Pack / Cell compression Optimized By Using Springs.

[Bob B]

I would prefer that this thread become a comprehensive thread about use of springs ...... but since it seems like other threads on the subject are springing up all over (pun intended), I may link to some of them here.
Here's one .... https://diysolarforum.com/threads/source-of-belleville-washers-for-300kgf-fixture.16733/

 

[cinergi]

FWIW I'm going to modify my build with springs. I'll document thoroughly in my build thread (https://diysolarforum.com/threads/c...lar-10-kw-inverter-rv-build.13786/post-189165) and summarize here, too.

 

[cinergi]

Some initial spring testing information on difference between 100% SoC and 0% SoC: https://diysolarforum.com/threads/c...lar-10-kw-inverter-rv-build.13786/post-195598

 

[Capt Bill]

It started with this information in an EVE cell specification sheet. There has been a lot of investigation of that and emails to EVE and also phone conversations with EVE.
I believe Lishen also recommends compression. 12PSI as the optimal compression has been confirmed from multiple sources and the Eve representative said that any compression was better than no compression as long as it was under 17PSI .... and that would be worse than no compression.
If you do a search for EVE cell compression, you will probably be able to unravel the trail ... or @Dzl may have a record of the trail.
We started this thread to center on using springs for the compression.

View attachment 30099

I am on my 2nd set of 8 EVE 280Ah cells; ... and as I study this thread topic of compressing cells for longer cycle life; ... I notice the 8 cells I have ordered via Alibaba and recently received in California from China are not perfectly flat on their sides (picture attached). One of my Question: Can compression plus cycling higher amp battery draws and charge cycles (that I would image heat the battery a bit) result in the sides material of battery softening, and then being pressed flatter together? 2nd question: Does non perfect sides slightly puffed sides of a 280Ah LiFePO4 cell = inferior lifespan?

I also added a picture of compression via thick exercise bands I obtained from Amazon; which would get flat plywood or some other material piece on outer edges of battery set to prevent distortion of battery at bands. I think the cells I received must be grade B cells. Is anyone getting perfectly flat-sided 280Ah cells; from whom? I noticed Will Prowse's recent 280Ah LiFePO4 mentions looking at the cells for being flat sided, and that is better quality. Have Questions; ... & looking for Feedback :+)

 

[Hedges]

I also added a picture of compression via thick exercise bands I obtained from Amazon; which would get flat plywood or some other material piece on outer edges of battery set to prevent distortion of battery at bands.

I doubt those are enough to reach the 750 pounds or so that is needed - unless those are sold for gorillas.

Or do a lot more turns:

Watch a watermelon wrapped in rubber bands explode in slow-motion

YouTube video by The Slow Mo Guys showing a watermelon exploding in super slow-motion

www.cbsnews.com

 

[Capt Bill]

I doubt those are enough to reach the 750 pounds or so that is needed - unless those are sold for gorillas.

Or do a lot more turns:

Watch a watermelon wrapped in rubber bands explode in slow-motion

YouTube video by The Slow Mo Guys showing a watermelon exploding in super slow-motion

www.cbsnews.com

Wow. 750 pounds needed ... Gona study this more; Plus my other 3 Question were much more primary: If anyone has insight opinions to share:

#1 Question: Can compression plus cycling higher amp battery draws and charge cycles (that I would image heat the battery a bit) result in the sides material of battery sides softening, and then being pressed flatter together? #2 question: Does non perfect sides slightly puffed sides of a 280Ah LiFePO4 cell = inferior lifespan? #3 Question: . Is anyone getting perfectly flat-sided 280Ah cells? ... from whom?

 

[Hedges]

12 psi times length times width. How many pounds does that work out to?

"Don't exceed 17 psi"

Force measured with a load cell varied +/-50% for a given torque.
12 psi + 50% = 18 psi.

Seems like something which measures force is a better way to go than torque.
Calibrated displacement of springs. Or measured elastic bands (except I don't trust them to remain unchanged with time.)
Some time ago I proposed stacking the batteries on their sides and piling a few hundred pounds of old lead-acid batteries on top (for stationary applications only)


I don't work these batteries so I can't answer your other questions well. But with cycles and warmth, I would expect the gooey assembly to redistribute, becoming more flat where pressed together, probably relieving some pressure.

 

[Gone]

Unless striving for perfection, half of that force will get you over the 'knee' on the graph (6 psi); not optimal, but pretty good.

