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How Tesla Calculates Range (hidden buffer)

Discussion in 'Model 3: Battery & Charging' started by TimothyHW3, Apr 11, 2020.

  1. TimothyHW3

    TimothyHW3 Member

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    This is my third video in the series of Scan My Tesla where I explain how the hidden buffer below 0% works and why you can't get the predicted rated range in the Model 3's Energy Graph from 100% to 0% (or any other Tesla) if you follow the consumption on screen.

    This has been discussed at lenght in other posts, but the TLDR:

    1. All Teslas have a "net" capacity that you can use - on the Model 3 it is around 77-78kWh when brand new

    2. Some of that capacity is being hidden below the 0%, but it is factored in in your 100% rated range. 4.5% Is hidden below 0%.

    3. The calculation of typical range you see next to the battery icon is based on a specific EPA constant (or Tesla constant) which is different for each model - 153Wh/km for Model 3 LR AWD or 245Wh/mile

    4. But even if you drive at the EPA constant - you can't reach the total range predicted, because you have to go below 0%. So the displayed 100% rated range is actually 104.5% or 4.5% less than what you see.

    Some people know about this, most unfortunately do not. Especially new Model 3 and Tesla drivers since most if not all other EVs use GOM and not an Energy Graph and their 0% is true 0% (most other EVs the car will die shortly after reaching 0% - with Tesla you still have 10-15 miles left)

    I have done the "visual" test - I charged to full and drove at the exact typical range constant (straight line in your energy graph) which theoreticaly should give me the typical range displayed in the screen at 100%

    But since Tesla starts to hide some of this as soon as you drive, the true typical range is 95.5% of what you see in your screen. Unless you want to go to below 0% to through 0.

    What I found out during my test is that the car will hide 5km every 100km so this is why most people will never notice the difference between rated range and real range even if you follow the energy graph.

    So when you drive 100km at the constant - you remove 105km from the battery icon.
    When you drive 200km you remove 210km and so on.

    Here is the video and I hope you will enjoy it - it took several hours to test this.

     
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  2. Three3

    Three3 Member

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    Thank you for doing this research! Does that mean, in an emergency, even if your car shows 0 km or miles remaining, there may be about ~4% of the total miles remaining? Or will the car simply shut down at that point? (I realize in either case it’s very bad for the battery to bring it to absolute empty.)
     
  3. SageBrush

    SageBrush 2020: Drain the Sewer

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    Let me see if I am following:

    If my consumption is 72 kWh to drain the battery from "100" percent down to "0" then my actual usable is ~ 72*1.045
    Second, since my new battery usable is ~ 78 kW, I have lost 78 - 72*1.045 kWh of capacity

    Is this correct ?
     
  4. TimothyHW3

    TimothyHW3 Member

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    #4 TimothyHW3, Apr 12, 2020
    Last edited: Apr 12, 2020
    "May be" is nicely put. If the BMS is ok - yes.
    And not 4% of the total miles, but 4.5% of your total capacity when you charged the car - usually about 3.3-3.5kWh. You can't think in miles or km, because they are based on the EPA constant.
    So this could mean you have 0 km if you drive with 200km/h on an uphill or 25 -30 km if you drive with 50 km/h on a nice flat road.

    So you really can't rely on that one. Plus not good for the battery to go extra low. But yes, if you reach 0km and you have to reach some Supercharger, I would dial down to 40-50km/h, turn off HVAC and hope I have 25km left.
     
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  5. TimothyHW3

    TimothyHW3 Member

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    Actually very wrong:)
    The consumption is measured in Wh/km or Wh/m

    kWh is your battery capacity.

    Think of it like this:
    kWh is your tank capacity -60Litres or whatever in gallons.
    Wh/km is your consumption - 6 litres per 100km for example.

    If you have a nominal full(including the buffer) of 72kWh your 0-100% is 95.5% of that or 68.76kWh
     
  6. ran349

    ran349 Member

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    Although technically there is capacity below zero, you should never assume that it is available to use, unless you don't mind being stranded on the side of the road because of that assumption.

