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The numbers don't add up...I think!

Discussion in 'Model S: Battery & Charging' started by Asciidv, Apr 11, 2016.

  1. Asciidv

    Asciidv Member

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    Location:
    Ponteland, Northumberland, England
    My S 90D (2 months old, 90% charge is 250 miles), told me today;
    [​IMG]
    90% charge should be 81kWh, so at this stage I should have used about 50% of the available battery power.
    However the range readout shows;
    [​IMG]
    94 miles as a percentage of 250 miles, is 37%.
    [​IMG]
    When switching to the remaining battery power percentage display it says 34% which is in general agreement with the 37% from the miles calculation.

    Both of these values are a lot lower than the 50% I was hoping to see from the power used so far display. Can anyone explain the differences and which power remaining number I should really trust?

    Thanks from Northumberland, England.
     
  2. kort677

    kort677 Active Member

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    try to force the pack to rebalance by running it down to as close to zero then doing a full charge and the range reported should adjust.
     
  3. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    A few points:

    * A Tesla "90 kWh" battery doesn't have 90 kWh of nominal capacity. There is another long thread on this - but bottom line is that 85 and 90 kWh batteries are about 80 and 85 kWh, respectively.

    * Not all of that capacity is available to the driver. On the 85 kWh battery, about 4 kWh is reserved for anti-bricking protection. End result of #1 and #2 is that out of 85 kWh, 76 kWh is usable for driving.

    * The "since last charge" isn't always accurate, either; I've found that it doesn't count energy consumed when the car is not in a drive "gear". In addition, I've also seen cases where the counter "skips" miles on road trips. The odometer is right, but the energy meters are not.

    Hope this helps,
     
    • Helpful x 2
  4. brec

    brec Member

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    No expert I, but it's my understanding that rebalancing and recalibrating are distinct. Rebalancing is a physical process affecting the cells in the battery and occurs when the state of charge is at least, if I recall correctly, 94%. Recalibration is a software process affecting the remaining range or charge displayed and occurs when the change in state of charge is large, from high to low and vice-versa.

    As to the original question, the usable energy in the battery is less than 90kWh. How much less is a matter of some debate, and there is also variation among individual cars. The imputed usable capacity from the one trip illustrated is 40.8/(.90-.34) or 72.9 kWh. That does seem low.
     
  5. Farnigus

    Farnigus Member

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    I've got a similar problem and was wondering if anybody could explain it?

    I've been logging my battery% and kwH since last charge. My daily consumes about 50% of my total battery.

    When you calculate the implied effective battery size, I get numbers from 75 to 79 kwh... but its a 90 kwh battery!
    I know that the 85 kwh batter is actually an 81 kwh battery, and (presumably) the 90 kwh battery is actually rated at 85 kwh.... and there's 4 kwH anti-bricking built in. So I should >80 kwh available. Its close, but not quite right. There's something else affecting the battery's effective capacity.

    I presume that the rate of discharge can affect the battery's effective capacity? Any battery experts know more?
     
  6. Muzzman1

    Muzzman1 Member

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    Along with this, the faster the energy leave the battery, the more is wasted. In other words, if you have any high wh/mi moments those consume more energy because the resistance in the system increases, so some power is lost to heat.
    Plus keep in mind the car is doing algorithmic calculations. It's never exact.
    I'm with @FlasherZ , just assume on long sustained low accelerations, (perfect conditions) you will get about 75.9Kwh out of the 85, and about 80Kwh out of the 90's.
     
  7. Asciidv

    Asciidv Member

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    Today I re-checked the figures from my last charge.
    [​IMG]

    [​IMG]

    If we say that the real available capacity of a S90D is 80kWh, then the implication from the top picture is that I have 20kWh left. The bottom picture shows that I have used 43 kWh making a total of 63kWh........an awful long way short of the 80kWh I was meant to have! You will see that the average energy use was not excessive and I was careful not to use aggressive acceleration as I was wanting to conduct an objective test.

    Is my battery pack defective?

    The only hesitation that I have is the talk of 'Vampire Drain' when the car is just sat there not being used. This test was conducted over 5 days and I cannot believe that the drain is greater than the equivalent of a 1kWh over a 24hour period. So that even if you take an extra 5kWh into consideration for 'Vampire Drain' I have still lost 12kWh. (The car is 3 months old).

    Can someone post similar pictures but showing numbers which do add up?

    Thanks in advance for all your help.
     
  8. Boatguy

    Boatguy Member

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    My 90D reports 292mi of RR at 100% and 264mi at 90% so your Your original post of 94mi / 34% suggests a total of 276 which is consistent with the 90% of 250; but both are well below what I see on my car.

    Calculating in the other direction:

    90
    - 5 no brick
    - 5 vampire (I lose 2-3 miles / day to vampire so I think 1kWh / day is probably a good guess)
    -43.4 for 151 miles
    = 36.6kWh that should be remaining which is 41% of 90 and obviously a larger percentage of any smaller denominator, so the 34% makes no sense.

    You did do this over an extended period, and temps are cooler in the UK than California so a combination of vampire and cooler temps might explain the difference.

    Try setting Controls > Displays > Energy Savings to ON and see if your results change at all. Maybe the vampire is higher than we think.

    You could also try taking a good long drive on one day to take the vampire out of the equation. Maybe pop up to Glasgow for a pint, and back home!
     
  9. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    If you have "energy savings" turned off, or "always connected" is checked and you're using a lot of mobile app traffic, the car will tend to use 10 miles or so per day of power due to vampire drain.

