Charging inaccuracy when charging to 80%?

[YaR]

Yesterday I charged the car from 30-80% using an Egg/PhoenixWorks charger at work. No apparent issues. The car said it stopped charging at 80%, about 45mins before I disconnected it, and the meter said 80%. It wasn't charging when I got to it as neither the charge light on the car nor the charging point was on, and I could just unplug the cable without needing to stop anything in either app. However I managed to drive a good 15 miles before the charge dropped from 80% to 79% and the estimated mileage changed. Looking at my bill it says I put in 35.37kwh - so clearly more than 50% of the battery capacity.

So why did it charge beyond the set limit and not indicate this on the range/battery display?

 

[JonnyG]

I can only think that there were losses between the charger unit and car which is quite normal I believe ? If the car stoppped at 80% at least it did as it was told !!

Losses During EV Battery Charging | Improve EV Battery Life | iCompario

Understanding losses during EV battery charging can help you maximise EV battery life. Learn about where this energy goes to make the most of your fleet.

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[YaR]

That doesn't explain why it took 15 miles of driving for the battery indicator to go from 80-79% though. At current miles/kwh that's about 4kwh which coincidentally is about what the bill says I put in over the selected charge...

 

[siteguru]

50% of 61.7kWh is 30.85kWh. If you were charged for 35.37kWh then that would give an efficiency of 87.2%. Was this a 7kW charge point? (That efficiency is slightly low but within reasonable margins for a 7kW charge point).

As to why the drop from 80% to 79% seemed to take some time .... ?‍

 

[YaR]

50% of 61.7kWh is 30.85kWh. If you were charged for 35.37kWh then that would give an efficiency of 87.2%. Was this a 7kW charge point? (That efficiency is slightly low but within reasonable margins for a 7kW charge point).

As to why the drop from 80% to 79% seemed to take some time .... ?‍

7kw charge point, but 6.54kwh in real terms as per the car's app and as expected - but that's 93% efficiency assuming 7kw actual.

 

[siteguru]

A 7kW charge point may actually deliver 7.36kW ... 32A x 230V = 7.36kW. So that would be 88.8% efficiency. Plus the charge rate isn't uniform - it fluctuates. So I think the stored charge vs delivered charge is about right.

But I can't account for the latter issue.

 

[fnegroni]

When was the last time the battery pack was balanced at 100%?
Do you ever take it to below 10% and then charge to 100%

 

[YaR]

When was the last time the battery pack was balanced at 100%?
Do you ever take it to below 10% and then charge to 100%

Around the 20th December it was charged from about 15% to 100% to allow balancing. The charge above was the first since then.

 

[JonnyG]

That doesn't explain why it took 15 miles of driving for the battery indicator to go from 80-79% though. At current miles/kwh that's about 4kwh which coincidentally is about what the bill says I put in over the selected charge...

Surely thats good then ? you should be pleased either way ? (i.e (i) the extra range or (ii) you got what you paid for ??) plus (iii) the car stopped the charge at the set 80%.

 

[Martinonline]

My Trophy gains 1% after charging when I go, mainly downhill, to the supermarket and its range increases as the battery warms. That could account for some of your extra distance.

 

[YaR]

Surely thats good then ? you should be pleased either way ? (i.e (i) the extra range or (ii) you got what you paid for ??) plus (iii) the car stopped the charge at the set 80%.

I don't believe in infinite energy

 

[YaR]

My Trophy gains 1% after charging when I go, mainly downhill, to the supermarket and its range increases as the battery warms. That could account for some of your extra distance.

The most plausible explanation is that the battery charged beyond 80% but the display did not update hence the 'free' miles. This is bad if the state of charge readings aren't accurate...

 

[Vingnut]

The SOC reading is normaly not accurate on the MG4 (nor many other EVs).
It should be correct at 100% and 0% soc (if balanced) the rest goes like this: 100-90% have more energy than 90-80% wich have more energy than 80-70% and so on.

 

[tsedge]

The SOC reading is normaly not accurate on the MG4 (nor many other EVs).
It should be correct at 100% and 0% soc (if balanced) the rest goes like this: 100-90% have more energy than 90-80% wich have more energy than 80-70% and so on.

I agree this is the case - but I don't see why manufacturers can't correct for this?