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

Frank in Thailand said:

How stupid would you feel to ignore the guidelines given by the producers, who do that "extra mile" themselves when constructing their own packs?
.............
You really believe Andy has more knowledge then the engineers over at BYD or EVE??
.............
Follow Andy's logic, or the factory engineering team.

Click to expand...

We haven't exactly gotten complete and detailed information from the manufacturers regarding compression...
AFAIK, the idea of compressing these cells with a certain force had to do with people in the DIY community becoming aware of a few lines mentioned in some of the lifepo4 cell data sheets which described the life cycle testing conditions.
These conditions are very specific and are very different from the type of service that would be expected in a solar storage application.

It does not make sense to simply extrapolate that 300KGf must be the ideal or required factor to gain long life in the use of these cells for our applications, and as far as I am aware(AFAIK in the english language), there hasn't been any specific guidance on that point from EVE, BYD, or similar manufacturers.

Is there some guidance that a factory engineering team has published about what the best way is to constrain or fixture these cells for long term use in solar storage applications? What published "instructions" about these cells are available from the manufacturers?

Ho quick question, I got them slightly compressed now and top balancing them in parallel to 3.6v.
After that, I would like to unmount them, turn them around and compress again.
But then the pressure would be released while they are at 3.6v. I think that is not a good idea?

So either leave them the way they are, or drain them to 50% or so, before releasing pressure?

After being schooled by RCinFLA over in the Chins thread about what is actually inside an aluminum cased cell (open wraps at top - entire case is the singular seal, rather than individually sealed pouches)

I offer up my best Monty Python Anne-Elk theory on Brontosaurus:

"SNUG" containment suffices rather than any specific pressure. My old GBS prismatics simply had an aluminum plate on each side, with straps holding them snugly together. But not so tight as to bend the plastic.

The reason is not so much for cycle-life, but not to allow too much sideways mechanical expansion, turning an uncontained bank into a U-shaped accordion under slight overcharge or enthusiastic charging.

If allowed to do so, too much vertical torque might be placed upon busbars and the terminals themselves. If the terminals are vertically torqued too much by overall sideways expansion, the case seal itself can be breached, and now the electrolyte is exposed to air, degrading the cell since the entire case of an aluminum cased cell is the sole seal.

Anne Elk thinks this is a great theory.

rhino said:

Off Grid Garage's video from couple weeks ago is pretty relevant to this discussion

Click to expand...

it would be better to use a fixture than doing nothing as Andy promotes....read the comments from "electrodacus" and also from "up north and personal".... no real scientific test to back Andy claim IMO.

Frank in Thailand said:

I have seen the video from Andy.

He is forgetting one main thing, that the cells are supposed to have a snug fit.
To prevent bulging, the walls of the cells simply are too weak to prevent this on their own in the long run.

2000-4000 cycles..
With charging during daytime and using 50-70% at night...
They can last ages.
Maximum life expectancy under most optimal conditions is 20 years.
They aren't Edison batteries!!

How stupid would you feel to ignore the guidelines given by the producers, who do that "extra mile" themselves when constructing their own packs?

You really believe Andy has more knowledge then the engineers over at BYD or EVE??

The whole spring "hoax" is over the top. "Too much of a good thing".
It won't hurt, also won't increase compared to a snug fit.

Can anyone produce a picture or video of 280ah cells that aren't snug / clamped after 2-3 years of continuous use?
And the same type with a snug fit?

Without it ..
We need to choose:
Follow Andy's logic, or the factory engineering team.

Up to you

Click to expand...

exactly, would you follow youtube entertainment clickbait or a manufacturing engineering team... i choose the engineering team!

Swing said:

Ho quick question, I got them slightly compressed now and top balancing them in parallel to 3.6v.
After that, I would like to unmount them, turn them around and compress again.
But then the pressure would be released while they are at 3.6v. I think that is not a good idea?

So either leave them the way they are, or drain them to 50% or so, before releasing pressure?

Click to expand...

It looks like you will get widely varying answers here, but I would discharge them before removing them from compression.

justgary said:

It looks like you will get widely varying answers here, but I would discharge them before removing them from compression.