 

[Gazoo]

Wow. 750 pounds needed ... Gona study this more; Plus my other 3 Question were much more primary: If anyone has insight opinions to share:

#1 Question: Can compression plus cycling higher amp battery draws and charge cycles (that I would image heat the battery a bit) result in the sides material of battery sides softening, and then being pressed flatter together? #2 question: Does non perfect sides slightly puffed sides of a 280Ah LiFePO4 cell = inferior lifespan? #3 Question: . Is anyone getting perfectly flat-sided 280Ah cells? ... from whom?

Some of us have received undulated cells much like the ones shown in your photos and the photos posted in this thread. Perhaps @AussieSim can comment on whether or not his has flattened out. Mine have not flattened out but I don't have them compressed with the proper force. The cells do breathe normally when charging and discharging. BTW, Will Prowse's test was of LIshen cells, not EVE cells.

I don't think anyone can answer your number 2 question. Only EVE could answer that. I do believe a capacity test of your bank will be telling. My 8S pack tests at 272ah's. That's still 97% capacity. After reading the many posts in this forum, I don't believe the cells are Grade A. And I don't believe they are used. The newer generation of EVE cells might be a better grade. That remains to be seen and one needs to keep in mind the newer generation will be priced higher, but still cost much less than if ordering directly from EVE.

Hopefully you will receive replies to your number 3 question. Did the first batch you ordered have flat sides?

 

[AussieSim]

Some of us have received undulated cells much like the ones shown in your photos and the photos posted in this thread. Perhaps @AussieSim can comment on whether or not his has flattened out. Mine have not flattened out but I don't have them compressed with the proper force. The cells do breathe normally when charging and discharging. BTW, Will Prowse's test was of LIshen cells, not EVE cells.

I don't think anyone can answer your number 2 question. Only EVE could answer that. I do believe a capacity test of your bank will be telling. My 8S pack tests at 272ah's. That's still 97% capacity. After reading the many posts in this forum, I don't believe the cells are Grade A. And I don't believe they are used. The newer generation of EVE cells might be a better grade. That remains to be seen and one needs to keep in mind the newer generation will be priced higher, but still cost much less than if ordering directly from EVE.

Hopefully you will receive replies to your number 3 question. Did the first batch you ordered have flat sides?

I have my 8s square packs compressed with 2 metal straps between 3 ply planks. I haven't noticed the undulations to change whatsoever.

 

[Capt Bill]

BTW, Will Prowse's test was of LIshen cells, not EVE cells.

I don't think anyone can answer your number 2 question. Only EVE could answer that. I do believe a capacity test of your bank will be telling. The newer generation of EVE cells might be a better grade.

... Did the first batch you ordered have flat sides?

I appreciated your feedback Gazoo. On my first set of LiFePO4s from March 2020, I spaced them slightly with double stick tape;. I did that with my first take from reading about max battery temps plus seeing videos of Will's fav Fortune LiFePO4 cell packs with an upper and lower case that pulls the battery bank together with noticeable spacing in between each cell. Since more recently reading about compression of EVE LiFePO4s for more cycles, I am still wondering about the value (or not). I did recently notice the outside edges of my first battery pack has a "slight" wave or wavy surface, as I can feel it with a hand slide. Re: Capacity Tests with two different 150W fan heat testers on my recent 280Ah Eve cells, ... I measured 271 Ah to 268 Ahs @20 A draws; while wondering if slightly higher voltage and amps I measured at battery and wires with DMM vs the 150W Ah tester LCD might be worthy of my calibrating those figures upwards (I'll find a different thread for my questions about that/ while wondering what results I might get with a 0.5C , 140 amp draw down to 2.5vdc ). ... Still wondering about compression of Eve Cells, and will be reading more. Thanks for reply.

 

[Gazoo]

You are welcome. The main reason I mounted my cells in a fixture was to prevent stress on the cells terminals. But I don't think that helps much. I think the consensus is turning to using braided busbars, cables or some kind of flexible interconnects.

Also from what I have seen, C rates for charging or discharging doesn't make much of a difference with regards to capacity. I would give it a go anyways and let us know. The more data the we have the better. Even at 268ah's you still have 95.7% capacity. People have different thresholds for what is acceptable. For what I paid I can't complain, but I don't like these suppliers advertising cells as being Grade A when clearly they are not.

