Why compressing battery cells is (not) worth it - Here is what I found...
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- เผยแพร่เมื่อ 25 ธ.ค. 2020
- Should you compress you battery cells or not? After having a look at the new updated specs of the battery cells, it clearly shows compressing the cells will prolong their life.
But how do you do it and is it worth it? I did some digging and here is what I found so far.
I would be interested on how you have compressed your cells and how you have found the right pressure? How do you ensure the pressure stays constant?
EVE-280 cells should these be clamped tight or spaced for expansion?
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Great research! I see it like this, If I want to use my battery as long as feasible, which I would say will be until they have 60% DOD in them, the difference in lifetime might be 5 years. And even if this technology is far overtaken by something better and cheaper in 10 years, I still don't want to bring it to the landfill. I can maybe just use this battery then for some smaller application. My take on compression is very little scientific in terms of exact pressure numbers. Just hold them tight when they are in the relaxed state, and let the cell build its pressure up by itself when it is charging. It's a corset, nothing else. And if 20 dollars in steel can extend the life for 5 years, thus saving me a thousand bucks, it would be quite stupid not to do it. People are spending hundreds of dollars for active balancers for those big LFP cells to shift a tenth of a percent of energy from one cell to the other. Does that make sense? I got my used cells already with around 15% degradation. And many cells had swollen. You have to understand, that you cannot undo an already happened expansion. The perfect time to put the cells into a corset is the day you put them into service. Keep on the great job, you will surely enjoy your journey. Schoene Gruesse!
Thank you Roland, that's a great comment and your thinking makes perfect sense.
Don't worry about landfill, lithium batteries will be recycled, it'll be a sought after chemical/metal.
I have a system with 112 of these cells. Cost of cells: aprox 10K. Cost of a few threaded rods and some thick plywood: 30 $... off course i compressed them. Just hand tightened it. Like you said, any compression is better than none.
May I ask what you are doing with a bank that large? Running a whole house off of solar?
@@ninorcsinned3465 my house and workshop. And charge my ev when needed
I am glad you are elaborating on this topic. There is certainly a lot of noise about it. An important point to note is the compression tests are done on a 1C discharge rate. That is the maximum recommended draw from the manufacturer. It only will give you those results as stated on the datasheet if you discharge at that rate. If you are discharging at a much lower rate (in my case between 0.1C to 0.3C), which I would imagine most people will be as well if its being used as an off grid power system, the data provided will not apply. As you know at a constant 1C draw rate the cell will be depleted in 1 hour. That is far more than 1 full cycle per day. The idea of an off grid system is to provide multiple days of power in case of bad weather. It's obviously possible to have shorter bursts of 1C discharge but a constant draw is highly unlikely in this use case.
The expansion and contraction of the cells are due to the increased movement of the lithium ions across the cathode and anode and the heat generated by the movement during high rate of charging and discharging. With repeated expansion and contraction, the internal cell structure will slowly delaminate which prevents the lithium ions from passing through the polymer membrane to become charged hence causing degradation. Compression is to prevent delamination which will not happen nearly as much at lower discharge rates since less heat is generated which minimizes the expansion. Without the high expansion and contraction, there is much less risk of delamination.
Bottom line is compression is more necessary when these cells are planned to be used regularly at max charge and discharge rates and not as necessary otherwise. Also the pressure of the compression will naturally increase as the cells expand and contract when a fixture is attached. There is no need to come up with any kind of complicated compression system to regulate the amount of pressure.
A lot of people are reading these spec sheets and trying to follow its recommendations without knowing why. I often make a metaphor of this to baking. Anyone can bake a cake by diligently reading and following a recipe but not as many of them can be real bakers who know exactly why the recipes are written as they are. It has to do with the mechanics and the chemistry behind it.
Thanks for putting these videos out to the community. They will certainly help some people out there.
I'd never heard of the need to clamp lithium batteries to prevent them from expanding, but I knew there must be some logical reasoning behind it. Thank you for explaining this. It makes a lot more sense now.
That is a great explanation, Dan. Thanks for that detailed post!
So I guess you haven't compressed your cells (yet)? I've seen the video where you put your 4 cells into your box and stuffed it with foam...
@@OffGridGarageAustralia no I have not compressed mine yet. I wasn't originally going to since my c-rates will be very low with only a 1kw inverter in the van. But I am now thinking I might upgrade the inverter in the future so its possible that I will end up compressing them at some point.
You need to build a bigger box then or get rid of this foam inside. I plan to use a 3kW inverter which is still less than 0.25C.
I also ready once they have expanded you cannot compress them any more, well, it would not make sense at least as the surface is not even any more. I'll show this in the second video for this series.
Great channel you have btw. I just subbed and am generally interested in your life style and living. Still in Croatia?
