EVE-280 cells should these be clamped tight or spaced for expansion?

[HaldorEE]

You mean like this ()() or like this (((( ?

The first method is in series. It increases travel. The second one increases clamping force.

I am thinking about doing the first one with a pair of face to face washers on each nut (on each side of the battery pack). That way I will have plenty of travel before completely flattening the washer stack. A completely flat 5/16" washer is over 3000 lb.

 

[HaldorEE]

Not sure how old you are Dzl, but it is rarely too late to start learning. I have a 3D printer less than one year. The design software I use is Fusion 360, free for home/non business use. Previously my 3D CAD skills were limited to cylinders and cutting holes in existing designs, but after a year of messing around with the program, I can do many things that i couldn't do before. Don't be afraid to dive in.

"Fundamentals of electricity" was literally the name of my first college electrical class, a 6 credit hour class that i took when I realized that in my job a good understanding of electricity would help me. So I went back to school at age 26. I remember worrying that the younger students would be far ahead of me but not so, as life experience helped me more than I would have guessed. Get you a meter and a beginner kit of some sort and get your feet wet. Nothing beats hands on learning and burning up a few things.

It is actually easier in my opinion if you get some life skills first. I started my EE degree program at age 30. I had been working as a field service technician for 10 years prior to that so I already had a lot of practical understanding of electrical and mechanical stuff going in.

I graduated Summa (4.0 GPA) so my late start didn't hurt my ability compete. The kids around me made me laugh. I recall one lamenting that he just didn't understand why he kept getting terrible grades. I pulled out a class syllabus and suggested that reading it and actually doing what it said might be a good place to start. A blank look of incomprehension was my reply. I think he just threw his copy away after the first day of class.

 

[Off-Grid-Garage]

Really ? I'm an EV dude, what make & model did you see unbound prismatic cells ?

I recently visited a workshop in Brisbane where they upgraded the battery pack for a Mitsubishi Minicab MiEV.

Just had a look at the video I took and snapped some photos. These are the modules containing 4 uncompressed prismatic cells each:


The modules have literally spacers in between the cells:



I have also seen the battery pack of a Mitsubishi Outlander PHEV which has a similar construct. Both vehicles have air-cooled batteries. The single cells can be just pulled out of these cages once the BMS and the top lid has been removed.

 

[Dzl]

Interesting, any idea what the make and capacity of those cells is?

 

[Off-Grid-Garage]

Interesting info, thanks for adding to the discussion.

I will point out 4 points worth pondering in relation to your post:

1. I think you need to followup with that viewer if you want to believe (or at least if you want others to believe) what they are saying. There are details (who told them, in reference to what cell, and when) that would help establish the credibility and context of that comment.

2. My understanding (not an EV guy) is that EV's have different priorities than energy storage systems. Solar the main concern is cycle life, EV's have to consider high c rates and thermal management in a way that solar ESS does not. Engineers may make the calculated tradeoff to sacrifice cycle life or cost for better cooling.

3. Form factor matters. A large prismatic cell, a small prismatic cell, or a cylindrical cell, are to a degree different beasts. Cell construction probably matters too. I can think of two small aluminum prismatics designed to have air gaps (CALB CAM 72Ah, Frey <100Ah) but I have never seen a large form factor prismatics designed this way. From the little bit I understand large form factor prismatic cells sacrifice strength for energy density. And the broad side of the cell is the weak point. I won't pretend to be an expert here.

3. One of our forum members spoke with two separate engineers at EVE, that was covered above so I won't go into detail, but they were pretty clear on fixture being recommended. The 12PSI seems somewhat universal, and based on other info from other sources (A123, etc) it seems this number is derived from the ideal pressure for the internals of the cell. Or at least that is how I have interpreted the info we have.

Cliff notes of the evolution of our understanding and discussion can be found here and here

edit: also I stumbled upon the video of that cell being deconstructed a few months back and found it super interesting

@Gazoo and @Dzl, I read the thread in total and also the conversation @ghostwriter66 had with EVE. Thank you all again for your information here.