    But even if you did successfully keep driving below zero, the BMS will always ensure that the battery shuts down before it gets to a level of damage.
     
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  7. SageBrush

    SageBrush 2020: Drain the Sewer

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    So much for clarity on my part. Let me try again (and I do understand power and energy units)

    I start at 100% battery charge per my screen
    I drive down to 0% battery charge per my screen

    My consumption meter of distance*Wh/distance = 72 kWh
    .... ....
    then my actual usable is ~ 72*1.045 ?
    Second, since my new battery usable is ~ 78 kW, I have lost 78 - 72*1.045 kWh of capacity ?

    Is this correct ?
     
  8. AdamMacDon

    AdamMacDon Member

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    Thanks for the very informative video and explanation. Nice to know exactly what is going on behind the scenes with the energy display. I never use it anyhow because honestly it's very useless in the hilly part of Canada I live in, I just stay with percent. The EPA rated range is useless. In the winter I can see consumption nearly double. I wish Tesla offered an option in the display screen to show the energy graph number (consumption data based on the last 50 kilometers).
     
  9. TimothyHW3

    TimothyHW3 Member

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    No it is not useless.
    You have that in the energy screen - you can toggle between 10-25-50km.

    If you navigate yourself with the Tesla Maps, ie set a trip, it will calculate every little hill on the way check the trip meter and look for ups and downs.

    The only place where it is useless is in Germany because it calculates the speed based on 130km/h, actually Google maps does it too, whereas most of the time you drive at almost double the speed:) But even then the trip meter is helpful as it shows you elevation on the upcoming route.

    I remember a trip to Norway, it calculated my arrival % and every little hill on the way there.

    But we are talking about something else here.
     
  10. TimothyHW3

    TimothyHW3 Member

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    #10 TimothyHW3, Apr 13, 2020
    Last edited: Apr 13, 2020
    Are you trying to catch your degradation? If Tesla doesn't do an update, you can actually do the rated range calculation.

    Rated range displayed when charged at 100% let's say 490km(but charged, in warm weather, not using Stats or the Tesla App)

    Then 4.9*15.3 is your total nominal full(including buffer )=75kWh

    If you want to find out your 0-100- 75*95.5%=71.6kWh(this is your 0-100%)

    If you drive from 100 to 0% on one go and you end up using 71.6kWh reverse math:
    71.6kWh/0.955=75kWh

    Or you can remember that you have roughly 3.3-3.4kWh Buffer

    These are all calculations for the 2018-19 AWD Tesla. Not SR+ and RWD LR.
    And I believe the AWD 2020 has a different constant too with the newest update.

    But the buffer and the hiding is available on all Teslas and is always around 4.5% I think on the 100D it might be closer to 5% (I believe it was 5kWh from 96-97kWh total)
     
  11. drtimhill

    drtimhill Member

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    It's this crazy use of units the EV makers are using...

    Energy is measured in Joules (abbreviation J), the SI unit. The battery is a reservoir of energy, and so you can measure its capacity, and how much charge it contains, in Joules.

    Work is a measure of the consumption of energy to perform a task, or how energy is consumed to do something for some length of time. The SI unit of work is the Watt (abbreviation W), which is defined as expending one Joule of energy per second. Because a Watt is a rather small unit, its easier to use kilowatts (kW). So when your microwave is using 800 watts, its output is 800 joules of microwave energy each second.

    A kilowatt-hour is the total amount of energy you use if you are doing 1kW (1000 Watts) of work for one hour. This is actually a bit crazy, since you start with energy (joules), then convert to work (watts), then go back to energy (watts for one hour). What this means is "kWh" is a unit of energy .. it's just Joules in disguise. How many? Well, one kW is 1000 Watts, and one hour is (60 x 60) seconds, which is 3600 seconds. So 1kWh = 1000 x 3600 = 3.6 million Joules (3.6 megajoules). A Wh is just the same, but 1000x smaller, or 3.6 kilojoules (kJ).