@@OffGridGarageAustralia yeah I will remove the foam if I compress them. The box should be plenty big for it. I am also planning to install a temperature switch to activate some heating pads for cold weather use. I would imagine that once the delamination has occurred you will have a hard time getting the capacity back. So its not so much that you can't compressed them any more but rather you won't be able to recover the degradation. Thanks for following along. Yes we are still in Croatia. Hoping for things to return closer to normal in the spring and we will head out again. Are you originally from Germany or Austria? I am just guessing from the sound of your voice.
i LOVE how detailed this video is about a single subject. The video could be summed up into a TLDR because you came with the argument yourself. 7 years without compression, 9,5 with compression to reach 80% DOD, and in 7 years we don't use this type of battery because some thing more efficient is on the market! On the point! Some times you need to flip it around and ask yourself, is this extra lifespan really worth the hassle? I would say no!
Instead of building a compression setup, why not place the batteries within a snug-fitting plywood frame to constrain their expansion? I'm guessing that unfetterd distortion of the cell is what contributes to reduced cell life & mitigating such distortion could help promote their cycle life?
Good thinking...
i just wrote this and then saw your comment...great minds think alike.... I think this is the best way...just build a case that is snug but not ratcheting them together...
@@OffGrit Pressure will not be constant, it do not work. You need a box with foam that will give some elasticity.
Thanks for this review of LiFePO4 cell compression. I use longer bus bars to make clear space around my 3 x 24v 280 Ah stationary battery cell banks (& would think differently for an EV application). What has never made sense to me is cells pressing themselves apart at higher states of charge while the bus bars are clamped tight. What does that repeated cycling do to the battery terminals, and (is it called) anoids of terminal into battery; what does the back and forth pressure do to the terminals. ??? That question is why I am Not Compressing my LiFePO4 cells, on top of that making my DIY builds easier. Be open to seeing a long term data collecting study on this subject. Thanks for this clip from Capt Bill member of DIYSolarForum 🏊🚣⛵🏄🎵
I compressed mine by using a piece of high tensile foam between each cell. Block of wood either end with threaded rods each corner and tightened to around 8psi. The foam allows for expansion while maintaining constant pressure.
How do you measure those 8 psi?
I also want to know how you measured the 8psi.
@@alexbahder search for an online torque calculator. It needs to calculate based on bolt diameter, thread pitch and surface area then divide by 4. It was a while ago but by memory mine worked out around 10 or so foot pounds per bolt. It wasnt much. That is compressing the long surface area of 2 cells.
@@crag8360 Thanks!
@@trougnouf maybe with a torque wrench
A sheet of hard/dense plastic ( 1-2mm thick) between the cells helps . The compression is to prevent gas from forming between the sheets of metal , that causes too much space between the sheets . So this is important . If you spaced the plates in a lead acid battery to far apart . The battery would not work . If you use 4mm plywood between the batteries and 15 or 20mm plywood , bolted together at the ends . I would use 2x6/12 and 1/8 or better plywood between the cells . Aluminum sheet , .5 or better can be used but plastic is safer . Cutter sheet/board works very well ( between the cells) . The reason for the plastic sheet between the cells is to stop heat transfer . Two sheets of plastic with aluminum between is best . The plastic insulates and the aluminum dissipates heat . That could add 1 or more years to the life of the batteries . Elvin Dekle PhD aerospace engineering .
I feel cleverer after watching your video. Thank you
Hahaha, that's great, Thank you :)
Many thanks for this very important and helpful Video. Will pass it on to some others because in channels I know in europe till now nobody been talking about it.
Thanks again and stay healthy with greetings from UK.
Thank you for putting all the info in one place.
really good info. thank you for showing specs and great evidence
I'm glad you did all the research for me. After this video I've decided that I'm going with no compression in my van conversion. I have appreciated all you hard work you've done on off-grid power systems and will keep following you.
Thank you very much. You will most likely draw not much power from these cells in a van? All these cycles they are mention are for 1C discharge. If you have lower amps, swelling will not be a problem, I guess.
I'd personally recommend a slight compression as in your usage as vibrations are a factor. If they are not compressed, the roll could begin to slightly de-laminate due to vibration over time. In your case, slight compression just holds it all together better.
I’d also recommend some compression in a vehicle to avoid stressing the terminals that would occur if individual cells can move in relation to each other.
@@brucebugbee6604 Right. The terminals on the top are molded into plastic (under the hood). That can break easily if the pack is not compressed.
Also plastic sheet is advised between the cells.
If you want to compress your cells, just place some polyurethane foam between your compression plates and the cells. That will compensate for the surface variations across the face of the cells.
That will work, but to produce the desired compression of about 12psi, it will take a much stiffer foam than ordinary PU foam, and it's compression rate should not increase drastically above the target rate, so that it cannot put too much pressure on the cells.
I am going to lightly compress my sells when they are all at 50% SOC, another reason for me wanting to do this is to keep the terminal screws from pulling as the batteries age. Thanks for making the video.
Yeah, the force on the terminals are a good point actually.
Thanks for your research on this topic. I agree that for most use cases the differences due to cycle life may not make too much difference. I have my batteries installed on a cart that can be moved (with much effort) from time to time for maintenance. I’m more concerned about movement of individual cells in relation to each other. I have compressed my batteries to keep them from moving and stressing the terminals connections after the bus bars are in place. I just used two 3/4” plywood bookends held together with four rods and snugged it up until they couldn’t move. No issues so far.
