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Stated Battery Capacity / EPA Economy / Mileage Does Not Add Up

Discussion in 'Model 3' started by Colgate2004, Apr 2, 2019.

  1. Colgate2004

    Colgate2004 Member

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    Hi all,

    Since I got my car (Model 3 Long-Range Dual Motor (not Performance)) I've been curious about the math behind the stated range & consumption.

    Tesla says the (long range) battery capacity is 75 kWh.
    They say the range on a full charge is 310 miles.
    If you do that math, 75,000 / 310 = 242 Wh/mi.

    So I've always looked at the consumption figure on the screen and thought if my consumption figure was higher than 242 Wh/mi I was getting worse than stated mileage, if the figure was lower I was getting better than stated mileage.

    Then this afternoon I looked again at the new-car sticker that came with my car, and the EPA figures on it.

    It says a range of 310 miles (cool) and fuel economy of "29 kW-hr per 100 miles," or 290 Wh/mi.

    Well, if the range is 310 miles at an economy of 290 Wh/mi, then the battery capacity would be 310 * 290 =
    89,900 Wh... or 90 kWh, not 75 kWh.
    If the battery is 75 kWh and the economy is 290 Wh/mi then the range is only 259 miles.

    So something is not right there.

    Anybody have any ideas?
     
  2. Colgate2004

    Colgate2004 Member

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    I know that Tesla recommends not de-charging to lower than 10%, and not regularly charging above 90%, meaning that you should only be regularly using 80% of the battery capacity. That shouldn't be relevant to this issue though; both Tesla's and the EPA figures should (?) be based on 100% of the usable battery capacity, which we know from EPA filings is about 78 kWh (with the extra 3 kWh being used as a reserve, yielding the quoted 75 kWh capacity).

    So I'm at a loss to explain this.

    (Perhaps relatedly, I don't believe I've been getting the mileage that my consumption figure would indicate... I believe my actual mileage has been higher than the car's dashboard consumption figure would indicate.)
     
  3. Ejl80

    Ejl80 Supporting Member

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    EPA numbers are based on the electricity going through the wall outlet. In other words charging losses are factored in (about 20%)
     
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  4. Daniel in SD

    Daniel in SD Active Member

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    EPA measures wall-to-wheel efficiency so it takes into account charging losses. The gauge is battery-to-wheel efficiency.
    IMHO the EPA numbers should be much worse than they are since they do not account for idle drain, vampire drain, or climate control.
     
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  5. BobAbooey

    BobAbooey Member

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    You got a window sticker?
     
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  6. M3BlueGeorgia

    M3BlueGeorgia Member

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    Tesla have been pretty careful not to say the LR Model 3 has 75 kWh. Various people have computed this.

    Anyway, when you are actually driving, its the 241 or 242 number that matters.
     
  7. insaneoctane

    insaneoctane Active Member

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    You're original approach is pretty close. The "rated" line in the energy graph does in fact correlate to 240 Wh/mi. Unfortunately, while your logic of expecting if you see a displayed value above this you'll get less milage (and below this you'll get more milage) is sound, it doesn't work out that way. It doesn't work out because the in car displayed Wh/mi value only calculates when driving. So, when you're in park, the energy is being used and not being monitored by the Wh/mi indicator. AC and heat, fans, defroster, etc while in park will remove precious range and you'll never see it in the Wh/mi indicator. It's definitely a shame that Tesla doesn't give us the option to toggle the displayed Wh/mi indicator between drive efficiency (currently the default) and overall efficiency so you could do the mental math you're trying to do....
     
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  8. Colgate2004

    Colgate2004 Member

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    AHHHH...... I see. That makes sense.
    20% charging loss? Ouch! I knew even good quality AC/DC rectifiers weren't very efficient, but 20% loss is more than I thought...
     
  9. AlanSubie4Life

    AlanSubie4Life Active Member

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    It's more like 12%. The EPA number is probably rounded, and you also have to be careful about what driving efficiency was calculated from the actual EPA drive test. I'm not going to try to back calculate it here and pretend that I can say exactly how they came up with the number; the 12% is just what I have seen from trying to measure actual wall-to-wheel efficiency and ASSUMING that the in-car meter is correct - it seems like it might read a few % low, though. So, call it 10% charging losses. And for sure the EPA number includes those losses.

    But this is the least of your worries, you will far exceed that number; expect about 33kWh/100mi, if you live in a nice warm temperate climate like SoCal. In New England, you will hit that 33kWh/100mi in the summer time. Probably 45kWh/100mi in the winter (I have no idea). I'm assuming you drive about 10k per year. You'll do better (on the 33kWh/100mi number) if you drive more.
     
  10. Colgate2004

    Colgate2004 Member

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    LOL. I got a sticker, it just wasn't stuck.

