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

sorsdt said:

Don't you think that by compressing the battery we only decrease its internal resistance? By doing this we reduce self-heating on high currents. From school chemistry, we all know that on every 10 Celsius degrees speed of reactions changes twice. That causes the degradation of cells. So if we use our batteries with low current we don't need to use compression. And one more thing that comes to my mind - such processes of changes mechanical dimensions can cause loosen bolt terminals between cells.

Click to expand...

Part of what I get from compressing my EVE 230s is constraining them from movement in my RV when it is bouncing down the road...

There are a LOT of things we don't know about compression.

We do know that it will prevent delamination.

We also know that (slightly) delaminated cells aren't as good as not delaminated cells. Less capacity, different internal resistance and so on.

Not all cells are created equal.
My 152Ah used the same casing as the 120Ah.
That casing/amount of layers wasn't a problem with 120Ah, but pushing 32Ah extra inside was.

They all started slightly bloating, not at he same time or pace, and not pillowed.

Enough to get all strange things.
Enough that i decided to want to stop the expansion/delamination and started to compress them.

That seemed like a good idea, and they debloated!!
Seemed like a good idea..
After a while a cell self discharged, taking many other cells with it.
Thousands of dollars damage...

Luckily the house didn't catch fire.
(My protective measures like concrete fiber sheets did play a big part in this)

Did this happen due compression of delaminated cells?
I think it did. Not 100% sure.
I used rigid busbars. Delamination and compression = different distance between the terminals / studs.
Alternatieve idea is that the expansion/contraction placed too much stress on that terminal and that is what caused it to malfunction.

Either way, if i would have known about the need for compression, i would have done it at the start.
If i would have known that compressing slightly delaminated cells would be this dangerous, I would not have.

Some of the cells I was able to re-use.
48* 152Ah , 32* 280Ah..

Now 16* 280 again in use, after monitoring them for 6 months, outside.
Gave them a few cycles to see how they hold up.

4* 152 in my daughters E-scooter
8* 280 outside in the farm for extra pump.
20* 152 went to a friend who was feeling brave .. he has 16 in use.
I didn't dare to use them again in my place.
The rest... Lost.

The 16* 280ah..
Not compressed, as due the fire some are bloating a bit.
I learned my lesson....

If they are slightly bloating, don't think about compression, just accept that they are and accept that you will loose a few % capacity.
You might want to invest in an active balancer as they are less capable of keeping the same SOC.

For me it's the 2A active balancer BMS Jikong, and it does wonders.

Even then...
Once every 3-4 months i need to manually discharge one of the 280Ah cells about 10Ah, as it start to spike.
Up and running fine besides this for 300 days now

as read,

compress from the start, acceptable

compress after bloat, avoid

Ampster said:

Then, one unexpected deep discharge event left them slightly expanded and strained the connectors. The cells retained their capacity but that is when I saw the benefits of some constraint just to protect against an event that was not planned but which could occur in normal use.

Click to expand...

Do you recall how deep the discharge which caused swelling was? I’m interested to know at what point this might occur. Thanks

Sverige said:

Do you recall how deep the discharge which caused swelling was? I’m interested to know at what point this might occur. Thanks

Click to expand...

Sorry, it was six years ago and it happened while I was away on vacation. I got home to find the cells slightly bloated and the refrigerator not working because I had not set up the inverter for grid backup.

Good news is, that even after they got slightly bloated... 6 years and counting ??

Airtime said:

kgf is just kg, but clarifying that it is force not mass. On Earth with 1g gravity, kgf=kgm=kg=2.2lbs. So 300kgf is 660lbs, not what I would call light pressure.

I’m trying to get clarification from EVE on the “fixture” and how the 300kgf force is applied.

Click to expand...

Kgf is just Kg in a vertical setting

Clamping or no clamping?
If you cycle the whole battery more than once a day, clamp it.
If you are going to use it in a moving object, clamp it
If you are only using parts of it every day, space it,

The aging effect will be greater than the ware and tare of it.

1,000 grams in a 1 G environment -> "1 kgf downwards"

(1 G -> 9.8 meters per second per second)

sometimes i wish the compression force specification would be specified in Newtons...

curiouscarbon said:

1,000 grams in a 1 G environment -> "1 kgf downwards"

(1 G -> 9.8 meters per second per second)

sometimes i wish the compression force specification would be specified in Newtons...

Click to expand...

In France we do not use kgf wich is not an SI unit, we use Newtons.

A worse abuse is for the weight ... many people say "i'm weighting 100 kg" while they should say : "My mass is 100 kg and my weight is 981 N"

Weight is a unit of force and mesured in N.
Kg is a unit of mass and mesured un Kg.

=> which would imply that our weight can vary depending on the distance to the center of the earth, if this guy was on the everest he would weight 978 N.

Since we're on the pedantic route I might add it's kg, not Kg https://en.wikipedia.org/wiki/Metric_prefix#List_of_SI_prefixes

I found an interesting paper involving Lithium Nickel-Manganese-Cobalt (NMC) batteries and force based capacity analysis. The researchers shared their test fixture data with pictures.

zissou001 said:

I found an interesting paper involving Lithium Nickel-Manganese-Cobalt (NMC) batteries and force based capacity analysis. The researchers shared their test fixture data with pictures.

