Capacity Loss on 2011-2012 LEAFs

[leafkabob]

How about a G+ circle?

I such a luddite, I don't know what a G+ circle is, or how to create or participate in one.

For now, anyone who wants to join me in approaching Nissan can PM me, then we can switch to private e-mail or phone.

 

[shrink]

How about a G+ circle?

I such a luddite, I don't know what a G+ circle is, or how to create or participate in one.

For now, anyone who wants to join me in approaching Nissan can PM me, then we can switch to private e-mail or phone.

LOL. Google+ Circle.

Good idea, Tick Tock.

Leafkabob, I'll email you and set up a time to chat or meet.

 

[opossum]

There are now at least two different cars in Phoenix that have lost the 2nd capacity bar!

As for the difference in charging habits between Phx and Tucson, the discrepancy in overall size of the metro areas could have a lot to do with it. In many cases, trips around Tucson are likely to be quite a bit shorter than trips in the Phoenix area, so folks in Tucson can likely afford to limit themselves to 80% more often. Phoenix alone covers over 500 square miles.

 

[RegGuheert]

2011 Nissan Leaf Battery Capacity Loss: Nissan Responds

...

http://www.greencarreports.com/news/1076847_2011-nissan-leaf-battery-capacity-loss-nissan-responds" onclick="window.open(this.href);return false;

One of the comments in Ed's link contained this link to a press release about cool pavement technology which contained the following quote:

For example, summer heat in downtown Phoenix can reach temperatures of 115°-118°(F) with asphalt surfaces averaging 150°-170°(F).

Thinking about the fact that the battery in the LEAF is passively cooled at the bottom of the vehicle indicates that parking on such pavement in the middle of a very hot day could result in additional heating above ambient (or at least greatly slowed cooling) after the vehicle is parked. The battery could already be at 130° F internally following a QC and some highway driving or perhaps some spirited driving to get back from work. When the car is stopped, the cabin would be at 80° F but would heat up quickly toward 140°-150° F. Under the car, the pavement would heat the air and would also radiate to heat the thin black plastic cover under the battery, which would probably quickly get to 130° F. I don't know what the thermal time constant of the pavement would be in this scenario, but I think it's pretty safe to say the battery could remain around 130° F for a couple of hours before it makes it down toward ambient.

Granted, that's not a normal day for a LEAF in Phoenix, but it could look something like this on the hottest days. I'm hopeful that LEAFscan will have data logging capabilities for the battery temperature, as it will be interesting to see what the thermal profiles look like for some of these cases.

 

[surfingslovak]

There are now at least two different cars in Phoenix that have lost the 2nd capacity bar!

As for the difference in charging habits between Phx and Tucson, the discrepancy in overall size of the metro areas could have a lot to do with it. In many cases, trips around Tucson are likely to be quite a bit shorter than trips in the Phoenix area, so folks in Tucson can likely afford to limit themselves to 80% more often. Phoenix alone covers over 500 square miles.

Another thing to note, according to http://average-temperature.com" onclick="window.open(this.href);return false;, the average annual temperature in Tucson is two degrees below Phoenix. Something to consider.

The battery could already be at 130° F internally following a QC and some highway driving or perhaps some spirited driving to get back from work. When the car is stopped, the cabin would be at 80° F but would heat up quickly toward 140°-150° F.

Reg, with all due respect, we had this before. Operational heat in those cells, even with spirited freeway driving, will likely result in just a few degrees above ambient. Most of our freeway driving happens between 0.5 and 2C battery load, and the cells barely break a sweat. I wish I had some real-world data to prove this point, but I have already posted a number of other things that would indicate that. At the very least, I would not compare a QC to freeway driving in terms of their relative thermal effects. That's way off, please take my word for it.

As to radiant heat from the pavement, that's an interesting consideration, and perhaps it has some effect.

