I was staying in Newcastle and I booked into Jesmond Dene House as they showed electric car charging. I was first a little shocked that they charged £1 per kWh but doubly so when the car reported that I received 47kWh but the charger reported 54. Is this normal? Am I being charged for the electricity being used by the charger with some energy losses? I can imagine the outcry were a petrol station with leaky hoses charge for 50 litres whilst only delivering 40.
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Received 47kWh charged for 54kWh
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SSonnentag
埃隆•馬斯克
They're charging for the amount of electricity they provided. Charging has a bit of heat loss inefficiency. If your heater was on the car doesn't show that power as going into the battery. Depending on the type and age of your car, that could be all the way up to 12kW of power draw (Model X running front and rear resistive heating on high). Other models will draw up to 6kW.
UkNorthampton
TSLA - 12+ startups in 1
Tesla charge for energy received, others for how much goes into the cable at dispenser, possibly how much dispenser used (mains power, cooling, etc).
Perfect, now I fully understand. It certainly makes me appreciate those hotels that do not charge at all for charging.
UkNorthampton
TSLA - 12+ startups in 1
It means that the price charged at a Tesla Supercharger can be even better value compared to other charging networks.
Scan of transcript:
Bjorn's rule of thumb was 10% loss, but he wanted to test it
Sentry mode shouldn't add much as car needs to be awake to control charging.
Slow charging (AC) could be less efficient than DC as computer is higher percentage of usage as car is charging/awake for longer.
He updates table after each test, this might be final one at 13 minutes:-
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WannabeOwner
Well-Known Member
I would go with 10% loss, as @UkNorthampton said, so that would make 47kWh into the battery about 52.2kWh from source - so maybe 54kWh is close-enough ...
I expect you were charging at 7kW or better, to get 47kWh (7-ish hours), but if you were below 7kW the losses would be higher because the car is using, say, 300W being "awake", and that becomes a bigger portion of the charging power the lower you go, especially once you get down to around 5AMPs
MrBadger
Badger out
Using that analogy, it’s more of a leaky fuel tank than hose. Most of the inefficiencies come from the car as that is what is doing the AC/DC conversion and also using other power such as keeping the car awake or, in this weather, possibly even heating the battery to keep it happy whilst charging.
DC charging is a different matter as it’s doing the AC/DC conversion before it gets to the car so really should be metered on the DC side as conversion losses are not under the control of the car owner so more closely matches your analogy. But DC charge metering is a bit of a can of worms.
Let’s say you left it overnight charging for 10h.
300W for sentry for 10h 3kWh.
AC/DC conversion and cable heat losses say 1% = 0.5kWh
Charge point standby current <2.5W over 10h 0.025kWh
Heating the battery (or the cabin in the morning) probably the rest 3.5kW.
You’re not being robbed- you used the electricity one way or another. The numbers above will vary but the principle is there.
300W for sentry for 10h 3kWh.
AC/DC conversion and cable heat losses say 1% = 0.5kWh
Charge point standby current <2.5W over 10h 0.025kWh
Heating the battery (or the cabin in the morning) probably the rest 3.5kW.
You’re not being robbed- you used the electricity one way or another. The numbers above will vary but the principle is there.
Thank you all; I am now much better informed. It was a cold night so it may well have been warming the battery and you are probably not far off with the 3 kWh for overnight sentry. As a final note, Jesmond Dene was full this weekend so I had to stay at a less nice hotel but it offered free EV charging. It was so good being able to not worry about keeping enough energy to make it to the Washington Supercharger on the way back South with the temperatures down to -6C. I am really grateful for your responsiveness and patience in helping me understand what is going on.
