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RegGuheert
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Leaf Number: 5926
Location: Northern VA

Module rotation to extend battery life?

Wed Feb 06, 2013 8:15 am

I've been thinking about how to get the longest useful life out of the LEAF battery and it occurred to me that this battery could benefit from rotating the modules within the pack in much the same way that tire wear can be evened out by rotating tires. Just like the tires on a vehicle, the modules in the battery pack live in different environments and likely will wear out at different rates. Also like the tires, we have the option to simply replace the modules which wear more quickly as they reach the end of their lives or we could consider rotating our modules to get even wear and potentially get a longer interval before any modules need to be replaced. It appears from the results of the "How long will you keep your LEAF?" survey there are more of us out there with long-term plans for this car than I had expected. Perhaps a few of us will find module rotation a worthwhile endeavor.

While we do not yet have any data on what the relative wear-out rates are for the different positions in the pack, I expect that information will emerge over time. (That is, assuming dealerships learn how to perform the cell voltage test properly at very low SOC. :roll: ) Depending on how much different the aging of the modules at various positions turns out to be, it seems reasonable that a rotation schedule could be developed which would optimize the life of the overall pack, allowing for it to be replaced when all modules have reached their end-of-life at nearly the same time. OTOH, if the modules tend to wear very evenly, there would be no point in doing this kind of a rotation. Personally, I suspect there will be locations which wear modules more rapidly than others due to higher temperatures. We shall see.

Of course rotating the modules in the LEAF is a much bigger and more technical job than rotating the tires, but note that the cost of replacing a module or replacing the pack is also a much larger expense.

Anyway, it is too early to start doing this today, but I thought I would get a dialog going. What say you?
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

adric22
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Leaf Number: 000768
Location: Fort Worth, TX

Re: Module rotation to extend battery life?

Wed Feb 06, 2013 8:31 am

This is something that has occurred to me before as well. But I haven't heard any experts talk about it and I'm not sure if the benefit would be enough to justify the huge amount of labor involved. At least the Leaf has only 48 modules. Imagine doing a Tesla!

We can probably look at the Toyota hybrids as a guide. Has anyone noticed if specific modules wear out faster? For examples, ones in the middle, or towards one side or another? I've replaced a few 1st generation Prius packs before but what I found is those modules were pretty much ALL either dead or close to dead. The problem with those packs was that they leaked electrolyte. So looking at a 2nd generation Prius pack that needs replacing (which those are probably far and few between) would be a good starting point.
2013 Blue Nissan Leaf SV
2012 Summit White Chevy Volt

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TickTock
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Location: Queen Creek, Arizona
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Re: Module rotation to extend battery life?

Wed Feb 06, 2013 8:35 am

I'd like to rotate my whole battery with one from the great white north! :-) What? no volunteers? Seriously, I guess the question is how uniform the temperature is throughout the stack. If some batteries get cooked more than others there may some value but it would have to be significant for me to go for it for fear the treatment(major battery surgery) is worse than the malady.

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RegGuheert
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Re: Module rotation to extend battery life?

Wed Feb 06, 2013 8:39 am

adric22 wrote:This is something that has occurred to me before as well. But I haven't heard any experts talk about it and I'm not sure if the benefit would be enough to justify the huge amount of labor involved. At least the Leaf has only 48 modules. Imagine doing a Tesla!

We can probably look at the Toyota hybrids as a guide. Has anyone noticed if specific modules wear out faster? For examples, ones in the middle, or towards one side or another? I've replaced a few 1st generation Prius packs before but what I found is those modules were pretty much ALL either dead or close to dead. The problem with those packs was that they leaked electrolyte. So looking at a 2nd generation Prius pack that needs replacing (which those are probably far and few between) would be a good starting point.
Keep in mind that the Tesla batteries have a liquid cooling system and therefore the modules all live in a fairly isothermal environment. Likewise the Toyota and Honda hybrid batteries are convection cooled, with the same intention of maintaining all of the batteries at the same temperature (although I do not know how successful they have been). The LEAF modules, OTOH are cooled by conduction and are stored in various locations and orientations, so they likely see different thermal environments. How different is yet to be determined. But it is almost certainly more different than the modules in a Volt or the cells in a Tesla will see.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

edatoakrun
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Delivery Date: 15 May 2011
Leaf Number: 2184
Location: Shasta County, North California

Re: Module rotation to extend battery life?

Wed Feb 06, 2013 8:53 am

I think the "rotation" will most likely only occur when the battery pack is removed for replacement.

The modules with the highest remaining capacity will be selected for "rebuilt" packs.

Those with lower capacity will be re-purposed for various stationary applications.

And only those with the worst performance, whether due to temperature, manufacturing variability, or other causes, will be sent to the recyclers.
no condition is permanent

Herm
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Location: Timbuktu, Mali

Re: Module rotation to extend battery life?

Wed Feb 06, 2013 10:55 am

What edatoakrun said..

The pack has four temperature sensors, you should be able to read each one with the proper equipment.

Long ago when I used to play with nimh packs, the outer cells used to die the fastest.. no idea why.

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RegGuheert
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Re: Module rotation to extend battery life?

Wed Feb 06, 2013 11:11 am

Herm wrote:What edatoakrun said..
...only addresses what might happen to the batteries once they are replaced. I am looking at what existing owners might be able to do to delay that replacement as long as possible.
Herm wrote:The pack has four temperature sensors, you should be able to read each one with the proper equipment.
Unfortunately I do not think temperature data from the outside case of four modules tells the story of how different modules in the pack will degrade over time. For instance, I expect the internal temperatures in the modules at the top of the front-seat stacks and in the middle of the back-seat pack to be the hottest.
Herm wrote:Long ago when I used to play with nimh packs, the outer cells used to die the fastest.. no idea why.
Interesting. Do you have any idea how much shorter the life of those cells was compared to others in the pack? (Not that I think there would be any way to know this...)

I do think the NiMH failures that are occurring in the Honda Civic Hybrid are related to the high self-discharge rate that those types have. Some cells seem to get much worse over time and even fairly short periods of non-use can result in a cell fully discharging and shorting. I suspect Li-ion will have very different failure characteristics.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

Herm
Posts: 3765
Joined: Sun May 23, 2010 3:08 pm
Delivery Date: 29 Aug 2012
Location: Timbuktu, Mali

Re: Module rotation to extend battery life?

Wed Feb 06, 2013 12:44 pm

RegGuheert wrote:Interesting. Do you have any idea how much shorter the life of those cells was compared to others in the pack? (Not that I think there would be any way to know this...)
No idea, I always thought the other cells were not too far behind in dieing.. we will know all this when you-know-who releases the Leafscan.

I am sure there are temperature differences inside the Leaf pack.

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mwalsh
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Re: Module rotation to extend battery life?

Wed Feb 06, 2013 12:58 pm

Herm wrote:No idea, I always thought the other cells were not too far behind in dieing.. we will know all this when you-know-who releases the Leafscan.
What is this mythical LEAFscan of which you speak? ;)
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TomT
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Re: Module rotation to extend battery life?

Wed Feb 06, 2013 2:15 pm

I'm now convinced my lease will be up before I ever see one... :lol: At this point, I'll likely just stick with my Gid meter...
mwalsh wrote:What is this mythical LEAFscan of which you speak? ;)
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
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