    When my car was delivered my sticker (the standard one which I'm pretty sure every new car sold in the U.S. is required by law to come with?) was sitting, unpeeled from its adhesive backing, on the area behind the rear seats under the rear window. It included all the standard sticker info, including options, pricing, EPA mileage info, gov't safety ratings, location of origin, etc.
     
  11. Daniel in SD

    Daniel in SD Active Member

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    The battery itself is not 100% efficient either, I bet that's a lot of the loss as well.
     
  12. Colgate2004

    Colgate2004 Member

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    Really? Oof. Yeah, I've had the car since the week before Christmas, so it's been cold since I've had the car (average temp since I've had it is definitely below freezing). I think last I looked my lifetime average was about 270 Wh/mi.

    Maybe I drive more grandmotherly than you? :D
     
  13. AlanSubie4Life

    AlanSubie4Life Active Member

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    #13 AlanSubie4Life, Apr 2, 2019
    Last edited: Apr 2, 2019
    Though, oddly, as far as I can tell, the Spark EV has just 6% charging losses. Not sure why it is noticeably better. Presumably something to do with the battery architecture, yes.

    Well, that's pretty good for New England. Of course driving style is part of it (I have 290Wh/mi lifetime in SoCal). The winter use is driven by cabin heating.

    Like I said, your 270Wh/mi, if you had a way to directly measure your car's electricity use, would be more like 330-350Wh/mi if you look at how much power you draw from the wall and divide by how many miles you've driven. But 270Wh/mi driving is pretty good for the winter - assuming you don't do any preheating of course - that's not counted in the number displayed in the car! My actual use (even from a "battery to wheels" perspective) is much higher than 290Wh/mi before accounting for charging losses, because I did often preheat the car in "winter." Makes the numbers look better! ;) My *guess* is my actual lifetime efficiency wall-to-wheel is in excess of 360Wh/mi, and I try to minimize heat use.
     
  14. MrMassTransit

    MrMassTransit Supporting Member

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    I’m impressed you actually got a sticker. I received the same thing, it was just printed on 11x17 paper and laid on the front passenger seat at pickup. I figured that’s what they did for all deliveries.
     
  15. Colgate2004

    Colgate2004 Member

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    That's probably why my numbers are good. I'm a Mainer... cold doesn't bother me, so I never use the heater!
     
  16. Colgate2004

    Colgate2004 Member

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    That sounds exactly like mine... Did you keep it? If you look closely, you'll likely see that that 11x17 piece of paper is actually an 11x17 sticker that still has the backing on it.
     
  17. Ejl80

    Ejl80 Supporting Member

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    I actually had to ask for mine and it was emailed to me haha.

    270 Wh/mi is awesome. This winter I've hovered around 300 and I'm in NJ. I did a lot better in the summer and if I only do highway driving.

    The 20% is a rough estimate. If you take 243 / 290 you come up with about 16.5%. Again, depends on your charger (240V is more efficient than 120V), temperature while charging, etc.
     
  18. novox77

    novox77 1.21 Gigawatts

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    #18 novox77, Apr 2, 2019
    Last edited: Apr 2, 2019
    Ok, I have to question how y'all are driving. I'm in New England, and I commute from NH to Boston. I did 100 miles today round trip for my commute and my car read 195Wh/mi for the trip. Ambient temp was 30F in the morning and 52F in the afternoon. I had the windows cracked on the way home because it was actually hot in the cabin from the sun. Most of my commute is on I-93, half of which is at 65-70mph and the other half in traffic. I rely on EAP heavily for this stretch.

    My efficiency number is only going to drop as the weather outside warms up more. Today, I was still regen limited at the start. In May, this commute will drop to around 165Wh/mi.

    These are readings from the car and doesn't factor charging losses. But I can't imagine how people are over 300Wh/mi. Are you flooring it at every light and going 90mph on the highway? Even my S is slightly below 300Wh/mi this time of year.

    -edit-
    grabbed a photo:

    upload_2019-4-2_20-2-44.png
     
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  19. Nate977p

    Nate977p Member

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    I did not know about the 20% loss on the sticker, great to know!

    I have to say, that 270 Wh/mi is incredible...

    I just got home from a 275-300 mile (I forgot to reset the trip meter until about an hour in) drive today all around Maine (around 95 mostly). I was impressed with my mileage, not nearly as bad as I thought. Only had to have 3 SC stops :)

    And today was a warm day (mostly in the mid 40s for the drive). Started in an underground garage (about 60-65 degrees, so not cold soaked). 20190402_193827.jpg
     
  20. Daniel in SD

    Daniel in SD Active Member

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    Yes.
    Also, AWD, hills, sticky tires.
     

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