Charging (In)Efficiency

  • Thread starter Thread starter JZ99
  • Start date Start date
  • Replies Replies 142
  • Views Views 13K
chrunck said:
Sure, you charged 14% of the battery (66% - 52%), and it used 4 kWh of juice. 14% of the total battery is 4.046 (0.14 x 28.9). The efficiency is 4.046 / 4 = 101% efficiency. Your house is magic!
Click to expand...

Public outdoor charging station, maybe the super cold air caused superconducting :D:D

JZ99 said:
Hey, I'm in Twin Cities too (Victoria). How's your mileage in these sub-zero conditions? Yesterday, my wife got a whopping 2 miles/kWh (1.3 measured at the wall).
Click to expand...

My 40-mile trip this morning in -13 ºF weather came out to 3.11 mi/kWh for a total calculated range of 89.83 (using @GvilleGuy's MINI EV Range shortcut). On days like this I add about 10% SoC during the day to make it home since my total trip is 80-85 miles.
 
teslarati97 said:
120V 8 amps to 240V 10 amps seems to be 13.08% difference. You can see reduced EV losses at 70A but the Cooper SE is only going to take ~32A max (7.4kW / 240V).
https://www.sciencedirect.com/science/article/pii/S0360544217303730

View attachment 14945
Click to expand...

This is pretty interesting. Charging efficiency is lowest for long low voltage charge events. This is the opposite of my prior. The reason is that the charger is operating well outside of it's design target, for a long time.
 
Here's my level 2 charge session at home overnight (inside unheated garage, Grizzl-E Classic set to 32 A output), I'm showing 86% efficiency: (1.00 - 0.23) * 28.9 / 26 = 0.85588.

level2home.webp
 
JZ99 said:
This is pretty interesting. Charging efficiency is lowest for long low voltage charge events. This is the opposite of my prior. The reason is that the charger is operating well outside of it's design target, for a long time.
Click to expand...

I don't know exactly the number for fixed losses for EVSEs, but let's say 0.300 kilowatts for easy math. DC fast charging would probably be 0.15kWh for 30 minutes, Level 2 7kW would be ~1.2kWh for 4 hours and Level 1 could be 7.2kWh for 24 hours of charging. It's probably much lower!
 
I have the Chargepoint Home Flex level 2 EVSE. I selected charging sessions where I used at least 20 kWh. I included some hot summer months along with recent cooler ones in South Carolina. I wish the Mini app could show a more precise value on kWh used.

Battery Charge Efficiency.webp
 
GvilleGuy said:
I have the Chargepoint Home Flex level 2 EVSE. I selected charging sessions where I used at least 20 kWh. I included some hot summer months along with recent cooler ones in South Carolina. I wish the Mini app could show a more precise value on kWh used.

View attachment 14947
Click to expand...

Since those were all going to 100%, did you have cabin preconditioning on? If that power usage is included you'd be understating your actual efficiency
 
Carsten Haase said:
Since those were all going to 100%, did you have cabin preconditioning on? If that power usage is included you'd be understating your actual efficiency
Click to expand...

No - that was just plugging the car in to charge overnight and walking away. And no departure stuff scheduled, either. I rarely do that. Is that what you meant?
 
Last edited:
GvilleGuy said:
No - that was just plugging the car in to charge overnight and walking away. And no departure stuff scheduled, either. I rarely do that. Is that was you meant?
Click to expand...

Yep the precondition for departure what what I was asking about. Seems weird to me that there is such a huge variation in efficiency. My thought was that there was something else using some of the power but if not the HVAC compressor I'm not sure what else it could be.
 
Puppethead said:
My electricity company offers off-peak rate of $0.04/kWh for EV charging. Totally worth adding a second meter.
Click to expand...
It's like $0.36 USD/kWh in Germany and $7 USD/gal. In the UK it's about $0.284 USD/kWh and $7.5 USD/gal plus BIK taxable benefits for company cars.
 
chrunck said:
I just calculated the charging efficiency on a few trips (I looked at the longest charges in my history) and show 60-66% efficiency. Anyone want to loan me a L2 charger to do a comparison? :p

The house itself is old, but I ran all the wiring to the detached garage a couple years ago so it's all new wire back to the main panel. The previous owners upgraded to 200A service, and I installed a 60A subpanel in the garage. It's only about 30 feet between the main panel and the garage so I wouldn't think line loss would be that bad.
Click to expand...

