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

[DarkStar]

Reason , not to maintain range that's for sure, it drops when pack temps are lower than 65 or so

So what's the reduction curve for the output of a LiMn2O4 battery due to temperature? You might be surprised by the results!

 

[kmp647]

Let me guess it's relatively flat til ....... -4F !

 

[DarkStar]

Let me guess it's relatively flat til ....... -4F !

Exactly. Personally I would be more concerned about the heat since most lithium manganese manufacturers don't recommend using when the battery temperature is above 100 degrees F.

 

[SanDust]

So what's the reduction curve for the output of a LiMn2O4 battery due to temperature? You might be surprised by the results!

Do you have a cite? I know Argonne found that compared to a reference temperature of 20C it was 9% at 0C and 13% at -7C. Not sure what Li-ion chemistry they were using but it won't be that different. FYI the vehicle was emulated so this reduction was solely due to inherent degradation and increased internal resistance.

 

[jumpjack]

Two questions:
1) Where can I read manufacturer statement about usable capacity?
2) How do I read battery charts like this? (fig. 1)

 

[surfingslovak]

Two questions:
2) How do I read battery charts like this? (fig. 1)

Ah, you found the Mars study. Very good! The information on AESC cells the Leaf is using is sparse, and all that's publicly available is on the manufacturer website. Make sure to use the data for high-energy cells for BEV vehicles:

http://bit.ly/aesccells" onclick="window.open(this.href);return false;

 

[TonyWilliams]

Two questions:
1) Where can I read manufacturer statement about usable capacity?

Doesn't exist publicly, to my knowledge. Plus, it's not a "one size fits all", as the usable capacity is affected by temperature, cell balancing (or lack thereof), degradation, or any individual cells that aren't playing nice.

Many just use 21 kWh as a baseline, and adjust from there. My rule of thumb, assuming a balanced and properly working traction battery:

Degradation: arbitrarily subtract 2% per 10,000 miles on the car.

Temperature: add 1% per 8F above 70F
....................subtract 1% per 4F below 70F

If you have a meter to measure watt/hours of the battery, that probably is the single best tool so far to estimate degradation and actual battery capacity, NOT compensated for temperature.

 

[Bassman]

I noticed that I not only get more capacity at warmer temps, but I seem to get higher driving efficiencies also. Typically I get 3.9 to 4.0 mi/KWh at 40 to 60 F on the way to work, but once temps get in the 70s and 80s or more I get 4.3 to 4.4 mi/KWh for the same route, driving the same way. Is it possible that the motor becomed more efficient at warmer temps? This seems counter to normal thinking in terms of resistance versus temp.

 

[DaveinOlyWA]

Actually its a combination of several factors. But the battery does have an optimum operating temperature at which it simply will hold more power

 

[Herm]

If you have a meter to measure watt/hours of the battery, that probably is the single best tool so far to estimate degradation and actual battery capacity, NOT compensated for temperature.

You mean a GID meter?.. GIDs probably are compensated for temperature and degradation.

 

[jkirkebo]

I noticed that I not only get more capacity at warmer temps, but I seem to get higher driving efficiencies also. Typically I get 3.9 to 4.0 mi/KWh at 40 to 60 F on the way to work, but once temps get in the 70s and 80s or more I get 4.3 to 4.4 mi/KWh for the same route, driving the same way. Is it possible that the motor becomed more efficient at warmer temps? This seems counter to normal thinking in terms of resistance versus temp.

One part of it: air is denser the colder it is. Warm weather => lower drag

 

[TonyWilliams]

If you have a meter to measure watt/hours of the battery, that probably is the single best tool so far to estimate degradation and actual battery capacity, NOT compensated for temperature.

You mean a GID meter?.. GIDs probably are compensated for temperature and degradation.

I'm glad you said "probably". Have you seen a Gid count on a -20C temp battery?

 

[Herm]

I'm glad you said "probably". Have you seen a Gid count on a -20C temp battery?

I'm going based on what Engineer said, that GIDs are calculated by coulomb counting, voltage and current.. since voltage will be dependent on temperature it should affect GIDs. He probably guessed it too

 

[jumpjack]

Two questions:
2) How do I read battery charts like this? (fig. 1)

Ah, you found the Mars study. Very good! The information on AESC cells the Leaf is using is sparse, and all that's publicly available is on the manufacturer website. Make sure to use the data for high-energy cells for BEV vehicles:

http://bit.ly/aesccells" onclick="window.open(this.href);return false;

As I said, I don't unserstand these charts and I need some help about them.

 

[surfingslovak]

As I said, I don't unserstand these charts and I need some help about them.

I see! My apologies, I think I misunderstood your question then. I would recommend Battery University, they have pretty good collection of articles, and hopefully this will get you started.

http://batteryuniversity.com/index.php/learn/article/discharge_methods" onclick="window.open(this.href);return false;

http://www.mynissanleaf.com/viewtopic.php?f=27&t=7151&start=40#p157929" onclick="window.open(this.href);return false;

 

[TickTock]

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.

Been almost three years since I first noticed degradation and I am now a 4 bar loser at 62% SOH so I thought it would be interesting to plot the voltage profile from turtle (5 gids) to 100% of my battery as it aged. Sorry, nothing very profound - just a graphical illustration of what everyone already knows - but I like graphs (in case it hasn't become obvious by now ).

 

[sparky]

Wow. That's a whopping loss (nice plot tho'). I'll try and make a similar plot of my current charging curve for my ~43 month old LEAF (still showing 12 bars).

 

[Stoaty]

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.

I haven't ever heard anyone say that driving past VLBW causes the weaker cells to degrade. I thought the Leaf was designed so you couldn't over discharge the cells. Do you have a reference for your statement?

 

[TickTock]

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.

I haven't ever heard anyone say that driving past VLBW causes the weaker cells to degrade. I thought the Leaf was designed so you couldn't over discharge the cells. Do you have a reference for your statement?

That quote was from Oct'11 and we know a lot more now. It is dangerous to go past the knee because of the steeper slope and proximity to fully discharged. You will see much larger variation in the voltage across each cellpair in this region but the general belief now is the BMS monitors all the cellpairs and stops you before significant degradation can occur to any. This may explain why the distance different cars can go after hitting turtle varies so much (I can barely go 100 yards once I hit turtle but I've heard others claim over a mile).

 

[DaveEV]

Been almost three years since I first noticed degradation and I am now a 4 bar loser at 62% SOH so I thought it would be interesting to plot the voltage profile from turtle (5 gids) to 100% of my battery as it aged. Sorry, nothing very profound - just a graphical illustration of what everyone already knows - but I like graphs (in case it hasn't become obvious by now ).

Nice chart - what's interesting is that you can see how much internal resistance has gone up as well by looking at the pack voltage after it hits the knee when charging from turtle.

When you had 255 GIDs the knee was at ~360V, 8 months later the knee was at ~363V and now it's up at ~366V.