 

[Pipcecil]

I still don't understand the condition in Arizona versus other places that have resulted in the faster battery degredation. Texas last year had an extreme scorcher summer, not on par with Arizona, but temperatures stayed well above 100 degrees usually averaging about 105. Would a 10 degree ambient temperature cause a whole set of batteries to freak out versus another set? That 10 degrees of ambient air seems statistically insignificant in comparison. Texas last summer also did not get the cooling affect that Arizona gets during the nighttime hours. We had long periods were the temperature never dropped below 90 degrees for weeks!

I am no battery/engineer guy, but something must be significantly worse in Arizona versus places like Texas. Humidity and dry air? Payment heating (could there be a difference from asphalt to concrete)? As of yet (knock on wood) no one in Texas has reported battery loss, and, you could easily make the comparison that Texas is mostly similar to Arizona for heat-wise that got early rollouts.

I am a little hesitant to quickly jump to "its a heat related issue only" since no one in Texas has had problems. There has to be more to the equation than this, it just doesn't add up unless that few degree difference makes an exponential impact to the battery degredation.

 

[RegGuheert]

Reg, with all due respect, we had this before. Operational heat in those cells, even with spirited freeway driving, will likely result in just a few degrees above ambient. Most of our freeway driving happens between 0.5 and 2C battery load, and the cells barely break a sweat. I wish I had some real-world data to prove this point, but I have already posted a number of other things that would indicate that. At the very least, I would not compare a QC to freeway driving in terms of their relative thermal effects. That's way off, please take my word for it.

Yes, I've read your comments on this before, but I do not agree with some of your assertions. Specifically, the test that you showed appears to show a single cell sitting on a bench, but perhaps with a heat sink below. This is an entirely different thermal environment than a cell packaged in a module and then sandwiched in a large stack of modules, all of which are dissipating power at the same time. Also, you have asserted that the total power dissipation is about 100W. That may be true at 10 kW and high battery voltage, but at 80 kW and low battery voltage, it appears that it dissipates about 3200 W. Regeneration runs above 30 kW so perhaps you could see 500 W of power. I'm sorry, but it seems very reasonable to get a 12F rise in the hottest part of this pack. I suspect the hottest spot will likely be much higher than that.

As far as what measurements we will get, I'm not clear what the four sensors measure. It appears they are attached to the cases of four of the modules. But that could be many degrees lower than the chemistry inside the cells in the modules. Still, even that data will be much better than what we currently have.

ETA: One test we could easily do today is to take the car out at some ambient temperature and see if you can cross a threshold on the temperature bars by only driving. For instance, driving at 62F to see if you can get the sixth temerature bar to show would demonstrate whether you could get a 12F rise (at the sensors).

 

[ztanos]

I still don't understand the condition in Arizona versus other places that have resulted in the faster battery degredation. Texas last year had an extreme scorcher summer, not on par with Arizona, but temperatures stayed well above 100 degrees usually averaging about 105. Would a 10 degree ambient temperature cause a whole set of batteries to freak out versus another set? That 10 degrees of ambient air seems statistically insignificant in comparison. Texas last summer also did not get the cooling affect that Arizona gets during the nighttime hours. We had long periods were the temperature never dropped below 90 degrees for weeks!

I am no battery/engineer guy, but something must be significantly worse in Arizona versus places like Texas. Humidity and dry air? Payment heating (could there be a difference from asphalt to concrete)? As of yet (knock on wood) no one in Texas has reported battery loss, and, you could easily make the comparison that Texas is mostly similar to Arizona for heat-wise that got early rollouts.

I am a little hesitant to quickly jump to "its a heat related issue only" since no one in Texas has had problems. There has to be more to the equation than this, it just doesn't add up unless that few degree difference makes an exponential impact to the battery degredation.

Maybe someone put sugar in their electricity. :lol: But seriously, Is Arizona comparable in humidity levels? Was the heat in Texas due to humidity or was it all sustained heat?

