What's the charging efficiency?

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jgc

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Feb 20, 2019
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3
I've looked around this board, and elsewhere, but can't seem to find an answer to what I hope is a simple question.
My LEAF is 40kWh ... but I don't know how much electricity it takes to charge it up to 40kWh. Is a bit more (say 45kWh) or a lot more (60kWh) or even more? I guess this will be different between different PVSE systems in different countries; ideally I'd want to know it for the UK for typical home charging pods (6kW in my case).

I'm interested to know this so I can more precisely understand what my 'fuel' costs are.
 
jgc said:
I've looked around this board, and elsewhere, but can't seem to find an answer to what I hope is a simple question.
My LEAF is 40kWh ... but I don't know how much electricity it takes to charge it up to 40kWh. Is a bit more (say 45kWh) or a lot more (60kWh) or even more? I guess this will be different between different PVSE systems in different countries; ideally I'd want to know it for the UK for typical home charging pods (6kW in my case).

I'm interested to know this so I can more precisely understand what my 'fuel' costs are.

Efficiency of charging is near to 85 percent. So if the battery was actually 40kWh, and it was empty, it would take about 47kWh to charge to full. This isn't realistic for several reasons. The battery is actually somewhat smaller than 40kWh when new. The capacity of the battery changes slightly with temperature. And charging from empty to full should be a very rare event.

Best practice would be to keep the battery from being much below 40% charge, and charging to 100% only when needed, and leaving within an hour or two.
 
Many thanks, @WetEV and @SageBrush. That's good enough for me to go with. I don't have a clean way of telling what my electricity usage is just for the car charging, so want to estimate it from what the car says it's taking in.
 
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=45416&flag=1
Page #6

The EPA metered the amount to charge the car from a SoC of zero to 100% using an L2 charger (~ the same as OP) at 44.8 kWh. Works out to 11% charging losses presuming 40 kWh maximum available

At the bottom of the same page Nissan reported 209 Wh/mile from the battery and 239 Wh/mile from the meter:
1 - (209/239) = 12% charging losses.
 
Or you can calculate that using what's available thru the instruments of the car.
What I did is write down the percentage and miles available before I start trickle charge overnight, which is 1,4 kWh as reported by the car on 120V 15A standard plug using the stock evse on 2018.
Assuming the battery is 40kWh at 100% you can figure out how much it went in at the end of your charging session. For me this is 10 hours(10pm - 8am) , which translates to roughly 30% gain in available charge/ range.
40kWh*0.3 =12 kWh(~45 miles) added in 10 hours and 10*1.4kWh = 14kWh. So used 14kWh to gain 12kWh in the battery, which translates to 85,71 % efficiency.
You might get lower efficiency if you charge on L2 (~7kWh) or QC due to more heat build up in the battery.
Will have to check this once I install L2 at home or record some of the L2 or QC public charging sessions to see what the efficiency would be.
The problem would be the QC since it's not a constant kWh rate and it fluctuates or rather tapers of to prevent overheating of the battery.


If you care about estimated cost of ownership you can download this app:
https://mygreencar.com/

not perfect but I can track my speed/distance and travel times and see how much it would cost me between my virtual cars.

They're still in beta and not sure if available at your Region.
 
I am only getting about 76% efficiency at L1 the way i calculate it.

I have a KwH meter on the plug, so i measure the KwH going out of the plug and into the car that way.

I reset the car's meter and the plug meter at the same time.

Here i'll illustrate my calculation. For 153 miles driven (across multiple charges), the meter reported 61.2 KwH. In the meanwhile the car reported 3.3mi/KwH corresponding to the same 153 miles. So, at 3.3 mi/KwH, simply dividing, the 153 miles = 46.4 KwH. I calculate that the car reported 24% less KwH than the plug [my calc: (61.2-46.4)/61.2 = 24%]. Those numbers are typical for other repeated measurements I've done (tracked for several months), always in the range 23%-25% less reported by car compared to plug.

I keep seeing people report much higher numbers, not sure why mine seem like so much more is lost, unless L1 is that much less efficient than L2. I was using climate control during this time (winter, but in Seattle so not too cold). I assume the 3.3 mi/KwH the car reported included the draw from climate control.
 
tomcon said:
I am only getting about 76% efficiency at L1 the way i calculate it.

I keep seeing people report much higher numbers, not sure why mine seem like so much more is lost, unless L1 is that much less efficient than L2. I was using climate control during this time (winter, but in Seattle so not too cold). I assume the 3.3 mi/KwH the car reported included the draw from climate control.

L2 efficiency is much higher than L1.
 
8leaf said:
... I start trickle charge overnight, which is 1,4 kWh as reported by the car on 120V 15A standard plug using the stock evse on 2018. ... You might get lower efficiency if you charge on L2 ....

Nope, L2 is more efficient because the electricity required to run the water pump and other systems is a smaller percentage of incoming power, and they run for a lot less time than they would with L1 charging.
 