Yeah, I found it difficult to find the right answer what compression is correct. Plywood and 4 roods seem to be the norm. I would need a bigger box though...
I am using Calb cells(plastic case). My compression technique is to use a corrugated cardboard piece between a 4-pack of cells and compress each pack with 2 giant tie wraps. The cardboard and tiewraps have some stretch to protect from distorting the cells while keeping pressure across the large side of the cells. Breaking the cells into tied blocks of 4 makes the cells easier to move around during assembly.
The gray ore blue calb cels they gray ones dont need compresion i work with them daily in electric trucks and they have a inner casing to not expand /but keeping them close together is perfect to keep the strain of the screw terminals
Tie wrap are not distributing pressure correctly, it's worse then nothing.
The graphite negative anode expands by about 11% when fully charged (stuffed with lithium ions). It is only about 10% of total cell thickness so net cell expansion at fully charged is in the order of 1% for total cell width.
The layers are laminated and the graphite anode and LFP cathode are printed onto their copper and aluminum foil, respectively. It would be good to avoid delamination over time. Sometimes compression can help reduce delamination.
The engineerng statement of improved longevity with compression is based on rather high discharge and charge rate current where self heating of cells becomes a factor. At less the 0.5C current rates the cell heating is minor to non existant.
Worse thing you can do is a hard fixed enclosure compression. With no compliance flexibility to control pressure, this can cause forces to skyrocket when cells are fully charged and crack the graphite or LFP material on electrodes. Any compression needs to be compliant and flexible. Neoprene or red silicon pad would be good candidates but you should consider the heat insulating effects and fire resistance of material.
If you run at less then 0.5C rate cell current there is little benefit to compression. If the use case subjects the cells to a lot of vibration and mechanical shock then compression is more justified to keep the 'guts' bound together.
That's my understanding too. With such low C rates most drive their batteries, it won't affect longevity. Heat is not a problem in these cases either. Even we had 40°C outside and I charged the Tesla from the battery, it did not get warmer than 35° inside the box I have them in. The inverter overheated far before that 😉
You offer lots for us to learn. I subscribed and thank you.
Thanks for the sub!
Thank You for sharing your knoledge. Thanks for your videos.
No problem, thank you.
I'm using 4 x 206ah cells which I've compressed with plywood, threaded rod and springs. If you refer to your life vs pressure graph it shows that with the correct compression i.e. 12psi that you'll get a projected 20,000 cycles. That's over 54 years worth versus the 8 years (3000 cycles) if you leave them uncompressed. Also as the batteries are so expensive yet the compression components are just a few dollars so you can get significant extended life span for next to no cost.
Argh, I just made another video where I said I will not compress the cells. I'm really on the fence with that. And you're right, it would not cost much and extends the lifespan. How did you choose the correct springs?
@@OffGridGarageAustralia you do not have to decide... Yet... just get more info on diysolar.
Thanks Andy. Good point. I have just ordered 16 of the 280 Ah from the company you suggested.
BYD batteries come factory compressed with straps. Once you cut the straps there is no way to put them back to their original form due to expansion.
Thanks for using the link. Interesting, so you have to leave them compressed? Do they expand once you cut the strap?
Thank you for the detailed video with thorough research. Compression indeed appears to be challenging for DIY projects. Your videos have consistently provided me with the answers to my questions. I am presently awaiting the arrival of batteries from China to Sri Lanka and seeking the best methods to set them up. Your support has been invaluable. Thank you so much, and take care!
Thanks a lot for your feedback and kind words. All the best with your battery project. Stay charged!
Thank you for hitting the Compression topic head on, Andy. Great job sharing the minutiae of detail. Remember, these are NOT BB batteries @ $950/100AH. These are $161/100AH cells- that's the first mistake we make. Then, in 10 years- what will we be looking at? A different chemistry altogether, no doubt. As Yoda sez " Compress or not, matter it does not" Ahhh, the answer we needed.
None of us are using these cells under the conditions as tested. We will discharge a lil, then charge up, discharge deeply, then recharge... who knows how much solar we get today, or tomorrow, etc? I don't even think we can approach a full 1C discharge rate, even if we use everything in the shed!!!
Thank you for putting the conflict to bed. I just don't want to rip the anode/cathodes out of the cells, so- I'll tape 'em together with some flattener on the ends, maybe strapping tape? Can't see getting too worked up, cuz I'll never load these cells even close to test...
These cells are cheaper than flooded/AGM and will last much longer regardless of what we do!
That's a fantastic summary, David. Thanks a lot!
Well said David! I've been in the business of designing, installing and maintaining off grid battery storage systems for over 25 years and would you believe I've never seen a battery die from cycles? Of course I'm talking about flooded lead acid batteries but my point is from what I've seen improper maintenance and general abuse gets most storage batteries, not cycles. I'd be will to say that improper charging plus being left severely discharged will end the life of 95% DIY batteries.
