Nissan Leaf Cells Test Data

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Re: Nissan Leaf Cells Test Data

Post by icecube57 » Oct 15 2014 6:38pm

The way the case is made I dont see how compression is being accomplished. Other than gravity compression when laying flat. You physically cant take a threaded rod and force tighten them like a123 does cause the packs have metal collars where the bar would go through which prevent it from compressing.

* I guess i answered my own question and then read it later in the forum post. LMAO.

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Re: Nissan Leaf Cells Test Data

Post by teslanv » Oct 15 2014 6:45pm

Yeah, but if the metal collars don't touch when you stack the individual units, then you can compress multiple units, no?
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Re: Nissan Leaf Cells Test Data

Post by icecube57 » Oct 15 2014 6:56pm

I see what you are getting at but I don't think the cell cases will compress and have an impact on the cell internally. Like a coke can is pretty strong and if you stand on it. It will support you. Put a ding in the case and you rupture the integrity of the can and make it weak. So putting any forceful compression on what is essentially sardine cans is a no go. Yes i know even a little pressure over a wide surface helps but again the collars were there for a reason so I think no clamping compression is advised. and the way they interlock and the way the cells is almost suspended free floating to an extent. The divot or design in the case isn't providing much pressure I dont think It clearly would have been deeper divot. Im a fan of cell compression in lipo but this isnt a high C rated cell so compression would help with IR when it comes to cell heating and electrolyte gassing bloating the cell but in the design I dont the the demand on the cell is that great to need the the additional pressure. A123 has much higher discharge rate and more cell heating. We abuse A123 in 1P configurations but here we have the nissan leaf cells in a 2P configuration by design. I could go on and on but Im not an engineer. Im just thinking logically off the top of my head and based on the brief time I had the cells in my possesion.

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Re: Nissan Leaf Cells Test Data

Post by icecube57 » Oct 15 2014 7:05pm

Looked at a picture of a virgin pack and the vertical packs are being held in place but not necessarily compressed. Here is a though if you do plan to compress them still via the holes in the corners. I think some type of hard material the size of the built in divot of the canister should be placed in between each canister and then a threaded rod should be put through it and tighten and do so with a torque wrench to make sure even pressure is applied.

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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 15 2014 7:21pm

icecube57 wrote:The way the case is made I dont see how compression is being accomplished. Other than gravity compression when laying flat. You physically cant take a threaded rod and force tighten them like a123 does cause the packs have metal collars where the bar would go through which prevent it from compressing.

* I guess i answered my own question and then read it later in the forum post. LMAO.
Nissan has the cells laying on their side. Very strong and rigid steel compression plates go on both ends of each 24 module string, and the threaded rods are used to crank down and hold the compression force of those end-plates. It cranks down enough force to shrink that stack of 24 modules by about 2.5" more than just stacking them, so the compressive force is substantial.

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Re: Nissan Leaf Cells Test Data

Post by agniusm » Oct 15 2014 10:44pm

If they were compression plates, they cut out most important part for compression - the middle:) Sure they tighten battery to be rigid and sure it will decrese (2.64mm per module according to your figure) in width but inside cells will feel little to none compression.

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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 16 2014 12:00am

agniusm wrote:If they were compression plates, they cut out most important part for compression - the middle:) Sure they tighten battery to be rigid and sure it will decrese (2.64mm per module according to your figure) in width but inside cells will feel little to none compression.
Of course there's significant compressive force. The part you're missing is that the design of the 2 large faces of the cans make them act as flat springs. Experts in the field have told us point blank that pouch cells require compression. Aren't you one of the guys who was running A123 amp20's with no compression, and didn't you suffer some premature failures? Sure they may have had other causes too, but I don't believe in coincidences. The A123 factory guy is the one who told us those need 4psi compression. Plus Icy measured greater capacity for leaf cells with simple compression. Plus there's no free space inside the faces of the leaf cans, so with the 24 module stack squeezed down to a 6cm+ shorter stack in the rack than stacked on the floor, it's quite obviously due to significant compression force. Otherwise the middle of the cans would be bulging out 3cm from both ends.

