How should Nissan respond to dropping capacity?

[DaveinOlyWA]

We don't have enough data, at least not enough to allow any conclusions, and I don't expect this to change. The few dozen vehicles we are talking about is an anecdotal sample, which suggests that there is a strong correlation (70 to 80%) between average ambient temperature and Gid count. This already takes individual differences into account, since there will never be two vehicles, even in the same locale, which will be exactly the same. It's because owners won't be able to replicate the same usage pattern, even if they tried.

Be it as it may, there is no magic number. Batteries degrade with use, and high temperatures and high SOC accelerate this process. While it's likely is a non-linear relationship, and degradation could speed up dramatically at some point, there is no demarcation line. Aside from the 120 F number quoted in the owner's manual, which will void the warranty, it's shades of grey, not black and white. *

The following table details Volt's TMS, and I referenced it often on the forum. The LG Chem batteries GM uses in the Volt are very similar to ours. From what we have learned so far, we know that it's OK to leave the Volt at about 23% SOC for an extended period of time.** We also know that the TMS won't attempt to cool the battery if it's below 86 F and the vehicle is not connected to a power source. Both of these conditions represent an engineering trade-off, and I would expect both of them to apply to the Leaf.

The reports from NREL are extremely useful, and they have a well-equipped lab, but the majority of their studies is based on graphite/NCA cells, which have different properties. While they give us good idea about the relationship between environmental factors, SOC and battery degradation, they should not be taken literally.

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* what that "gray" tells me is degradation will happen to some degree however slight below 120º but extended exposure over 120º will cause a physical or chemical change to the composition of the pack which will show as a failure and not degradation.

** i FREQUENTLY have my LEAF at low SOC (under 20%) for several hours (up to 10 hours but generally 2-5 is typical) so i have to question the level of degradation low SOC causes

this low SOC situation i have probably done at least 100 times if not more

 

[Nubo]

There is no fan. This keeps coming up and it does not exist in the pack.

It appears there might have been a fan, at least at the stage of development where Siry got his info.

Just speculating of course, but if it was in a late-stage design then it might not be as big of an engineering hurdle as we think to re-include that design element. While a simple internal fan can't reduce the pack temperature below ambient, it can help to redistribute heat and avoid hot spots. If the heat-degradation curve is truly exponential then it's conceivable that the high battery loss could be strongly skewed towards a small subset of the pack modules that experienced temps well above the pack average.

 

[DaveinOlyWA]

There is no fan. This keeps coming up and it does not exist in the pack.

It appears there might have been a fan, at least at the stage of development where Siry got his info.

Just speculating of course, but if it was in a late-stage design then it might not be as big of an engineering hurdle as we think to re-include that design element. While a simple internal fan can't reduce the pack temperature below ambient, it can help to redistribute heat and avoid hot spots. If the heat-degradation curve is truly exponential then it's conceivable that the high battery loss could be strongly skewed towards a small subset of the pack modules that experienced temps well above the pack average.

this seems to back up my hypothesis that maybe Nissan originally designed a pack with the appropriate BMS including temp control but was too expensive and in order to intro the car at "acceptable" pricing the additional cost was removed with plans to add it in later when the TN plant started running and Nissan could greatly reduce its manufacturing costs?

ok, a bit of stretch i admit...

 

[Herm]

Be it as it may, there is no magic number. Batteries degrade with use, and high temperatures and high SOC accelerate this process.

There are two magic numbers, SOC and temperature..From an NREL study, and probably similar to how the Leafs battery would age, average July temperature in Phoenix is 34° C, so from that graph your SOC cant exceed 80% if you want 5 years of battery life, if your battery is hotter than this due to aggressive driving, charging or hot pavement then its much harder.

 

[DaveEV]

The following table details Volt's TMS, and I referenced it often on the forum. ... Both of these conditions represent an engineering trade-off, and I would expect both of them to apply to the Leaf.

