Charging efficiency of PIP

I've seen many people provide an "estimate" of a 15% charging loss for the PIP. This number seemed high from my experience, so I decided to do some measurements.

First some definitions:

efficiency = Energy(out)/Energy(in)
charging loss = 1 - efficiency
Energy(out) = number displayed on the EV driving ratio screen in the PIP (this is a bit problematic since the granularity is 1 kwh)
Energy(in) = measured at the wall via a watt-meter, such as a kill-a-watt or watt-ups Pro...or from a commercial charger such as a Charge Point, that keeps a logged report for you. Both provide data with ~1-10 watt-hour level of precision...but it is unlikely that the cheap meters are actually that accurate, but if they are within 10 watt-hours on a ~3000 watt-hour charge that is within 0.3%

Over a week I charged the first 8 times at a 240V L2 ChargePoint at work and used 20.4 kwh, plus one 250 wh charge at home (to make sure I could get back to work on EV that day).
My goal was to make the full 124 miles before the gas engine was forced on, but at about 116 miles I was on a 10-mile-each-way trip and knew I'd need to use gas...so I manually switched to HV at ~55 mph on the low-traffic freeway for 5 miles...then switched back to EV as I exited the freeway. My "EV miles remaining" went from 8.0 to 9.1 so I added some watt-hours that the gas provided...you'll see this tiny amount doesn't make a big difference.

Results:
Charge Point, 240V 20.4 kwh (8 charges)
Home, 120v 8.44 kwh
HV mode: 0.23 kwh (full charge range normally at 13 miles => 2700wh/13 = 207 wh/mile => 230 wh for 1.1 miles)
total: 29.07 kwh
battery SOC: full at 13 miles to start, empty at 0.0 miles at end (I have no scan gauge)

Displayed consumption: 26 kwh for 132 miles of EV (and 0 gal for 5 miles of HV)

efficiency = 26 / 29.07 = 89.4% => charging losses = ~10.6%
Of course the 26 kwh consumed could easily have been at 26.9, ready to click over to 27 which would change the numbers to 26.9 / 29.07 = 92.5%, losses = 7.5% (this is the problem with the granularity of the readouts) But we know that the most realistic number is somewhere within this range.

I went about 2 or 3 miles before I noticed the consumption had rolled over to 27 kwh, so a good guess is ~26.5...or 91% efficiency and 9% losses.

For me at least, this refutes the widely used 15% charging losses claims on these boards.
I hope someone else can reproduce this test and report their results. Even better if they have the ability to compare L1 and L2 charging independently over at least as far a distance. I tried to estimate the efficiency at the end of each day but the granularity of the EV consumption is just too big for this.
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In order for me to have seen charging losses as big as 15% I would have needed to lose 1.5 kwh somewhere in my measurements. This is 7-8 miles of travel and more than half a battery's worth of a charge. Of course, there are more losses between the power plant and the wall socket...widely reported that the national average is 5-7%. If you were to say this is 6% and that the PIP charging loses 9%, maybe this is the true source of the "15% losses" number, perhaps originating from some industry white paper comparing EV driving and oil, etc.

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Also I hope that people realize that correcting for a ~10% (my belief) or even 15% charging loss has a correct mathematical formula to be used. If your input data is from the EV driving ratio screen, this provides the car's estimation of the Energy(out). To obtain Energy(in), you use the efficiency value, as a fraction, like this:

E(in) = E(out) / efficiency

for example (with 10% losses or a 90% efficiency and 300 kwh shown on the display)

E(in) = 300 / 0.90 = 333.33 Please, NOT this: E(in) = 300 * 1.1 = 330

Yes the answer is only ~1% off. And yes the data collection and efficiency estimation is not that precise. But it is not a good reason to use the wrong formula...at least if you are going to type out the formula you are using then use one that is right. Hopefully I have not made any mistakes in my math.


Mike

 

I don't know where the 15% number comes from...can you provide a definitive source?
What do you mean charger battery motor combination? That is what I measured.

Mike

 

If you show 100kwh and you have 9% charging losses you should divide by 0.91 ( which is very close to multiplying by 1.1)
The difference in losses between L1 and L2 as best as I could see was smaller than the uncertainty in the measurements caused by the granularity of the EV driving ratio kWh readout...maybe 1-2% more or less in losses. It will be very difficult to do a more accurate test because it requires longer distances for more kWh, but the ICE will always kick on at 124 miles

Mike

 

Yes, really you charged with 110 kwh and with 91% efficiency thus the car reported 100 kwh after battery charges and driving.

Mike

 

IMO none of these explanations make any sense. And I don't know where the 3.2 kwh comes from...I can rarely see more than 2.9 with the chargepoint L2.

Mike

 

In the original post I account for this...but it was so small it is noise...I drove 132 miles in EV and 5 in HV. The ICE added 1.1 miles of EV range while in HV that one time. That is less than 1% of the miles driven in the test.

Mike