
    Los Angeles
    Battery percentage is a reading from an integrated circuit known as a fuel gauge. It most likely contains an algorithm based on actual measured battery parameters under a variety of loads to that outputs a percentage of available power, and then tracks that available power by measuring the voltage across a very small value, high power resistor (generally less than 0.01 Ohms, 1% tolerance or better) to provide real time battery output current measurements. Battery University/Google have plenty of articles on fuel gauge operation.

    Rated range is an extrapolation of this number to generate a number friendly to nearly every driver who is used to a "Distance to Empty" measurement from their car. This may be the EPA estimated range in the US, or some other governing body elsewhere, or may be an estimated range based on driving factors averaged over a time period or distance.

    You are correct in that the fuel gauge algorithm should update for battery degradation, otherwise it would be an instant measure of how much the battery has degraded. However, the charge circuitry charges based on the trickle/CC/CV cycles for Li-based batteries, finishing a charge cycle when the cells have reached approximately 4.2V. Obviously with a large pack, there is inaccuracy for leveling, inconsistent cell degradation, etc. When the charge cycle is complete, this is the new 100%. Comparing the added or used energy versus the battery percentage provides the real battery capacity. This can then be compared to the "known" measurements from wk057 to observe either degradation or vampire drain, which is exactly what I'm after. The answer I'm looking for are: which is it? and why does it appear to be more significant than anticipated/expected?
     
  8. Electric700

    Electric700 Active Member

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    May 21, 2013
    Messages:
    1,316
    Location:
    Florida, United States
    Brgr, battery balancing might help. You can do this by charging to at least 94% and letting the charge complete. Once you do, you should drive it immediately afterward. If you charge to 100% once a year specifically for battery balancing purposes, and drive your car immediately after the charge session completes, I believe the detrimental effect should be minimal to zero.

    You've verified that your rated range is 228 miles at 100%, and you're now getting 150 miles actual where you expect a range of 180 when using about 80% of the pack's available energy from maximum? Keep in mind that Los Angeles temperatures have recently been lower, even in the 40s. The car might need to use additional energy because of that.

    One last thing, try doing a full reboot by pressing the brake and both center scroll wheels for 10 seconds. Then do the same for the top control buttons above the scroll wheels.
     

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