Excellent content, super informative. I guess most people *will not* discharge their batteries at a constant 1C! Solar charges the batteries very gently and discharge is normally ver low with peaks every now and then with induction loads. And as you said, if you are cycling your batteries 0%->100%->0% every day may be you should revisit your design. All these factors will make the batteries last much longer.
Keep up the good work, greatly appreciated.
Thank you very much for you kind comment.
Some have said that even with lower C rate usage, the cells will slightly expand/contract. So who knows what to do. It's really 50/50 what you hear and read...
Thanks for the great info! Ok, you have me thinking now, and here is what I come up with. Use aluminum plates that cover 100% of the largest face of the battery, 3 plates on threaded rod. On one side, keep it solid against the full face of the battery. On the opposite face, is the other two with springs between them, one hard against the nuts, and the other floating, with springs between the 2. Tightening the four nuts on the four rods would increase the spring pressure. 4 springs, threaded over the 4 rods, so they apply even pressure across the entire floating plate, which is against the face of the battery. With the battery fully charged, adjust the nuts until the pressure is the desired 10-12 PSI per cell. As the batteries drain, and their internal pressure relaxes, contracting the batteries, the springs will relax as well, but still maintain pressure at all times. Yeah, by the time the batteries reach their extended end of life, new, improved tech will exist - but why not maximize the return on the investment already made? The argument that maintaining for extended life is unwarranted because new technology is always being developed and released would also direct us to never change the oil in our car’s engine- but just because new tech is released doesn’t mean we can afford to upgrade, or that the utility of the old technology ceases. A kilowatt is still a kilowatt.
definitely compress your cells if you can, helps to avoid formation of dead volume within you electrodes and maintain useable capacity over more cycles
Thank you for all your time and videos!
I have variable compression so my cells can breathe.
And indeed within 7 years there will be better technology again, but what do we see now?
Each new technology will be many times more expensive than the last... and will we be able to afford it by then?
The trick now is to ensure that you can continue with your old stuff for as long as possible.
I like Your videos, because I easily I understand Your English... thanks
Thanks Gerhard!
I bought a 12V battery pack, 100AH LiFePO4 and inside are 50AH cells, 8 of them and around are fiberglass boards as insulation with an external metal sheet (same height as the cells and the fiberglass boards) as belt or frame securing the whole battery pack. On the outside of the metal sheet are foam boards materials around and the external casing is a thick metal sheel box painted black. Very heavy 12V battery pack in metal case. I never thought there is another metal case inside snug fitting the battery assembly and it is done very well.
Thanks for making the video - took a bit to get into the interesting part but I appreciate how you laid out information once you got there.
Here's my take: you design your system to cover your energy needs, with some margin so you're not fully charging and discharging every cycle, so there's some headroom for your energy needs to grow, and so that when the cells have aged and are giving only 75 or 80% of their original capacity, you're still within your operational requirements.
New battery technologies arriving that make LiFePO4 'obsolete' should be irrelevant. The only criteria relevant to replacing the system really ought to be: is the system still covering my needs.
In my mind then, if the capacity of your battery is designed to fit your needs well, you've set yourself up for environmental concerns to take on primacy... I think that's a great place to be. Ideally, we get more years from our system because buying a new system has environmental costs?
From that perspective, building in some conservative compression makes sense and I plan to do it on my upcoming built. I'll do all the reading I can to make sure my intuition is correct, but I'm thinking tightening the structure so that it basically fits the cells at 50% SOC means compression will only kick in above that SOC, increasing up until whatever SOC ceiling you have determined (I think 80% in your case, and for me too I think). This SEEMS conservative to me, but again, I'll do my best to quantify what this approach actually translates into, in terms of pressure applied.
I plan to have rows of 8 cells, so that's a total maximum of 4mm expansion at a 100% from empty, so maybe 2mm if we're cycling only 50% of the capacity... maybe halved again since we're not compressing until the batteries reach 50% SOC during charging... so in the end, I'll be impeding an expansion of roughly 1mm for the row of 8 cells.
Thank you for sharing and doing all the hard work and putting the time in to do the research. Very much appreciated.
Thanks, you're very welcome. I'm so glad it helps others as well...
Thank Andy for your research, I have one remark, on the specification lots of data concerning cycle life are speculation and projections, so we are free to believe...or not 😊
very well done - a great explanation on the subject!
Werner from Southern Germany
Thank you - for a pragmatic view of cell compression. In particular the observation that without compression, the batteries will still last 7 years of 100% cycling. In practice the batteries are hardly ever cycled 100% of their capacity - so the life is likely to be much longer.
The batteries I order on Aliexpress (310 Amh) arrived alredy a little swollen in the midle (unlike yours). So I prefered to compress them. The advantage of compressing is that it stresses less the fixations on the top I think (because when the batteries breath they pull on the top fixations I fear). And it reduces delamination during time. It is easy to do (for my 2 x16 batteries) so I did.
