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Efficient home charging

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...
 
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.
 
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%
 
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Yev000

Active Member
May 3, 2019
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Knaphill
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?

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
 

Adopado

Well-Known Member
Aug 19, 2019
5,754
4,363
Scotland
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.

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

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