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How accurate are the "energy economy" figures?

Posted: Fri Jun 24, 2011 9:42 pm
by aqn
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.

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 12:51 am
by rainnw
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)

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 2:37 am
by garygid
The "instant" mi/kWh "freezes" at 8 until your recently-Regen'd energy is used up. It is a design "feature".

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 8:10 am
by DaveinOlyWA
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.

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 1:52 pm
by aqn
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.)

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 3:40 pm
by DaveinOlyWA
aqn wrote: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

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 8:33 pm
by aqn
aqn wrote: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 wrote: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.

Re: How accurate are the "energy economy" figures?

Posted: Sat Jun 25, 2011 9:24 pm
by planet4ever
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

Re: How accurate are the "energy economy" figures?

Posted: Sun Jun 26, 2011 6:54 am
by ttweed
aqn wrote: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

Re: How accurate are the "energy economy" figures?

Posted: Sun Jun 26, 2011 7:58 am
by evnow
aqn wrote: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 %.