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Charging efficiency

Discussion in 'Model S: Battery & Charging' started by RuiP, Jul 8, 2018.

  1. RuiP

    RuiP Member

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    #1 RuiP, Jul 8, 2018
    Last edited: Jul 8, 2018
    It's a relatively known fact that, when charging any EV, there are losses.
    These:
    • Are mainly related to the efficiency of the car’s onboard inverter in the AC/DC conversion, but can also result from
    • active cooling of the battery during charging. That happens when charging at higher amps and/or for a long time and/or in a hot climate,
    • the cabling from your electrical box to your charger. When charging at 16kW, you can have a ~3% loss (484W loss) on a 50 meter 4.0mm2 cable from the electrical box to your charger
    This means that, for every EV, you pay more energy to your electric utility, than the energy that ends up in your car’s battery.

    The experiment:
    • The hardware:
      • Car: Model S 85D (pre-facelift) with 11kW European onboard charger.
      • Charger: Tesla Mobile Connector, connected to the meter with an 18 meter 4.0mm2 cable run. Therefore, the cable losses are around 0,5%.
      • Meter: Eastron SDM630-Modbus (MID compliant) at the electrical box, double checked with readings from Teslafi.com.
    • The charging:
      • Over 200 home charges, for a total of 4.000 kWh added to the battery.
      • Excluded charges of less than 1 hour.
      • Charged from anything between 1x5A (1-phase) to 3x16A (3-phase).
      • I believe losses to battery cooling were minimized, because ambient temperature was 15 to 20ºC and charging only started several hours after the last daily drive, giving enough time for the battery to cool down.
    • Charging efficiency = Energy added to the battery / Energy measured at the electrical box (and paid to the utility). 100% = no losses.
    Plotted data (+200 charges):
    [​IMG]

    To exclude voltage differences as a possible explanation: data regarding of the charging sessions between 227v and 233v (56 charges):
    [​IMG]
    (same pattern as previous graph)


    Conclusions regarding charging efficiency:
    • The best charging efficiency, of around 89,5%, was obtained at 3x13A (9kW)
    • If you can charge at 3x16A… don’t! You’re wasting energy. Lower to 3x13A.
    • At 1x13A (1-phase), charging efficiency was around 80%.
    Out of curiosity: with an electricity rate of €0,10/kWh, for 25.000 Km/year, the difference of 80% to 89,5% is around €70/year. Not a huge deal, but a figure you can subtract to your ROI of installing a 3-phase outlet in your garage (€700 saved in 10 years + a faster charging rate).

    Summing it up: nothing new, just some measurements of the famous charging losses.

    This other topic, however, is a real doozy!
     

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  2. hacer

    hacer Member

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  3. RuiP

    RuiP Member

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    Thanks for pointing that out but, as you mention on that thread, that one has "no data on the old chargers but others may have." This thread is precisely the data for older pre-facelift cars.

    Posting your data here for comparison, it's also clear that (as most people know), the new cars have a better charge efficiency.
    While my 85D struggles to get to 90% charge efficiency, your 75D can easily get to over 96%:

     
  4. hacer

    hacer Member

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    If you look over that whole thread (or maybe it was another one), @wk057 did the same thing for the older (US) chargers; he concluded the peak efficiency was at max current (40A @ 240V). I don't remember what the peak efficiency was, but it wasn't as good as the new chargers. Your data may be the first shown for the European chargers.
     
  5. Drezla

    Drezla New Member

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    Jul 2, 2018
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    Durham
    folks...I'm a newbie here and looking for basic info that I've not been able to find so far; bought a 2013 P85+ 3 weeks ago after canceling my 3 reservation; LOVE the car! Was driving a Leaf for 6 years, so I was stoked about getting 265 miles/charge; it's hot here in NC, so AC is used sometimes, but I try not to and I'm aware of how this car easily drives (incredible pick up!); best I've been able to get on a single charge is 113 miles; my settings are correct; I'm the 2nd owner and bought it w/ 42K miles; also, I'm using the converter when I use my "Leaf" charger; noticed I'm getting 25 miles/hour on the charge vs. 48 miles/hour using a Tesla charger (hotel based)...any input on this 2 parter is appreciated...
     

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