All pouch cells require compression. Without compression they swell and gas comes out of solution easier causing them to puff. We've seen it with all pouch cells when they aren't properly compressed. Those metal pieces that seem like spaces are out beyond the borders of the cells inside. Their purpose is to spread the forces evenly, so the faces can act as springs, which combined with the large plastic pieces inside provides a nice even compression across the cells.

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Re: Nissan Leaf Cells Test Data

Post by agniusm » Oct 16 2014 12:36am

OK, I will argue no more but measure force in the middle of the module when 2 modules are stacked with leaf hardware today for the sake of science :)

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Re: Nissan Leaf Cells Test Data

Post by agniusm » Oct 16 2014 10:51am

Here is your proof that they are not compressed at all:






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Re: Nissan Leaf Cells Test Data

Post by inedible » Oct 16 2014 11:07am

drees wrote:4.18V seems very high when Nissan only charges them to 4.10V (or maybe 4.11V). A 80%/long-life-mode charge only charges them to about 4.02V.

Will be interesting to see how long they last for you. How long do the cells sit fully charged before you use them?
Source? I always heard they were charged to 4.2 in the car. I was charging them to 4.1 to be safe, until I watched this episode of EVTV Motor Verks: https://www.youtube.com/watch?v=jzb51NSB0bM&t=85m

He shows a graph of the charge curve for these batteries and he's convinced there's no "asymptote" at the end by 4.2v. Typically the graph curves upwards sharply at the end of the charge, but you don't see that in these batteries at 4.2v. He goes on to theorize they're designed for 4.3 or 4.4v but that would boil some electrolyte or something on the cathode side. At any rate he specifically says "I don't recommend charging these to 4.1, they should be totally fine at 4.2" or something to that effect.
999zip999 wrote:inedible what is the size of that pack ? 67v ? and how much does it weigh ? It looks big next to the hyperion, but the camera always puts 5lbs on me.
Yep, it's 16S. 60V nominal, 67v fresh off the charger. It weighs about 30lbs. I believe these modules are 7lbs apiece, and I've got 4.

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Re: Nissan Leaf Cells Test Data

Post by drees » Oct 16 2014 1:26pm

inedible wrote:Source?
I have a LEAF and the CAN bus tools to read individual cell-pair voltages along with pack voltages.

A "100%" charge - which the LBC claims is around 94-95% absolute capacity - has the total pack at 394V - 96 cells in series so that comes to 4.104V on average. Typically you see anywhere from 0.01-0.04V difference between min/max, so you can see individual cells up at 4.12 with the entire pack voltage around 395V - newer LEAFs in particular (2013+) seem to charge the cells slightly higher so you more often see voltages of 4.12 or occasionally 4.13V, but nothing higher than that.

An 80% charge - which is an actual 80% SOC according to the LBC - has the total pack at 386V - or about 4.02V / cell.

The car goes into "turtle" when the lowest cell measures appx 3.0V at rest. It can dip under that under power.

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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 16 2014 3:50pm

agniusm wrote:Here is your proof that they are not compressed at all:
Where you measured didn't prove anything. I could have told you putting the sensor there wouldn't have compression. That's not where the cells are and not where compression is needed. Plus the spacers actually prevent pressure where you measured. Put the pressure sensor within 1cm or 2 of the middle of can and watch what happens. That test will come up short of full pressure without the full end plates, but I think it should show at least some pressure despite the flex in part you are using as an end plate. The real end plates are 2cm thick steel structures with 2 arched reinforcements for rigidity with all 3 contact points well within the cell area and one dead center. The structure could serve no other purpose than to ensure compression, and there's no way Nissan would include such a structure with the weight & space penalty to make the end plates so rigid if they didn't absolutely know from testing that it was needed.