Yes, the Volt's chemistry is most similar to the LEAFs out of production plug-ins today - safe to assume that what is good for the Volt is good for the LEAF.

what that "gray" tells me is degradation will happen to some degree however slight below 120º but extended exposure over 120º will cause a physical or chemical change to the composition of the pack which will show as a failure and not degradation.

Extremely high temperature simply accelerates the aging process. It is a logarithmic curve - once you exceed a certain point even small changes in temp result in large changes in calendar life. This is probably one reason why temp bars 5-6 have such large range compared to the higher/lower ones.

i FREQUENTLY have my LEAF at low SOC (under 20%) for several hours (up to 10 hours but generally 2-5 is typical) so i have to question the level of degradation low SOC causes

I do not think that storage at low SOC causes any extra degradation, though it probably depends on the chemistry. Typically, high rates of discharge at low SOC can be more damaging. At least for you, it certainly doesn't seem to be causing any extra degradation, so I wouldn't sweat it!

There are two magic numbers, SOC and temperature..From an NREL study, and probably similar to how the Leafs battery would age

That is a big leap of faith! Very dangerous to draw any specific comparisons between different battery chemistries, please stop assuming that the chart is representative of the LEAFs battery without having any real data to back it up! I never should have posted that reference where you would find it.

 

[surfingslovak]

** i FREQUENTLY have my LEAF at low SOC (under 20%) for several hours (up to 10 hours but generally 2-5 is typical) so i have to question the level of degradation low SOC causes

this low SOC situation i have probably done at least 100 times if not more

Right, and we discussed this several times before. The best answer I can give you is that the processes that alter the spinel structure of the battery at low SOC are slow. The reports we found measure these effects after several weeks, not hours. You will have charged back up before any crystalline changes occurred.

Based on what we have learned here, I would not hesitate to drive the Leaf to the very low battery warning when needed. A shallow discharge cycle is preferable however. For what it's worth, the best Gid reading in my area so far was from a Leaf owner with a very short commute. He only drives 10 to 20 miles a day, and then charges back up to 80%.

I your case, I believe that the moderate climate in the PNW is helping you. If you look at the NREL reports, the differences between varying usage patterns are not so great at low ambient temps.

There are two magic numbers, SOC and temperature..From an NREL study, and probably similar to how the Leafs battery would age

That is a big leap of faith! Very dangerous to draw any specific comparisons between different battery chemistries, please stop assuming that the chart is representative of the LEAFs battery without having any real data to back it up! I never should have posted that reference where you would find it.

Tell me about it! There is a reason why Nissan tells us precious little. As the old saying goes "Give 'em enough rope..."

 

[Herm]

The chemistry is similar, the big difference is that a plug-in hybrid suffers higher battery stress.. supposedly NMC chemistry has higher heat resistance. I think the conclusion that its a combination of temperature and SOC is valid... and thanks for the link

 

[surfingslovak]

The chemistry is similar, the big difference is that a plug-in hybrid suffers higher battery stress.. supposedly NMC chemistry has higher heat resistance. I think the conclusion that its a combination of temperature and SOC is valid... and thanks for the link

We could try to work out the differences between graphite/NCA and LMO cells. Would anyone care to write to NREL and inquire?
They have published lots of interesting information over the years, but it's all based on the graphite/NCA chemistry. Wonder why that is.


Click to open

 

[DaveinOlyWA]

the link basically says 2 things

1) LEAF batteries are more temperature tolerant of high temps but does not specify

2) temps above 30C increase degradation

so basically every time you see 6 TBs you are degrading the pack ever so slightly.

**edit** i guess i should make that "7TB" i thought 6TB range was warmer than the reported 74-80F

 

[surfingslovak]

the link basically says 2 things

Sorry, which link was that?

1) LEAF batteries are more temperature tolerant of high temps but does not specify

2) temps above 30C increase degradation

so basically every time you see 6 TBs you are degrading the pack ever so slightly.