Click to expand...

Yeah, widely varying answers. Like there's a random answer generator at work.

My anecdotal experience: Top balanced 8 cells in a compression fixture. Removed the compression fixture, rearranged the cells into two 4s batteries. No issues, no discharge after top balance.

Ok great. That would save me quite some days because I don't have much lying around to draw much current at the 3.6v in a fast way.

justgary said:

Several folks here have shown cell swelling with one top balance charge.

Click to expand...

All it takes is one over-voltage charge. Electrolyte breakdown greatly accelerates above 4.3 vdc cell voltage.

justgary said:

The LFP chemical equation, as far as I can tell:

The cathode reaction is:
LiFePO4 ⟶ FePO4 + Li(+) + e(−)

The anode is:
Li(+) + C6 + e(−) ⟶ LiC6

I can't find any papers that discuss any significant gas generation during charge or discharge of an LFP cell. Please cite a source so I can learn.

Click to expand...

Your information only states the desired intercalation process.

There are many peripheral chemical reactions that happens at different rates and conditions. Some are good and necessary, some are bad, and some are part of normal cell aging process.

First important peripheral chemical reaction, done during initial manufacturer charge forming process, is the SEI, Solid Electrolyte Interface chemical reaction that forms the protective barrier in anode to greatly reduce electrons from getting into electrolyte during charging which is the primary cause of electrolyte decomposition. The initial SEI formation consumes some of the lithium reducing cell available capacity but it is absolutely necessary to get reasonable cycle life from cell. This initial process does create some electrolyte decomposition and gas bloating but the gas is relieved before manufacturer seals pressure relief vent on cell so customer does not see the bloat. Newer anode pre-lithiation process can cause some minor bloating on first few cycles of cell.

SEI protective layer does get some damage during normal cycle use from graphite full charge expansion and continuously regrows during life of cell. Over cycle life, continued SEI growth consumes some more of available lithium reducing cell capacity over time and the thickening of SEI layer over time restricts lithium-ion migration through cell increasing cell impedance. This is the primary normal use degradation that limits the useful lifetime of cell.

Most of this has not a lot to do with compression benefit, other than excessive compression pressure may increase damage to SEI layer which will accelerate cell capacity loss and cell impedance degradation.

Frank in Thailand said:

I have seen the video from Andy.

He is forgetting one main thing, that the cells are supposed to have a snug fit.
To prevent bulging, the walls of the cells simply are too weak to prevent this on their own in the long run.

2000-4000 cycles..
With charging during daytime and using 50-70% at night...
They can last ages.
Maximum life expectancy under most optimal conditions is 20 years.
They aren't Edison batteries!!

How stupid would you feel to ignore the guidelines given by the producers, who do that "extra mile" themselves when constructing their own packs?

You really believe Andy has more knowledge then the engineers over at BYD or EVE??

The whole spring "hoax" is over the top. "Too much of a good thing".
It won't hurt, also won't increase compared to a snug fit.

Can anyone produce a picture or video of 280ah cells that aren't snug / clamped after 2-3 years of continuous use?
And the same type with a snug fit?

Without it ..
We need to choose:
Follow Andy's logic, or the factory engineering team.

Up to you

Click to expand...

Yo Frank in Thailand from Bill in Northern California. I wonder if you (or any others here) ... have an opinion about: Could a set A- to B grade 280Ah LiFePO4 cells (that have slightly wavy sides). ... Benefit from compression AFTER ... being online and cycled for a year or two???? ... or is the benefit available MOSTLY ... IF compression was applied when 1st put online? Personally ... I would only compress my cells with flexible bus bars, which were not supplied with the batteries ( and for me, not yet obtained). ... IMO: LiFePO4s suppliers who made it easy to compress LiFePO4s by supplying flexible bus bars would get attention on this forum, and stand out as ahead of the pack ...

Swing said:

Ho quick question, I got them slightly compressed now and top balancing them in parallel to 3.6v.
After that, I would like to unmount them, turn them around and compress again.
But then the pressure would be released while they are at 3.6v. I think that is not a good idea?

