Nice Presentation on Leaf Battery

Stoaty · Sep 12, 2011

I just ran across a presentation surfingslovak made at the Bay area Leaf meeting on the Leaf battery:

https://acrobat.com/app.html#d=GSYITUXYDvH4EPENbJ4KjA" onclick="window.open(this.href);return false;

The description of the meeting is interesting, too (middle of page):

http://www.mynissanleaf.com/viewtopic.php?f=24&t=3415&start=420" onclick="window.open(this.href);return false;

Nicely done! Learned a few things I didn't know.

DarkStar · Sep 12, 2011

I saw this over on the Tesla forum and unfortunately there is a lot of speculation and rumors contained in that presentation. Right off the go, the Department of Energy determined the "user accessible" portion of the battery to be just over 24 kWh and Ingineer stated seeing a CONSULT III diagnostic on the battery that seemed to indicate a total capacity of between 27-28 kWh.

surfingslovak · Sep 12, 2011

DarkStar said:
I saw this over on the Tesla forum and unfortunately there is a lot of speculation and rumors contained in that presentation. Right off the go, the Department of Energy determined the "user accessible" portion of the battery to be just over 24 kWh and Ingineer stated seeing a CONSULT III diagnostic on the battery that seemed to indicate a total capacity of between 27-28 kWh.

Stoaty, thank you for posting the link and for your kind words. I agree, some of the information is extrapolated from the data sets made available by other owners and it should be taken with a grain of salt. I'm not aware of the discussion on the Tesla forum, and I might not have much time to spend on the forum this week. Suffice it to say that the 21 kWh usable capacity estimate is carried by a consensus of several owners and it aligns with both the driving range we are getting and with the amount of energy required to charge from turtle to full when assuming 85% charging efficiency. I looked at the EPA numbers as well, but once again I had to extrapolate and use charge efficiency estimates. If EPA published a detailed test report with greater level of detail, I would love to see it.

I personally don't agree with the 27-28 kWh total capacity at all, but I have not seen how it was determined, and I can't really comment. Every piece of data I looked at, including and especially the AESC product sheets, indicates rated capacity of 24 kWh and about 21 kWh of usable capacity available to the driver. That being said, I don't claim this report to be 100% accurate, I simply presented what worked for me and a few other owners. Although I firmly believe that these numbers are close to reality, your mileage might vary. If you saw inaccuracies or room for improvement, please PM me.

LEAFfan · Sep 12, 2011

Stoaty said:
I just ran across a presentation surfingslovak made at the Bay area Leaf meeting on the Leaf battery:
https://acrobat.com/app.html#d=GSYITUXYDvH4EPENbJ4KjA" onclick="window.open(this.href);return false;

The 85% efficiency for 3kW hs is not what I've been getting. I've been doing better than that as it only takes mine about 20-25 mins. per bar. Once, I charged from 5-10 bars in 1/1/2 hours so even if the fifth bar weren't empty, four would still give me 22 mins/bar, not thirty as in the PDF. Other than that, nice presentation. Thanks!

surfingslovak · Sep 12, 2011

DarkStar said:
Right off the go, the Department of Energy determined the "user accessible" portion of the battery to be just over 24 kWh.

DarkStar, I appreciate the comment. Would you know where the DOE has published this number and how it was determined? Yes, the 21 kWh is an approximation, but it's something I had to include because the guessometer is so erratic and we have successfully used 21 kWh in range predictions on the forum. If I'm reading the AESC chart correctly, once cell has about 125 Wh rated capacity (33.3 Ah and 3.75 V nominal voltage). Nissan has confirmed that the pack has 192 cells, which correlates with 24 kWh total rated capacity. Please correct me if I'm wrong, but based on this chart alone, I simply don't understand how one cell could provide 140 or 150 Wh.

adric22 · Sep 12, 2011

Interesting that 110V charging is less efficient. Is it because of the charger having to up-convert the voltage?

DarkStar · Sep 12, 2011

surfingslovak said:
Would you know where the DOE has published this number and how it was determined?

The report has been published here a few times, but it's probably been about 8 or 9 months. I'll try to find it and get it posted here too.