As I said, one of my followers talked to them as well and this is what he stated:
Note that there are two different versions of the LF280 mentioned in the datasheet. One with and one without an N on the end. The latter can handle lower temperatures. But then again the “N” might be another error/typo in the datasheet. And I agree with you about the changed data/graphics for the cycle count. I wonder how they are going to explain this to existing customers. I had a chat with EVE and they told me that the case was basically the 280-320kgf fixture. It’s even mentioned in the drawings of the datasheet. Just look at the bottom of the 71.5mm side on the drawing.

There are also some people believing that the text about the 300kgf is probably misinterpret or translated in the wrong manner.
My interpretation of that text (about the 300 kgf) is that, if the battery is charged, it will generate a force equiv. to 300 kg - meaning that in a discharged state the force will be 0 and charged it will be 300 kgf - but this does not mean that you have to compress it with 300 kgf (in a discharged state) but "just" that you have keep it in a enclosure that has to withstand those 300 kgf (... rem: like the aluminium case the cells come in). But if you could get the original Chinese text then I could manage to get a proper translation for it.

Tbh, I read the text like this as well at the beginning and then people started saying I have to add this pressure again to the cells.
The specs for the LF280 also show, that these 3500 cycles will be achieved with applied fixture but also 0.5C charge and 1C discharge (at 25°C). Not many people will be charging or discharging their cells wich such high C rates in a solar environment. I think you will even get 6000 cycles out of these cells without compression, low C rates and a healthy DoD.

 

[Off-Grid-Garage]

Interesting, any idea what the make and capacity of those cells is?

Not sure about the manufacturer of these new cells. The original cells coming with the car where 50Ah and they bought a complete new set from China with 94Ah capacity for this vehicle. The have the same dimensions, well, almost, so they modified the module cages a tiny bit to make them fit. When I was there, they were still balancing the cells. The vehicle's BMS did complain about cell errors when they put the whole pack in the first time without balancing. They solely relied on the manufacturers balancing before they sent them over. I told them to parallel all of the cells for 2-3 days. This made it work eventually. Almost doubled the EV range to 200km with the new pack.

 

[Gone]

Some nice size studs there, reminds me of pictures of Fortune cells I've seen; perhaps more robust construction allows the spacing shown.

 

[Gazoo]

Tbh, I read the text like this as well at the beginning and then people started saying I have to add this pressure again to the cells.
The specs for the LF280 also show, that these 3500 cycles will be achieved with applied fixture but also 0.5C charge and 1C discharge (at 25°C). Not many people will be charging or discharging their cells wich such high C rates in a solar environment. I think you will even get 6000 cycles out of these cells without compression, low C rates and a healthy DoD.

Thanks for more information on this. However my cells expand and contract when charging and discharging at very low C rates. I doubt they are LF280N. The specification code for my cells is 66 and that's what I have noticed with the majority of these cells. I don't know of anyone who has received a LF280N cell. But I do wonder why EVE told @ghostwriter66 the suggestions for compressing the cells. Doubtful anything was lost during that communication since she speaks Chinese. And I wonder why they told me to mount the cells in a fixture to prevent expansion. They didn't go into the detail with me they did with ghostwriter, but then I wasn't speaking with them on the phone and I don't speak Chinese.

It makes sense to me the jelly roll contained within the pouches will delaminate over time more quickly if the cell is not compressed. I do agree many cycles beyond 2000 will be possible. I have also pointed out in several threads few will be charging and discharging at high C rates and running full cycles. My biggest concern is the strain put on the terminals if using busbars even if the cells are contained in a fixture since these cells like to breathe.

 

[Dzl]

Not many people will be charging or discharging their cells with such high C rates in a solar environment. I think you will even get 6000 cycles out of these cells without compression, low C rates and a healthy DoD.

A general musing and point to ponder:
I think if you have a gentle use-case and expect/hope to get 6000 cycles out of your cells, it may be MORE reason to worry about mechanical factors like compression. You could treat your cells as gentle as you want electrically/chemically, but it probably won't matter if you have a mechanical failure of one sort or another after a few thousand cycles.

