Nissan Leaf Battery

I was just wondering about the reasoning behind Nissan decided to go with air cooling and not water cooling/heating of the traction battery.

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

myleaf said:

I was just wondering about the reasoning behind Nissan decided to go with air cooling and not water cooling/heating of the traction battery.

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

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I can't speak for Nissan. But it seems to me that the air cooling seems to work perfectly fine. I drove my Leaf this Summer in 110 degree weather for like 2 months and it never even approached the "red zone" of the temperature gauge. That being the case, I would imagine air cooling is cheaper and more reliable than liquid cooling. After the issue with the Volt, I'm kind of glad the Leaf is air cooled.

myleaf said:

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

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all of the above plus weight savings.

It works fine as is. Why spend money to add complexity and reduce reliability?

myleaf said:

I was just wondering about the reasoning behind Nissan decided to go with air cooling and not water cooling/heating of the traction battery.

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

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I don't think that it's even really "air cooled". The pack is sealed and there's no air flow around the batteries. There's simply no active cooling at all.

As I understand it, the primary reason Nissan can safely rely on simple air circulation for the LEAF battery pack is its inherently stable chemistry. If I'm not mistaken, the Volt battery pack is more similar to that of the Tesla, which also relies on a liquid-based temperature management system. The Tesla uses lithium colbalt batteries, which perform very well but are also very unstable. Therefore they have to use a complex liquid cooling method. The Nissan Leaf uses some variant of lithium iron polymer batteries which don't store quite as much energy, but also do not require such complex apparatus to ensure their safety.

johnr said:

If I'm not mistaken, the Volt battery pack is more similar to that of the Tesla, which also relies on a liquid-based temperature management system.

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From what we have collectively learned, this is not correct. Volt's pack is closer to the Leaf than to Tesla with regards to its chemistry. GM relies on a thermal management system for other reasons. I believe that it has something to do with warranty requirements for PHEVs, and they felt the need to design a more complex pack to be able to meet these requirements. It's also possible that the batteries they are using don't match the thermal properties of Leaf's AESC cells, which in turn helped catalyze the decision to include a thermal management system.

Because The LEAF power is limited water cooling is not needed. This saves weight, money, reduces complexity, improves system reliability, easier to service and can be packaged smaller. There is no air circulation as the pack is pressure sealed like a can of Tuna.

Yes - we covered this is great detail before the car started to ship. Unfortunately it's difficult to find.

The Leaf's LiMn2O4 cells are one of the two 'safe' variants (along with LiFePO4) so they didn't need to use extraordinary measures to prevent a run-away fire. That's one of the reasons for the cooling system in the Tesla Roadster battery - the lithium cobalt cells.

The Leaf battery doesn't generate as much heat in use compared with a hybrid due to the differences in the way power is used and recharged. Hybrid power pulses are strong and relatively short in duration, and hybrids use a smaller battery capacity to reduce cost and weight. Making a smaller battery work much harder - and still provide the emissions warranty lifespan - requires more than passive cooling.

The Leaf uses thin cells with a lot of surface area, subjects them to lower charge and discharge loads, and uses a cell chemistry that is more efficient. All of these together mean that the battery doesn't generate much heat during charge or discharge - and heat that isn't generated doesn't have to be removed. The conductive cooling just plain works.

myleaf said:

I was just wondering about the reasoning behind Nissan decided to go with air cooling and not water cooling/heating of the traction battery.

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

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Before Mark Perry jumped in and put his normal BS happy face on it, the product guy from Nissan said they would have lost the fifth seat. Plus Nissan wouldn't have had the time to implement it. http://www.wired.com/autopia/2010/01/nissan-leaf-2/" onclick="window.open(this.href);return false;

While the AESC manganese spinel/NMC batteries used in the Leaf are not as stable as LFP batteries, a thermal management system isn't designed to prevent fires, it's designed to prolong battery life. Nissan just decided that the cost of replacing some battery packs would be less than the cost of putting a thermal management system in every Leaf, a decision based on the projection that leasing would be more popular than buying. Plus again, they probably didn't have enough time.

FYI the Leaf battery pack is not air cooled. There is a fan but its purpose is to keep all the cells at a similar temperature and to avoid hot spots in the pack. It won't cool anything.

SanDust said:

myleaf said:

FYI the Leaf battery pack is not air cooled. There is a fan but its purpose is to keep all the cells at a similar temperature and to avoid hot spots in the pack. It won't cool anything.

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Where exactly is this mystery fan hiding in the pack. Exact location please because form what I can see there is no fan period.

I'm about to head out of town for a few days. I remember reading somewhere that I should not leave the battery fully charged. Is that correct?

There is not a fan in any LEAF battery drawing, or mockup, that I've physically seen.

The battery is neither air cooled (with or without a fan), nor liquid cooled. The closest thing to cooling is conductive losses through the car's steel body.

As stated, the battery is sealed so that it can pass the 700mm of water test:

[youtube]http://www.youtube.com/watch?v=xxL4LVgdP7E[/youtube]

SanDust said:

myleaf said:

I was just wondering about the reasoning behind Nissan decided to go with air cooling and not water cooling/heating of the traction battery.

