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Charging losses?

  • 24-04-2022 2:59pm
    Registered Users Posts: 803 ✭✭✭


    I seem to be having circa 20% charging losses with my Kia eSoul? Or am I misunderstanding something?

    I finally have a proper charger at home, so overnight I charged it from 47% to 80% (the 80% limit is set in the car itself). That would be a 33% top up, and as the battery capacity is 64 kWh, I'd expect 33% to be 21 kWh.

    The charger reported charging for 26 kWh. 21/26 = 0.807(etc)

    I thought losses should be 10 to 15 percent - why am I getting 20? Or is the charging percentage calculated some other way?

    I will try to calculate the kWh better this time by following the car's "driving log" where it has the distance and kWh/100 km for every "drive" (not sure how it separates "drives" as it does not always reset with a new car start).


  • Registered Users Posts: 11,049 ✭✭✭✭the_amazing_raisin

    There's a few things at play there. So the 64kWh is the gross capacity, but the usable capacity (0-100%) is less than that. So 33% is not 21kWh, it'll be a bit less than that

    The other thing is that battery capacity is a fairly inaccurate process. There's no real way to measure the amount of energy in the battery at any given time. You need to drain the battery down to empty, take that as 0% and then charge to full and take that as 100%.

    That's how they calibrate the battery in the factory. From then on the car estimates the percentage based on the energy added or consumed from the battery

    The estimate can get inaccurate over time so you can calibrate the battery by driving until the car is basically out of power and then charging up to full. It's a fairly long and tedious process because you end up driving in circles around a charger to use up tbr last bit of charge. Also if you get it wrong you'll be calling a tow truck

    Finally, there's inaccuracies in measuring the energy going into and out of the battery. I think most EVs measure the current into the battery AFTER it's converted from AC to DC. In other words the conversion losses won't be counted. If you put an energy meter on your home charger (or if it's got one built-in) you'll probably see the charger is giving more energy than what's going into the battery. Then of course, you'll need to take the errors in that measurement into account as well

    Long story short, there's a lot of places the calculations can go wrong 😁

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 12,097 ✭✭✭✭KCross

    The state of charge percentage on the dash also isnt linear.... i.e. 100-70% isnt necessarily the same as 70-40%.

    I thought losses should be 10 to 15 percent

    The losses should be less than that... more like 5-10% when charging on AC.

  • Registered Users Posts: 803 ✭✭✭MichaelR

    I am indeed using the energy meter in the charger. So I am indeed looking at total losses.

    But I did now get proof that the dashboard percentage is not linear. After driving for 40 km I saw the charge drop from 80% to 70%, while the average consumption for the drive was very close to 20 kWh/100 km (much but not all of this distance was motorway so the value is kinda normal). This means that the 10% drop corresponded to 8 kWh, which would be impossible with a linear percentage as the battery is only 64 kWh.

    I don't want to do a full calibration as it can wear out the battery. I'm even avoiding 100% charges unless a road trip is expected.

  • Moderators, Sports Moderators Posts: 18,814 Mod ✭✭✭✭slave1

    Eliminate the energy meter, take a typical overnight usage from your meter box and then one where you charge the car and see does it “add up”

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  • Registered Users Posts: 12,097 ✭✭✭✭KCross

    I don't want to do a full calibration as it can wear out the battery. I'm even avoiding 100% charges unless a road trip is expected

    Not unless you are doing it constantly or leaving it at 100% for days/weeks. A test for one night where it spends a few hours at 100% won’t have any affect at all.

    Note: 100% isn’t really 100%. The car manufacturer hides capacity from you so you can’t damage the battery.

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  • Registered Users Posts: 803 ✭✭✭MichaelR

    So I did a different estimate. Not a full calibration as I did not drive it to 0%. But the car got charged to 100%, followed by a road trip that left it at 30%, then it was charged to 100% again. This most recent charge pumped in 51.75 kWh, according to the meter in the charger. (I don't have a good estimate of typical night usage, so using the house meter was not really an option)

    The road trip took 46.66 kWh according to the "fuel economy history" (it shows the distance and the kWh/100 km consumed, so that's trivial math).

    The charging losses work out at 10%, a value many articles claim as rather good for AC charging.