On an unrelated note:

Note that there are two different versions of the LF280 mentioned in the datasheet. One with and one without an N on the end. The latter can handle lower temperatures. But then again the “N” might be another error/typo in the datasheet.

My understanding (which has been at least partially confirmed by EVE) is that the LF280N is the new iteration of the LF280. I have never seen both models referenced in the same datasheet, but I have not seen the datasheet your follower was referencing. In the resources section of the forum, you can find separate datasheets for LF280N and LF280. As far as I know, nobody on this forum owns the newer LF280N and they are not available at this point through resellers (this is hard to know for sure since most resellers don't even advertise the manufacturer let alone the model). One very notable change between models LF280 and LF280N is that the former was designed with m6 threaded terminals, the latter is designed to be laser welded.

 

[HaldorEE]

One very notable change between models LF280 and LF280N is that the former was designed with m6 threaded terminals, the latter is designed to be laser welded.

Well, that right there means the LF280N is unlikely to become a DIY favorite.

 

[ArthurEld]

Well, that right there means the LF280N is unlikely to become a DIY favorite.

Probably harder to sell used as new too.

 

[Gone]

They look like they could be drilled and tapped easily enough...

 

[ArthurEld]

I remember reading somewhere that EVEs come undrilled from the factory too. So, I guess we will see used being sold as new.

 

[Dzl]

Well, that right there means the LF280N is unlikely to become a DIY favorite.

The Rep indicated that the cells could be tapped by special order (not sure what quantity that would require), so if these cells do hit the grey market at any point, it might be possible for resellers to tap the terminals themselves (as is already done in some cases).

The rep also indicated that they have improved their 'production management process' which has resulted in a substantial reduction in the amount of grade B and grade C cells in general and a reduction in the amount of EVE cells being sold unofficially on the grey market (which they note they have not authorized, are not responsible for supporting or warranting, and should be assumed not to have passed QA). Probably not coincidentally this warning was made a little before the resellers first started promoting Lishen Cells (late summer/early fall) and indicating EVE cells would be drying up.

 

[Sverige]

My company makes these. You probably don't want to pay what we charge for them.

LW General Purpose Load Washer Load Cell Thru-Hole

LW General Purpose Load Washer Load Cell Thru-Hole - Stainless Steel Wide Selection. Through hole load cell typically used for measuring tension on fasteners. This product is available in capacities ranging from 5 lbf to 100K lbf (22.2N to 444.82 kN).

www.interfaceforce.com

I can see it now, add motorized tensioners plus a control system to dynamically adjust tension in real time.

I can totally see spending $10K to extend the life of a $1K battery pack.

Haha, yeah - I’ll skip that one. Nice product though

 

[ghostwriter66]

Thanks for more information on this. However my cells expand and contract when charging and discharging at very low C rates. I doubt they are LF280N. The specification code for my cells is 66 and that's what I have noticed with the majority of these cells. I don't know of anyone who has received a LF280N cell. But I do wonder why EVE told @ghostwriter66 the suggestions for compressing the cells. Doubtful anything was lost during that communication since she speaks Chinese. And I wonder why they told me to mount the cells in a fixture to prevent expansion. They didn't go into the detail with me they did with ghostwriter, but then I wasn't speaking with them on the phone and I don't speak Chinese.

It makes sense to me the jelly roll contained within the pouches will delaminate over time more quickly if the cell is not compressed. I do agree many cycles beyond 2000 will be possible. I have also pointed out in several threads few will be charging and discharging at high C rates and running full cycles. My biggest concern is the strain put on the terminals if using busbars even if the cells are contained in a fixture since these cells like to breathe.

About a year ago the new EVE specification sheets that they send out and publish talk about compressed vs non-compressed (Chinese calls it FIXTURE and W/O-FIXTURE)... If you look under LF280-72174 VERSION E (must be E) dated April of 19 .. you will see that they NOW add different thicknesses for different charges -- i think its on page 2/11 ... In the new documentation that have broken out they say with NO compression that you are looking at x>2500 cycles (preferred cycles being 10% to 80%) ... WITH FIXTURE its X>3500 ...

