Only 18 KWh Usable Energy for MY Leaf--Retest Shows 20.3 KWh

TonyWilliams said:

I thought it was YOU who told us that the Nissan engineers in your area were specifically doing heat related studies, and reported verbally to you of a reduction in range? Did I misunderstand that?

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Yes, you misunderstood. The only thing I was told about the 'heat testing' here was that QCing up to 6X a day did no more degradation to the battery pack than L2 charging. My theory is that the really 'cold' temps will definitely lower m/kW h, but not the hot temps.

LEAFfan said:

Yes, you misunderstood. The only thing I was told about the 'heat testing' here was that QCing up to 6X a day did no more degradation to the battery pack than L2 charging. My theory is that the really 'cold' temps will definitely lower m/kW h, but not the hot temps.

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Interesting. I went back to Tom Moloughney's blog and pulled up his estimated range chart. It shows clearly that the ideal temperature band is between 70 and 75F. I don't know what exactly the guessometer in his MINI-E is factoring into the range figure. What we do know is that this chart is reportedly based on 1,000 data points and that the MINI-E is likely using lithium manganese batteries manufactured by Molicel in 2008. Yes, it's pretty clear that the AESC cells the Leaf is using are far superior in their thermal properties. What's interesting is that GM limits the upper cell temperature to 72 F in the Volt, presumably for the sake of longevity.

Stoaty said:

Charged to 80% (226 gids)
Drove 44.3 miles
SOC at end 105 gids
Efficiency center console (not carwings) = 6.2 miles/KWh (assume 6.0 for dash, just to be safe)
Total usable miles = 44.3*(281/(226-105) = 102.9
Usable KWh in pack = 102.9/(6.2-.2) = 17.1 KWh

Conclusions: Previous work commute came out about the same, actually a little better. Either the efficiency number is a made up bunch of crap, or my battery pack has gone from almost 21 KWh usable to 17 KWh usable over a matter of days.

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Other assumptions you are making are that (a) SOC gids are precise and reliable; (b) they are a proportional measurement of battery charge; (c) you could have charged your battery to 281 gids; and (d) you could discharge it to 0 gids. I'm not sure any of those assumptions are proven.

However, I am also becoming suspicious of the m/kWh display, or at least the one in my car. I have been noticing some sudden large jumps. Today I was at 4.3, then looked down a moment later and it was at 3.8. A quarter of a mile later it had jumped back to 4.2. I hadn't done any hard acceleration or regen to cause that, in fact I had been holding at two to three bubbles. Later I was at 5.1, running on a country road (roughly 0.2% downgrade) at 50 mph. I slowed for a stop light, using ECO mode, and had to stop. I looked down, and it said 4.8! This makes no sense. The temperature was mild today, so I was using no climate control at all, and I verified that several times by checking the climate pie chart, which always showed zero. I had the fan on at 2 clicks and the temperature set at 60.

Maybe we need to start referring to m/kWh as "GOM2".

Ray

planet4ever said:

No, I'm pretty sure they are talking about something like 3.8 kW going into the charger and 3.3 kW coming out of it, which would be 87% efficiency. Remember, the charger is liquid cooled, which means it must be generating quite a bit of heat, so a 500W loss there should not be too surprising.

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Maybe it's just semantics of what "at the battery" or "leaving the charger" means. The charger is really just converting AC to DC and applying the correct voltage to the cells. The majority of losses would occur as the cells heat during charging, meaning that the energy which arrives at, and is applied to, the cells will not be the energy stored by them.

SanDust said:

The charger is really just converting AC to DC and applying the correct voltage to the cells. The majority of losses would occur as the cells heat during charging, meaning that the energy which arrives at, and is applied to, the cells will not be the energy stored by them.

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Oh, good point. I was overlooking that. My first reaction was that couldn't be right, because Nissan has decided they need to cool the charger and not the battery, but obviously the battery pack has far more mass, so it would take much longer for 500W to heat it appreciably.

Ray

planet4ever said:

However, I am also becoming suspicious of the m/kWh display, or at least the one in my car. I have been noticing some sudden large jumps. Today I was at 4.3, then looked down a moment later and it was at 3.8. A quarter of a mile later it had jumped back to 4.2. I hadn't done any hard acceleration or regen to cause that, in fact I had been holding at two to three bubbles. Later I was at 5.1, running on a country road (roughly 0.2% downgrade) at 50 mph. I slowed for a stop light, using ECO mode, and had to stop. I looked down, and it said 4.8! This makes no sense. The temperature was mild today, so I was using no climate control at all, and I verified that several times by checking the climate pie chart, which always showed zero. I had the fan on at 2 clicks and the temperature set at 60.

Maybe we need to start referring to m/kWh as "GOM2".

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Are you referring to the one on the dash, or the center console? I used the center console, because I am using the dash for my lifetime average (which may be a waste of my time, given my suspicions). Anyone else see rather unpredictable/unbelievable data coming from GOM2?

Stoaty said:

Anyone else see rather unpredictable/unbelievable data coming from GOM2?

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The only difference between the dash and center console m/kWh data is about 0.1.

Both are reasonably accurate with using a 21 factor for range from 100% charge.

TonyWilliams said:

Stoaty said:

Anyone else see rather unpredictable/unbelievable data coming from GOM2?

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The only difference between the dash and center console m/kWh data is about 0.1.
Both are reasonably accurate with using a 21 factor for range from 100% charge.

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+1! I find mine very accurate when predicting my range using 17 and 21.

TonyWilliams said:

The only difference between the dash and center console m/kWh data is about 0.1.

