It's not just about converting AC to DC. When you're charging, the car is effectively "on". The electronics are on, the coolant pump is on, the coolant fan might be on, and in extreme cases, the compressor could even be on. You can see some of this consumption via Car Scanner, by viewing the ICCU 12v output amperage & voltage (but not compressor or battery heater, as those are high voltage). If I remember correctly, it can typically be somewhere in the neighborhood of 250-300w (in addition to the conversion losses). That overhead of keeping the car operating while charging can be a much larger percentage when charging at a low rate than at a high rate. On the flip side, you get slightly higher resistance losses at higher currents, but in most cases, probably trivial compared to the operating overhead.

 

My recent charging has been midnight to 6am in a garage in the UK in April and May. Temperature is probably around 8 to 10°C. Should I really expect a 33% inefficiency in these conditions?

 

Very good point. Also, I'm never sure which battery capacity number to use when doing calculations like this. Should you use 77.4kWh or the lower number?

 

I've wondered why most people install a 'home charger'. In the UK they are typically 7 kW so only 3 times faster than a 'granny cable'. If you can get all the daily range you need at 2.2kW why pay for a wall box?
Maybe the answer is the inefficiency of the EV6 and maybe all EVs in converting AC to DC. In my case If I charge the car for 6 hours at 2.2kW AC I 'input' 13.23 kWh (this is based on actual meter reading). This 13.23kWh gains me 12%charge at the car. If we assume the usual quoted figure of a useable 74kWh battery for UK 2024 EV6 this equates to only 8.88kWh. This is 33% less than I'm putting in! I realise there are losses to heat etc. The usual quoted figure is 10%.
So - is the EV6 spectacularly bad at converting AC to DC? What losses do others see when charging with AC? What about the majority of you that charge with DC? Has anyone with a DC home charger ever calculated how may kWh are actually going INTO the DC charger using their electric meter to get 1kWh of charge at the car?
If I get a similar 33% loss at a rapid public charger for which I'd pay 75-85p per kWh in the UK that would work out about twice the cost per mile of a diesel car!

There will always be energy loss when moving electrons (or vibrating them in terms of AC) due to wire thickness, length, material and temp. There will always be loss when transforming AC to DC (heat). Kia has overreacted to keep the ICCU cooled. I find that the fans are running for an L2 charge session even on a mild day 70°F/21°C. Maybe the battery is being heated?

Some folks have graphed their Tesla's charging efficiency (this graph is from a UK owner so similar to you but not sure how the higher kW were obtained). There have been posts about L1 barely charging due to the overhead of the cooling/heating of the ICCU/battery. I only charge at 32A 1-phase 240V(ish)->7.2kW so I don't have any efficiency graphs with varying kW. I do have a monitor on my circuit box and can see more kWh being used than stored. From a charge yesterday to 80%, 26.95kWh used by the charger, 31% added so 23.7kWh ->12.1% loss.

This graph shows lower efficiency at lower kW. What are your end SOC%? I would think that as you get closer to 100%, efficiency would drop.

 

My figures are pretty constant over all SOCs. In this example I went from 62 to 74% SOC. I'm comfortable with an approx 10% charging loss as this is the oft quoted figure. But I'm scratching my head at 33%. I'm not in the 80-100% SOC and I'm not in the extreme ends if any temperature range. My question really is would I get the same in the same conditions if I were charging with a DC charger?

 

Losing 25% while granny charging is pretty normal. 33% is maybe a bit much but I am not surprised.

If you can get by without an EVSE you're entitled not to install one. I really need the 7 kW every now and then to make sure I have enough charge the next day after coming back from a trip. Moreover, I am wary of using the granny for anything other than incidental charging. Too much to go wrong in cabling and sockets. And indeed, charging at 7 kW only gives about 10% losses instead of 30%.

 

33% does seem a tad high, and I can't tell you where it's all going, but there are losses all along the way. Your house wiring will shed some heat due to resistance. And the EVSE cabling. And the cabling in the car. Plus the AC/DC conversion process, not just to charge the battery, but also to provide the 12v that the car is operating on while charging (that 250-300w is before conversion losses). Even the battery is not a lossless storage tank. It heats up while charging, and while discharging. These are all reasons why when the EPA measures EV efficiency, they measure it based power leaving the wall socket, not energy readings based on the battery. But based on their testing, the EV6 is still reasonably efficient.

 

Fast DC chargers are around 94-97% efficient.
All the energy lost in changing AC to DC, running pumps, and powering the charger's electronics gets added to your bill (or raises the cost per kWh).
There's no such thing as a free lunch, not even if you get free charging sometimes.
Then there are users on the vehicle side when rapid DC charging session is ongoing.
But this would be another discussion.

 

For better estimates, you should know the voltage under load (sag under load). No-load and under-load voltage are way different when you're doing the calculations. Voltage drop or sag is directly related to heat loss from wiring resistance.

 

My question was not the newbie 'how come 1kWh in doesn't get me 1kWh out?'. It was 'AS I have measured that my home AC charging is 33% inefficient, could anyone tell me the efficiency of home DC charging please?'. I'd like to know if anyone has measured the kWh they need to put INTO a home DC charger to get 1kWh at the car.

 

This is also consistent with the fact that when charging at 3x the rate, the constant overhead loses would be about 1/3 as much of the total, as a percentage.

 

The Ioniq Guy on YouTube did some testing comparing US 120v vs 240

Your losses match up pretty well to his data.

I think our 800v batteries are also slightly less efficient for low voltage AC than EVs with 400v.

 

It is washout. If you look at losses when 400V architecture is used for propulsion unit inverters to propell vehicle.
400V architecture is less efficient regarding propulsion units efficiency.