You probably got grade b cells, unfortunately if you go look at some videos will prowse did you'll see what I mean. Most of the time those cells don't meet capacity which means they were either defects sold as a lower ah, or used, .... either way still better to compress.
a most refreshing view...........TY
Thanks John.
Maybe put an air bladder between each cell, and one on each end. I wonder if hot water bottles would work...with rigid plates (plywood) as end caps, pulled together by threaded rods to get to 12 psi. I was going to put the battery in my minivan but now it's too big and will need its own trailer. :) Nice thing about an air bladder is that the curvature in the cell walls won't matter.
Springs seems more precise and will last longer.
This explains their smaller size yet larger capacity than my CALB batteries, my first reaction is that they must be made very poorly if so much force is needed to get full performance but the cost/weight/capacity and size gains are pretty amazing. I wonder how much of that gain is lost with everything needed to get the required compression.
You are 100% correct the chemistry changed.
I'm glad to have seen your video before try anything on cells, I'm totally agreed with your technical point of view. I guess the pressure must leave in a scientific research level only for now, until have more clear new information.
Thank you for sharing this info, have a nice day.
Thanks for your feedback.
very interesting. I was on the fence about this before watching this and am still on the fence...lol I think I will just design a case for them and have them nice and snug and call it good... thanks for the research!
Great video. It looks like it's just mechanical stress that's aging the batteries quicker but like you say, cycling them between 20-80% charge will negate that to some extent anyway.
Very informative, thank you!
Thanks Robert!
I love the logic! Thank you
Most of the information on these batteries is either conjecture or regurgitation of
TH-cam sheep. Glad to see
Something truly informative.
Thank you.
This chemistry might not be popular in 7 years, but it will still be around. Lead acid is still popular for car batteries, and it's over 100 years old. You can even buy nickel-iron batteries for off grid systems, and that's older technology than lead acid batteries.
Good Info THANKS
Thanks! Do you suggest to put any kind o layer between cells? What do you think about 1mm of polypropylene?
Swelling results from thermal expension of matter if not subject to external stress or change in chemistry during the operation. This process is quite difficult to evaluate without true scientific experimentations. So... I agree with most of what you said. This is way beyond what DIYers can actually do. For my part I decided to not bother with all these considerations. I chose to minimize the heat induced in the electrode by limiting the charging or discharging current down to 50A with a DC circuit breaker. Literally, I'm actually operating at less than 0.18 C of 280Ah and no heat is being generated by the current flowing through the electrode. Moreover the outside temperature never reaches above 80F. In addition the BMS is set to very conservative range of 20%-80% capacity. After a year of normal use, I have not notice much change in swelling, but it's still early in the game and I'm not charging a Tesla so the current demand is minimal. The only change I noticed is a reductio of 90% in my energy bill. I'm actullay getting some rewards ffrom PG&E incentive energy saving bills in California. But I still power my house's appliances and tools without problem. I do avoid to operate them at the same time with the dryer even if the system can take it because the hybrid charge controller can easily power the dryer direcly from the solar panels, around noon, without drawing any battery current. Conclusion: I save myself some times and effort in making enclosures which I estimate is not needed for my consumption level. Stretching battery life is nice but comes at a cost, Those batteries are relatively cheap (I paid $1850 for 16x 280Ah cells) and i don''t mind buying more when they go down in price. As Andy said rightfully so, technological obsolescence will works in our favor. Perhaps by then, they'll have better alternatives.
"In seven years time we are not using this kind of battery tech anymore" - that's ONLY true for new installations. These things are going into houses, caravans, boats, and even cars with the hope that they won't come out for 20+ years, so clearly compressing them is a good idea, and clearly using something with a spring rate is also a good idea, though tight at full and loose empty would be better than nothing. I personally have experience with a gel cell lead acid battery that's 15 years old and still in service. It's crap now, maybe 20% of capacity, but it is usable, barely. It'll be replaced with cells like yours sometime soon and the thread you linked will come in handy for sure. Thanks for posting the video, I did know it was a thing, and I understand why reasonably well, but the spec sheet differences and thread existence are nice to know about. Cheers. PS, those are PDFs not spreadsheets. You can call them PDFs, documents, manuals, data sheets, but not spreadsheets :-D Cheers :-)
You could do a time lapse video of one single cell on side position doing a full cycle of charge, discharge and finally discharge 2.5->3.65->2.5 so this way all we’d see it expanding and contracting, it could help to take decisions.
Hmm, that would be cool...
Maybe need a dial indicator or something like it to show the change. Visually, it's pretty small to see, even with time-lapse.
Thank you, sir.
thanks for the info.
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 discarged 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 discarged state) but "just" that you have keep it in a enclosure that has to withstand those 300 kgf
But if you could get the original chinese text then I could manage to get a proper translation for it.
I first read it like this too and @DIYProjects mentioned EVE told him the aluminium enclosure the cells are in is the actual fixture. There is another cell type a LF280N which actually states that in the drawing. I'll show this in my next video. Thanks for your comment, much appreciated. I'll try to get the original specs in Chinese. Maybe there is some more info in there which got lost in translation.
