How accurate are the "energy economy" figures?

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aqn

Well-known member
Leaf Supporting Member
Joined
Oct 1, 2010
Messages
832
Location
Austin, TX
How does the LEAF measure power usage? Would it be anything like how my utility meter knows how much electricity I use? How accurate is the power usage measurement?

What I actually would like to know is, how accurate are the "energy economy" figures? If the display says "3.8 mi/kWh", have I really averaged 3.8 miles per kWh drawn out of the battery since the last reset? And if not, what do you think is the margin of error?

Thanks.
 
The car is pretty accurate, however, I have noticed that on occasion it "freezes". For example, it completely missed the fact that i was accelerating from a stop and beginning to level off before it went from its max reading down to nearly zero. While its not much energy, the car missing some of the largest consuming moments of energy makes me wonder.

Many places where energy is being read though:

Your power company bill
Your power meter
EVSE
Car
CARWINGS (although inaccurate)
 
ok... "my" Leaf does not have an "instant" energy usage gauge. mine has about a 2-3 second delay. i attribute this the gauge update cycle is i consider to be relatively slow. i only have my Prius to compare with which "seems" to give near instant feedback on energy consumption with gauge updates in the one second range.
 
OK, that's the "instant" energy consumption readings. How about the "energy economy" readings e.g. "3.8 mi/kWh"? Any opinions as to how accurate those are?

(I've been recording all the pertinent numbers in a spreadsheet, and the "kWh per state-of-charge bar" figure is surprising, at least to me. I derive the "kWh per state-of-charge bar" from the energy economy figures, tripmeter reading, and number of SOC bars, so I just want to find out more about the accuracy of the "energy economy" figures.)
 
aqn said:
OK, that's the "instant" energy consumption readings. How about the "energy economy" readings e.g. "3.8 mi/kWh"? Any opinions as to how accurate those are?

(I've been recording all the pertinent numbers in a spreadsheet, and the "kWh per state-of-charge bar" figure is surprising, at least to me. I derive the "kWh per state-of-charge bar" from the energy economy figures, tripmeter reading, and number of SOC bars, so I just want to find out more about the accuracy of the "energy economy" figures.)


well, that is a good question. i reset the energy screen every day and the gauge on the dash once a month. they do not agree with each other. the one on the dash consistently reads .1=.2 kwh lower so not sure how that is happening.

unfortunately, its the only thing we have to judge the amount of charge we have used. Carwings is simply wrong
 
aqn said:
OK, that's the "instant" energy consumption readings. How about the "energy economy" readings e.g. "3.8 mi/kWh"? Any opinions as to how accurate those are?
DaveinOlyWA said:
well, that is a good question. i reset the energy screen every day and the gauge on the dash once a month. they do not agree with each other. the one on the dash consistently reads .1=.2 kwh lower so not sure how that is happening.
So far, the LCD panel's energy economy figure averages 97.8% of the center panel's.
 
I am coming to the conclusion that everything -- except the three odometers -- is subject to random voltage variations, or other non-linear analog measurements. I've driven the car pretty hard today, starting with a 100% charge and traveling 87.1 miles, mostly freeway, more than a third of it at 65-70 mph, almost all of it with A/C on. That's not too shabby, and I must say I am pleasantly surprised. Oh, my energy economy for the day? Only 4.0.

But, here's the reason for this post. I was 15 miles from home with one bar showing when I got the "low battery" warning. 'Oh, oh', I thought, 'this is going to be a squeaker.' I decided to take the old highway home rather than the freeway. It has half a dozen traffic signals and speed limits of 45 or 50 most of the way. Since my wife was with me, and I was determined not to strand her, I held my speed to 40 and cut the A/C, leaving the fan on. Ten miles later I still, to my amazement, had one bar showing, so I sped up to 45. Guess what -- I pulled in and stopped at home and still had one bar showing, though the guessometer was flashing 4. Naturally, no "very low" warning.

Fifteen miles after the low battery warning without even losing bar 1?? When we normally think of that warning as coming in the middle, or near the end of bar 1? It seems to me the BMS or dash computer must have seen a momentary voltage drop from the battery, and panicked. It seems to me I dropped from two bars to one prematurely, and got that low battery warning sooner than I should have. So, good luck on calculating kWh/bar, Andy. You may have to tack "+/-0.5" on your answer.

Incidentally, I was within a mile of South County Nissan in Gilroy when I got the warning, and I could have panicked too, insisting we stop there to juice up for at least half an hour. I'm glad I didn't; my wife would have hated it, and it obviously wasn't needed.

Ray
 
aqn said:
How does the LEAF measure power usage? Would it be anything like how my utility meter knows how much electricity I use? How accurate is the power usage measurement?
I have to say there is a large difference between what you pull out of the battery and what you pull out of the wall. The numbers reported by Carwings for electricity usage are far lower than those reported by my utility. Last month we went 1216 miles on 336 kWh of energy usage, as billed by SDG&E on our separate EVSE meter (doing all our charging at home). That comes out to 3.619 m/kWh drawn from the wall. During the same period, Carwings says I am averaging 6.3 m/kWh. We do almost all our driving in Eco mode after charging to 80%, so it must be regen and charging losses that account for the difference? Or an optimistic Carwings calculation...

