Lifepo4 cell compression, for a stationary AND low capacity set up, useful or useless ?

[akumd]

Sorry, I know this topic is discussed in different threads and it seems to be a matter of opinion (mostly for high capacity setups)

I saw below OffGrid Garage video, As I understood, for a high capacity stationary setup(since cycle count is low), compression might NOT be useful.

BUT if we limit the scope for a stationary AND low capacity set up(for a Off Grid Solar system where daily cycle count could be 1 to 2 - i.e. for a year 365-730 cycle count), compression is clearly advantages right (since we are likely to utilize 3000-4000 "good" cycle count within 5 years) ?

 

[rhino]

Sorry, I know this topic is discussed in different threads and it seems to be a matter of opinion.

I saw below OffGrid Garage video, As I understood, for a high capacity stationary setup(since cycle count is low), compression might NOT be useful.

BUT if we limit the scope for a stationary AND low capacity set up(for a Off Grid Solar system where daily cycle count could be 1 to 2 - i.e. for a year 365-730 cycle count), compression is clearly advantages right (since we are likely to utilize 3000-4000 "good" cycle count within 5 years) ?

If you are cycling 1 or 2 times per day in a stationary setup then it is poorly designed and/or configured. But otherwise if you did have 1 or 2 cycles per day then yes, it would be advantageous to compress.

 

[Ampster]

One of the advantages to compression is that when the cells compress, as they eventually will, there will be less strain on the terminals. It is not so much a question of whether compression is useful so much as a process that can prevent damage to the terminals.

 

[rhino]

One of the advantages to compression is that when the cells compress, as they eventually will, there will be less strain on the terminals. It is not so much a question of whether compression is useful so much as a process that can prevent damage to the terminals.

If there is enough of an air gap between cells that shouldn't be an issue.. it's just that in order to get that air gap you'd either have to have custom busbar cell connectors, try to drill holes in the standard busbar, or arrange you cells in suboptimal arrangement that takes up more space to allow using the standard busbars.

 

[akumd]

If you are cycling 1 or 2 times per day in a stationary setup then it is poorly designed and/or configured. But otherwise if you did have 1 or 2 cycles per day then yes, it would be advantageous to compress.

@rhino, "If you are cycling 1 or 2 times per day in a stationary setup then it is poorly designed and/or configured", could you please clarify this a bit more .
Say the setup is 24v-100AH (i.e. 2KW), [this is in-addition to the grid use, so no need to consider running multiple days only on Solar]
- Is it a bad design intending to use all of 2KW (or 1920 WH considering 80% DOD) within the night time ? [i.e. at least 1 cycle per day]
- Additional cycles comes from the Sun light variations during the day time

Could you please clarify the disadvantages of above setup (which makes it a bad design)

 

[rhino]

- Additional cycles comes from the Sun light variations during the day time

I don't think there is a standard definition of what a cycle is but in general it would be from 100% to 20% during a day. It does not matter if it fluctuates during the day. So if you aren't going from 100% to 20% during the day then it would not be considered a cycle.

 

[S Davis]

What does the cell manufacture say? EVE doesn’t rate cycle life without compression.

 

[zorlig]

Compression is the manufacturer instruction.

The only reason why it's unclear is that people won't know or acknowledge results until they really have gone through the 10+ years of use.

The off grid garage positions are generally a bit foolish, he doesn't know and his positions aren't necessarily anymore than opinions about what's working for him.

We're near the point now though where people should be able to start saying confidently that it was correct to compress.

 

[rhino]

Compression is the manufacturer instruction.

The only reason why it's unclear is that people won't know or acknowledge results until they really have gone through the 10+ years of use.

The off grid garage positions are generally a bit foolish, he doesn't know and his positions aren't necessarily anymore than opinions about what's working for him.

We're near the point now though where people should be able to start saying confidently that it was correct to compress.

Actually he referenced a German engineer who worked in the battery industry.. see video that is referenced in description of this video:

 

[DIYrich]

I use flexible busbars to deal with the strain on connections problem. Let's say you have X pounds of pressure on each end of a 16 cell battery bank, and that is initially equal between the cells. I'm guessing that if the cell in the middle starts expanding, the friction of the cells on each side will result in more compression than intended.

 

[zcskywire2]

What does the cell manufacture say? EVE doesn’t rate cycle life without compression.

View attachment 208972

They used to back in the day, this is for an original LF280, dated April of 2019. Compression has just become a standard and mandated practice in industry now.

 

[Skypower]

If you’re already using those cells. It’s probably not a good idea to compress them.

 

[Brett V]

I put a few good tight wraps of filament tape around the cells, followed by a wrap of Kapton. Never had any problems.

 

[AshleyL]

If you’re already using those cells. It’s probably not a good idea to compress them.

Indeed, in this forum, we had few users who had the cell "exploded"/"venting" suddenly after compressing those "old" cell.

 

[S Davis]

They used to back in the day, this is for an original LF280, dated April of 2019. Compression has just become a standard and mandated practice in industry now.

