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Energy Consumption Doesn't Match Battery Usage

Discussion in 'Model 3' started by Amendale, Oct 9, 2019.

  1. Amendale

    Amendale Member

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    Can someone help me understand the reported kWh usage in the Model 3 menu. I have the LR RWD. I charged this morning to 80% and went for a drive. I travelled 81.5km and the battery dropped to 55%. Energy used is shown as 14 kWh. This was all within the span of a couple of hours and I only spent maybe 10 minutes parked in the car.

    If I am consuming 25% of the battery and using only 14kWh, that would mean that at full capacity I only have 14/0.25 = 56 kWh? If I understand correctly the LR battery should have a capacity of 75kWh?

    Am I missing something or is there something wrong with my battery at only 20,000km mileage?
     

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  2. Celledral

    Celledral Member

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    I myself have been closely monitoring my usage vs rated miles as well. It seems totally off on my SR and I would have to be using 190 wh/mi to actually get the rated range, instead of 219/220. My kWh usage matches the wh/mi, but the remaining miles/percentage is always lower than expected.
     
  3. animorph

    animorph Active Member

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  4. jdcollins5

    jdcollins5 Member

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    If I am doing my match correctly, 171 Wh/km = 275 Wh/mile. The rated is 240 so you are consuming more range miles than rated. Also, as stated above, the Trip Meter kWH does not include any accessory usage (AC, etc.) when not in gear.

    Other things that can impact range is temperature, wind, rain, altitude.
     
  5. Amendale

    Amendale Member

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    Yes I understand that accessory usage when in PARK is not reported, however as I said this occurred within a couple of hours with short times spent between stops, so I expect that the vampire drain and accessory energy usage when in PARK was minimal. For 25% battery usage I would expect to see 19 kWh consumed, while the menu reports only 14 kWh. The 5 kWh difference seems excessive to account for energy loss in PARK during the short time.
     
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  6. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #6 AlanSubie4Life, Oct 9, 2019
    Last edited: Oct 9, 2019
    There may be, but it is very hard to say for sure, if you are displaying %.

    You should switch your battery display at least temporarily to miles/km, rather than %.

    It's possible you have a lot of battery degradation, if you spent no significant time in park as you say. Or you may have had some insane vampire drain for unknown reasons (seems unlikely). 10 minutes of maximum heating (if it's getting cold for you) would result in a lot of drain though - so if your 10 minutes spent in park was at the beginning of the drive before the car was warmed up, that could be a contributor to the result.

    Your trip meter numbers should extrapolate to about 71.5kWh for an undegraded battery for a discharge from 100% to "0%" (quotes because 0% is not actually 0% due to the reserve). Yours extrapolate to ~55.6kWh as you say. (Note that 71.5kWh is not the battery capacity - it's more like 79kWh for an undegraded battery, but that's another topic.)

    Assuming you had no heating drain while in Park, it looks to me like if you switch to km, you'll see about 408km at a 100% charge, or 326km at 80% (rather than an undegraded result of 521km/417km). Meaning: your battery has lost 21% of its original capacity.

    An undegraded battery would lose only 19.5% of its capacity for a 14kWh discharge, rather than the 25% you saw.

    Switch it and see. It's sufficient to read the %, switch to km, and read the km. Then report both of those numbers.
     
  7. KenC

    KenC Active Member

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    Yep, seems excessive. What does your car show for rated range at 80% when you started? 397km?
     
  8. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #8 AlanSubie4Life, Oct 9, 2019
    Last edited: Oct 9, 2019
    For the SR you need to be getting ~209Wh/mi on the trip meter to have parity on the battery gauge rated miles (mile-per-rated-mile rolloff). You can measure the actual value yourself if you want.
     
  9. SageBrush

    SageBrush 2020: Drain the Sewer

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    Your calc looks correct to me but jumping to the conclusion that you have a problem with the battery is premature. Changes in battery temperature cause transient changes in capacity that lead to errant conclusions. I suggest you charge up at a supercharger some 30-50% and then repeat your test.
     
  10. Amendale

    Amendale Member

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    So I brought my battery down from 80% to 15% within the course of 3 days. The consumption meter was showing 40kWh. I then charged to 80%, which showed 47kWh to charge. At 80% the estimated range corresponded to 400km.

    The charging metrics seem to indicate battery health is ok, as 47kWh / (80-15)% = 72kWh, which I understand is the “usable” capacity of the Model 3 LR battery. Also 400km / 0.8 = 500km, which is the advertised range.

    However does 7kWh seem excessive for battery drain and accessory energy usage over 3 days? In my area temperatures are dropping down to 10C (50F), and I have been starting to use the heater.
     
  11. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #11 AlanSubie4Life, Oct 12, 2019
    Last edited: Oct 12, 2019
    Ok, these numbers seem relatively normal. You used 40kWh/0.223kWh/rmi = 179rmi (287rkm) while driving. And you added back 47kWh/0.234kWh/rmi = 201rmi (322rkm).

