EV Charging losses and Vampire drain.

JKenH

This topic was touched on in a recent exchange on the BEV thread but I felt it would be worthwhile having a separate thread as other issues were overshadowing it. 

When I first got an EV I didn’t have a wall charger and just used a granny plug (230v, 2.3kW I think) and never took much notice of charging cost. I would just look at the miles/kWh (mpk) shown on the car display and assume that if I was getting 4.0 mpk and my electricity cost 16p/kWh then it was costing me 4p per mile to fuel my Leaf. It was only when I got my Zappi charger and compared the kWh “added” with the battery kWh shown by the LeafSpy app that I saw there was a discrepancy. What I also found was the discrepancy was not consistent but was around 10%. (I did later try Leaf Spy with the granny charger and think I was seeing around 1.8kW but I will check next time I granny charge.)

This obviously has implications both in terms of cost of running the car and the CO2 cost per mile. 

I would assume that what the  Zappi shows as “added” is what I pay for at the meter (when I am charging from the grid) as the AC to DC conversion is done on the car. However I don’t know if this is the case when I charge the car at a Rapid (DC) charger although one of the videos I will post suggests that I am paying for the kWh that reaches the battery and the owner of the charger absorbs the AC/DC conversion loss. If anyone knows whether this holds for all Rapids please let me know. 

Something else to also bear in mind is that while the car is charging other functions may be operating (e.g. to manage the charging process or heat/cool the battery). If you are sitting in the car then some of what is coming from the charger may be driving the HVAC to maintain an adequate cabin temperature. 

From what I have read so far there is no one right answer for the % of charging losses as it will vary from car to car, with one type of charger to another, ambient weather conditions, temperature of the battery pack and no doubt several other factors I haven’t thought of. From what I have seen so far it can vary from 5% to 40%.

I should add it is quite likely that there may be a significant bias towards Tesla experiences in this thread as many Tesla owners are enthusiasts who want to know and share what is going on and of course there is far more Tesla material on the internet than for any other EV. 

As with many issues, personal experience will vary and I hope people will share their own experiences or any other third party comments so we see a broad range of opinion. At the same time I hope we can respect any other experiences reported as being genuine even if they don’t accord with our own. 

Edit 14 May 2022. I have extended the title of the thread to include Vampire drain whether it exists or not. 

JKenH

Charging loss on Tesla Model 3 on AC and DC

Here is a YouTube video from Bjorn Nyland which contains the following table. Please see the video for explanation of the difference between the two 50kW results.

The result with the 2.3kW charger is better on the Tesla than I recall on my Leaf. Either the Tesla is more efficient at AC/DC conversion or I need to check my LeafSpy results again.

https://youtu.be/iLmIIe9N_aI

JKenH

EVs Explained: Charging Losses

When adding energy to an EV's battery pack, more is expended than what makes it into the pack. How much varies considerably depending on the electrical output and ambient conditions.

Using the 2021 Tesla Model Y as an example, Tesla's own data—buried deep in 49 pages of certification documents filed with the EPA—shows it took 87.868 kWh to add 77.702 kWh to the battery of the Long Range version. That's a 13 percent overage. For the Model Y Performance version, adding 81.052 kWh to the battery required 92.213 kWh, or 14 percent more.

Worth noting: those sessions used 240-volt Level 2 charging equipment, but took batteries from zero percent to a 100 percent state of charge, which is more challenging for a battery than typical use. 

Our long-term 2019 Tesla Model 3 Long Range Dual Motor test car is currently averaging 95 percent efficiency from a Level 2 Tesla 240-volt wall connector. Staffers charging at home using a typical 120-volt wall outlet saw efficiency of, at best, 85 percent, and it dropped to as little as 60 percent in very cold weather, when charging the battery requires expending significant energy to keep it warm.

https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/

JKenH

Bjorn Verifies, Debunks ADAC’s Claimed Tesla Model 3 Charging Loss

https://insideevs.com/news/456957/bjorn-nyland-charging-loss-video/
Please read the article/watch the video for Bjorn Nyland’s take on the ADAC report on charging losses
 In the comments below the article was the following Tesla owners comments on his own experiences.

Perhaps some real world data would be of interest here. 
I own a Tesla model 3, dual motor, long range. Since April 2019 I 
have charged it 130 times collecting statistics from every charge. I 
have a separate kWh meter connected to my Tesla Wall connector. The 
first 8 months I charged it outdoors the rest indoors, except on the to 
long trips I have made. Outdoor temperatures while charging has varied 
between -2 C and 25 C. Indoor temperature never goes below 15 C. On 
average I start charging the car when it is at 30% and charge it to 79% 
except on long trips where I charge to 98%. 
I have charged the car 2 times in Tesla SuperChargers during a summer
trip and 4 times during a winter trip. And also 4 times in destination 
chargers (11kW). 
The average charging efficiency during these 130 cycles is 76%. 
Meaning, if I input 100 kWh to the charger the car uses 75 kWh to propel
it forward, on average. The minimum is 56% and the maximum is 97%. The 
higher efficiency (97%) has been achieved when using a Tesla 
Supercharger in the summer, driving immediately after completing the 
charging. The lowest (56%) efficiency was during winter with a long 
stand still and probably several cases of preheating the cabin before 
driving. 
This indicates that the numbers from ADAC are quite accurate at least
compared to my numbers. Another take from this is that the efficiency 
depends on several factors, like temperature, standstill time and 
preheating.