88% or 89% as Sagebrush noted for L2 charging is about right if charging from low SOC to full with 6 kW onboard charger. Efficiency is less at higher SOC because charge rate tapers and cooling pumps/control module power use is constant. Efficiency of L1 charging is much lower, as Nubo noted. If charging from VLBW to full charge, there is significant difference in total energy from the wall at 240 volts using 12-ampere EVSE vs. 30-ampere EVSE with 6 kW onboard charger (higher rate is more efficient).
 
Still, there are advantages to L-1 charging. Aside from not having to install new wiring if you have a good 120 circuit, L-1 charging adds little or even no net heat to the battery, because in many circumstances it seems to radiate the heat away at the same rate L-1 adds it. Not all circumstances, but L-1 is still usually the better choice for lower heat charging.
 
LeftieBiker said:
Still, there are advantages to L-1 charging. Aside from not having to install new wiring if you have a good 120 circuit, L-1 charging adds little or even no net heat to the battery, because in many circumstances it seems to radiate the heat away at the same rate L-1 adds it. Not all circumstances, but L-1 is still usually the better choice for lower heat charging.
6 kW is pretty light. It is ~ equivalent to driving 30 mph
 
SageBrush said:
LeftieBiker said:
Still, there are advantages to L-1 charging. Aside from not having to install new wiring if you have a good 120 circuit, L-1 charging adds little or even no net heat to the battery, because in many circumstances it seems to radiate the heat away at the same rate L-1 adds it. Not all circumstances, but L-1 is still usually the better choice for lower heat charging.
6 kW is pretty light. It is ~ equivalent to driving 30 mph

Put another way, assuming a 24kW pack, it's a 0.25C charge rate. Quite gentle.
 
Nubo said:
SageBrush said:
LeftieBiker said:
Still, there are advantages to L-1 charging. Aside from not having to install new wiring if you have a good 120 circuit, L-1 charging adds little or even no net heat to the battery, because in many circumstances it seems to radiate the heat away at the same rate L-1 adds it. Not all circumstances, but L-1 is still usually the better choice for lower heat charging.
6 kW is pretty light. It is ~ equivalent to driving 30 mph

Put another way, assuming a 24kW pack, it's a 0.25C charge rate. Quite gentle.

I'm not saying that L-2 charging is harsh, just that it seems to usually result in a net gain of heat for the pack.
 
LeftieBiker said:
Nubo said:
SageBrush said:
6 kW is pretty light. It is ~ equivalent to driving 30 mph

Put another way, assuming a 24kW pack, it's a 0.25C charge rate. Quite gentle.

I'm not saying that L-2 charging is harsh, just that it seems to usually result in a net gain of heat for the pack.

Assuming 6.6 kW for L-2:

I = 6.6 kW / 360 = 18.3 amps (ideally)

P (battery dissipation) = I^2 X R (battery resistance) = 18.3 ^2 X 60 mohms (.06) = 20 watts (fairly cool on the touch)
 
lorenfb said:
Assuming 6.6 kW for L-2:

I = 6.6 kW / 360 = 18.3 amps (ideally)

P (battery dissipation) = I^2 X R (battery resistance) = 18.3 ^2 X 60 mohms (.06) = 20 watts (fairly cool on the touch)
Yes, and presuming a 4 hour charge, 80 Wh of heat into the pack mass. I've looked it up before but have forgotten -- what is the specific heat capacity of the pack ?
 
SageBrush said:
lorenfb said:
Assuming 6.6 kW for L-2:

I = 6.6 kW / 360 = 18.3 amps (ideally)

P (battery dissipation) = I^2 X R (battery resistance) = 18.3 ^2 X 60 mohms (.06) = 20 watts (fairly cool on the touch)
Yes, and presuming a 4 hour charge, 80 Wh of heat into the pack mass. I've looked it up before but have forgotten -- what is the specific heat capacity of the pack ?

Very negligible temp rise, most likely within the accuracy of measurement.
 
jgc said:
I've looked around this board, and elsewhere, but can't seem to find an answer to what I hope is a simple question.
My LEAF is 40kWh ... but I don't know how much electricity it takes to charge it up to 40kWh. Is a bit more (say 45kWh) or a lot more (60kWh) or even more? I guess this will be different between different PVSE systems in different countries; ideally I'd want to know it for the UK for typical home charging pods (6kW in my case).

I'm interested to know this so I can more precisely understand what my 'fuel' costs are.

Charging efficiency is based on the speed of the charge. Speaking only on charge to the pack, QC's run 95-96%.

L2 depends on the speed because of overhead used by BMS and cooling system (only cools charger BTW) so the faster the charge, the higher the efficiency simply because less of the power from the wall is used to run the BMS (100% of the time) fans (very rarely) or water circulation pump (variable speed but runs prob 80-90% of the time)

At 6.6 KW, you are looking at prob 91-92%. I am running at 5.8 KW due to limitations of my 50 year old breaker panel and getting roughly 88-89%. The bottom end is level 1 or 120 volts @ 12 amps which runs 75% efficient (yeah one kwh lost for every 3 stored.)

NOTE; All numbers above determined by metered power output from the wall and the miles/kwh reading from the dash. QC figures based on LEAF Spy power meter verses "billed" kwh from public charging provider.
 
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