EV Charging losses and Vampire drain.

JKenH

EVs Don’t Rely Solely on Their Own Efficiency: Onboard Chargers Also Count

Valle presents some interesting numbers in his article. According to them, the VW e-Golf (90.13%), Kia Soul 64 kWh (90.12%), Hyundai Kona (89.9%), and Audi e-tron 55 (89.8%) have some of the most efficient onboard chargers available. 

When you check the numbers for the least efficient chargers, the worst one is that of the BMW i3 120 A, with 80.39%. Surprisingly, the Tesla Model 3 Long Range AWDis the second-worst, with an onboard charger that is just 80.62% efficient, followed closely by the Nissan Leaf e+, with 80.7%.

https://www.autoevolution.com/news/evs-dont-rely-solely-on-their-own-efficiency-onboard-chargers-also-count-167661.html

JKenH

Lucid Air DC Fast Charge Follow Up: Charging Losses Explained

Quite a lot in this article about various types of charging loss. I have though picked out the following comment as it appears to confirm that very few people reporting on EV understand about charging losses and (unknowingly) make misleading statements.

Tesla Superchargers for instance do not have a display. They rely on the vehicle to display the energy received. However, the car only shows the net energy it receives, not the gross.

Therefore, you don't get a full picture of how much energy was dispensed, and it gives the impression that the vehicle is 99% efficient when charging - and that's not the case. The video questioning the capacity used a recent Car and Driver article in which they claimed the Model S was 99% efficient when Supercharging because they evidently don't quite understand EV charging either. This is new to everyone and it's going to take a while before the traditional car review outlets understand the intricacies of electric vehicles as thoroughly as EV-specialist sites like InsideEVs do. 

https://insideevs.com/news/550923/lucid-air-charging-losses-explained/

JKenH

More on the Lucid charging losses.

https://insideevs.com/news/551500/lucid-battery-size-charging-analysis/

JKenH

It was a while since I last completed this exercise but I had done 123 miles in my car yesterday and  a dull day was forecast so it was a good day to do another charging efficiency check. I added 34.72 kWh from my Zappi on Go Faster and LeafSpy showed the charge in the battery had increased by 29.3 kWh- charging efficiency of 84.4%. Or to look at it another way, for each 1 kWh added I drew 1.185 kWh from the grid, around 6.5p/kWh.

Edit: For the record, the car battery gauge was showing 11% when I started and as I have a 40kWh Leaf I could say I added 35.6kWh to the battery from 34.72 kWh drawn from the grid. Now that would be good. Unfortunately I do have LeafSpy so I can’t kid myself. 

JKenH

Rather than start a new thread I have extended the title of this thread to include vampire losses.

I have been away on holiday for a week and took battery readings using LeafSpy before and after. My 40kWh Leaf has lost 0.4kWh over 8 days or around 50wh per day which equates to a drain of around 4 watts per hour. The car had 50% charge and was inside my garage and not plugged in. I believe the car’s HV traction battery tops up the 12v battery so this represents the total electrical drain.

Over a year that’s just 18.25 kWh or £1 on my Octopus GoFaster tariff. I’m quite happy with that and imagine it is comparable if not better than a lot of modern ICE cars. 

I would be pleased to hear other users experience. 

Edit: replaced “the” with “other” in last sentence.

JKenH

I shared this article on the Motoring thread in response to a question as to why an EV’s HV battery loses charge. I am adding it to this thread as logically this is where it belongs.

Will my battery go flat if I leave my EV parked for too long?

https://evcentral.com.au/will-my-battery-go-flat-if-i-leave-my-ev-parked-for-too-long/

JKenH

I have noticed that Green NCAP quote the charging efficiency (measured from a 11kW charger) in their reports as for this Nissan Ariya which is the most efficient at charging of all the cars tested at 91.6%. Most of us charging at home are limited to 7kW or even use a granny charger. Charging efficiency is lower at lower wattages (see the figures from Bjorn Nyland earlier in the thread). There is a search function on the GreenNCAP website to check out other models tested. What isn’t clear, though, is the testing procedure, as other factors such as state of charge and battery temperature can impact charging efficiency. 

Nissan’s Ariya shows a grid-to-battery-output efficiency of 91.6% - the highest measured by Green NCAP so far. This is important as it decreases the amount of energy lost as well as the cost for consumers.
Dr. Aleksandar Damyanov, Green NCAP’s Technical Manager

https://www.greenncap.com/press-releases/volkswagen-t-roc-becomes-the-cleanest-petrol-car-tested/

Edit: For anyone who just read the above and wants to understand more about where the energy is lost, there is a simple explanation in the link below from suppliers of charging equipment, go-e.com.