 

[RegGuheert]

Pipcecil, I agree that Phoenix is only marginally hotter than many parts of Texas.

As of yet (knock on wood) no one in Texas has reported battery loss,

While it is true that no one from Texas has yet reported that their LEAF has lost a battery capacity bar, there have been several reports of battery capacity loss in Texas. IIRC, some have reported losing about 10% of their battery capacity based on GIDmeter readings.

I am a little hesitant to quickly jump to "its a heat related issue only" since no one in Texas has had problems.

I would say that no one in Phoenix has had problems, either, but both groups have had some battery capacity loss.

There has to be more to the equation than this, it just doesn't add up unless that few degree difference makes an exponential impact to the battery degredation.

I think what we are seeing can be fully explained by aging effects that are being accelerated at higher temperatures. I think of the Phoenix LEAFs as "canaries in the coal mine" in that they will show the effect earlier than other LEAFs on the road. Unfortunately, Texans may well be the next group to report battery capacity bar losses.

 

[DaveinOlyWA]

I am no battery/engineer guy, but something must be significantly worse in Arizona versus places like Texas. Humidity and dry air? Payment heating (could there be a difference from asphalt to concrete)? As of yet (knock on wood) no one in Texas has reported battery loss, and, you could easily make the comparison that Texas is mostly similar to Arizona for heat-wise that got early rollouts.

i believe we have reported degradation in TX and CA

 

[surfingslovak]

Yes, I've read your comments on this before, but I do not agree with some of your assertions. Specifically, the test that you showed appears to show a single cell sitting on a bench, but perhaps with a heat sink below.

Yes, a test bench setup is something different than what we have in the car, but please don't try to invalidate test results with speculation. What the AESC graphics shows is that their cells go up about 20F in extreme conditions. I would not expect more than that in the Leaf, even if the cells were less well heat sunk. The test used sustained 26C load, about five times the current the Leaf will see during jackrabbit starts, and about ten times the current drawn at high freeway speeds.

This is an entirely different thermal environment than a cell packaged in a module and then sandwiched in a large stack of modules, all of which are dissipating power at the same time.

This would imply a temperature gradient, perhaps something on the order of 5F between cell cores and the outer metal case of the car. While that's entirely possible, I believe that you will have hard time proving that.

Also, you have asserted that the total power dissipation is about 100W. That may be true at 10 kW and high battery voltage, but at 80 kW and low battery voltage, it appears that it dissipates about 3200 W. Regeneration runs above 30 kW so perhaps you could see 500 W of power. I'm sorry, but it seems very reasonable to get a 12F rise in the hottest part of this pack. I suspect the hottest spot will likely be much higher than that.

Please, my claim of 100W was in an entirely different context, and it was an average value. I have admitted in a conversation with Tom that more heat is developed during freeway driving. I just don't think it's going to be as much as during a QC, which is another assertion you seem to favor.

As far as what measurements we will get, I'm not clear what the four sensors measure. It appears they are attached to the cases of four of the modules. But that could be many degrees lower than the chemistry inside the cells in the modules. Still, even that data will be much better than what we currently have.

I think it's pretty clear that the sensors are taped to the outside wall of four different cell enclosures. If I recall correctly, their location is indicated in the shop manual.

ETA: One test we could easily do today is to take the car out at some ambient temperature and see if you can cross a threshold on the temperature bars by only driving. For instance, driving at 62F to see if you can get the sixth temerature bar to show would demonstrate whether you could get a 12F rise (at the sensors).

Yes, I've done something like that, along with other random observations, and I stand by my claim that we will see about 10F rise in sensor temperature when driving at sustained high speeds on the freeway, and much less than that at lower speeds in city driving.

