EV Charging losses and Vampire drain.

JKenH

Apopros the discussion on efficiency on the EV discussion thread, I was doing a bit more reading around and came across this article from Recurrent which explains how charging efficiency can vary with state of charge. I have downloaded a table from one of the papers quoted showing how, in the SoC range 80-100%, charging rates can double. I am presuming Nick and Grumpy have batteries which Tesla recommends only be charged regularly to 80% and so will experience lower charging losses than those who charge to 100%, which I frequently had to do with the Leaf because of its limited range. The article also explains how ambient temperature affects charging efficiency.

Is your EV battery getting all the energy you pay for?

But is there also a relationship between charge efficiency and SoC? 

Yes - several studies indicate that as SoC increases, not only does the rate of charge decrease, the charging efficiency also decreases, which is more pronounced once above 80% SoC. However, this relationship is also dependent on the power of the charger used. 

One study revealed that charging losses doubled between 80-100% SoC when compared to the losses associated with charging from 20-80% SoC (Kostopoulos, 2019). 

https://www.recurrentauto.com/research/why-doesnt-your-battery-get-all-the-energy-you-pay-for

Grumpy_chap

JKenH said:

I am presuming Nick and Grumpy have batteries which Tesla recommends only be charged regularly to 80% 

Yes, when I collected my car Tesla recommended 90% as the "daily use" charge level then they sent an update that 80% is more appropriate.

michaels

I wonder if losses are a function of time rather than kwh transferred as charging is also much slower when the SOC is higher.

1961Nick

During the cold weather I generally do fewer longer charges to cut down on the number of battery preconditioning sessions. I usually have the SOC set to 90% in winter & use the Tesla recommended 80% SOC in summer. 

Reed_Richards

I charge my car with a granny charger connected via a Tapo P110 that can control the On/Off times and also measure the power drawn.  If the information that I have a 50 kWh battery in my car is accurate then when I checked three times in November my charging efficiency was 90% when charging to around 90% of full battery capacity.  The remaining 10%, which would have been equivalent to about 230 W for the duration of the charge, was heating something, presumably.

Qyburn

Grumpy_chap said:

So, I've been sitting in and playing with all the controls on my car over the past week and the amount of battery charge consumed for everything including whatever would be associated with just sitting there shows as around 6%.  I don't think that's outrageous.  It would be higher if I was doing things like sentry mode or cabin temperature control etc.

As a comparison, with the amount of "playing" I've done, I would have flattened the 12V battery on a regular ICE car.

No real surprise given an IC car's battery is less than 1kWh. You probably have something like 50kWh, in which case you used 3kWh. Another comparison would be how much fuel an IC car would use just ticking over while you played around for how ever many hours that was.

JKenH

There’s quite a bit in this article - just a snippet below.

Electric vehicle charging cable care: what you need to know

She said there are “so many variables” including the efficiency of the charger and the impact of different systems within the car on its energy usage and storage.

“It might not be the cable that’s losing anything at all, it might be what the manufacturer has stated versus what you’re physically able to get.”

Research conducted by German automobile club ADAC last year showed that charging losses vary greatly, depending on how charging is carried out – at home using a domestic AC plug socket, using a wallbox with up to 11kW or with half the power.

It found that charging losses at the household socket are between 10-30%, while charging losses via a wall box are between only 5-10%

It noted that the on-board electronics and some of the vehicle’s control units are active during the entire charging process, and therefore consume electricity.

When charging with AC, the rule of thumb applies, it says. “The higher the charging power, the shorter the charging process and thus the time in which charging loss occurs,” adds ADAC.

EV Cables has done its own research on this issue, and found the power loss increases as the cable gets longer.

https://www.fleetnews.co.uk/features/ev-charging-cable-care-what-you-need-to-know

Grumpy_chap

JKenH said:

EV Cables has done its own research on this issue, and found the power loss increases as the cable gets longer.

Hardly rocket science.  Any school boy physics class would teach you that.

Reed_Richards

Grumpy_chap said:

JKenH said:

EV Cables has done its own research on this issue, and found the power loss increases as the cable gets longer.

Hardly rocket science.  Any school boy physics class would teach you that.

True, but school person physics would also tell you that you can minimise these losses by using thick wires so their resistance per unit length is reduced.  This may be telling you that some manufacturers are keeping their costs down by using the thinnest wires required to achieve the specified charging current instead of thicker wires that reduce running costs for the user.  

JKenH

I bought a 3m cable which was just perfect for supermarket fast chargers (which all were free, as in no cost, in my day). It didn’t drag on the ground and get muddy and was a lot quicker to put away in its bag than the 6m cable which came as standard with the Leaf. It would, though, probably have taken 100 years or more to pay for itself in electricity savings, even at current fast charger prices.