TEG · Sep 12, 2011

surfingslovak said:
...I personally don't agree with the 27-28 kWh total capacity at all, but I have not seen how it was determined, and I can't really comment. Every piece of data I looked at, including and especially the AESC product sheets, indicates rated capacity of 24 kWh and about 21 kWh of usable capacity available to the driver...

When Tesla first published Roadster specs, the battery pack capacity started out something like ~56kWh then got revised down to ~53kWh.
http://www.teslamotorsclub.com/showthread.php/648-ESS-53kWh-or-56kWh" onclick="window.open(this.href);return false;

Maybe something similar here where ~27kWh is the "theoretical maximum" capacity if you push the cells to their limits?
But then they may "derate" it a bit because they want to never charge to max voltage, and never drain dangerously low to preserve pack longevity?
I don't know for sure, but I suspect they use a more conservative number just to make sure they never overstate the capacity of a particular car.
(Could even be there to account for manufacturing differences between cars.)

GregH · Sep 12, 2011

That is a great presentation! Especially the link to the rated Ah capacity.. I had been assuming 3.6v nom and 70Ah, but 3.75v and 66Ah makes more sense.. Also the hint at a few more Ah above the charge ceiling of 4.1v is interesting (and understandable for better cell life). So we're really looking at 60-62Ah usable? And more importantly,

Can we say for certain that the raw SOC # we've been looking at represents remaining Wh capacity in steps of 75Wh?

Boomer23 · Sep 12, 2011

surfingslovak said:
DarkStar said:

I saw this over on the Tesla forum and unfortunately there is a lot of speculation and rumors contained in that presentation. Right off the go, the Department of Energy determined the "user accessible" portion of the battery to be just over 24 kWh and Ingineer stated seeing a CONSULT III diagnostic on the battery that seemed to indicate a total capacity of between 27-28 kWh.

Click to expand...

Stoaty, thank you for posting the link and for your kind words. I agree, some of the information is extrapolated from the data sets made available by other owners and it should be taken with a grain of salt. I'm not aware of the discussion on the Tesla forum, and I might not have much time to spend on the forum this week. Suffice it to say that the 21 kWh usable capacity estimate is carried by a consensus of several owners and it aligns with both the driving range we are getting and with the amount of energy required to charge from turtle to full when assuming 85% charging efficiency. I looked at the EPA numbers as well, but once again I had to extrapolate and use charge efficiency estimates. If EPA published a detailed test report with greater level of detail, I would love to see it.

I personally don't agree with the 27-28 kWh total capacity at all, but I have not seen how it was determined, and I can't really comment. Every piece of data I looked at, including and especially the AESC product sheets, indicates rated capacity of 24 kWh and about 21 kWh of usable capacity available to the driver. That being said, I don't claim this report to be 100% accurate, I simply presented what worked for me and a few other owners. Although I firmly believe that these numbers are close to reality, your mileage might vary. If you saw inaccuracies or room for improvement, please PM me.

A small comment on the charging efficiency and/or usable capacity question. When I ran my LEAF down to turtle, the 100% recharge at L2 took 26.1 kWh per my TED system. Using an 85% efficiency figure, that would yield 22.2 kWh usable. Admittedly, my TED isn't calibrated.

TomT · Sep 12, 2011

It's primarily due to the fact that the fixed parasitic loads, such as the charger cooling pump, extract a larger portion of the output of the charger on 120 than on 240.

adric22 said:
Interesting that 110V charging is less efficient. Is it because of the charger having to up-convert the voltage?

SanDust · Sep 12, 2011

Boomer23 said:
A small comment on the charging efficiency and/or usable capacity question. When I ran my LEAF down to turtle, the 100% recharge at L2 took 26.1 kWh per my TED system. Using an 85% efficiency figure, that would yield 22.2 kWh usable. Admittedly, my TED isn't calibrated.

The EPA measured it as being 24.82 kWh from the wall. At 85% efficient that's 21.097 kWh. One possible explanation of why their numbers don't align with yours, other than measurement error, is that the EPA stops the test once the car can no longer perform the cycle. That might be before your car signals turtle mode, so you may have used more of the battery capacity before recharging.