TT
 
aqn said:
So far, the LCD panel's energy economy figure averages 97.8% of the center panel's.
That is because the center panel uses carwing's (GPS?) miles driven rather than the odometer. Carwings is consistantly lower by a few % - thus the m/kwh is higher by a few %.
 
planet4ever said:
I am coming to the conclusion that everything -- except the three odometers -- is subject to random voltage variations, or other non-linear analog measurements. I've driven the car pretty hard today, starting with a 100% charge and traveling 87.1 miles, mostly freeway, more than a third of it at 65-70 mph, almost all of it with A/C on. That's not too shabby, and I must say I am pleasantly surprised. Oh, my energy economy for the day? Only 4.0.
Hmmm, so 87 miles and 4.0 mi / kWh? My 82 mile trip today the dash read 4.3 mi / kWh so in theory I should have been able to drive 93 miles - but made it home after 2 hours of trickle charging with 2 bars and 13 miles remaining...

This was actually the first time I've charged to 100% since I got the car 2 weeks ago - now have a bit more than 500 miles on the odometer but have to wonder if the battery or car will "break-in" more as some have suggested that the range seems to get better with some time. I know that new tires tend to be less efficient for at least a thousand miles or so before the loosen up.

My mi / kWh from the wall is very close to ttweed's - right around 3.6. I pretty consistently get 4-4.2 mi / kWh on the dash. Carwings currently indicates 5.5 mi / kWh over 464 miles.
 
planet4ever said:
No, the new firmware. Note my delivery date on the left.

Ray
That is strange - and also the fact that your miles / kwh was low. Was your m/kwh changing in the last few miles ?

I got a total of some 18 miles from battery low to turtle. But I lost the last bar at the same time I got the battery low.
 
evnow said:
planet4ever said:
No, the new firmware. Note my delivery date on the left.
That is strange - and also the fact that your miles / kwh was low. Was your m/kwh changing in the last few miles ?

I got a total of some 18 miles from battery low to turtle. But I lost the last bar at the same time I got the battery low.
The last mile was in town, mostly 35 mph, but the 10 miles before that was a four-lane country highway (US 101 many years ago) that I mostly drove at 40 mph, some 45. It looks flat, but actually rises 120 ft very gradually. I think m/kWh was 4.1 when I started that section, but I'm not sure. I seem to remember seeing 4.1 somewhere along there. It may have been 4.0, or even 3.9 when I got the battery low warning.

My car's "normal" behavior (based on a small sample - perhaps four times) is to give low battery somewhere in the middle of the last bar, with the bar disappearing 2-5 miles later. Something definitely seems wrong for the bar to hang on for another 15 miles (at least, since it never disappeared). It also seems odd to go 15 miles after 'low battery' without hitting 'very low', though I guess my very cautious driving during that time might explain that. The bottom line is I have to believe that either 'low battery' was signaled early or 'zero bars' wasn't signaled when it should have been, or both.

Ray
 
I've been keeping record of, among other things, energy economy figures (miles/kWh, from LCD display and from center display), tripmeter miles, and starting & ending SOC bars. From those figures, I calculate kWh's per SOC bar: (tripmeter miles / energy economy) / (staring SOC bars - ending SOC bars). So far, over 16 "tankfuls", leaving out the two largest and two smallest values and averaging the rest, the average is 1.44 kWh per SOC bar. The big unknown here, as this thread's title suggests, is the accuracy of the car's energy economy figures.

It would be great if more than one person collect this data; it'd be interesting to compare notes.

Note 1: it only took a few "tankfuls" to converge on the figure of 1.44 kWh/SOC bar: 12 "tankfuls", ignoring four largest/smallest values, averaging 8 values.)

Note 2: 1.44 kWh/SOC bar is different than the 1.7 kWh/bar (Boomer23) and 1.6 kWh/bar (TonyWilliams) arrived at via reverse engineering some CAN bus data. Why? I dunno, but we will need to see if their results converge on a different value if/when they collect more data.
 
aqn said:
I've been keeping record of, among other things, energy economy figures (miles/kWh, from LCD display and from center display), tripmeter miles, and starting & ending SOC bars. From those figures, I calculate kWh's per SOC bar: (tripmeter miles / energy economy) / (staring SOC bars - ending SOC bars). So far, over 16 "tankfuls", leaving out the two largest and two smallest values and averaging the rest, the average is 1.44 kWh per SOC bar.
It's in no way rocket science, but just in case someone is interested: I've uploaded my spreadsheet to a Google doc.

The columns are in the same order as the LEAF's displays, left to right. I go left to right copying down the numbers (and resetting them where possible) so as to not forget anything, since there are eight numbers/time. Every time I charge and enter them into the spreadsheet later.

The columns are:
_ start - guess-o-meter miles
_ start - bars *
_ mi/kWh LCD display *
_ average speed
_ odometer
_ tripmeter *
_ end - guess-o-meter miles
_ end - bars *
_ mi/kWh center display *
_ time charging start *
_ charge to 100%? *
_ time charging end *
_ notes

The pink shaded columns (marked with * in above list) are necessary for calculations
The unshaded columns are for record keeping only.
The blue shaded columns on the right are calculated from the pink shaded columns on the left:

_ charging time
_ charge time per bar (minutes)
_ miles/ bar
_ % diff bet. LCD disp and center disp
_ kWh/bar, according to LCD disp
_ kWh/bar, according to center disp
 
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