The recommended fixture strength is 300 kgf (which was used sometime before I was born I think in the American moon program) or 96526 N/m2 OR BETTER yet - 14 PSI ...

So the ONLY way you are going to be able to maintain a constant 14 psi is through springs ... otherwise i guess yu could charge 100% -- then take it down to right at 50% - tighten to 14 PSI -- and then cross your fingers ... at 17 PSI the benefits are gone and I think 11 PSI they are gone ... so narrow window ..

BUT yes -- if you take a fully charged 280ah and put a straight edge ruler or metal across the side of it you can see a baby bump that not only goes away but sucks in at 20% charge ..

NOW taking all that craziness into mind ... the chemical engineers that i work with that are allot smarter than I am in all of this -- says that really - if you don't charge anymore than 80% (YEP I was wrong) (80% seems to be a happy point) ... but the difference in cycles between a 280ah at 80% compressed at 14 psi constantly and 80% NOT compressed is right at 1000 cycles ...

BUT that still means that after 4000 or 3000 cycles you still have a battery life of 80% -- so that means that my 280aH battery running UNCOMPRESSED for 7 years is now down to 224aH ... YEAH I can live with that ....also with as fast as battery technology is changing - LiFePO4 will probably not be around as the "GO-TO" in 2 years ...

 

[Dzl]

@ghostwriter66 I think your numbers have wandering slightly.
If you refer back to the numbers that You -- and I originally arrived at (separately) 12PSI was the target, 17PSI was the upper limit and the lower limit was less crucial (I believe the takeaway was "any compression (under 17psi) is better than no compression") but the sweet spot was roughly in the 6-17psi range. At least that is my recollection.

Edit: for anyone coming into this post late (and not eager to read back through 25 pages of discussion), you can find direct links some of most important comments here.

 

[ghostwriter66]

@ghostwriter66 I think your numbers have wandering slightly.
If you refer back to the numbers that You -- and I originally arrived at (separately) 12PSI was the target, 17PSI was the upper limit and the lower limit was less crucial (I believe the takeaway was "any compression (under 17psi) is better than no compression") but the sweet spot was roughly in the 6-17psi range. At least that is my recollection.

Edit: for anyone coming into this post late (and not eager to read back through 25 pages of discussion), you can find direct links some of most important comments here.

so we have allot of communication back and forth with the EVE guys - mainly chitchat and why there are 7X more lawyers than engineers in the US and 7x more engineers then lawyers in China - and why do some of these EE in China literally make $4 an hour and work 60 hours a week ... but I digress..

So your range is correct -- plus or minus ... as of today - which will be different then tomorrow or yesterday -- the EVE guys are telling us that 14 seems to be the magic spot with any benefits of compression disappearing at BELOW 11 PSI and ABOVE 17 ... there graph literally looks like opne of those new England farm houses with the gable roof -- the PEAK of the roof is 14 PSI .. the two sides of the roof are 11 and 17 and after that its just a shear drop ... the main thing to take away was that they decided that springs would be the only true way to maintain it perfectly BUT anything was better than NOTHING ... also they taught me the trick of baby bump vs sucking in ... so if the battery has a baby bump forming its above 50% charged .. if its middle (more toward positive) is sucking in - then its less than 50% ...

TOTALLY UN-SCIENTIFIC .. but still cool .. but get a fully charged battery and throw a ruler or level or something over it - heck just rub your hand - and you should be able to see baby bump ... and likewise the "sucking in" ...

 

[Off-Grid-Garage]

So no compression but a fixture is recommended by EVE.
Well, I'm still not quite sure what the difference is. A fixture would be some strong tape as @Steve_S suggested at the beginning of this thread while a compression is the plywood or steel setup with threaded rods and springs?

 

[Ampster]

As the communication says no compression is needed but a fixture is needed to prevent swelling. That is easy enough for me to understand. That is why my fixture consists of plywood held to the cells by four threadrods. I tighten the thread rod until the split washers compress and the cells are firmly fixed in the fixture.