Click to expand...

This thread title is about EVE LFP cells. I would be happy to discuss NMC chemistry on a new thread.

I've got a bunch of yellow Winston LFP cells from 2015 (it is almost 40kWh).
They are coming out of an EV. 2 out of the 200 cells are dead, and they are barely bloated.
In the EV, they were there in pairs of 4, with the 4 hard plastic lines/straps around them.
There is another beam that just holds them in place loosely, it did not have any starting compression and it doesn't seem designed to compress them, even if they would bulge a bit.

I am thinking to reuse all of them, just keeping them in the packs of 4 with the plastic straps, and not do anything more in terms of compression.
So in the packs of 4, put them in some kind of wooden or metal boxes that I can find for little money. Cheap wooden boxes that I can close of well enough to avoid humidity. But it might be plastic or metal boxes, whatever is cheaper.
The original battery boxes aren't that convenient to use because of the size.

(and then to decide if I keep the high voltage setup, or to parallel them to something like a 16s system, for cheaper BMS and 48v convenience, but that is another topic)
Currently, they are all in series.

Swing said:

Winston LFP cells

Click to expand...

Those are already in a hard plastic enclosure. EVE LFP cells only have a thin aluminium enclosure. They're not really comparable.

upnorthandpersonal said:

Those are already in a hard plastic enclosure. EVE LFP cells only have a thin aluminium enclosure. They're not really comparable.

Click to expand...

Well, the Winston cells can also bulge, as is said in this topic. I think they do that much less than the EVE LFP cells, but they still do it.
Although it might be about corner cases, for example the cell is used out of spec (too hot, or under/overcharged etc), that is not entirely clear to me.

After all, they are LiFeYPo4 instead of LiFePo4.

Compression is not used to prevent bulging - that's a sign of over discharge/charge (electrolyte decomposition). The reason for compression is to prevent the delamination of the electrodes.

upnorthandpersonal said:

Compression is not used to prevent bulging - that's a sign of over discharge/charge (electrolyte decomposition). The reason for compression is to prevent the delamination of the electrodes.

Click to expand...

Compression is for rapid charge/discharge multiple times a day.

Bergum said:

Compression is for rapid charge/discharge multiple times a day.

Click to expand...

No, the electrode will change size independent on C rate. It's more pronounced at higher C rates, and obviously will happen more pronounced with more cycles, but it does occur at lower C rates as well.
Whether or not compression is really useful at low C rates, well, I'm not getting into that discussion again and leave that decision up to the reader of this very long thread.

upnorthandpersonal said:

No, the electrode will change size independent on C rate. It's more pronounced at higher C rates, and obviously will happen more pronounced with more cycles, but it does occur at lower C rates as well.
Whether or not compression is really useful at low C rates, well, I'm not getting into that discussion again and leave that decision up to the reader of this very long thread.

Click to expand...

I can agree to not starting that discussion again. ??

Swing said:

I've got a bunch of yellow Winston LFP cells from 2015 (it is almost 40kWh).
They are coming out of an EV. 2 out of the 200 cells are dead, and they are barely bloated.
In the EV, they were there in pairs of 4, with the 4 hard plastic lines/straps around them.
There is another beam that just holds them in place loosely, it did not have any starting compression and it doesn't seem designed to compress them, even if they would bulge a bit.

I am thinking to reuse all of them, just keeping them in the packs of 4 with the plastic straps, and not do anything more in terms of compression.
So in the packs of 4, put them in some kind of wooden or metal boxes that I can find for little money. Cheap wooden boxes that I can close of well enough to avoid humidity. But it might be plastic or metal boxes, whatever is cheaper.
The original battery boxes aren't that convenient to use because of the size.

(and then to decide if I keep the high voltage setup, or to parallel them to something like a 16s system, for cheaper BMS and 48v convenience, but that is another topic)
Currently, they are all in series.

Click to expand...

Good idea to keep them strapped, as that's they way they have been for years.

I have sadly some experience with slightly bloating cells and compressing them.

At start it looks like they slowly de-bloat.
Not long after i had a cell self-discharging/ thermal runaway, what made several adjoining cells go crazy also.

Luckily the house didn't burn down, many thousands of dollars LifePo4 lost.

Compressing a slightly bloated cell is seldom a good idea.

Leaving it just the way it is, seldom a problem.
Yes, you lost a few Ah de the blood / delamination.
You won't be able to fix that.

Compressing won't fix that nor will it stop the process.
As other do expand, and they have no room to do so, the weakest cell will endure the combined pressure from clamping/compressing and the expansion of the adjoining cells..

Some of the cells are recovered after the fire.
Almost all slightly bloated.

I've tested them for 9 months before starting to use them again.

They kept charge and had reasonable amount of capacity left.

After a year of use, they didn't bloat more, and are reasonable stable.
I use 17 cells, 2 in parallel as they act "wierd" on their own.
Together, all "OK".

Lucky, not all of the 1028Ah @51.2v are lost.

Compressing can be good, do it when the cells are fresh and not bloated at all.

Compressing slightly bloated cells...
That might have results you didn't expect and potentially dangerous.