 

[Ingineer]

It's not uncommon for me to see a 5-10 degree F rise in pack temp after a long charge, and that's here in the mild San Francisco Bay Area where my pack almost always starts below 70 degrees. The heat is mainly from the internal resistance of the battery, and some from the battery management system (balance resistors). Note that the temperature readings are what I'm seeing reported by Nissan's Battery Management System computer (Battery ECU) which uses 4 sensors spread throughout the pack to determine temperature.

Th internal resistance of my healthy pack is reading 92 milliohms. If my math is correct, This means carefully cruising along at about 55mph (assuming 20kW load) you'll be generating a minimum of 250 watts of heat in the pack. If you drive aggressively, it could easily be well over 1kW. Full throttle driving will create over 5.7kW of added heat!

I've noticed I can start out with a pack temp of 70, then take a long drive and return home with it reading only a few degrees higher, but still slowly climbing. It will continue to rise once the car is parked (even when inside a building with cool temps and not charging) and sometimes I've seen it get close to 80 before it starts to cool back off. This process takes hours because of the large thermal mass of the pack. If you start charging right away it exacerbates this issue and the temp climbs even higher. Another argument for charging early in the morning!

I could imagine in Phoenix after an aggressive drive and a return home to charge, the pack is going to be very very hot, enough to likely to cause degradation.

-Phil

 

[RegGuheert]

Yes, a test bench setup is something different than what we have in the car, but please don't try to invalidate test results with speculation. What the AESC graphics shows is that their cells go up about 20F in extreme conditions. I would not expect more than that in the Leaf, even if the cells were less well heat sunk. The test used sustained 26C load, about five times the current the Leaf will see during jackrabbit starts, and about ten times the current drawn at high freeway speeds.

I agree it is a brutal and impressive test, but the thermal environment is completely different, so those results do not tell anything about temperature rises within the LEAF battery system.

This would imply a temperature gradient, perhaps something on the order of 5F between cell cores and the outer metal case of the car. While that's entirely possible, I believe that you will have hard time proving that.

There certainly IS a temperature gradient between the cell cores and the outer metal case of the car since the power is being dissipated in the cell cores and the thermal resistance is not zero. Agreed, I cannot prove what the gradient is, but I think 5F sounds pretty low, but could be in the ballpark.

Please, my claim of 100W was in an entirely different context, and it was an average value. I have admitted in a conversation with Tom that more heat is developed during freeway driving. I just don't think it's going to be as much as during a QC, which is another assertion you seem to favor.

I'm sorry, but I never made any comparison between heat dissipated during QC and driving on the highway. But I will say that I see no reason why temperature rise in the battery could not be higher in city driving if you are accelerating and braking hard. The cooling is less at lower speeds and heat dissipation can be very high.

I think it's pretty clear that the sensors are taped to the outside wall of four different cell enclosures. If I recall correctly, their location is indicated in the shop manual.

Thanks! That's what I remember, too!

Yes, I've done something like that, along with other random observations, and I stand by my claim that we will see about 10F rise in sensor temperature when driving at sustained high speeds on the freeway, and much less than that at lower speeds in city driving.

It sounds as if we are in violent agreement, then! I have proposed a 12F temperature rise to the cell chemistry and you are claiming 10F to the sensors on the cases. Perhaps I wrote something different from what was intended?

Please note also that I was talking about a 12F rise from BOTH QC and driving.

 

[RegGuheert]

Thanks for all the information, Phil!

It's not uncommon for me to see a 5-10 degree F rise in pack temp after a long charge, and that's here in the mild San Francisco Bay Area where my pack almost always starts below 70 degrees.

You are talking about L2, correct?

Note that the temperature readings are what I'm seeing reported by Nissan's Battery Management System computer (Battery ECU) which uses 4 sensors spread throughout the pack to determine temperature.

Thanks for that. Somehow I thought LEAFscan had access to each of the four sensors individually. I guess not. If it somehow combines these, do you know what it does? Average? Peak? Something else?

