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Battery efficiency

Discussion in 'Model 3' started by gbajor, Sep 23, 2019.

  1. gbajor

    gbajor New Member

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    I have a meter thast tells me how many kwh it took to charge my model 3. I find it takes many more kwh to charge than what I get back. For example, the screen tells me I used 40 kwh since last charge, yet it takes over 60 kwh to recharge the battery to the same level I started with. That's only a 66% efficiency. Anyone else have experience with this?
     
  2. bijan

    bijan Member

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    Meter in the car isn't always accurate. I would go off percentage or rated miles added times the size of your battery. Efficiency should be 85% maybe 90%.

    Edit: for example if you added 100 miles on a long range. That would be 100/310 x 75 = 24.2kwh and compare to what your meter says.
     
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  3. Daniel in SD

    Daniel in SD Well-Known Member

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    Any energy used while not in drive is not metered on the display. That's vampire drain (1kWh a day or so), Sentry mode (if you're using it), sitting in the car while in park, opening the door to get something out of the car (surprisingly high drain from that!). It all adds up. Also charging off 120V is much less efficient (mostly because the car draws a few hundred watts whenever it's not sleeping).
     
    • Informative x 1
  4. doghousePVD

    doghousePVD My grandfather’s car

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    Heating or cooling batteries, air conditioning, vampire loads all contribute to efficiency.
     
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  5. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #5 AlanSubie4Life, Sep 23, 2019
    Last edited: Sep 23, 2019
    Basically all answered above:

    - Meter does not count significant vampire and feature drain

    - Even putting that aside, the trip meter in the car will read about 5% (4.7%) lower than the “energy added” screen present during a charge session. (e.g. For AWD, ticking off 100 rated miles will show 23kWh of use, but to add 100 rated miles, the charging screen will show it takes 24.5kWh (you need to switch between miles & % to see it) - note this number on the screen is not wall energy, it is energy added to battery; does not include charging losses.)

    * This is a topic of extended discussion which you can find elsewhere here if you search.

    - Charging efficiency is dependent on your charging power. It is about 93% efficient for 11.5kW charging and closer to 70% efficient for 1.4kW charging (these are approximate numbers). The primary reason for the dependence is the ~250-300W overhead present during charging, though voltage and AC-DC converter efficiency dependence on input/output power (nominally about 95% efficient it appears) may also be minor factors. The 95% AC-DC efficiency quoted probably includes any losses inherent in charging a battery - might be slightly more efficient on a pure watts-out/watts-in basis. Not easy to break out all the losses individually.
     
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  6. jdcollins5

    jdcollins5 Member

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    I have a meter on my charge circuit also. What is your average WH/mile?

    My lifetime average is 238 WH/mile. I am seeing about an 82% efficiency. I am guessing your WH/mile is higher than mine. Also do you use Sentry Mode, Cabin Overheat Protection, etc.? They all consume power not recorded by the car Trip Meter.
     
  7. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #7 AlanSubie4Life, Sep 23, 2019
    Last edited: Sep 23, 2019
    The way the question was posed, the driving efficiency number wouldn't really matter much here. In fact, generally the higher the driving Wh/mi usage, the better the overall battery efficiency (trip meter energy/wall energy) will look (because vampire/feature drain is a less significant (though still significant!) contributor). Of course, that's not a great way to look at the efficiency (lots of ways to define it depending on what you're trying to figure out)...better to look at wall Wh/mi (which will obviously get better the more efficiently you drive). But the OP framed "Battery efficiency" as energy out of the battery as indicated in the car, while driving, relative to what is pulled from the wall, which is a valid measure.

    For sure, as you say, the trip meter does not record all those other sources of drain.
     
  8. ZOMGVTEK

    ZOMGVTEK Member

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    'Merica
    Are you charging off a regular 120V outlet and monitoring it with a kill a watt or similar?

    66% sounds to be in the range of sensibility if that’s the case. 120v charging is very inefficient due to the relatively high power consumption from the car when it’s awake.
     

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