So either leave them the way they are, or drain them to 50% or so, before releasing pressure?

Click to expand...

Just remove the bus bars before removing the fixture. Depending on your setup, you might have a tough time getting the bus bars off after removing the fixture. I learned that the hard way.

EDIT: Also readjust your fixture after the battery has reached < 50% SoC. It will be loose.

cinergi said:

Just remove the bus bars before removing the fixture. Depending on your setup, you might have a tough time getting the bus bars off after removing the fixture. I learned that the hard way.

EDIT: Also readjust your fixture after the battery has reached < 50% SoC. It will be loose.

Click to expand...

According to HRTKD it should be okay to loosen them at full charge.

I was hoping not to drain them back down again because it will be time consuming. I don't have anything to drain them quickly at 3v.

Swing said:

According to HRTKD it should be okay to loosen them at full charge.

I was hoping not to drain them back down again because it will be time consuming. I don't have anything to drain them quickly at 3v.

Click to expand...

Well, that's not quite what he said. He said it worked for him.

A caveat here is that you should allow the cells to rest for a number of hours after a top balance and before unclamping. That, in and of itself, will allow the cell voltage to relax down to a lower amount.

Capt Bill said:

Yo Frank in Thailand from Bill in Northern California. I wonder if you (or any others here) ... have an opinion about: Could a set A- to B grade 280Ah LiFePO4 cells (that have slightly wavy sides). ... Benefit from compression AFTER ... being online and cycled for a year or two???? ... or is the benefit available MOSTLY ... IF compression was applied when 1st put online? Personally ... I would only compress my cells with flexible bus bars, which were not supplied with the batteries ( and for me, not yet obtained). ... IMO: LiFePO4s suppliers who made it easy to compress LiFePO4s by supplying flexible bus bars would get attention on this forum, and stand out as ahead of the pack ...

Click to expand...

Why flexible busbar???

When you make a snug fit, it's not moving
No flexibility needed.

Sure, extreme situation busbar might get warm/expand.
Then you should have better busbars hahaha....
In a good match, thickness and width, they won't heat up .

After a few years of usage...
Highly depending on the cells!!

People might want to look at my experience with fire...
IMO result of compressing slightly bloated 152AH cells...
Spontaneous self discharge, one terminal practically molten, lots of damage.

What happens when you compress slightly bloated cells? They de-bloat.
Not back to original state, just less bloating.
So...
No more snug fit, compress some more..
And more..
And.... Fire

The 152Ah had a gap of 3-4 mm when placed side by side.

Typical for this capacity, as it's the same housing for 100, 120 and 152Ah..
Too much sheets in the thin aluminium housing without compression or snug fit (2.5 years ago).... Not good.
Back then the knowledge was more limited, even more then it is now.

I lost 48x 152 and 16 280Ah...

16 X 280 where OK, I kept them outside the house for 6 months for safety.
Stayed OK and are now in use with my 3x260 BYD packs (those are factory build)

No, I would not compress them.
Perhaps give it a snug fit.

After placing the cells, you place the busbars and tighten with torque meter.
Do NOT attempt to clamp, tighten, fit with the busbars attached!! (And tightened)
(For me would be impossible with 16 cells)
4 cells probably can.. but please... Don't.

Place and tighten the busbars after the snug fit.

I didn't clamp / compress my EVE 280's.
They have tiny space between them, after 40 days in use, no change.

I'm not that worried.
They where already written off...

Expensive lesson, I was prepared for fire, now even better with a lot extra prevention and (electric) fire distinguishers.

Don't clamp bloated cells.
Period.
It all seems to go great...
Till it doesn't.

Swing said:

Ho quick question, I got them slightly compressed now and top balancing them in parallel to 3.6v.
After that, I would like to unmount them, turn them around and compress again.
But then the pressure would be released while they are at 3.6v. I think that is not a good idea?

So either leave them the way they are, or drain them to 50% or so, before releasing pressure?

Click to expand...