Perfect video! you are really do a good work, thank you
Thank you, much appreciated.
How about putting some VHB tape in the center where the concave area is, to join your cells and then use a box to fit the cells. This would apply. pressure only when the cells are trying to bulge because they are charged. I know, not a scientific or accurate way to do it.. but maybe better than nothing or trying somehow to put pressure when you need to. Let it apply it's own pressure when it needs to.
Just a thought, and you are awesome and I so enjoy your thoughtful demeanor.
Thanks for the research effort Andy. Greatly appreciated.
Thank you for choosing a decent OS
Thanks for the info, the reason I compress cells is to reduce the build-up of gasses inside the pouch cells. They eventually increase in size over time compressing them prevents this from happening and they last longer well also look better I hate the puffy look that happens if you don't compress them. Not info specific to these batteries but projects that I have done over the years with pouch cells.
Yeah, OK, that must be different cells then. These ones apparently don't have pouch cells inside.
@@OffGridGarageAustralia They are considered prismatic cells which are similar to pouch cells so figured I would mention the info from pouch cells that I have learned. Prismatic have some compression built in but not much the aluminum case is pretty thin.
There is also a debate about using the cells standing, or (much cooler in a cabinet) lying on top of each other, or on the narrow side.
Some say it must be used on the standing position.
Yes, I have seen this discussion.
It may depend on the manufacturer specs of different brand cells.
For instance I have the grey CALB and believe they should be upright.
@@offgriddreaming5403 I heard all prismatic cells should be used standing/upright (this EVE cells too). There was some debate about loosing capacity if not.
Thanks 😊
033021/1105h PST- Brisbane 0405h. Thanks. I’m with you. Soon enough LiFePo4s will be obsolete and the “compression” theory sounds .. Aw well! SS Batteries are being developed tested and used in several high load environments and found quite reliable and safe. So NO COMPRESSION for me. Thanks for your comments. 73s...
Great video, excellent research! Makes me (try to) think... As a total layman, it would seem to me that if you strapped the batteries together at 2.5V, when they are fully charged they would apply their own compression if your strapping was consistent across the surfaces (and you would have to be careful not to ground the cases together).
Thank you Peter.
The isolation between the metal cases is a big headache, I think.
Let me suggest something. Use Springs on the all thread right before the nuts. That way when you do have an issue? You will see a problem before it becomes a problem. Such as puffing cells etc.
I'll try to make a video on how to do this in the future.
PS: The compressive strength (PSI) of foams increases somewhat with increasing deflection (inches), but it's easy to get close to 12psi @ 25% & 50% compression of a thin sheet of foam. Most foams have compressive (PSI) ratings @ 25% & 50% compression.
thank you, learnt loads :)
I'm building a 4s 12v LiFePo4 batter pack and I'm wondering if it's OK to stack them on their flat sides? I ask because they fit best in my DIY batter case that way. Thanks.
Thanks for sharing this useful information Andy. I am expecting my first 16 EVE 280K cells in some weeks and this answers exactly my questions I had (even you are not shure to compress or not 🙃).
My concern is that the "breathing" of the cells will put too much stress on the terminals because of the massive and non-flexible busbars.
Since the net 280K versions have two M6 screwholes to fasten the busbars on, there are no flexible solutions available, unless I overlooked them.
I will try to make a flexible 35mm2 busbar that has two mounting plates at the ends with 6 mm holes in them. Then the busbars make a nice and smooth U-turn between the terminals and prevent too much force on the terminals while "breathing" 😀.
Again: thank you for sharing.
Thank you. I leave a gap in between the cells so they can expand if they want to without putting and force or stress on the terminals.
I've got the 280K cells incoming but they have only one hole per terminal.
Two individual cables per terminal (1/stud) is what I'm considering doing with my new 280k cells and using compression with springs to keep them loaded to close to 12 psi across the full SOC. Unsure what size wire is needed though? Twin 3 or 4 ga. with just a little slack should do it I would think. Or multiple smaller ga. per stud?
Any good/reasonable sources for tinned copper connectors with close to a 6mm hole?
I think for my RV I would put a thick plastic on the ends and tighten with my plastic banding tool used for shipping. For RV the containment may be more important then the gain from the compression
Thanks
Great information. Inexpensive compression can be accomplished by putting a suitable material (thick plywood in my case) on the ends of the battery packs then wrapping a ratchet strap around the pack. The plywood distributes the straps force at the ends, protecting the cell corners and also protects the battery cases from gouging while the ratchet strap buckle is tightened. The nylon/poly strap (lightest duty one I could find) becomes the spring and provides as much force as you wish. I'm guessing my pack has around 300lbs distributed by the plywood ends. It should allow for small dimension changes as the pack cycles while maintaining compression. I think it would be possible to use a torque wrench to be precise and retorque them to a known value as the strap ages... perhaps annually.
How do you apply force to the side walls of the cells though?
Thanks for this useful video, but how you can configure an 80% charging?
The curve for cycle life "with fixture" is a very dubious extrapolation xD.
Great research.