 

[HaldorEE]

You are welcome. The main reason I mounted my cells in a fixture was to prevent stress on the cells terminals. But I don't think that helps much. I think the consensus is turning to using braided busbars, cables or some kind of flexible interconnects.

Also from what I have seen, C rates for charging or discharging doesn't make much of a difference with regards to capacity. I would give it a go anyways and let us know. The more data the we have the better. Even at 268ah's you still have 95.7% capacity. People have different thresholds for what is acceptable. For what I paid I can't complain, but I don't like these suppliers advertising cells as being Grade A when clearly they are not.

I think what they are is new old stock, grade A cells. As in they were Grade A back in 2018, but after sitting in a warehouse for 3 years, well, what you actually get varies.

I don't care, we are getting 250+ AH cells for the price of 100AH cells. That is a fantastic deal. And we can thank Covid-19 for killing the domestic Chinese market for electric vehicles in 2020. Otherwise we would never have gotten these so cheaply. This could be a once in a decade opportunity. If you haven't taken advantage of this you are going to be kicking yourself next year when the price triples.

 

[Gazoo]

Possibly, but the suppliers should still make it clear what they are selling. And why are so many receiving cells that are not flat on the sides? Like shown in this thread. From reading the forum since I joined, people were not having these problems.

 

[Dzl]

Spoiler: Off Topic

I think what they are is new old stock, grade A cells. As in they were Grade A back in 2018, but after sitting in a warehouse for 3 years, well, what you actually get varies.

The EVE rep I spoke with confirmed many of the EVE cells being sold by unofficial/grey market resellers are Grade B cells, and cells get designated grade B for many reasons from electrical/chemical to cosmetic, etc (old stock is certainly one possible reason). And that once they are batched that way, there isn't an easy way, (even for EVE) to distinguish the reason they did not pass QA. Or at least that was my takeaway from the exchange.

In (I think) August, they officially put out a warning/disclaimer (attached) to customers that cells being sold through unofficial channels are not qualified or supported and may have defects. You will notice the time of this warning was shortly before the suppliers began transitioning to Lishen cells, and stating EVE cells would no longer be readily available. Here is a snippet of the conversation:


It is worth noting, while I have marginally more trust in an official rep relative to small grey market resellers, I also am quite conscious of the fact that this is a sales rep I am talking to, so not a fully unbiased source. Still everything he says here is basically what many here already expected to be the case and have seen evidence of.

I don't care, we are getting 250+ AH cells for the price of 100AH cells. That is a fantastic deal.

I agree, they are a great deal for our purposes. But I also agree with Gazoo, at this point its quite clear they are not grade A cells (cells with dents, cells under capacity, cells with scratched QR codes are verifiably and objectivily not grade A), that doesn't automaticall make them a bad deal, I think in most cases they are a very good deal, just not an unrealistically great deal. At the end of the day, Cell grade is just a classification, what matters is if a cell (1) meets your needs (2) performs to your expectations and continues to over time (3) is a good value in the eyes of the buyer.

 

[HaldorEE]

Spoiler: Off Topic

The EVE rep I spoke with confirmed many of the EVE cells being sold by unofficial/grey market resellers are Grade B cells, and cells get designated grade B for many reasons from electrical/chemical to cosmetic, etc (old stock is certainly one possible reason). And that once they are batched that way, there isn't an easy way, (even for EVE) to distinguish the reason they did not pass QA. Or at least that was my takeaway from the exchange.

In (I think) August, they officially put out a warning/disclaimer (attached) to customers that cells being sold through unofficial channels are not qualified or supported and may have defects. You will notice the time of this warning was shortly before the suppliers began transitioning to Lishen cells, and stating EVE cells would no longer be readily available. Here is a snippet of the conversation:

View attachment 34055
It is worth noting, while I have marginally more trust in an official rep relative to small grey market resellers, I also am quite conscious of the fact that this is a sales rep I am talking to, so not a fully unbiased source. Still everything he says here is basically what many/most already expected to be the case.



I agree, they are a great deal for our purposes. But I also agree with Gazoo, at this point its quite clear they are not grade A cells (cells with dents, cells under capacity, cells with scratched QR codes are verifiably and objectivily not grade A), that doesn't automaticall make them a bad deal, I think in most cases they are a very good deal, just not an unrealistically great deal. At the end of the day, Cell grade is just a classification, what matters is if a cell (1) meets your needs (2) performs to your expectations and continues to over time (3) is a good value in the eyes of the buyer.