Based on what I've heard and read on LMO cells, they are generally considered to be less heat resistant than other common lithium-ion variants. I would tend to agree with what drees said above that the relationship between temperature and degradation was logarithmic. Yes, going above 75 F (six temp bars) means that the battery will degrade a bit faster. And going to seven temp bars (98 F) will accelerate this process even more.

 

[DaveinOlyWA]

oh? oh maybe link in another thread here

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

 

[RegGuheert]

The main thing that is stopping us from finding the magic number is the fact that we do not have a good information on what the battery temp really is. For example 6 battery temp bars is somewhere between 74 and 98f.

It's actually much less specific than that. Those values are from the "old" Service Manual. The temperature chart has been replaced by a graph in the April 2011 Revision of the LEAF Service Manual and the temperature ranges given are different:

RELATIONSHIPS OF THE NUMBER OF LIGHTING SEGMENTS OF LI-ION BATTERY TEMPERATURE GAUGE AND LI-ION BATTERY TEMPERATURE
0 Bars: Up to -5C (23F)
1 Bar: -15C (5F) to -2C (28F)
2 Bars: -12C (10F) to 2C (36F)
3 Bars: -8C (18F) to 4C (39F)
4 Bars: -5C (23F) to 15C (59F)
5 Bars: -3C (27F) to 27C (81F)
6 Bars: 10C (50F) to 38C (100F)
7 Bars: 23C (73F) to 47C (117F)
8 Bars: 36C (97F) to 49C (120F)
9 Bars: 47C (117F) to 52C (126F)
10 Bars: 49C (120F) to 56C (133F)
11 Bars: 52C (126F) to 59C (138F)
12 Bars: 56C (133F) and above
Note:
- Li-ion battery temperature gauge shows Li-ion battery temperature by correcting it according to the battery capacity. Consequently, the number of lighting segments of Li-ion battery temperature gauge can be different regardless of the same Li-ion battery temperature.
- This graph shows corrected temperatures. These to not agree with the CONSULT temperature shown in data monitor item "BAT TEMP".

(Please note that I have interpreted the graph so that the range values can be read as numbers.)

In other words, if you see six bars, your battery temperature can be anywhere from 50F to 100F. Hopefully Phil's LEAFScan will give us more exact data. Even better would be a capability to log temperature data from the battery probes over time.

 

[surfingslovak]

The temperature chart has been replaced by a graph in the April 2011 Revision of the LEAF Service Manual and the temperature ranges given are different. (Please note that I have interpreted the graph so that the range values can be read as numbers.)

In other words, if you see six bars, your battery temperature can be anywhere from 50F to 100F. Hopefully Phil's LEAFScan will give us more exact data. Even better would be a capability to log temperature data from the battery probes over time.

Thank you for doing that! Any chance we cold get this graph online? For what it's worth, I have never seen six bars at 50 F. It generally takes some time at or below 70 F for the gauge to transiton from six to five bars, at least that's what I see. It actually happened couple of days ago when I drove the Leaf home from the gym. It was about 69 F out. My car is on April 2011 firmware.

 

[DaveinOlyWA]

ya, i have to dispute the 6 TB thing to. in Summer we bounce from 5 to 6 all the time but rarely do i see 6 unless its in bright sunlight with temps in mid 70's and up or unless i have QC'd.

now, i did QC 4 times in one day last week with temps in high 70's low 80's. only saw 6 TB (have never seen 7 before)

once again, a realistic temp bar should have #7, 8 and 9 in orange and red should probably be bigger than it is now

 

[KJD]

Hopefully Phil's LEAFScan will give us more exact data. Even better would be a capability to log temperature data from the battery probes over time.

Back in March when I first read about LEAFScan I was pretty stocked to buy one. Now that it is end of July ...................

http://www.mynissanleaf.com/viewtopic.php?f=37&t=8251" onclick="window.open(this.href);return false;

Maybe Nissan could respond to this dropping capacity problem by adding a digital display to the Temp bar graph.

 

[RegGuheert]

Thank you for doing that! Any chance we cold get this graph online?