I have a full rack of 24 and won't break it up any time soon, so I can loosen the bolts and slide a pressure sensor in there easy enough. As much as I hate wasting my own time when I know the results in advance, if it stops just one person from building their pack without compression, then I'll do it. I don't have a sensor. Is this one on Ebay ok? http://www.ebay.com/itm/US-Shipping-FSR ... 2a42f67090

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Re: Nissan Leaf Cells Test Data

Post by agniusm » Oct 17 2014 12:06am

Yes, that is the sesor I got. I did measure module in a place where it is most elevated. The middle would have 2mm larger gap. 24s stack does have large end plates but look at the 8 and 4 module stacks, they dont even have same sort of plate on top and if compression was needed dont you thing that all stacks would be with same plates? Another aspect is a shape of module can. A123 cells do have even surface on aluminium heat sink separatos and end plates are even. Leaf module cans are uneven so some pats of a cell would be compressed while others wouldnt. We must not forget that the chemistry is different and we cant apply same rules as wb9k described some time ago.

Image

You can clearly see small gap between modules, same i got putting spacers.

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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 17 2014 5:02pm

The shape of the can makes the center parts work as a flat spring with the rigid plastic rectangle inside ensuring that the force is spread evenly. Looking more closely at the structure and way they use those spacers, I think you are right that the compression force on the cells isn't from pushing the faces of the cans together. Instead, each can is squeezed at the edges by those spacers, so the can itself via the flat spring faces puts the cells inside that can under compression. It's likely that the can itself puts some compression on the cells even without some outside force, but in the rack definitely adds to that as evidenced by the difference in height of the stack while in the rack. I'm talking about a stack of modules with no spacers at all being 2.5mm thicker per module than those in the rack.

That even helps me understand why all those heavy steel spacers are used. They help maintain a slight airspace between modules for better cooling, while still putting the cells under compression, and also allow a bit of space for thermal expansion and contraction.

What year Leaf is yours from? The rack of 24 modules I have was built in late 2012 and has all of the modules on their sides. I'm wondering if the horizontal stacking is a newer or older.

I only opened up one can...a real pain in the butt. If I decide to take more cells out of the cans, I'll do it by grinding off the lip that holds the top on. If I can do that cleanly, then I'll be able to see how much it pops up as that flat spring is released. That might even give us an idea of the compressive force.

Now that I think about it, I will definitely open 1 that way. If the combination of the top and the plastic proves to be a sufficient spring and way to spread the force, then I can use one can to make a 1p20s pack, and have leftovers for a flat spring for both ends of my Amp20 pack to provide compression. Coming up with good flat springs for my A123amp20 is why my 31 cells still sit unused. My batteries never have thermal issues, so I can get away with face to face cell stacking even with these lower C rate Leaf cells without having to worry about cooling.

If anyone has come up with a method or solvent to release the strong sticky stuff without disturbing the cell at all, I'm all ears. I'd want to get rid of all but the two end pieces of 2mm thick plastic.

Here is a crude drawing of how it works and why the test showed no compressive force:
How Nissan Leaf modules compress cells.JPG
How Nissan Leaf modules compress cells.JPG (19.27 KiB) Viewed 3713 times
Last edited by John in CR on Oct 17 2014 5:36pm, edited 1 time in total.

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Re: Nissan Leaf Cells Test Data

Post by drees » Oct 17 2014 5:36pm

John in CR wrote:What year Leaf is yours from? The rack of 24 modules I have was built in late 2012 and has all of the modules on their sides. I'm wondering if the horizontal stacking is a newer or older.
The layout of the modules in the LEAF pack has not changed for all production LEAFs from 2011-2015, though Nissan did change the design of the can for 2013+ LEAFs to reduce weight and cost.

24 modules are stacked on their side on the rear of the pack, 8 modules are stacked flat 2 high in front of those and in front are 16 modules stacked 4 high.