The 80% capacity mark is a hang over from lead acid tec, the reason being that at 80% the degradation and loss of capacity increases a lot, and the battery is really at the end of its life. This accelerated degradation does not happen with lithium batteries so the life time is still good after reaching the 80% mark.
That's a very good point. I didn't think about that but you're very correct with that!
Edit: missed the context. Don't mind me.
Hi I’m new to all this so just an idea sir put them in fairly tight at half charge without compression allow a little movement either way I think
Swellin on the anode more that on kathode also means not to layer them criss cross to apply shore busbars but better on the same direction and need longer, flexible busbars. Right?
Maybe using the Jägermeister bottles help you, deciding what you should do :-).
My two cents:
Save two cents.
Compress the cells. You will not cycle them 100% everyday. Most set their range to 20%-80% of usage. You will extend the life this way and with compression you can see an easy 15 years with this chemistry.
As for new chemistries, yes they will come but at what cost initially? 20 years ago lipo4 was the gold standard and you definately had to have a lot of gold to go there. Now they are a bargain.
Anything new is expensive, the bleeding edge. In 15 years when your lipo4s are dead you can get the "new" tech at the bargain you got these lipo4s for.
😉
Liked and subscribed! Thanks for the great content, Andy. I've been following your video series as I received the same 280AH Eve (8) cells to build a 12v 560AH for my 2020 Ford Transit van conversion. Personally I'm planning on "compressing" the cells by building a plywood box, likely lined with 1/4" closed cell foam (though I'm doubtful it meets the 300 kgf criteria, I'm also in a mobile situation compared to you). I haven't heard you discuss BMS's yet? I'm planning on using the Chargery BMS8T - do you have plans to use one and will you test any in particular?
curious if you've put together this plywood+foam battery box, how it has been, and what you've learned.... ?
in the process of planning and putting together the same... with 3/4" holes on all surfaces for ventilation and weight, and mounting most of the other electric components on the outside... thinking i'll line the box and in between cells, is that what you did?
spring seems to be great solution. You can measure how much force, spring need to 2cm (or 1") compression, and than find proper springs. All springs together compressed ideal in 50% need give you needed force. Longer springs- means less difference of compression force when cells have different dimensions when they are hot/cold and empty/fully charge.
Foam (or soft rubber) isolators should to cover the entire adjoining areas between individual cells and the perimeter. Select a material with a specific compressive strength that will provide the manufacturer specified pressure when the batteries expand according to the manufacturer's specs. The expansion is mostly in the flat areas; the separator compresses, providing the desired pressure. 12 psi is also the approximate stiffness of the compressible separator between the cells. That's about 50 on the Shore 00 scale, or between 0 - 10 on the Shore A scale. That's about like a soft gel or soft rubber band. Minicel T380 EVA foam is in this range, as are many other commonly available materials.
Thank you Sir for the very informative video. Regarding charging and discharging, 80 %dod means I will charge it only until 90 % and discharge until 10%. Is my understanding correct sir?
Great video. Could you please post a link to where I can find the documentation for the cells?
Hi Joe, links are always in the description: off-grid-garage.com/batteries/
Maybe it's a simple mechanical problem with the terminals. If you use busbars to connect the cells, you will apply force to the terminals when the cells expands.
Maybe this reduces the contract or something like that.
Would be interesting to know whether there is a difference when the single cells are connected with flexible cables.
I thought same - expanding cells will put stress on the terminals as busbars won't expand as much as the cells - I reckon that cables instead would avoid tension on the terminals
very useful thx
Honestly, once I specify and purchase my cells for the requirements of my application, I do not care what new battery technology might become available until my battery is no longer suitable for my application. I want that to occur as far into the future as possible, so I certainly would design and build a fixture that applies the force specified by the manufacturer.
We would be well to learn if the fixture is to be rigid so the force varies with the state of charge, but the cells do not move, or if the fixture should be spring loaded so the force remains practically constant, and we then must make allowances for cell movement, ie flexible inter-cell connectors.
One opinion is that on the very first charge compression is crucial. After that the advantage is not that large.
hey amazing man :) do you have a review of your garage - how your workspace is organized? I believe it might be quite interesting and useful for DIYs :)
thnx for great content
I'll put this on my list of future videos. Thanks for the suggestion.
Very interesting
I am discovering this video 3 years after it’s been made.
Compression is good but hard to do for DYI. Too hard I’d say.
I’ve been designing battery modules for Mercedes EQS. Special compression foams are used, special assembly method and carefully designed enclosure that holds the pressure.
By the way the bus bars need to be designed thinking that basically the cells are moving away and back from each other.
Maybe a simple DIY way would be to stack the cells flat on top of each other and apply a gravity force on top… you might still need some foam in between to smoothen the load between cells… imagine 300kg on top of your stack: crazy.
Awesome!
Yes.our cells is 3000N. With those force, cycle life will be better for sure. That is why the size is different when 30% SOC and 100% SOC
Because when charging, battery will swelling, so when 100% SOC, size will be bigger than 30%. So we need give a force to the cells to let it swelling, but can not let it swelling as the cells want.