Cost, results of risk/DFMEA analysis, simpliciy, advanced battery technology, all of the above, none of the above ??

Click to expand...

Before Mark Perry jumped in and put his normal BS happy face on it, the product guy from Nissan said they would have lost the fifth seat. Plus Nissan wouldn't have had the time to implement it. http://www.wired.com/autopia/2010/01/nissan-leaf-2/" onclick="window.open(this.href);return false;

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This piece - written by someone that moved from Tesla to Coda - was penned during the period when other car companies were bashing Nissan for not following the rest of the pack (pun intended) regarding battery climate control. Tesla uses lithium cobalt 'laptop' cells in a very high performance application - they NEED thermal management. Coda and GM make hybrids - they NEED thermal management. The Leaf does not.

SanDust said:

While the AESC manganese spinel/NMC batteries used in the Leaf are not as stable as LFP batteries, a thermal management system isn't designed to prevent fires, it's designed to prolong battery life. Nissan just decided that the cost of replacing some battery packs would be less than the cost of putting a thermal management system in every Leaf, a decision based on the projection that leasing would be more popular than buying. Plus again, they probably didn't have enough time.

FYI the Leaf battery pack is not air cooled. There is a fan but its purpose is to keep all the cells at a similar temperature and to avoid hot spots in the pack. It won't cool anything.

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There is zero need to cool these cells because of their efficiency, their pouch configuration, and the relatively low demand on the battery when powering the car.

There is no fan inside the battery box. We've seen the battery, we have the service manuals with battery parts breakdown and electrical system details.

The only upgrade to battery thermal management is the addition of a HEATER as part of the cold weather package. That's right - the cells are so efficient they need HELP STAYING WARM in the winter. :lol:

TonyWilliams said:

There is not a fan in any LEAF battery drawing, or mockup, that I've physically seen.

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That's because there is no fan. I looked at every part in the pack and I don't see why people think there is a fan. To distribute the air properly there would need to be several, not one.

BrainDonor said:

I'm about to head out of town for a few days. I remember reading somewhere that I should not leave the battery fully charged. Is that correct?

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Yes, that is correct. Leaving battery at 100% is not good for it. That's why 80% charge is called Long Life Mode. Actually, it is a combination of time and temperature at the higher voltage of a 100% charge that isn't good for the battery. I wouldn't leave it at more than 80% charge. Personally, I stick to the optimal 40-60% charge if I am not using the car or will be gone for a few days to a week.

Stoaty said:

BrainDonor said:

I'm about to head out of town for a few days. I remember reading somewhere that I should not leave the battery fully charged. Is that correct?

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Yes, that is correct. Leaving battery at 100% is not good for it. That's why 80% charge is called Long Life Mode. Actually, it is a combination of time and temperature at the higher voltage of a 100% charge that isn't good for the battery. I wouldn't leave it at more than 80% charge. Personally, I stick to the optimal 40-60% charge if I am not using the car or will be gone for a few days to a week.

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Thanks, Stoaty. I plan to leave it at about 40%, then charge it back to 100% just before the drive back home (which is about 45 miles on the highway).

EVDRIVER said:

That's because there is no fan. I looked at every part in the pack and I don't see why people think there is a fan. To distribute the air properly there would need to be several, not one.

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I don't know about anyone else, but I think there is a fan because a few years ago at a conference Nissan said there was. :lol: I remember that the explanation was that the purpose was not to cool but to keep the temperature throughout the pack even so as to ensure better cell balancing. Could the fan be external?

Note that Siry had the same understanding and he clearly spent time interviewing folks from Nissan: "Nissan has opted to use only an internal fan that circulates the air within the sealed pack to evenly distribute the heat, which escapes by passive radiation through the pack’s external case."

No fan makes it more interesting.

SanDust said:

EVDRIVER said:

That's because there is no fan. I looked at every part in the pack and I don't see why people think there is a fan. To distribute the air properly there would need to be several, not one.

Click to expand...

I don't know about anyone else, but I think there is a fan because a few years ago at a conference Nissan said there was. :lol: I remember that the explanation was that the purpose was not to cool but to keep the temperature throughout the pack even so as to ensure better cell balancing. Could the fan be external?

Note that Siry had the same understanding and he clearly spent time interviewing folks from Nissan: "Nissan has opted to use only an internal fan that circulates the air within the sealed pack to evenly distribute the heat, which escapes by passive radiation through the pack’s external case."

No fan makes it more interesting.

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There was also writing form Nissan I saw early on that quoted a 6.6kw charger but I'm quite sure its not there. Rather then speculate on rumors one could easily check as I did a very long time ago and there is no fan in there. Besides, it makes no sense if there were, but according to the detailed parts list, wiring diagrams, etc it is not there. I doubt there ever was.

TonyWilliams said:

The battery is neither air cooled (with or without a fan), nor liquid cooled. The closest thing to cooling is conductive losses through the car's steel body.

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Isn't the underside of the pack exposed? That would make the pack as a whole passively air-cooled by the airflow under the vehicle.

Based on what I've read on this forum, the pack does not need active cooling even in a Phoenix summer. What it needs is heating in the colder climates. That's essentially the opposite problem and one that's addressed by adding heating pads inside the pack.
=Smidge=