The internal resistance of my healthy pack is reading 92 milliohms. If my math is correct, This means carefully cruising along at about 55mph (assuming 20kW load) you'll be generating a minimum of 250 watts of heat in the pack. If you drive aggressively, it could easily be well over 1kW. Full throttle driving will create over 5.7kW of added heat!

I have been using 50 mohm for my calcs. Does anyone have any idea what the resistance will be toward the end of the pack life?

I've noticed I can start out with a pack temp of 70, then take a long drive and return home with it reading only a few degrees higher, but still slowly climbing. It will continue to rise once the car is parked (even when inside a building with cool temps and not charging) and sometimes I've seen it get close to 80 before it starts to cool back off.

O.K. That means that something in the pack was above 80F when you parked. How much above 80F is hard to say without a thermal model.

 

[EdmondLeaf]

After questions, Nissan still claims 80% capacity for Leaf battery after 5 years
http://green.autoblog.com/2012/06/15/nissan-still-claims-80-capacity-for-leaf-batt/
edit
Like with everything in your life, you always have right to have your opinion about what other are saying, writing.

 

[surfingslovak]

I agree it is a brutal and impressive test, but the thermal environment is completely different, so those results do not tell anything about temperature rises within the LEAF battery system.

Right, and while I agree that the thermal conditions are different, I believe that this sets a cap to the temperature rise we will see when operating the vehicle.

There certainly IS a temperature gradient between the cell cores and the outer metal case of the car since the power is being dissipated in the cell cores and the thermal resistance is not zero. Agreed, I cannot prove what the gradient is, but I think 5F sounds pretty low, but could be in the ballpark.

Right, but that's the core of our argument. You seem to claim that the cell core temperature is at least 7.5F higher than ambient on average for the life of the vehicle, and I'm of the opinion that it's lower. Perhaps even much lower.

I'm sorry, but I never made any comparison between heat dissipated during QC and driving on the highway. But I will say that I see no reason why temperature rise in the battery could not be higher in city driving if you are accelerating and braking hard. The cooling is less at lower speeds and heat dissipation can be very high.

If you meant to say that it's QC in addition to freeway driving, then I apologize, because I misunderstood that, like you seem to have misread my post about 100 Watt of average dissipated heat.

It sounds as if we are in violent agreement, then! I have proposed a 12F temperature rise to the cell chemistry and you are claiming 10F to the sensors on the cases. Perhaps I wrote something different from what was intended?

Yes, perhaps I misunderstood your post, and I apologize if I did. Also, while my posts might seem argumentative and adamant, I'm just trying to get a better understanding of the car, much like yourself and everyone else on this board.

Please note also that I was talking about a 12F rise from BOTH QC and driving.

Right, that sounds reasonable, and probably even too low. Nissan went on record indicating that more heat is developed when charging than during vehicle operation. I mentioned that before, but I can't seem to find the quote.

It's not uncommon for me to see a 5-10 degree F rise in pack temp after a long charge, and that's here in the mild San Francisco Bay Area where my pack almost always starts below 70 degrees.

Yes, great data, thank you Phil! For what it's worth, I can confirm that I regularly see six temperature bars following a level 2 charge in a similar climate. I typically only see 5 bars here during vehicle operation and thereafter, which means that the sensors are reading 72F or below.

Note that the temperature readings are what I'm seeing reported by Nissan's Battery Management System computer (Battery ECU) which uses 4 sensors spread throughout the pack to determine temperature.

Thanks for that. Somehow I thought LEAFscan had access to each of the four sensors individually. I guess not. If it somehow combines these, do you know what it does? Average? Peak? Something else?

I believe that Phil answered that in one of his earlier posts, and Leafscan is displaying an average value computed from the four sensors.

The internal resistance of my healthy pack is reading 92 milliohms. If my math is correct, This means carefully cruising along at about 55mph (assuming 20kW load) you'll be generating a minimum of 250 watts of heat in the pack. If you drive aggressively, it could easily be well over 1kW. Full throttle driving will create over 5.7kW of added heat!