If you look closely at the rear modules you can see a slight difference in the design of the can/case of the modules.

2011-2012 LEAF pack:
Image

2013+ LEAF pack:
Image

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Re: Nissan Leaf Cells Test Data

Post by agniusm » Oct 18 2014 2:02am

John, my cells are from a brand new pack but I dont know the year of manufacture. Your drawing is spot on but have you considered that each mounting hole has steel tubes in them?
My theory is that the shape of the can allows for very slight compression and it is there for cells not to flap inside. There are 3 types of spacers, one with 2 bolts for the front, one with single bolt for the back and one without the bolt for other modules. I would like to shuvle the sensor inside the can between the cells but that is not possible for any of us. I just hope that someone from inside will join ES to tell us the tale

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Re: Nissan Leaf Cells Test Data

Post by blisspacket » Oct 24 2014 9:37am

This should be headed Nissan Leaf modules practical experience data

On Oct 3 I competed in the Wye River Challenge, a 24 mile electric boat race out of St Michaels MD. I used a Torqeedo Cruise 4 electric outboard, and 24 Leaf modules. The motor took between 100 amps to 90 amps all the way, 2.6 hours more or less. Starting voltage on the modules a veraged 4.00, ending voltage 3.58. Average speed was 9.5 mph in a beamy 15' of my own design.

I assembled 3 modules into one battery of 25 lbs, and had eight of them aboard. Each battery was paired in series to crank out 48 volts. The four pairs were wired in parallel to handle the amps.

Each battery was an sandwich of 3/16ply, three modules with ply spacers replacing the steel spacers that Nissan uses, and another ply end cover. I charged these modules with a Hyperion 1420 RC charger, about 8 amps output. Long and tedious, but it's all I had. Never did I encounter any warmth in the modules.

During the race, none of the wires (6 and 8 gauge) got warm. None of the modules got warm to the touch--very unscientific, but not much reason to do differently with no sign of any stress.

The parameters and requirements of an international auto mfg plant have to be extremly rigorous. Selling Leafs to the public, who will then flog the cars along roads everywhere, means absolutes that I don't have to deal with when I tie my batteries down in a boat. Yes, we have to be prudent, safe--within our individual expectations. The breathing space for Leaf modules is an interesting subject. What considerations, what extremes the engineers were accounting for, will probably be something few of us ever learn of.

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Re: Nissan Leaf Cells Test Data

Post by blisspacket » Oct 24 2014 9:42am

Torqeedo 4.0 drawing 100 amps, speed here about 10mph
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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 25 2014 10:17pm

24 miles at 10mph with a 15ft eboat, awesome job Blisspacket!

Let's get you some foils for next year for a far smoother ride, and far greater speed and efficiency through the water. Forget the surface drive you were trying before you had to empty your wallet on those Torqueedos. Keep one so you have an eboat in the meantime, and sell the other which would be more than enough to fund an appropriately sized drive to deliver the necessary torque and rpm without the noisy high speed motor and noisy gear reduction, so you can have a much closer to silent eboat like they should be. PM me if you want some assistance in that regard.

John

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Re: Nissan Leaf Cells Test Data

Post by blisspacket » Oct 26 2014 6:54am

Thank you John in CR. Yes, Foils are the future. A different boat sported two Torqeedos; mine only wore one. And the Cruise 4.0 are much quieter than the older models, but yes the gear reduction in the pod has to be sucking off some emf.
My sense is that the Leaf batteries rule. When one module is rated at 500Wh, they have to be the battery of choice.

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Re: Nissan Leaf Cells Test Data

Post by John in CR » Oct 26 2014 10:27am

blisspacket wrote:Thank you John in CR. Yes, Foils are the future. A different boat sported two Torqeedos; mine only wore one. And the Cruise 4.0 are much quieter than the older models, but yes the gear reduction in the pod has to be sucking off some emf.
My sense is that the Leaf batteries rule. When one module is rated at 500Wh, they have to be the battery of choice.
As long as you can use 30ah (60ah is better) and have space for the dimensions, then yeah they're one of the best deals in batteries as long as you don't need really high power.