There's a really interesting article at https://chargedevs.com/features/a-c...harging-losses-from-the-breaker-to-ev-part-1/

While every home is built differently (different gauge wire and wire lengths), a 3% voltage drop tolerance could mean line losses of Level 1 81W range while a Level 2 40A could top out at 288W. This is on the extreme side, but the Smart EVSEs and the MINI app won't factor in the line loss. As for auxiliary and parasitic losses for the coolant circulation pump and heat exchanger fan, the article cites a "few hundred watts". Maybe my 300 watt estimate was actually not too far off, but I'd imagine it the load would cycle on and off.
 
There seems to be discrepancies between MINI app and ChargePoint home-flex app on how much juice was used to charge 87% of battery.

Per MINI app ~ 31 kWh used => 81% efficiency: (1.00 - 0.13) * 28.9 / 31 = 0.8110

Per ChargePoint app 29.06 kWh used => 86% efficiency: (1.00 - 0.13) * 28.9 / 29.06 = 0.8652

Not sure which one to trust [emoji848]
 
e22mini said:
There seems to be discrepancies between MINI app and ChargePoint home-flex app on how much juice was used to charge 87% of battery.

Per MINI app ~ 31 kWh used => 81% efficiency: (1.00 - 0.13) * 28.9 / 31 = 0.8110

Per ChargePoint app 29.06 kWh used => 86% efficiency: (1.00 - 0.13) * 28.9 / 29.06 = 0.8652

Not sure which one to trust [emoji848]
Click to expand...

I noticed that in my Chargepoint app, as well. The kWh values differed from Mini app by a bit.
 
GvilleGuy said:
I noticed that in my Chargepoint app, as well. The kWh values differed from Mini app by a bit.
Click to expand...

The smart EVSE might not have a revenue grade consumption tracker (less than +/- 0.5% accuracy). You could alternatively put trackers on your main panel and then you can monitor each breaker.
 
I was inspired to make my own spreadsheet to track charging sessions. My estimated $$ is $0.125 per kWh.

upload_2022-1-20_21-3-36.webp


Note that the charging on the 1st was at Electrify America. All others were at home using a Grizzl-E at 24A on a 30A 240V circuit.

Rob
 
teslarati97 said:
The smart EVSE might not have a revenue grade consumption tracker (less than +/- 0.5% accuracy). You could alternatively put trackers on your main panel and then you can monitor each breaker.
Click to expand...

When I started this study, I thought the app reported numbers must be wrong, since my calculated efficiency numbers were so bad. So I purchased a watt meter with a claimed accuracy of around 1%. It's reported kWh values are consistent with the app reported numbers, although it is higher resolution than the app, which rounds to the nearest kWh, which is kind of not-great, especially for short charges. For a one kWh charge, the Mini app has a precision of +/- 50%!
 
Last edited:
Teddydogno1 said:
I was inspired to make my own spreadsheet to track charging sessions. My estimated $$ is $0.125 per kWh.

View attachment 14949

Note that the charging on the 1st was at Electrify America. All others were at home using a Grizzl-E at 24A on a 30A 240V circuit.

Rob
Click to expand...

Thank you for posting.

What was the charge method at Electrify America? L2 or L3? Charge rate? I'm wondering why the efficiency is higher. It must be DC.
 
JZ99 said:
Thank you for posting.

What was the charge method at Electrify America? L2 or L3? Charge rate? I'm wondering why the efficiency is higher. It must be DC.
Click to expand...

Yes. It was DC fast charging. I think the peak I saw was 47 kW (50 kW max theoretical for the Mini). I posted the charging session afterwards.

Rob
 
You must log in or register to reply here.
Back
Top