    So an undegraded LR RWD will have
    325rmi * 234Wh/rmi = 76kWh of charge capacity (you have ~72kWh)
    And
    325rmi * 223Wh/rmi = 72.5kWh of discharge capacity.

    So a few % degradation but no big deal.

    Does not quite work this way. The charge and discharge kWh cannot be aligned this way. You used 40kWh. This would normally take this much energy to recover:

    40kWh (out) * 234Wh/rmi (in) / 223Wh/rmi (out) = 42kWh (in). (Instead, it took 47kWh.)

    So you had closer to 5kWh (charging scaled kWh) of drain over 3 days, not 7kWh. (5kWh of charging corresponds to 4.76kWh of discharge.)

    That corresponds to ~35km over 3 days, or about 10 rated km per day.

    That is entirely possible. Be sure to turn off Summon Standby Mode and Sentry and disable your USB TeslaCam (no red dot on the camera icon when you leave the car), if you want to reduce this drain.

    In short, all seems pretty normal here.
     
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  12. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    Just to be clear, accessory use while not in Park is already accounted for on the trip meter. So other than vampire drain, only the accessory/heat use while in park would contribute to this 7 (actually 5) kWh of drain number.
     
  13. Amendale

    Amendale Member

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    Is there any published data to back up these numbers? I’ve seen a few different numbers floating around so just curious where it’s coming from.
     
  14. SlimJim

    SlimJim Member

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    Tesla is never transparent about this matter.
    But it is what it is.

    ICE gas tank size is clearly published down to 1/10 gal.
    Tesla battery size is not.
    Only the range is published.
    This is probably partly due to Tesla selling cars with software limit on battery capacity.
    They may even unlock few cells each time battery cell dies prematurely or degrades unexpectedly.
     
  15. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #15 AlanSubie4Life, Oct 12, 2019
    Last edited: Oct 12, 2019
    Nothing is published but these numbers are solid.

    You can measure your own discharge constant. (It will be about 223Wh/rmi.). Just note before and after rated miles, do a long continuous drive, then calculate Wh/mi * miles / (rated miles used). Just do not include any other losses.

    You can see your charging constant from the screen. stop the charging session, then just note kWh added, switch to miles display, then bring up charging screen, read off the miles added. Divide the two numbers. kWh/rmi will be 234Wh/rmi (after eliminating rounding errors). This relationship is always constant.

    Then just multiply these separate constants by the number of rated miles you have at 100%. Someone with the 325 range at 100% will have the numbers I quoted.

    For the AWD the constants are 245/230, and for the SR they are 219/209.

    Whether these numbers line up (they don’t) with the actual capacity of a car with 325 miles (which is 78-79kWh based on the EPA submission) does not really matter. There are a number of possible reasons for that discrepancy - could be reserve below zero miles, could be just all the meters reading low. But it does not matter - all that matters is how your numbers align with a car with 325 rated miles. And yours looks like around 310 rated miles at a full charge, so about 5% capacity loss (assuming your constants are 234/223) (for now). Which is normal.

    Overall it is nice - assuming the BMS is not confused, there is zero guesswork involved in figuring out how your battery is doing and how much energy it contains.
     
  16. diamond.g

    diamond.g Active Member

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    Eh there is a battery sticker. It should say 75 kWh on it. They don’t do trim on battery size anymore because no one should care how big the battery is for the range quoted (Tesla perspective). Plus they don’t have to lie like they did on the 85 and 90 batteries.
     
  17. insaneoctane

    insaneoctane Active Member

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    I have analyzed this problem far too much and never was able to really satisfy my desired level of "tracability". I often take trips and can't make the numbers add up. No stops. No heater. No AC. Amazingly low GUI efficiency (~200 W/mi), Put the car in park and it doesn't add up....ie if I use below (or well below) the rated W/mi for the trip with no accessories and fair weather then I would expect to have used fewer range miles vs actual miles travelled....but I've seen many times where this just isn't what I witness. Not much I can really do with so little information that Tesla actually provides us.
     
  18. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #18 AlanSubie4Life, Oct 12, 2019
    Last edited: Oct 12, 2019
    That is weird. It has always lined up EXACTLY for me. Always 230Wh/rmi. (And 245Wh/rmi for charging of course.) Just verified extensively on my road trip. It was perfect for over 1200 miles for a range of state of charge from 306 miles to 22 miles.

    Did you ever figure out your weird post-park decay problem? Maybe there is some unusual issue for you that delays the reflection of state of charge. But I would expect you to calculate high Wh/rmi in that case. (Should appear that you are using very few rated miles, at least immediately after parking, but sounds like you are saying the opposite occurs.)
     
  19. insaneoctane

    insaneoctane Active Member

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    My numbers definitely don't line up. My post-park decay appears to be approximately symmetrical because I see the opposite phenomenon after my commute home park (my battery adds about 10 miles within an hour). Strange stuff for my battery indeed.
     
  20. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    Yeah, that is weird. I think for most people it lines up exactly. I only have tried it on two vehicles of course personally (both AWD). But every now and again someone posts good data here, and it lines up perfectly then, too.
     

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