    The thing to remember is Wh and kWh sound like a measure of power because of the word "Watt" but in fact they are measures of energy.

    Oh, and calories? They are an old pre-SI unit of energy, equivalent to about 4 Joules. And to make things even messier, the "calories" you see on food labels are actually KILO calories (1000 calories), presumably because that makes the numbers easier for consumers to understand.

    So, according to my calorie app, the Apple Fritter donut I ate for breakfast had 300 calories. That's food calories, so it's actually 300,000 real calories, which is about 1,200,000 Joules, or 1,200 kiloJoules (kJ). For simplicity, lets assume my Tesla M3 uses 300 Wh/mile. That's equivalent to 300 x 3.6 kJ, or 1,080 kilojoules (kJ) per mile, which is pretty close to the energy in that donut, with a bit left over for music and A/C.

    So, my car needs to be fed one donut to drive a mile. Clearly, we should be using donuts/mile as the unit of energy consumption :)
     
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  12. AdamMacDon

    AdamMacDon Member

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    I think you misunderstand, the energy display by the battery icon in "miles/km of remaining range" is useless. The energy graph and trip graph are very useful (even though they presume I am doing the speed limit, which is generally wrong). EPA rated range means nearly nothing driving in a mountainous region of Canada. I almost never use the navigation system so trip graph is irrelevant for most of my driving. Hence why I use percent for my energy display.
     
  13. TimothyHW3

    TimothyHW3 Member

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    No, I did not misunderstand you.

    First, the miles/km next to battery is not useless, if you know what it represents(if you watch my Video, towards the end I explain how you can convert it easily to "real" range)
    It also is "useful" to track battery degradation and/or BMS unbalance. If you always keep your car on% you will be oblivious to battery degradation. If you don't care for range then ok.
    They are a representation of your remaining battery capacity in km based on a simple math formula.

    The energy graph does not presume anything and is not using EPA, it calculates the range based on your real consumption either in the past 10/25 or 50km. Exactly what you want.
    However, you have to again factor in the buffer and remove about 4% from that range(also explained at the end and beginning of the video)

    Finally - on your next route, start a trip via the nav system and watch the trip meter next to energy consumption - it will show you all the hills and downslopes almost to the km and calculate the % at each stage. Follow it through and you will see how accurate it is.

    You can use percent, but then you have to know your full capacity, follow your consumption constantly and do reverse math to see true range. Otherwise you will just be looking at percentage disappearing without having any idea what is causing this and how far you can go.

    If you know how the car calculates things, km/miles is better and more informative.

    Change to km and follow my advice at the end of the video and you will be golden.
     
  14. AdamMacDon

    AdamMacDon Member

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    As a UI/UX designer, here is my standpoint. Tracking battery degradation is not something I do every trip (or heck, every week). I rarely worry about it. Hence, having it front and center on the main display at all times is fairly useless to me. If I think I am seeing some large amount of energy capacity loss, I switch to the KM display mode and do a 10% to 100% supercharge to see the results. Having the ACTUAL range my car can go on a charge hidden in a secondary menu that blocks the right side of my screen is also not really ideal, especially if I WAS using the navigation. Having to flip between it and the map is kind of annoying and not a great user experience. If that number displayed on the energy graph could be up beside the battery icon, I would find it far more useful and intuitive.

    Now this is just my personal opinion, you may have a different one and that is fine. But for me, the percentage is much more useful. I know in work in freezing weather it will take 7% to get me to work and 9% to get me home. In the summer, it's like 2% to work and 3% home. I know my distance never changes (about 7km each way), but if I use the "distance" display, the number of KMs consumed for each trip are drastically different. Sure you can do the math in your head (divide by 4 to get your percentage, roughly), or you could just use percentage and skip the need for doing math on the fly to track your SoC. I'm not saying Tesla should replace the "distance" display option, but supplement it with a "real distance" choice, which I would find far more useful.
     
