Battery capacity / Charging / Daily electricity usage

[EricBayArea]

I'm still learning a lot about the world of electric cars, volts, amps, watts, etc., so bare with me...

From my reading here, the car can use approximately 21kWh from 100% to dead-ish.

Assuming the above is true and I didn't use a single drop of electricity at my home that entire day outside of charging my car, would my daily usage (as observed by my online SmartMeter info) show 21kWh of usage? Or, in order to absorb 21kWh into the traction battery, it actually will draw more - like 22/23/24/etc.?

The reason I ask is because on days I don't charge (yes, I sometimes charge every other or every two days) I typically use between 5 and 7 kWh. Add to that the charging of the car to 80% on most charging events and to 100% once a week or so, I'm seeing higher kWh readings from the SmartMeter than I'd expect the car is taking in: One day has about 29 kWh and another has 36 kWh.

I'm trying to understand if the electricity usage is actually more than the amount taken in by the battery. This way it helps me to explain my energy usage a little better.

Additional thoughts... If electricity is wasted during charging, is a higher percentage of electricity wasted when charging from 80% to 100% than from <80% to 80%?

 

[waitingforaleaf]

From Dave's post (http://www.mynissanleaf.com/viewtopic.php?f=4&t=3625&p=145354#p145354),

yes. the power from the wall does not match the rating of the charger due to efficiency rating and active cooling overhead.

charging at;
A; 240 volt 16 amp = 85%
B; 240 volt 12 amp = 83.3%
C; 120 volt 12 amp = 75%

if you take the top figure 85% which btw is 3.3/3.84 that is why the charger is rated as such.

I've also read elsewhere that some people indicate that they've gotten near 90% efficiency, but based on the maximum pull from a Coulomb Chargepoint EVSE I got while plugged in, I'd say that 85% efficiency looks to be more accurate.

 

[EricBayArea]

Interesting, thanks. FWIW I am using a Blink charger at home.

So can I calculate an average of 85% efficiency this way:

20kWh (into the pack) / 0.85 (85% efficiency) = 23.59kWh used?

If I'm only charging 10Kwh into the pack then I would see (10 / 0.85) 11.76kWh used.

 

[waitingforaleaf]

Shouldn't it be

(kWh into the battery pack) / 0.85 = kwh used

or inversely

kWh used * 0.85 = kWh into the battery pack

?

 

[waitingforaleaf]

Oh I also forgot to add that the Blink charger itself has a phantom draw by just being plugged in and on. Think it was 7 watts with the screen off. So, about 5 kWH a month just being plugged in.

 

[EricBayArea]

Shouldn't it be

(kWh into the battery pack) / 0.85 = kwh used

Thanks for setting me straight. So...

20kWh (into the pack) / .85 = 23.59kWh used

Oh I also forgot to add that the Blink charger itself has a phantom draw by just being plugged in and on. Think it was 7 watts with the screen off. So, about 5 kWH a month just being plugged in.

Really? Wow that seems high. Makes me almost want to unplug it when I'm not using it.

 

[TonyWilliams]

Interesting, thanks. FWIW I am using a Blink charger at home.

So can I calculate an average of 85% efficiency this way:

20kWh (into the pack) * 1.15 (85% efficiency) = 23.59kWh used?

If I'm only charging 10Kwh into the pack then I would see (10 * 1.15) 11.5kWh used?

I'm not really following your angle here.

You burned up 20kWh (and were no doubt in Very Low Battery!!), and now you want to know how much power that you're going to PAY for from the grid?

Sure, your 23.59kWh number multiplied by whatever your cost you have per kWh is the dollar amount of that trip.

The 11.5 number "used" means drawn from the grid to put 10kWh into the battery? If so, then of course, at 85% charger efficiency, that makes sense.

 

[EricBayArea]

I'm not really following your angle here.

You burned up 20kWh (and were no doubt in Very Low Battery!!), and now you want to know how much power that you're going to PAY for from the grid?

Sure, your 23.59kWh number multiplied by whatever your cost you have per kWh is the dollar amount of that trip.

The 11.5 number "used" means drawn from the grid to put 10kWh into the battery? If so, then of course, at 85% charger efficiency, that makes sense.

You followed my angle perfectly. I was looking for the amount of power I'm pulling from the grid for any given charge. The 20kWh and the 10kWh into the pack were just examples.

 

[abasile]

Additional thoughts... If electricity is wasted during charging, is a higher percentage of electricity wasted when charging from 80% to 100% than from <80% to 80%?

Yes, though I don't know if anyone has really quantified this. Close to 100%, charging tapers off, meaning that the charge rate decreases. We already know that L2 charging is more efficient than L1 charging, since at a lower charge rate, a greater percentage of input power is consumed by overhead. In addition, as the SOC approaches 100%, the battery itself becomes less efficient at accepting charge, resulting in heat generation.

 

[JasonMurray]

From Dave's post (http://www.mynissanleaf.com/viewtopic.php?f=4&t=3625&p=145354#p145354),

yes. the power from the wall does not match the rating of the charger due to efficiency rating and active cooling overhead.

charging at;
A; 240 volt 16 amp = 85%
B; 240 volt 12 amp = 83.3%
C; 120 volt 12 amp = 75%

if you take the top figure 85% which btw is 3.3/3.84 that is why the charger is rated as such.

I've also read elsewhere that some people indicate that they've gotten near 90% efficiency, but based on the maximum pull from a Coulomb Chargepoint EVSE I got while plugged in, I'd say that 85% efficiency looks to be more accurate.

Thank you for sharing the link bro! It was useful... I just got my first electric car and I'm still studying its proper way of charging it.