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Re: Nissan Leaf Cells Test Data

Post by hillzofvalp » Oct 27 2014 2:39pm

agniusm, please upload more pictures of the pack up close from all different angles. I'm quite curious. If you can make an estimation on how many 18650s you could practically fit in there (safely), that'd be great too.

I have a leaf.. when the pack gets down to 70% and I do not make the warranty, I'm going to consider putting my own cells into the original battery housing.

In your estimation, would it be pretty easy to re-use the bms in there? Is it distributed or centralized?

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Re: Nissan Leaf Cells Test Data

Post by MitchJi » Nov 01 2014 10:23am

Hi,
I have a leaf.. when the pack gets down to 70% and I do not make the warranty, I'm going to consider putting my own cells into the original battery housing.
IMO that is a bad idea. If you buy modules from a newer Leaf that is wrecked you will yet better quality batteries for less money. If you wait for the next generation Leaf, you'll probably have substantially better capacity as well. Plus it will be much easier.

Compression:
This is clearly a very important issue (agreeing with John). But is it actually necessary to compress the cells or just apply enough pressure to Cell prevent expansion?
Best Wishes!

Mitch


Buying a new Tesla? Use a referral code and get six month's of free supercharging. Please consider using our referral code:
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The best quality batteries and lowest priced batteries for DIY EV's are tier 1 OEM Quality Cells from salvaged (wrecked) EV packs. Three examples are Chevy Volt and Nissan Leaf and Tesla Model 3 packs.

Nissan Leaf Module specs are here
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Re: Nissan Leaf Cells Test Data

Post by dnmun » Nov 01 2014 10:42am

MitchJi wrote:Hi,
I have a leaf.. when the pack gets down to 70% and I do not make the warranty, I'm going to consider putting my own cells into the original battery housing.
IMO that is a bad idea. If you buy modules from a newer Leaf that is wrecked you will yet better quality batteries for less money. If you wait for the next generation Leaf, you'll probably have substantially better capacity as well. Plus it will be much easier.

Compression:
This is clearly a very important issue (agreeing with John). But is it actually necessary to compress the cells or just apply enough pressure to Cell prevent expansion?

in all of the batteries i have rebuilt there is usually just one or two cells that have lost capacity and limit the overall capacity of the battery so that just replacing the one cell with a replacement will restore most of the battery capacity.

the compression is there to try to prevent the electrodes from pushing away from the separator when the gases are formed during charge and discharge at the electrode/separator interface from how i understand them. that is how i understand the literature on the gel VRLA batteries too. so i now stand the gel VRLA in my car on end so that the electrodes are stacked horizontally like pancakes one above the other so gravity can keep the sandwich together during charging as gases are formed at the electrode electrolyte interface.

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Re: Nissan Leaf Cells Test Data

Post by MitchJi » Nov 01 2014 3:20pm

Hi,
the compression is there to try to prevent the electrodes from pushing away from the separator when the gases are formed during charge and discharge at the electrode/separator interface from how i understand them....
I think it's also important to prevent the cycles of swelling and shrinking that would happen with repeated heating and cooling of the cells.
Best Wishes!

Mitch


Buying a new Tesla? Use a referral code and get six month's of free supercharging. Please consider using our referral code:
https://ts.la/lynnem96959

The best quality batteries and lowest priced batteries for DIY EV's are tier 1 OEM Quality Cells from salvaged (wrecked) EV packs. Three examples are Chevy Volt and Nissan Leaf and Tesla Model 3 packs.

Nissan Leaf Module specs are here
Chevy Volt Pack Info - Salvage 16kwh Packs Under $2k here

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