    Also note that this is "since last charge" - did you confirm that when you were unplugged that the car had charged to full? If you unplug prior to the car being completely charged, it will reset that meter.

    Was there any time that you had preconditioned the cabin? or passengers were sitting in the cabin with the climate control running? Climate control drain doesn't get counted while the car is off / in "P" / in "N".

    If none of that fits your case, then you might ask them to look into your battery.
     
    • Informative x 1
  10. Boatguy

    Boatguy Member

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    #10 Boatguy, Apr 25, 2016
    Last edited: Apr 25, 2016
    I think FlasherZ has the answer. I tried something similar to your test. I didn't charge over a period of a couple of days when I didn't drive much, and spent some time in the car with climate on, etc. fiddling with settings and what not. I had Energy Saving OFF and Always Connected ON. These were my numbers:

    Since last charge: 37.5 mi 14.9kWh
    Range: 200mi Remaining: 68%

    First, we don't know if the reported percentage is of the total battery of 90kWh, or something less than that after allowing for "no brick", so let's assume it's based on 85kWh.

    The 68% remaining with an RR of 200mi works out to a total RR of 294mi, which is quite close to the 292 that I see at 100% charged. So far so good.

    68% remaining means 32% consumed = 27.2kWH. From that, I surmise that the kWh "since last charged" is strictly while the car is being driven. In my case this implies 12.3kWh of "vampire", or non-driving consumption. A very large number, far more than we would have assumed.

    The 10mi/day that FlasherZ suggests is roughly 3kWh/day which in your case would have been 15kWh of "vampire".

    If we take your reported 40.8kWh for driving and add 15kWh of vampire, you would have consumed 55.8kWh or about 65% of an effective 85kWh battery, leaving you with about 35%, quite close to your reported 34%.

    So the bottom line is:

    - The effective battery size of the 90D appears to be 85kWh
    - Vampire can be really high!
    - Experiment with Energy Saving and Always Connected settings until you are comfortable with the vampire drain.

    That said, my understanding is that rated range is based on the US EPA number of 294. If that were the case, then at 94mi of RR your battery should have shown 32%. Your imputed 100% RR is 276 which is definitely low, about what would be expected from an 85kWh battery (i.e., 94% of 294).

    There are probably people in these forums who have figured out how to hack into the service information that reports actual battery capacity or percentage of original, similar to how an iPhone or MacBook can report its battery health. You might want to search for those people and see if they can provide insight into how you can access the health of your battery.
     
  11. Boatguy

    Boatguy Member

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    I just did the math on this to understand it for myself. I charged my S90D to 90%, then drove the car about 10 miles, parked for an hour and a half, drove home 10 miles, and then did the math. The point is that these numbers have minimal vampire loss. Here's the math:

    100% RR = 292
    90% RR = 264

    After driving 20 miles:

    RR = 242
    Battery percentage = 82%
    Consumption last 15mi = 300 Wh/mi
    Projected range = 232

    Projected range / Rated range = 232 / 242 = 95.9%

    Wh/mi to achieve Rate Range = 300 x .959 = 288 Wh/mi

    Implied battery capacity = 288 Wh/mi * 292 Rated Range = 84 kWh

    Implied "reserve" or "anti-brick" = 6 kWh

    In practice, I consume about 310Wh/mi so my 100% range is about 84,000 / 310 = 270 miles

    YMMV!
     
  12. JonnyHelen

    JonnyHelen New Member

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    We also have a 90D. You cannot check the capacity over a few days.
    The best way to check your usable kWh is to charge to 100% and then drive at a consistent speed until the battery runs out. In practice this is not realistic, so run it as low as you dare and then take the remaining Typical Miles and multiply it by your Typical Miles Wh/mi algorithm. Add this to the "kWh used since last charge" and you have your total usable kWh.

    I have tested our 90D range many times and I cannot access any more than 76kWh from our 90kWh pack.
     
  13. Asciidv

    Asciidv Member

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    Boatguy and FlasherZ, I really do appreciate you taking the time to offer an explanation and to do some trials yourself. At the weekend I intend to make some tests ( like going to Glasgow for a pint doesn't!t seem a bad idea! ) to really see where we are with this. My 90% is 249 miles which seems low for such a new car. I tried discharging it down to 50 miles with a low ( 260 ) Wh/m and this did not alter the 90% value.
    Tonight I made a quick test which gave a more promising result.
    This was the start values;

    [​IMG]

    [​IMG]

    and here are the end values after a 30 minute drive around English country roads;

    [​IMG]

    [​IMG]

    If you take that 12% of battery power was used ( this may be generous but the actual start and end percents can only be rounded to 1 percent) which equated to 10.1 kWh then my battery capacity is just over 84kWh! So quite possibly nothing is amiss at all.


    (JohnnyHelen, was is your 90%?)

    Thanks again.
     
  14. Boatguy

    Boatguy Member

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    Looking at your display, I see the temperature is 39F. This most likely explains the lower 90% rated range. I have been driving a BMW i3 the last two winters and when the temp in Northern California dips from our usual 60-70F to 40-50F my range drops by about 5-10%. That would totally explain your 90% of 249 versus my 90% of 264.
     
  15. Boatguy

    Boatguy Member

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    For what it's worth, Tesla tech support says rated range is based on 300 Wh/mi.

    With a rated range of 294 that would imply 88.4kWh capacity and a very small allocation for "anti-brick". I'll keep an eye on that, but I'm not sure I believe that number just yet.
     
  16. Boatguy

    Boatguy Member

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    In the last 24hrs, with Energy Saving OFF, I lost 6mi of RR, or almost 2kWh.
     

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