Sir, Can You explain for us internal structure of the cell. I think there is no "jelly roll". Is there multiple pouches connected in parallel, or single stack. Is the case intentionally connected to one of the terminals. Thank You in advance.
@@askostadinov
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@@SeplosTechnology Excuse me, are you thinking of making battery cell holders or metal boxes for this size of 280ah cells? I have seen all your videos and the cells you use are smaller than these
@@videoando4810 we already have it, we will make a video about it soon, both plastic house and steel box.
Hi. My batteries are bulged after two years of use. If I make the compression now, will I damage them?
HOLY smokes.. EXACLY what I was looking for
Wonderful
@Off-Grid Garage what about the increase of thickness when full charge and low charge? wouldn't that mean the cells might move and the busbar distance is not big enough? isn't that itself a possible hazard? Just a random though.
IV seen a clip off Wills channel in USA....got some plastic caped cells, when he built the battery up they was a air gap between each cell......
Hmmm, is it good to clamp or not?????
I'm going to lightly clamp mine, I will not be doing big c discharge or charge.
Marc
The manufacturer talks about a fixture, not a compression to start with. Also, the benefit if compressed will be noticeable if you have high C rating charging/discharging (like in an EV). For solar it won't make much difference.
Looks like you have upset a troll . More good, easy to understand info . Thanks bro . Also I agree with you on the leaps in battery technology . We will be probably using more efficient and greener technology as the decades roll on . Plus like you say, their will be days of no discharge and maybe days of full discharge . But the latter will be very infrequent if you size your system right . I have an acquaintance who is off grid and he says his average DOD is roughly 55% of his usable capacity . So I am thinking that there is probably more than ten years use before 80% capacity is reached . And probably a real world usage of about 15-20 years ?
I think the same, 10+ years should be easily achievable, 15 years would be great and worth the investment.
@DIY Projects yes, that's correct. Will they replace faulty cells in 4.5 years? Unlikely as there will be different cells available. So a refund maybe? Still does not really help if you have 15 cells + one faulty one 😁
We just assume, everything works out and the product will last a looooooong time.
@@OffGridGarageAustralia And because of this, and because one cell could be weak in the pack ... so I bought an extra cell (and boxed it and will charge it every 3-4 months to 60%).
My observations; Yes they do swell at full charge/top balance. They swell a bit more with a heavier charge rate 50A> (272/320ah cells). They never come completely back to where you received the battery, about 20% return to original size at discharge. They swell as much as 1/16” per side. My opinion: If you didn’t “compress” the cells before doing any type of charge, don’t bother because whatever happened, happened and you could may actually harm them by reshaping the sides. Besides potentially prolonging the cells life by compression, compression may reduce terminal damage and/or buss bar loosening as the distance between terminals and cells remain more constant though thousands of cycles. That being said if you don’t compress, I feel it is very advantageous to give batteries a small gap between them to expand and contract as well as not put a sideways strain on the terminals when they do (for stationary install). For mobile, non compression(but restrained), 6mm thick VHB tape strips on each side and let the battery middle be free. Arrange the cells so that polarities are all on the same side and make cable jumpers to connect diagonally. Much less stress on the terminals than a buss bar in mobile vibration environments. CHECK YOUR TERMINAL TORQUE! They do loosen in all applications!
I did not see any swelling or contraction so far at all. EVE also talks about a fixture, not a compression...
@@OffGridGarageAustralia
Did you actually measure with calipers at what you called the “jelly roll” before the first charge and after? In the video it actually looked bigger. Most cells when you get them, they set completely flat together. After the first charge, not so much. At least from what I’ve observed.
@@SkypowerwithKarl nah, they all get cycled a few times to capacity test them. All my 4 deliveries weren't perfectly flat on any side. I'm not bothering with compression. In one of the recent videos I showed the result of the last 6 months operating this battery and I had only accumulated 7 full cycles. Once I get more cells, this will even decrease further. They will just last forever as they are.
@@OffGridGarageAustralia
Your absolutely correct about cycles and life. And getting more will just make them all last a lot longer. By that time we’ll probably be gone lol. Not bothering with compression (fixturing) here either. Just being carful about terminal stress. I think that’s going to be the big future issue in time.
300kgf is 660lbf, assuming the entire side surface of the cell is in compression, using my lf280 cells and a tape measure (6.75×7.875inches) is 53.16 square inches...660lbf/53.16in^2=12.4psi, right in line with the graph you showed. So that's neat...but then we need to calculate bolt torque to get clamp load of 660lbf...let's say we are using 3/8 rod and Zinc plated hardware, no lubrication...plugging that into a calculator because I'm lazy we get 4 foot pounds torque to achieve the suggested clamp load of 660lbf using 3/8 hardware, however that is one bolt...we have 4 contributing to clamp load, so we divide that by 4 and get 1 foot pound torque...or 12 inch pounds...very minimal and very easy to overshoot...I would think people are probably over compressing. Does this make sense or am I missing something?