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Efficient home charging

Discussion in 'The UK and Ireland' started by Cwmwd, Nov 27, 2019.

  1. Cwmwd

    Cwmwd Member

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    Now that I'm getting used commuting and topping up every night I got to wondering whether letting the battery drop lower and charging less frequently might be more efficient by making the most of the part before the taper? For example, last night I charged at 28A and topped up the car from 70% to 80% in about an hour and a quarter (about 8.2kW consumed at 97.1% efficiency). Would it charge up any faster by starting at a lower SoC or is that only a thing when using high power DC charging?

    Hypothetically would it be more efficient (in terms of energy and/or time) to let the battery run down to, say, 40% before topping up to 80% every four days or over a weekend? Alternatively, would I be better off going from 45% to 55% each day instead? Obviously, starting at a lower SoC is going to take longer to get up to a "trip" level SoC so this might be impractical in the real world but might be an interesting discussion...
     
  2. tsh2

    tsh2 Member

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    I only see charge starting to tail off from 30A at 95% charge. Are you selecting 28A, or is your charge slow for some other reason?
     
  3. Cwmwd

    Cwmwd Member

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    The charger is fed off a 32A breaker so I'm limiting to 28A 'till I get round to having a 40A one fitted. To be honest I might not as it's doing fine as it is unless I really need that extra 900W in the future...
     
  4. 12Pack

    12Pack ..

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    Theoretically keeping the charge level as near 50% (least amount of plating on the electrodes) as possible, and charge as slowly as possible. But likely no noticeable difference as long as its not within 20% of the extremes.

    I find it easiest just to hook up everyday,so I don't have to think about it. I restrict all the way down to 16A (I have enough time to get to 80%) so that the car's been charging for a while before I leave in the morning. I adjust when I know I'm going on a trip.
     
  5. vitesse

    vitesse Active Member

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    AC charging rates are fairly linear until you get to over 90% when the pack will start to do cell-levelling. The last few percent can take up to an hour longer. It's DC rapid charging (e.g. Supercharging) where the lowest SoC is the fastest, then the rate slows down (tapers).

    Tesla's advice is to AC charge daily and limit to 90%
     
    • Like x 1
  6. Yev000

    Yev000 Active Member

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    Efficiency in this context charge added vs charge used. So if you manage to get that last 3%, that would be 3% earlier finish, however that 3% is normally waste heat, so you can't recover it.

    Home charging @ 11 KW or less SoC basically makes no difference. Meaning you will still get 11 KW at 99%. There is not enough current to damage anything.

    On a 150 KW supercharger - where the charging is controlled by the charger, not the car - you will see a big slow down the more SoC you have. Fastest charge speed is around 5-50 I think - assuming the battery is warm (~40 C). Then falls off and is around domestic speeds 90-100.

    curve.JPG
     
    • Informative x 3
  7. Adopado

    Adopado Active Member

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    That's a very interesting graph and confirms what I had guesstimated. What is the source?
     
  8. Stefanoh

    Stefanoh Member

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    Not to hijack the thread but I’ve a question linked to this subject.

    I have a Pod Point charger at home and when I plug in at say 10pm but set car to scheduled charge from 1am - 8am the Pod-Point app shows my charge as the full time the plug is connected to the car even thoughts scheduled to start as per the time I’ve mentioned above.

    Anyone got any ideas?
     
  9. Tessaract

    Tessaract Member

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    Yes. The car draws current from the charger to maintain climate control, if you happen to leave that on, or a door is not properly closed. ANd perhaps the Pod Point is just built that way, to assume it's charging whenever it's connected to a car.
     
  10. NorfolkMustard

    NorfolkMustard Active Member

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    Hi. I guess you’re using the “schedule” button on the incar battery display page?

    that’s an easily misunderstood setting, because of the way it’s laid out, but only start time OR departure time settings are active at any one time - depending on which tab you leave it on when you close the settings page

    leaving “depart at” active will leave the car to decide its own charge start time, with a goal to reach the current charge level target by 0600 the next morning.
     
  11. Yev000

    Yev000 Active Member

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    I just googled "supercharger graph" and went to pictures.

    Pick your poison
     
  12. Alex987854

    Alex987854 Member

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    Exactly that. Mine does exactly the same thing - read it as connected time rather than charge time.
     
  13. Stefanoh

    Stefanoh Member

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    Ok thank you - I assume my electricity company will only charge me the actual charge time?
     
  14. NorfolkMustard

    NorfolkMustard Active Member

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    They'll charge you for the kWh your main meter says, no different now you have a charger and/or an EV [​IMG]
     

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