Sure! Should I put it on the Wiki near the other one?

For what it's worth, I have never seen six bars at 50 F.

Me neither.

It generally takes some time at or below 70 F for the gauge to transiton from six to five bars, at least that's what I see. It actually happened couple of days ago when I drove the Leaf home from the gym. It was about 69 F out. My car is on April 2011 firmware.

The lowest I've seen it was about 65F, maybe slightly higher. An overnight soak after no driving that day down to that temperature did not get the LEAF down to 5 BT bars. 62F yesterday morning finally got it to drop down to 5BT, but not right away. It came back up to 6 BT bars today just after driving in the sun at 75F ambient.

Take a look at the notes after the table. I don't have any comprehension of what a correction of temperature for capacity means, but perhaps it is some way to better model temperatures while there are changes in electrical resistance of the pack? Or perhaps it is a way for Nissan to make battery temperature "look" higher to LEAF owners with a severely degraded pack so that they will take better care of it. No idea.

 

[Nubo]

One thing Nissan needs to do, it seems to me, is to revise their battery test output where everyone gets 5 stars. The worst I've seen, iirc, was someone had 4 stars on one section and 5 stars on the rest.

 

[edatoakrun]

="RegGuheert"... perhaps it is a way for Nissan to make battery temperature "look" higher to LEAF owners with a severely degraded pack...

IIRC, someone has posted a degradation correction chart that shows exactly that. Again, IIRC, the second, higher temperatures in the list you posted below, was stated to be correct for a battery pack with 100% capacity, with the bars appearing at progressively lower temperatures, as the battery capacity is reduced.

This closely matches my observations of battery temp bars bars after reaching ambient temperature, in that I have never seen below Four-to-seven range of bars.

Six bars, for example, does seem to correlate closely to the 81-100 F (or, alternately, 74-98 F) range, for my LEAF.

I'm fairly sure my car never showed 6 bars, with a battery temperature below 70-something F.

And the very few times I got seven bars last summer (not seen that yet, this year) the ambient temp had been over 100F for an extended period of time, and/or I had just significantly discharged or charged my battery.

="RegGuheert"... The temperature chart has been replaced by a graph in the April 2011 Revision of the LEAF Service Manual and the temperature ranges given are different:


LEAF Service Manual, Revision: 2011 April, pages MWI-20-21 wrote:
RELATIONSHIPS OF THE NUMBER OF LIGHTING SEGMENTS OF LI-ION BATTERY TEMPERATURE GAUGE AND LI-ION BATTERY TEMPERATURE
0 Bars: Up to -5C (23F)
1 Bar: -15C (5F) to -2C (28F)
2 Bars: -12C (10F) to 2C (36F)
3 Bars: -8C (18F) to 4C (39F)
4 Bars: -5C (23F) to 15C (59F)
5 Bars: -3C (27F) to 27C (81F)
6 Bars: 10C (50F) to 38C (100F)
7 Bars: 23C (73F) to 47C (117F)
8 Bars: 36C (97F) to 49C (120F)
9 Bars: 47C (117F) to 52C (126F)
10 Bars: 49C (120F) to 56C (133F)
11 Bars: 52C (126F) to 59C (138F)
12 Bars: 56C (133F) and above
Note:
- Li-ion battery temperature gauge shows Li-ion battery temperature by correcting it according to the battery capacity. Consequently, the number of lighting segments of Li-ion battery temperature gauge can be different regardless of the same Li-ion battery temperature.
- This graph shows corrected temperatures. These to not agree with the CONSULT temperature shown in data monitor item "BAT TEMP".

 

[EdmondLeaf]

Another viewpoint is that 2 and a half years ago the climate conditions in the US especially in the Southwest were much less severe than they are today. Given the design lifecycle of a vehicle is about 3-4 years, you have to place your bets way in advance. A key part of the analysis is cost, weight, supply chain capabilities, etc. So the bottom line is that 3 - 4 years ago, the LEAF was testing adequately for what the projected US severe environment was at that time.

