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Usable KW Doesn't match up??

Discussion in 'Model S' started by Richardbankd, Jul 11, 2017.

  1. Richardbankd

    Richardbankd Member

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    So i recently did a little test with my Model S 75D. I charged to 100%, and ran the battery down almost to zero miles left to see what the usable Kw were (just approximate). What I found (fig.) is that the number was not even close to what people have reported as the usable KW for a model 75 Battery (72.6 I believe). Can anyone explain this difference? At 10KM left,
    since the last charge the used KW is 59.6. Seems like about 12KW of usable power have vanished. (BTW this test was done over less than 24 hours, so shouldn't be that much "vampire drain"). IMG_4151.JPG
     
  2. Rafaelm

    Rafaelm Member

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    I have found temperature plays a huge role. Did you keep below 300w/mile the entire battery usage? Did u ensemble range mode? Remember the range is impossible assuming you always drive like your grandma unlsss she was a race car driver.
     
  3. Rafaelm

    Rafaelm Member

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    On same token try matching an EPA MPG if every car MFG. same drama.
     
  4. JohnnyG

    JohnnyG Weee!

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    @Richardbankd - Those are actually really good numbers.... The "trip" readout only shows energy used by the drivetrain. The whole rest of the car uses electricity also (i.e. heater, A/C, steering, brake booster, autopilot, lights, stereo, etc), not to mention loss from heat, inefficiencies, etc.

    @Rafaelm - Your points are good for range, but he's not referring to range... he's referring to energy consumed verses energy capacity available.
     
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  5. MasterT

    MasterT Member

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    Are you sure about that? I was under the impression that all energy is counted. I know for a fact that I can shave my Wh/m number by 30-40 for the same trip if I don't use A/C (I have very short commute, less than 1.5 miles, and I think because of that my A/C usage is so much more noticeable, at least I thought so)
     
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  6. EvanLin

    EvanLin Member

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    This might be wrong. I heard it shows ALL energy used under D&N gear.
     
  7. Rafaelm

    Rafaelm Member

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    We should ask Elon
     
  8. Tesmotorfaqcom

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    I asked Tesla the same question and the lead service person told me you can't use that to compute your energy as even with 0 miles left your Tesla still have usable power but of coz they won't say how much is it.
     
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  9. JohnnyG

    JohnnyG Weee!

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    My explanation above was worded about as bad as possible, which lead to a tad-bit confusion here; also, I by no means am the end-all expert on this (Elon is ;->).

    Wh/mi counts most (if not all) energy consumed, but only while the vehicle is in gear. If you are parked in your driveway on a 100 degree day with the A/C maxed-out, stereo cranked, all the lights on, etc, it's not going to count against you on your Wh/mi. Likewise, if you are pre-heating or pre-cooling your car, it also won't appear in the kWh consumed. This is why, for example, last winter, there were days where it showed I only consumed roughly 45kWh, even though I used approximately 70% of my battery.
     
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  10. Richardbankd

    Richardbankd Member

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    Hmmm. I suppose that would make sense, But it seems a bit high to be using 12 Kw for "other" power consumption out of gear.
     
  11. JohnnyG

    JohnnyG Weee!

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    I'd recommend using TM-Spy. I think it will have all the data you're looking for to determine the capacity and health of your battery. There's a few primary threads on TMC for it. I'll include the ones I know.

    Using TM-Spy to see Model S data
    Using TM-Spy for iOS
    Using TM-Spy for Android
     
  12. MasterT

    MasterT Member

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    Again, I dont think that's accurate and I base my comment on this: the gym I go to is about 1 mile from my house and by the time I'm home, my trip shows about 315-325 Wh/m. If I pre-cool the cabin for a few minutes before getting in, the same trip shows close to 500 Wh/m. The precooling is done outside of D or N Gears, but, based on my observations, it is counted.

    I think, all energy is always counted and applied to Wh/m calculation, which means, the OP is missing 12 kWh somewhere ....
     
  13. JohnnyG

    JohnnyG Weee!

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    That's why I suggest using a tool like TM-Spy, rather than "seat of your pants" type assessment. This topic has been widely discussed, and generally accepted that energy consumed outside of the car being on and in gear is not counted in the Wh/mi or total consumed energy. Using TM-Spy (which reads data directly off the CAN bus) will give you much more information to more accurately judge this.

    Making any type of definitive conclusion based off of a 1 or 2 mile commute is about impossible. I have easily reached well over 1200Wh/mi within the first mile, depending on slight driving changes, and yet other times be closer to 360Wh/mi for that same 1 mile. That applies for any statistical metrics: no where near enough averaged data points. In your case, my assumption is, if it was warm enough that you pre-cooled, it was probably warm enough that the A/C was still working hard when you got in and drove that 1 mile. But forget about both of our assumptions, and use a tool meant to give you objective definitive results.

    Cheers!
     
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  14. Richardbankd

    Richardbankd Member

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    @JohnnyG I appreciate the links for TM-Spy app, but I think that goes beyond my technical experience. I feel like I need an electrical engineering degree to understand it. lol. I suck at math... thats why I went to Law School. lol.:confused:;)
     
  15. JohnnyG

    JohnnyG Weee!

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    @Richardbankd - Maybe you and I could work a deal to trade legal services for engineering services, LOL! :p
    Another option might be TeslaFi. I'd suggest giving that a try. I don't know if he's still offering a free trial, but he was at one point. It's way easier to use and understand. It does all kinds of interesting logging and you can set reminders to charge or change charge rates after a long trip, etc. It does all of this via Tesla servers, so no need to connect anything to your car.
     
  16. snd92

    snd92 Member

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    Limited to 72.6 KW? Temperature (K = Kelvin) times power (W = Wattage)

    Or

    72.6 kW = 97.4 hp? That is indeed a slow accelerating car.

    Or

    72.6 kWh denotes value of energy capacity

    Keep your units on track when discussing technical properties ;)
     
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  17. zentage

    zentage Member

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    216 wh/km seems way to high for a normal summer trip at 20celcius.
    I did a 160km roundtrip yesterday at 160wh/km . If I kept on driving like that I wouldve gotten more about 330km out of it.
    And thats in a 60kwh! This was mostly highway speeds at 100km/h.

    I wonder what speeds you've been driving, or if this was alot of small trips with loads of AC usage (although Cooling uses far less energy than heating). Perhaps it wasent a roundtrip? perhaps up a mountainside?

    having less than 10km and used only 60kwh also seems odd to me, since its summer and A/C dosent take up that much energy (around 1-2kwh an hour).

    21' rims with bad fuel index tires can also have a negative impact, decent 19's with good tires is the way to go for best energy usage.
     
  18. u00mem9

    u00mem9 Member

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    THAT, my friend, is why you should accept what JohnnyG has told you and ignore your original analysis. These details have been investigated several times by the forum and revisiting it to assist the non-expert isn't something anyone wants to spend their time doing.
     
  19. Richardbankd

    Richardbankd Member

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    I drive 120-130 KM/hr, But I am also in Vancouver, Canada... So very mountainous terrain.
     
  20. Richardbankd

    Richardbankd Member

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    I will give that a try. Thanks. I might just try to stop trying to understand, and simply accept. :(
     

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