  15. animorph

    animorph Active Member

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    There is no single "real distance" that Tesla can calculate unless you enter your destination into the nav. Even then, it doesn't know if you're going to drive at 50% of the average speed or 150%, if it's raining or snowing, or if you'll have a headwind or tailwind. All the threads complaining of missing energy and calculated battery capacities have demonstrated that some energy is lost to the battery's internal resistance, unmeasured. So the faster you discharge the battery the less total energy you can get out of it.

    Rated miles works fine as a charge level number for me. I like it better than percent because it comes close enough to "real" for local drives and 100% of a degraded battery is not equal to 100% of a new battery. The energy in "1%" will change over time, as will the distance you can travel. A rated mile is a specific amount of energy in the battery, though still just an estimate by the BMS..
     
  16. AdamMacDon

    AdamMacDon Member

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    Of course there is no perfect way to calculate range, but one is measurably more accurate than the other. Basing off the last 50 kilometers driven is more accurate than EPA rated range for most drivers, especially in cold climates. I'm just saying the option would be nice, not that it should replace EPA rated range for those who prefer it.
     
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  17. TimothyHW3

    TimothyHW3 Member

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    I think I now understand what you are saying and I have seen this a lot from people coming from ICE cars or other EVs.

    Other EVs have exactly what you are saying - they have an imaginary boundary at X km back from the calculation point, take the consumption and capacity and divide it to reprsent some remaining miles/km. That is called a GOM or guess-o-meter, because it is exactly that - a guesstimation.

    I don't see how this will be helpful to you though - on your way to your work it will show you double the amount of range since it will take your last trip which was down - not useful.
    On your way down it will show you half of the range you have since it will use the way to your work as a reference (uphil), but you will be driving downhil...

    Tesla has it better with factoring elevation and weather and speed.

    I think most people are just too familiar with how the ICE cars worked, but the thing is that ICE cars are more linear than EVs - they do not regen and the HVAC is more or less coming from the motor heat. And they are very dumb.
    EVs have regen and some of the secondery consumptions like HVAC could hurt the range. I think what Tesla does is pretty good, especially the trip meter estimation.

    As a UI/UX designer, how will you design the screen so that you still can have the energy graph in direct sight and still maintain some sort of range estimator?
    If I were to design it, I would have the energy graph accessible with one click and not 2-3 clicks and have it overlay somewhere at the bottom, maybe where the trip meter is. That's it. But I will still want to keep the way the calculation is done now.
     
  18. Zcd1

    Zcd1 Member

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    All of the confusion and consternation regarding displayed remaining range could be addressed by simply adding a 3rd option to the miles/percentage choice: Miles remaining based on recent driving. This is what ICE vehicles have offered since those types of displays were first introduced.

    This wouldn’t even require any new calculations; just display the number that’s available in the Energy graph, based on the most recent 30 miles/50km.

    I honestly don’t understand why that option hasn’t been there from the beginning.
     
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  19. TimothyHW3

    TimothyHW3 Member

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    This will be a GOM like any other EV has it. I guess Tesla could implement it, but then you have to have an under menu where you choose wether you need 10-20 or 50km. And this information is already available in the energy graph, two clicks away, why the redundancy? Tesla should make the energy graph more easily available and front and center and keep everything else as it is (except for the rated range using full capacity for the calculation instead of 96% this should be removed:) And explain how it works to every customer that walks out with a Tesla. That's it.

    I mean, it never hurts to use some mental math from time to time if you need it, our brains are getting dull anyways...
     
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  20. Zcd1

    Zcd1 Member

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    No, I'm not suggesting an option that would include choosing which of the various distance measurement estimates to display - just a 3rd option under the percentage/miles remaining interface. It's one addition virtual button - that's it.

    Yes, this would make the car similar to most other vehicles on the road. In this instance, I'd suggest that would be a good thing, as everyone already knows how those estimates work, and that the estimate will change based on recent energy usage.
     
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