EV Charging Losses: Where Does The Energy Go?

https://go-e.com/en/magazine/ev-charging-losses#

Edit 2: EVs are far more efficient at converting stored energy into forward motion than ICE cars. These comments on charging efficiency relate solely to the losses occurring during charging which you may or may not want to take into consideration when calculating running costs and comparing different options for charging. 

michaels

When granny charging I calculated miles per kwh using the reading from an energy meter on the plug socket.

JKenH

michaels said:

When granny charging I calculated miles per kwh using the reading from an energy meter on the plug socket.

I always calculate my mpg by dividing the miles covered by the number of gallons of petrol to refill. You just can’t rely on onboard fuel gauges. I am sure manufacturers gear them to overread and I suspect that some (if not all) EV manufacturers do the same. My Golf isn’t too bad, overeading mpg by 4-5% but my wife’s Kia is about 10% optimistic. 

My son in his Leaf arrived at our house, earlier this month, having used 79% of his battery (indicated 97 down to 18) covering 100 miles. The Leaf said it was doing 4.2 mpk. It took 31.6kWh from the Zappi to recharge to 100% (adding 82%) so would have needed about 30.4 kWh to put back the 79% used. 100miles/30.4 = 3.3mpk (compared to the 4.2 reported by the car as being used). 

It is possible the car may still be correct (or within a few%) when it says it has used 4.2mpk which would equate to around 24kWh and the extra 6 kWh may by accounted for by charging losses - around 80% efficiency. 

The only issue is that while the car  may only be using 4.2 mpk then, unless, like you do, you measure the actual energy coming from the plug you may get a false sense of the cost per mile. On a cheap overnight tariff it’s probably only costing a fraction of a penny per mile so neither here nor there compared to running an ICE car but, personally, I don’t like to see the headline mpk figure quoted from the car’s dashboard and then applying this to home charging tariffs. Fair enough if you are topping up at a much more efficient DC charger, it probably does give a reasonable indication of cost per mile but it’s not right to mix the two.

I imagine as this is a money saving forum, many of us do keep accurate records of energy in and energy out but, beyond your comment that you measure your mpk from the plug, I don’t recall many instances (if in fact any) of this basis of calculation being applied. It is more frequently, (not just on here but on many forums), stated that my car reports X mpk and my home tariff is Y pence per kWh so the cost per mile is Y/X without any further adjustment/comment. (And the same sort of thing, of course, happens with ICE drivers reporting running cost based on mpg indicated by the car.)

Bit of a ramble, sorry.

michaels

JKenH said:

michaels said:

When granny charging I calculated miles per kwh using the reading from an energy meter on the plug socket.

I always calculate my mpg by dividing the miles covered by the number of gallons of petrol to refill. You just can’t rely on onboard fuel gauges. I am sure manufacturers gear them to overread and I suspect that some (if not all) EV manufacturers do the same. My Golf isn’t too bad, overeading mpg by 4-5% but my wife’s Kia is about 10% optimistic. 

My son in his Leaf arrived at our house, earlier this month, having used 79% of his battery (indicated 97 down to 18) covering 100 miles. The Leaf said it was doing 4.2 mpk. It took 31.6kWh from the Zappi to recharge to 100% (adding 82%) so would have needed about 30.4 kWh to put back the 79% used. 100miles/30.4 = 3.3mpk (compared to the 4.2 reported by the car as being used). 

It is possible the car may still be correct (or within a few%) when it says it has used 4.2mpk which would equate to around 24kWh and the extra 6 kWh may by accounted for by charging losses - around 80% efficiency. 

The only issue is that while the car  may only be using 4.2 mpk then, unless, like you do, you measure the actual energy coming from the plug you may get a false sense of the cost per mile. On a cheap overnight tariff it’s probably only costing a fraction of a penny per mile so neither here nor there compared to running an ICE car but, personally, I don’t like to see the headline mpk figure quoted from the car’s dashboard and then applying this to home charging tariffs. Fair enough if you are topping up at a much more efficient DC charger, it probably does give a reasonable indication of cost per mile but it’s not right to mix the two.

I imagine as this is a money saving forum, many of us do keep accurate records of energy in and energy out but, beyond your comment that you measure your mpk from the plug, I don’t recall many instances (if in fact any) of this basis of calculation being applied. It is more frequently, (not just on here but on many forums), stated that my car reports X mpk and my home tariff is Y pence per kWh so the cost per mile is Y/X without any further adjustment/comment. (And the same sort of thing, of course, happens with ICE drivers reporting running cost based on mpg indicated by the car.)

Bit of a ramble, sorry.

Or 'proper' charger reports throughput but I don't think it is very accurate (and it is unclear whether it records energy drawn from the grid or sent to the car (it is a DC charger so the conversion losses will be in the charger).  Do you know if your zappi is accurate - could you turn everything else off and compare against your smart meter?