I have been using 50 mohm for my calcs. Does anyone have any idea what the resistance will be toward the end of the pack life?

This is great! I believe that it's close to the 100 mOhm Tom and I have determined with Gary's meter. If I recall correctly, aging models typically predict similar percentage change for both capacity loss and internal resistance rise. Another thing to note, if I eyeballed it right, then 55 mph is about 0.5C load and about 100W of heat is developed in the pack, 80 mph is about 1C and 360 Watts of heat, and 87 mph is about 1.5 C and 800 Watts worth of heat in the pack.

I've noticed I can start out with a pack temp of 70, then take a long drive and return home with it reading only a few degrees higher, but still slowly climbing. It will continue to rise once the car is parked (even when inside a building with cool temps and not charging) and sometimes I've seen it get close to 80 before it starts to cool back off.

O.K. That means that something in the pack was above 80F when you parked. How much above 80F is hard to say without a thermal model.

I think this observation, while anecdotal, could have implications for battery longevity. If you assume that an average vehicle spent only about 15% of its life charging or driving, and it needed twice the amount of time to dissipate the accumulated waste heat, then the cells will spend significant amount of time above ambient.

 

[palmermd]

After questions, Nissan still claims 80% capacity for Leaf battery after 5 years
http://green.autoblog.com/2012/06/15/nissan-still-claims-80-capacity-for-leaf-batt/

Once again, an article that has no reference as to who at Nissan made the comment, and when those comments were supposedly made. This is just another typical "journalist" reading an article somewhere and then rehashing it on their website.

 

[DaveEV]

After questions, Nissan still claims 80% capacity for Leaf battery after 5 years
http://green.autoblog.com/2012/06/15/nissan-still-claims-80-capacity-for-leaf-batt/

Once again, an article that has no reference as to who at Nissan made the comment, and when those comments were supposedly made. This is just another typical "journalist" reading an article somewhere and then rehashing it on their website.

Yep, nothing new there, they even list their source as the GreenCarReports article from 2 days ago. ABG in general has very crappy "reporting".

 

[TickTock]

It's not uncommon for me to see a 5-10 degree F rise in pack temp after a long charge, and that's here in the mild San Francisco Bay Area where my pack almost always starts below 70 degrees. The heat is mainly from the internal resistance of the battery, and some from the battery management system (balance resistors). Note that the temperature readings are what I'm seeing reported by Nissan's Battery Management System computer (Battery ECU) which uses 4 sensors spread throughout the pack to determine temperature.

Th internal resistance of my healthy pack is reading 92 milliohms. If my math is correct, This means carefully cruising along at about 55mph (assuming 20kW load) you'll be generating a minimum of 250 watts of heat in the pack. If you drive aggressively, it could easily be well over 1kW. Full throttle driving will create over 5.7kW of added heat!

I've noticed I can start out with a pack temp of 70, then take a long drive and return home with it reading only a few degrees higher, but still slowly climbing. It will continue to rise once the car is parked (even when inside a building with cool temps and not charging) and sometimes I've seen it get close to 80 before it starts to cool back off. This process takes hours because of the large thermal mass of the pack. If you start charging right away it exacerbates this issue and the temp climbs even higher. Another argument for charging early in the morning!

Not sure about the Nissan pack chemistry, but many batteries are endothermic during discharge (will actually absorb heat) and exothermic during charging. I suspect this is the case for the Leaf pack since you saw a large rise in temperature during charging and a very small rise during driving (which typically pulls more power then charging). This could also explain why they limit the regen to 20kW but will let you have 80kW for accelleration.

 

[surfingslovak]

Just wanted to bring up an older post from Tony, which seems to indicate that multiple QCs combined with freeway driving can raise battery temperature by 80F or more. Note that maximum daily temperature in Ashland, OR was 47F that day (March 19, 2012).