Yes I know I have some LF280N cells, but they haven’t for a while now.

 

[Daddy Tanuki]

I use flexible busbars to deal with the strain on connections problem. Let's say you have X pounds of pressure on each end of a 16 cell battery bank, and that is initially equal between the cells. I'm guessing that if the cell in the middle starts expanding, the friction of the cells on each side will result in more compression than intended.

I'm sorry but what does friction have to do with compression or pressure? friction of two items sliding could cause heat... but thats about it.

 

[Luk88]

Compression is the manufacturer instruction.

The only reason why it's unclear is that people won't know or acknowledge results until they really have gone through the 10+ years of use.

The off grid garage positions are generally a bit foolish, he doesn't know and his positions aren't necessarily anymore than opinions about what's working for him.

We're near the point now though where people should be able to start saying confidently that it was correct to compress.

Exactly. If you want to give your cells the best chance you should follow manufacturer's recommendations. Personally I think too much compression may be worse than no compression at all. So if you're doing it. Buy some cheap disc springs (some people call them spring washers, but they are not "split" spring washers) put their parameters in a calculator (or ask here) and you now have the right amount of compression for your cells.

To anyone that says "I don't worry about compression and I'm fine". Unless you have another one of exact same packs in the same load and you've cycled it 5k times you don't know if you're loosing anything.


There is an argument to be made (partially after the "off grid garage guy" in Australia) that if you live in a hot climate your cells will experience calendar degradation well before they reach the cycle numbers where you notice a difference with compression. Whether this argument is worthy considering or not depends on your situation. What is the average temperature? Are cells going to be stored at 100% SOC for half a hot day every day? Perhaps then it doesn't matter? Are the cells going to be stored in 10C on average at 50% and cycled a lot? Then yes, I'd use compression.

Then let's briefly touch on the standard "epoxy board and tape" method. IMO this method does provide some compression for all but the first and last cell. This is so as long as you wrap it tightly before the very first charge, or you discharge a lot after equalising.

Then there is the effect of non flexible bus bars providing compression. My 16S setup was definitely held in compression by bus bars, because I noticed the fixture flexing under load only after I removed busbars.

So unless you have an air gap between your cells. You may actually be applying compression without even knowing.

But then, what about plastic encased "aviation" cells like this:

I see no mention of compression in the only datasheet I saw for such cells. Does anyone else?

 

[Daddy Tanuki]

Exactly. If you want to give your cells the best chance you should follow manufacturer's recommendations. Personally I think too much compression may be worse than no compression at all. So if you're doing it. Buy some cheap disc springs (some people call them spring washers, but they are not "split" spring washers) put their parameters in a calculator (or ask here) and you now have the right amount of compression for your cells.

To anyone that says "I don't worry about compression and I'm fine". Unless you have another one of exact same packs in the same load and you've cycled it 5k times you don't know if you're loosing anything.


There is an argument to be made (partially after the "off grid garage guy" in Australia) that if you live in a hot climate your cells will experience calendar degradation well before they reach the cycle numbers where you notice a difference with compression. Whether this argument is worthy considering or not depends on your situation. What is the average temperature? Are cells going to be stored at 100% SOC for half a hot day every day? Perhaps then it doesn't matter? Are the cells going to be stored in 10C on average at 50% and cycled a lot? Then yes, I'd use compression.

Then let's briefly touch on the standard "epoxy board and tape" method. IMO this method does provide some compression for all but the first and last cell. This is so as long as you wrap it tightly before the very first charge, or you discharge a lot after equalising.

Then there is the effect of non flexible bus bars providing compression. My 16S setup was definitely held in compression by bus bars, because I noticed the fixture flexing under load only after I removed busbars.

So unless you have an air gap between your cells. You may actually be applying compression without even knowing.

But then, what about plastic encased "aviation" cells like this:
View attachment 210243
I see no mention of compression in the only datasheet I saw for such cells. Does anyone else?

Winston cells which CALB (blue nylon cased), Sinopoly (black nylon cased) and Winston (yellow nylon cased) were at one time the same company before splitting apart, actually sells a stainless steel compression banding kit to go with their cells.
I opted for not needing it as I was making a compression rig that also acted as a cold weather heater. (aluminum plates, springs, and threaded rods. with heating pads on the aluminum compression plates to spread the heat out.

so in a nutshell yes, they recommend compression with the kit they provide.

 

[JoeHam]

I believe that calendar aging and technological advancement will render any possible increase in cell life insignificant.

My cells live uncompressed.

 

[DIYrich]

I'm sorry but what does friction have to do with compression or pressure? friction of two items sliding could cause heat... but thats about it.

The expanding cell pushes against the cells around it. The cells around it push back. The first level of pushback is the compression of the cells. All else being equal, they all see the force (300 psi?). However the cell in the middle sees the 300 psi, plus whatever force it takes to move the cell next to it to equalize the pressure. It has to overcome the friction of the cell sitting on the case to budge it. For a heavy battery, that is not trivial. Way more than 300psi can build up in the middle.