Both are reasonably accurate with using a 21 factor for range from 100% charge.

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I believe that I am an exception to that rule, but need to do a test where I charge to 100% and run the battery pretty far down to see what range I get. There is no way I am going to get 126 miles (6*21) out of my Leaf driving to and from work. If I do, I will take it all back. :mrgreen:

planet4ever said:

Oh, good point. I was overlooking that. My first reaction was that couldn't be right, because Nissan has decided they need to cool the charger and not the battery, but obviously the battery pack has far more mass, so it would take much longer for 500W to heat it appreciably.

Ray

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For what it's worth, the battery pack heats appreciably on an L2 charge, and it heats more while charging than when driving. This was voiced in an old thread as well, and I can confirm that based on several observations made over the course of the last month.

Stoaty said:

planet4ever said:

Maybe we need to start referring to m/kWh as "GOM2".

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Are you referring to the one on the dash, or the center console? I used the center console, because I am using the dash for my lifetime average

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I was referring to the one on the dash. I reset that every time I charge, because it is so simple. I just use two fingers to hold down the bottom left and top right buttons in the cluster of four to the left of the steering wheel for about a second to reset m/kWh and trip odometer, then reach down and pop the charging port cover.

I rarely see the one on the center console, because either I have the console on the Energy Usage (not Economy) screen or my copilot has it on the XM Radio screen. At this point my console m/kWh is an (almost) lifetime number, though I've been thinking of resetting it once a month so the history will show monthly averages.

Ray

SanDust said:

TonyWilliams said:

To my knowledge, 20C is the "ideal" temp for this battery chemistry.

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Yes 20C is the "ideal" temperature for Li-ion batteries. But ideal in this context involves a trade-off between performance and longevity.........
The only reason I can think of why you'd get less range from the battery at higher ambient temperatures is if the Leaf doesn't fully charge the cells at those temperatures. This wouldn't be a bad idea BTW.

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This doesn't seem to agree with this data:

http://www.mynissanleaf.com/viewtopic.php?p=140369#p140369" onclick="window.open(this.href);return false;

I'm convinced that the only answer is a back to back endurance run, one at 100+F, the other at 70F. Then compare the range.

Tony

TonyWilliams said:

This doesn't seem to agree with this data:

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The temperature related trade-off between battery life is well known. I just hit Google and this was the first thing to pop up. http://www.discover-energy.com/files/shared/Discover_temperature_effects_charging.pdf" onclick="window.open(this.href);return false; You can easily find dozens of additional references.

That hotter batteries produce more range is simply an an application of the principle that adding heat to any chemical reaction releases more energy.

SanDust said:

TonyWilliams said:

This doesn't seem to agree with this data:

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The temperature related trade-off between battery life is well known.

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So, does the battery work best at 130F, or whatever temp is just below thermal runaway? (no concern for long life)

TonyWilliams said:

So, does the battery work best at 130F, or whatever temp is just below thermal runaway? (no concern for long life)

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It looks like NREL did a study on this. It's an older paper, but they used SAFT lithium ion cells of some kind. The paper SanDust referenced seem to be a little more generic.

I honestly, don't know why Tom Moloughney's chart indicates lower range at higher temperature. It's been suggested that the car charger might limit the amount of energy one can put into the pack when it's hot outside. I'm not sure how realistic this idea is, and I wouldn't put much faith into that. Perhaps the guessometer in Tom's car factored in lower average energy economy in summer months. The hotter it gets, the more energy is spent to keep the passenger cabin nice and cool on any given day. If this were true, then the estimated range figure on the other side of the spectrum would factor in heater usage as well. This is a really interesting problem, and I will try to get more info from him when I get a chance.

At any rate, the NREL chart suggests about 10% capacity change when dropping from 77F down to 50F. If I got the numbers right, this would translate to about 2kWh less usable capacity for the Leaf.


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Based on the battery only getting more and more efficient, and heat raises density altitude (reducing aerodynamic drag), for longest range, I need really hot, flat, high elevation test track.

The salt flats in Bonneville might work. Or sub Sahara Africa.

Not sure what heating (or salt) does to rolling resistance. I would think hot tires are "stickier" than really cold ones.

TonyWilliams said:

Based on the battery only getting more and more efficient, and heat raises density altitude (reducing aerodynamic drag), for longest range, I need really hot, flat, high elevation test track.

The salt flats in Bonneville might work. Or sub Sahara Africa.

Not sure what heating (or salt) does to rolling resistance. I would think hot tires are "stickier" than really cold ones.

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then again, frozen lakes are pretty flat too

TonyWilliams said:

I would think hot tires are "stickier" than really cold ones.

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Less. Warmer tires have greater elasticity.

SanDust said:

TonyWilliams said:

I would think hot tires are "stickier" than really cold ones.

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Less. Warmer tires have greater elasticity.

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is that the reason or is it higher temps mean higher pressures which means less rolling resistance?

we need to keep in mind that ALL the rules have sweet spots.

Using two diffrent canbus logs (one as I drove the car from GOM=6 to dead (discharge) and the other logged during a charge to 100%(charge)) I was able to plot battery voltage versus gids across the full range (keep in mind my 100% charge stops at 244 NOT 281 like most of you). I was able to empirically establish that the ESR of the battery (and any wire between the sense point and the battery) to be about 70mOhm since any value higher or lower resulting in larger variation in the formula (battery_volts-battery_amps*esr) during my discharge log. I also labled the points where I recieved LBW, VLBW, turtle, and dead. As you can see once you get VLBW, you are past the knee and really need to stop driving or you can degrade your weakest cells by over discharging.