JKenH

Looking back through some notes I made last year (August) I charged my Leaf from 12.1 to 38.2kWh (measured on LeafSpy) so 26.1 kWh added. My Zappi showed 31.66 kWh were supplied by the charger which translates to charging efficiency of 82.4%. Other shorter charges I noted in March and April last year produced efficiencies of 88.7%, 86.5%, 83.5%, 82.6%, 86.0%, 85.0%, 86.0%, 86.0%, 85.5%, 85.8%, 91.6%, 76.8%. I would say, therefore, that somewhere in the region of 85% is typical for me. As the car was being charged at home the car was switched off and no ancillaries were in use. My car lives and is charged in my well insulated garage so no extremes of temperature are experienced. Please note I don’t record everything that happens with my car but every now and then I will decide to investigate something, hence the charging efficiency figures from March and April. The August figures were recorded as part of an exercise monitoring the indicated % state of charge on the car dashboard against % indicated by LeafSpy. Also for what it is worth there was a period during lockdown where the car stood for 12 days and the state of charge dropped 3.0% measured both by the car and LeafSpy. The vampire drain is therefore 0.25%  (0.095 kWh) per day.

QrizB

Very interesting thread, thank you.

JKenH said:

Also for what it is worth there was a period during lockdown where the car stood for 12 days and the state of charge dropped 3.0% measured both by the car and LeafSpy. The vampire drain is therefore 0.25%  (0.095 kWh) per day.

95Wh per day is pretty much 4 watts. Mrs QrizB drives an diesel Nemo and the starter battery went flat a couple of times during lockdown; when I investigated that I found there was a 2-3 watt parasitic drain, not that dissimilar to your Leaf. The big difference being that the Qubo has a 12V 60Ah = 0.72kWh battery and 3w for 10 days will flatten it!

matelodave

All batteries have an efficiency loss when charging them, ie you have to put in more that you get out.

Some is due to the charger efficiency and the rest is down to the chemical conversion and heat. Even lead acid batteries need 10% or more put in in that you get out. There's also quite a drain with some cars, the electronic system. alarm systems etc. and batteries, just by their very nature lose power due chemical decomposition over time. If left disconnected from anything and open circuit a battery will slowly lose charge.

Petriix

My experience of the MG5 charged from the Zappi is losses of 15-25%. It's not entirely clear how much usable battery there is because the miles per kWh reported by the car doesn't match with the percentage of the battery used, implying it might be bigger than published. Consequently losses might be lower.

Losses seem to be higher when trickle charging at 6a from the solar. When charging at 7kW it's more like 15% loss. There is also an overhead every time I charge to full and the battery is balanced.

AntonyTewks

Thought I'd experiment. Charged via our solar today with our Solaredge charger, around 1.5-3kw. Took our 40kwh Zoe from 52% to 70%, so about 7.2kwh give or take. Solaredge said it had added 7.11kwh. So doesn't indicate major losses

JKenH

AntonyTewks said:

Thought I'd experiment. Charged via our solar today with our Solaredge charger, around 1.5-3kw. Took our 40kwh Zoe from 52% to 70%, so about 7.2kwh give or take. Solaredge said it had added 7.11kwh. So doesn't indicate major losses

That’s interesting. Thanks for the input.

My Leaf’s battery gauge gets pessimistic the closer it gets to 0% so I tend to rely on LeafSpy to get a more accurate indication of the state of charge and kWh remaining. When I get to zero% on the car’s display I have around 9% or 3.5 kWh remaining. I did discharge the car recently until turtle appeared (and then fully charged) to reset the BMS and at that point 0.2 kWh was remaining. Effectively, with my Leaf, over the whole range from 0 to 100%, every 10% shown by the gauge equates to around 9% in real life. 

Hopefully your battery % gauge in the Zoe is a bit more accurate than in the Leaf I have.

Edit: charging back up when I did the BMS reset from 0.2 kWh to 37.1 kWh (100% on LeafSpy and the car’s gauge) used 43.11 kWh from the grid which equates to 85.6% efficiency.

JKenH

I don’t know if any of you watch this gentleman’s YouTube videos but towards the end of this one he compares the miles/kWh (mpk) shown on his car’s dashboard (4.9mpk) against the miles/energy consumed from the grid recorded by his Zappi charger (3.9mpk.) 

https://youtu.be/wdLA7ydRod4