If they are good cells I doubt it is an issue. But you don't know until they are unstrapped.

If compression or restraint is to be used, I recommend going direct to the series battery configuration at the start.
Wire in parallel if the parallel top balance seems that important.

Frank in Thailand said:

Re: Why flexible busbar??? ... & ... (your) ...
look at my experience with fire... IMO result of compressing slightly bloated 152AH cells...
Spontaneous self discharge, one terminal practically molten, lots of damage.
What happens when you compress slightly bloated cells? They de-bloat.
Not back to original state, just less bloating.
So... No more snug fit, compress some more.. And more.. And.... Fire

Click to expand...

Flexible Bus Bars if Compressing LiFePO4s ???? I think Frank's LiFePO4 Fire Story Deserves Some Attention on this forum !!!

... I have thought compressing my 8 x 280Ah cells (x 2 or 3 battery banks) would result in cells expanding and contracting at their rectangular cell sides, ... and have thought that solid bus bars would put stress on the battery terminals when such push and shove, and then contraction happens. I have heard comments in other compression thread discussions showing similar thoughts (... just some thoughts). ... I appreciate hearing Frank in Thailand' views because I have seen his story sharing comments over last couple of years showing me lots of experience.

... WOW ... First time I have heard compressing a bloated LiFePO4 could lead to a fire. Re: Frank's "Spontaneous self discharge, one terminal practically molten, lots of damage." Frank : : THANKS for HEADS UP !!! Question: When you mention: "one terminal practically molten" : : Any possibility that molten terminal might have stayed in better shape with a "Flexible Bus Bar"? ... Could Compressing (more, and then more) with Solid Bus Bars make a terminal more susceptible to Spontaneous self discharge, and then spontaneous combustion ??? ... " .... Could solid bus bars on a LiFePO4 set that gets more and more compression (like Frank mentioned), possibly be the cause of a tweak battery terminal (if one did not loosen and re-tighten solid bus bars to reset after each new compression cycle), and then Frank's ... ""Spontaneous self discharge, one terminal practically molten, lots of damage." ??? I am wondering out loud for all of us: Frank: ... Did you loosen, and re-tighten the bus bars on each cycle of your "more and more" compression cycles ??? Wondering Out Loud :+) and with Condolences for that Story.

"Spontaneous Combustion" is something we all (including family and neighbor kids) ... all need to know about, to tweak our habits for safety, especially after paint jobs and deck sealing. IMO: Even oily paper towels in an open plastic trash can under your kitchen counter can cause a fire disaster when no one is there, like those fire created by paint crews leaving their garbage mess at back of building on a wooden deck. ... IMO: Having a small metal trash can for oily trash is a smart in both your shop and home.

... I love learning more all the time, including from other people's mistake. ... While I know I will also be learning from my own mistake ... as the DIYer with my hands on the details ... ;+)

ADDED LATER NOTE: after posting this, I got in a personal conversation with Frank; then figured out this topic has been thoroughly reviewed / ... I found that 2021 thread by searching for "Fire" with Frank's name. Frank let me know: The Fire was NOT the result of compressing cells while the bus bars were tight. Also saw many possible reasons for the Fire. ... The one I might share was Frank saying: @Will Prowse made a video over bloated cells that he strongly recommend to throw away and never use. With my experience till that time, I challenged that statement, all seemed to be fine, yes? Turns out you are right Will. Bloated cells are not safe. ...

Along side my study of the Frank's Fire related threads: I have recently updated my battery room to include a smoke alarm above battery banks, plus I just added the white colored Regular Dry Chemical Classes "B, C" extinguisher to my Battery/ Solar Wall Room; ... that is designed for electrical plus fuel fires ... using sodium bicarbonate as its agent. I liked reading that Sodium bicarbonate will not damage your property, and would be much easier to clean up, plus completely safe to use. ... Already had the red colored Multi-Purpose Dry Chemical Classes A, B, C Mono ammonium phosphate is the agent used in this type of extinguisher. (read) That chemical can damage anything it touches, so it is important to wash away all residue of the agent as soon as possible following its use.