As the Phoenix area is returned to an uninhabitable desert, the need for even more severe-duty equipment and cars will be necessary.

It this is true looks like very poor planing and rush to market with unfinished product. I had no problem driving my 2005 Camry to PHX recently, as well driving it in here where temp is not that different than previous years. We should not blame weather for Leaf battery problem after all Nissan told us is well prepared to handle relatively high temp without TMS.
To me temp in my area is normal summer weather and over 100F will stay here for a while like every summer

 

[edatoakrun]

"EdmondLeaf"

Another viewpoint is that 2 and a half years ago the climate conditions in the US especially in the Southwest were much less severe than they are today. Given the design lifecycle of a vehicle is about 3-4 years, you have to place your bets way in advance. A key part of the analysis is cost, weight, supply chain capabilities, etc. So the bottom line is that 3 - 4 years ago, the LEAF was testing adequately for what the projected US severe environment was at that time.

As the Phoenix area is returned to an uninhabitable desert, the need for even more severe-duty equipment and cars will be necessary.

It this is true looks like very poor planing...

Also, IMO, very poor planning, to fuel America's ICEVs, with ethanol derived from a crop that is far more sensitive to global heating than LEAF batteries. It is beginning to look like America will either have to suspend the ethanol mandate, of the world food price spike will cause untold suffering among the worlds poorest people.

The heat wave that lit up a vast swathe of the mid-west could not have come at a worse time for this year's corn.

Or delivered more of a shock to farmers. All signs had been pointing to a bumper crop this year.

A mild winter, a balmy spring – most farmers elected to plant some of their fields a few weeks earlier than usual. Mike Buis, who farms in west-central Indiana, put some of his corn in on 9 April.

Some farmers didn't even hold on that long, planting as early as March.

By 1 June, the early corn was shoulder high.

But corn, it turns out, is a sensitive creatures. June's combination of extreme heat and long dry spell proved a deadly combination.

For the late planting, the extreme heat made it too hot to pollinate. "They got zapped big time," Buis said.

Corn goes sterile if the temperature stays above 95 degrees for several days running, he said...

http://www.guardian.co.uk/environment/2012/jul/22/drastic-weather-doom-american-corn" onclick="window.open(this.href);return false;

...The US is crucial to global food markets as the world's largest exporter of corn, soy beans and wheat, so the impact of the drought will be felt across the globe.

Corn prices have already shot up 40% since June to hit all-time highs, soy bean prices have jumped 30% to record levels, and wheat has surged 50%.
It is not just the US. Unseasonal weather, thought to be caused by climate change, is affecting farmers across the world.

South America has been hit by a drought, which could damage the soy bean harvest, while UK wheat has been damaged by the rain.

Flash flooding in Russia could also affect the wheat harvest. Traders are particularly concerned about the latter as Russia might limit exports if it is worried about wheat supplies at home, causing further price spikes.
Shortages have been compounded by huge orders for corn and soy beans to make biofuels, in order to meet quotas in the US and Europe...

http://www.guardian.co.uk/environment/2012/jul/22/food-price-crisis-weather-crops" onclick="window.open(this.href);return false;

"EdmondLeaf" ...To me temp in my area is normal summer weather...

That only reflects your own limited powers of observation.

Check any historic climate database for your area, such as the several I've posted on this thread.

State of the Climate
Global Analysis
June 2012

National Oceanic and Atmospheric Administration

National Climatic Data Center

...The Northern Hemisphere average land temperature, where the majority of Earth's land is located, was record warmest for June. This makes three months in a row — April, May, and June — in which record-high monthly land temperature records were set. Most areas experienced much higher-than-average monthly temperatures, including most of North America and Eurasia, and northern Africa. Only northern and western Europe, and the northwestern United States were notably cooler than average...

http://www.ncdc.noaa.gov/sotc/global/2012/6" onclick="window.open(this.href);return false;