The cells I bought were represented as being unused, new old stock, grade A, 280 AH cells.

The cells I received did not look used. The terminals are not scratched, there are no dents and the QR codes are legible and have not been defaced. I would expect cells that have been sitting on the shelf for 3 year to have lost some capacity. If I get 255AH capacity or better then I am going to be ecstatic. If I get better than 240AH I will grumble a bit but accept them. If I get less than 240AH, then I am going to be talking to my vendor, since this indicates to me that these cells were either not stored properly or else these cells were in fact rejected (Grade B) cells when they were made.

Research shows that capacity loss of approximately 12% would be typical for cells stored at reasonable SOC and temperature.



The lower the SOC (as long as it is not 0%) and the lower the storage temperature the better.

Calendar ageing of LiFePO4/C batteries in the second life applications | Semantic Scholar

Lithium-ion battery second life usage might be an interesting solution for certain applications and it can bring not only environmental benefits but also e.g. lower electric vehicles or hybrid electric vehicles total cost of ownership. However, the electrical performance and performance...

www.semanticscholar.org

 

[Dzl]

Spoiler: Off topic

The cells I bought were represented as being unused, new old stock, grade A, 280 AH cells.

Which reseller?
Some say new old stock, "grade A",
Some swear they are new 2020 cells and "grade A",
A couple have been upfront from the beginning and stated they are not grade A but not coincidentally nobody opted to buy from them.
Personally I believe they are all selling the same cells and most are being dishonest about cell grade.
At the end of the day, they all may be partially right, some may be misinformed or misrepresenting the truth. We can't fully know. This is why I think the term grey market is very fitting there is very little transparency and a lot of misinformation.

The cells I received did not look used.

You may misunderstand the terminology (or maybe you are just responding to the specific part of the quoted text that referenced possible used cells). A/B/C grade is a totally separate from new/used, all these cell grades apply to new cells.

The terminals are not scratched, there are no dents and the QR codes are legible and have not been defaced. I would expect cells that have been sitting on the shelf for 3 year to have lost some capacity.

Exactly, which is why manufactures will downgrade the rating after some period of time. This--along with cells that come up a little short on capacity from the factory-- (in my eyes) would be the absolute best type of B grade (or "A-" depending on the manufacturer and level of fade) cell to get (ones that just age out of their new A grade status but were otherwise good and healthy cells). But this is just one of a half dozen or more possible reasons, not all of which are readily observable. If you look at the variability among cells received I think it supports the idea that the cells we buy from resellers are a mish-mash of cells discounted for various reasons.

If I get 255AH capacity or better then I am going to be ecstatic. If I get better than 240AH I will grumble a bit but accept them. If I get less than 240AH, then I am going to be talking to my vendor, since this indicates to me that these cells were either not stored properly or else these cells were in fact rejected (Grade B) cells when they were made.

My understanding is the capacity threshold between A grade and non-A-grade (for an EVE cell) is >280 vs <280, (of course, with our limited means to test, measurement error is quite possible so it makes sense to be more forgiving, especially for a single test).

Research shows that capacity loss of approximately 12% would be typical for cells stored at reasonable SOC and temperature.

View attachment 34062
Those charts appear to show extremely high (to the point of negligence on the part of the seller) storage temperatures. But I get your point (and agree) some capacity fade over time just from sitting in a warehouse is normal and to be expected with old cells.

Anyways, I didn't mean to contribute to pulling this thread off topic, sorry @Bob B
@HaldorEE if you want to discuss more lets continue in PM or we can just move along

 

[Bob B]

Spoiler

OH .... just wanted to try out the spoiler since it is so popular now... LOL

 

[Dzl]

OH .... just wanted to try out the spoiler since it is so popular now... LOL

?
Not sure if it helped or hurt. I think I may be the only one on the forum that uses the spoiler tag, and I'm definitely a frequent user/abuser of it, since I tend to write 100 words where 10 would suffice ?

 

[Bob B]

?
Not sure if it helped or hurt. I think I may be the only one on the forum that uses the spoiler tag, and I'm definitely a frequent user/abuser of it, since I tend to write 100 words where 10 would suffice ?

I just wanted to be one of the cool guys. LOL
Guess it's kind of the polite way to post off topic with minimal disruption.