The old Boy Scout Moto I remember is "Be Prepared" ... and I would add: along side best efforts for proper fuse sizes, and wire sizes, and cement board (or whatever else) for fire protected posts and walls etc. ... I say THANKS to Frank for sharing all he did for our mutual education; ... and Condolences . Best Wishes, Bill

Swing said:

According to HRTKD it should be okay to loosen them at full charge.

I was hoping not to drain them back down again because it will be time consuming. I don't have anything to drain them quickly at 3v.

Click to expand...

I'm agreeing that you can loosen at full charge; just remove the busbars first.

You don't have to drain them down immediately or on a per-cell basis. Just put the fixture back together, hook up the battery, and use it.. Once it reaches 50% SoC or less, tighten the fixture down -- it will be loose. No harm done.

RCinFLA said:

All it takes is one over-voltage charge. Electrolyte breakdown greatly accelerates above 4.3 vdc cell voltage.

Your information only states the desired intercalation process.

There are many peripheral chemical reactions that happens at different rates and conditions. Some are good and necessary, some are bad, and some are part of normal cell aging process.

First important peripheral chemical reaction, done during initial manufacturer charge forming process, is the SEI, Solid Electrolyte Interface chemical reaction that forms the protective barrier in anode to greatly reduce electrons from getting into electrolyte during charging which is the primary cause of electrolyte decomposition. The initial SEI formation consumes some of the lithium reducing cell available capacity but it is absolutely necessary to get reasonable cycle life from cell. This initial process does create some electrolyte decomposition and gas bloating but the gas is relieved before manufacturer seals pressure relief vent on cell so customer does not see the bloat. Newer anode pre-lithiation process can cause some minor bloating on first few cycles of cell.

SEI protective layer does get some damage during normal cycle use from graphite full charge expansion and continuously regrows during life of cell. Over cycle life, continued SEI growth consumes some more of available lithium reducing cell capacity over time and the thickening of SEI layer over time restricts lithium-ion migration through cell increasing cell impedance. This is the primary normal use degradation that limits the useful lifetime of cell.

Most of this has not a lot to do with compression benefit, other than excessive compression pressure may increase damage to SEI layer which will accelerate cell capacity loss and cell impedance degradation.

Click to expand...

Interesting, but you still didn't address your proposed gas formation during normal charge/discharge cycles.

In any event, the cathode LiFePO4 in a charged state has a different density (3.47 g/cm3) from FePO4 in a discharged state (2.78 g/cm3). The Carbon anode also changes density as it receives Lithium and forms LiC6. In other words, the crystals on each side of the electrolyte are constantly changing density with varying state of charge. Reducing physical motion while these changes occur is what compression addresses.

Several members here have reported compressing their cells, top balancing, and then removing compression, only to discover that the bus bars are hard to remove because the cells are wider when charged. This is due to the physical crystal changes, not gas. I personally don't think it is a good idea to remove charged cells from compression if the intent is to increase lifespan by using compression.

Capt Bill said:

I have thought compressing my 8 x 280Ah cells (x 2 or 3 battery banks) would result in cells expanding and contracting at their rectangular cell sides, ... and have thought that solid busbars would put stress on the battery terminals when such push and shove, and then contraction happens. I have heard comments form others in compression thread discussions showing others w similar thought (... just some thoughts).

Click to expand...

If someone needs flexible bus bars then they must not think much of their compression frame. My cells are compressed and they aren't moving. I certainly don't want springs in there. I want ZERO movement between the cell terminals. I've checked the fasteners on my two 4s batteries and they're fine. I'm more worried about vibration from the road loosening a fastener than about cell expansion loosening a fastener.

It would be interesting to connect terminals on a compressed 4s battery and then run it through a few rounds of state of charge between 100% to 5%. While the test is ongoing, use a micrometer to test if the distance between the cells changes.

I top-balanced mine without compression, to 3.65V and zero current, then built the battery. Never any expansion. Solid bus bars with slotted holes fit perfectly. Eve LF230 cells. Works perfectly. Maybe I just lucked out. [shrug]