SanDust · Sep 12, 2011

TomT said:
It's primarily due to the fact that the fixed parasitic loads, such as the charger cooling pump, extract a larger portion of the output of the charger on 120 than on 240.

An alternative way of saying the same thing is that you have a fixed loss per unit time, and since charging at 120V takes twice as long you end up with twice the losses.

Stoaty · Sep 12, 2011

SanDust said:
The EPA measured it as being 24.82 kWh from the wall. At 85% efficient that's 21.097 kWh. One possible explanation of why their numbers don't align with yours, other than measurement error, is that the EPA stops the test once the car can no longer perform the cycle.

That doesn't fit with the statement from Darkstar that the EPA found "user accessible" portion of the battery to be just over 24 kWh... unless he means the user can send 24 KWh from the plug, not how much gets in to the battery.

Methinks one of you must be wrong.

TomT · Sep 12, 2011

The highest I have seen to date on my TED was 26.8 KwH when I ran it down to dead once... My TED tracks within 1 percent of my utility meter (I have two MTUs, one on the house and one on the Blink)...

Boomer23 said:
A small comment on the charging efficiency and/or usable capacity question. When I ran my LEAF down to turtle, the 100% recharge at L2 took 26.1 kWh per my TED system. Using an 85% efficiency figure, that would yield 22.2 kWh usable. Admittedly, my TED isn't calibrated.

surfingslovak · Sep 12, 2011

TomT said:
The highest I have seen to date on my TED was 26.8 KwH when I ran it down to dead once... My TED tracks within 1 percent of my utility meter (I have two MTUs, one on the house and one on the Blink)...

Tom, yes, and I remember our discussion well. I wish I had an explanation for this discrepancy, but I don't. The model claims 5% accuracy and the number you referenced represents a delta of about 8%. It's the highest number I'd be aware of, and although Boomer's number is on the high side as well, it's within the 5% band. To be fair, Waidy reported something below 21 kWh and we'll likely see other diverging reports as well. The model is based on a fairly small data sample, and I have not performed any statistical analysis. All we can do is collect more data. It's a fascinating topic, and I'm sure that our understanding of Leaf's design will evolve over time.

DarkStar · Sep 12, 2011

Stoaty said:
SanDust said:

The EPA measured it as being 24.82 kWh from the wall. At 85% efficient that's 21.097 kWh. One possible explanation of why their numbers don't align with yours, other than measurement error, is that the EPA stops the test once the car can no longer perform the cycle.

Click to expand...

That doesn't fit with the statement from Darkstar that the EPA found "user accessible" portion of the battery to be just over 24 kWh... unless he means the user can send 24 KWh from the plug, not how much gets in to the battery. Methinks one of you must be wrong.

The report I saw was 24 kWh from the battery, not from the wall.

surfingslovak · Sep 12, 2011

DarkStar said:
[The report I saw was 24 kWh from the battery, not from the wall.

It would good to find that report. I won't have much time this week, and I'm limiting my activity to this thread for the moment.

To be clear, I expected to see 24 kWh of available capacity too and I called Nissan couple of weeks after purchasing the Leaf to inquire about this. My energy economy was 4.5 in mixed urban driving, with about half of it on the freeway. I would routinely get about 70 miles before I would hit one bar. Nissan customer support advised me to dip into the "reserve", which I did, and it added about 10 miles. Unless the energy economy number was incorrect, with 24 kWh of available capacity, I would expect to see 108 miles of range on one charge. I don't know about you, but I never got anywhere near that figure in my driving.

Herm · Sep 12, 2011

Soon (I have been saying this for months

) one of you seekers of truth will either buy a spare module from a dealership or "borrow" one from an existing car.. then test it to find out the actual capacity.. I suspect many of you will be surprised how conservatively Nissan is using the battery.

garygid · Sep 12, 2011

DOE measured energy "From the Wall".
The LEAF shows no measurement of "energy used" for the DOE to use.

Nice Presentation on Leaf Battery

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