Compression question for EVE LF280K

[Dzl]

Yes BB uses cylinrical. Lion Energy uses prismatic and, again, there does not appear to be a compression mechanism and they claim 3K cycles and offer a lifetime warranty. Just curious on the various packaging schemes I could consider in building my 4s packs.

One possibility is that the drop in replacement batteries that have been on the market for a while tend to be smaller (100Ah-ish). My speculation is that it is the larger form factor aluminum cased prismatic cells where external compression and protection is the most necessary. Smaller cells as a rule have lower Energy/Mass and Energy/Volume ratios, but the flip side of that is that the smaller cells may be somewhat more physically robust. Or at the very least can be made more robust, Frey (Fortune) for instance, makes very robust cells which are designed to be installed with no airgaps and no compression, but importantly they do not make a cell over 110Ah, and do not make a cell with a broad face. Likewise the nylon cased prismatic cells (CALB, WInston, Sinopoly, GBS) devote a lot of volume and a little bit of weight to making a very robust cell casing and cell. Its unclear whether the nylon cells benefit from external compression or not, though they do call for (and some like GBS are designed with) fixture.

Do you have any images of the Lion Energy internals? Its likely they user smaller cells, maybe more robust cells, or maybe they just assume wihtout compression there cells will make it to 3k (or the warranty rate will be low enough that it wont matter if they don't). Realistically the 3k is not that much better than the numbers EVE gave for non-compression, IIRC, EVE stated 2500 cycles without compression, and that is with a big 280Ah cell with a big broad side and a relatively flimsy construction. A smaller cell may possibly be able to achieve an extra 500 cycles (20%) just by nature of being smaller. But bear in mind a lot of the above is either speculative or best guesses based on a bunch of bits and pieces of data picked up here and there.

 

[curiouscarbon]

cylindrical cells are “pre compressed” in a sense.

 

[curiouscarbon]

indeed Jiangsu Frey 100Ah cells have stronger casing and no need for compression to protect aluminum shell. Frey cell also known as Fortune aka Overkillsolar. very robust cells. terminals are M10x1.25 and easy to safely attach. downside of higher cost per storage from some sources vs larger cells. but darn, they are very rigid. have a few 100Ah frey cells for reference.

 

[Rogermija]

One possibility is that the drop in replacement batteries that have been on the market for a while tend to be smaller (100Ah-ish). My speculation is that it is the larger form factor aluminum cased prismatic cells where external compression and protection is the most necessary. Smaller cells as a rule have lower Energy/Mass and Energy/Volume ratios, but the flip side of that is that the smaller cells may be somewhat more physically robust. Or at the very least can be made more robust, Frey (Fortune) for instance, makes very robust cells which are designed to be installed with no airgaps and no compression, but importantly they do not make a cell over 110Ah, and do not make a cell with a broad face. Likewise the nylon cased prismatic cells (CALB, WInston, Sinopoly, GBS) devote a lot of volume and a little bit of weight to making a very robust cell casing and cell. Its unclear whether the nylon cells benefit from external compression or not, though they do call for (and some like GBS are designed with) fixture.

Do you have any images of the Lion Energy internals? Its likely they user smaller cells, maybe more robust cells, or maybe they just assume wihtout compression there cells will make it to 3k (or the warranty rate will be low enough that it wont matter if they don't). Realistically the 3k is not that much better than the numbers EVE gave for non-compression, IIRC, EVE stated 2500 cycles without compression, and that is with a big 280Ah cell with a big broad side and a relatively flimsy construction. A smaller cell may possibly be able to achieve an extra 500 cycles (20%) just by nature of being smaller. But bear in mind a lot of the above is either speculative or best guesses based on a bunch of bits and pieces of data picked up here and there.

 

[Rogermija]

Thank you for your comprehensive response. My cells are EVE230 in 12v blocks of four. Because of space limitations, there will be a modest compression with thin but firm foam separators (Poron/Noseal) or perhaps a more solid plastic. The final design is evolving as more info is collected.

 

[Dzl]

Thank you for your comprehensive response. My cells are EVE230 in 12v blocks of four. Because of space limitations, there will be a modest compression with thin but firm foam separators (Poron/Noseal) or perhaps a more solid plastic. The final design is evolving as more info is collected.

If you haven't come across it already, I suggest a glance at this comment and the following few pages of discussion. Its a year old now, but its the post that kickstarted the discussion on cell compression, and consolidates most of the scattered info we had at that time (and pulled in many bits from other sources), and gives a lot of links and breadcrumbs for further research and understanding.

 

[Rogermija]

If you haven't come across it already, I suggest a glance at this comment and the following few pages of discussion. Its a year old now, but its the post that kickstarted the discussion on cell compression, and consolidates most of the scattered info we had at that time (and pulled in many bits from other sources), and gives a lot of links and breadcrumbs for further research and understanding.

Thanks. A question... is there a curve showing cycles/compression/charging current. Isn't the EVE data for 1C cycling? It seem low charging currents would minimize or remove need for compression. For my application, there will be about 700 Ah of LFP for the purpose of occasional high discharge requirements but mostly the demands will be smaller. Charging will be up to 150a or about 0.2C. Also the SOC will be in the range of 60% to 80%. Your thoughts?

 

[Dzl]

Thanks. A question... is there a curve showing cycles/compression/charging current. Isn't the EVE data for 1C cycling? It seem low charging currents would minimize or remove need for compression. For my application, there will be about 700 Ah of LFP for the purpose of occasional high discharge requirements but mostly the demands will be smaller. Charging will be up to 150a or about 0.2C. Also the SOC will be in the range of 60% to 80%. Your thoughts?

Don't know about a curve or test data, but I do know that a few other members (I beleive @cinergi, @Gazoo, and others) have mentioned that swelling (or 'breathing') was a factor even at low C-rates.

While I haven't seen a specific recommendation that you should use compression at low C-rates, I also haven't seen any statements or data that suggest you shouldn't worry about compression at low C-rates.

 

[Gazoo]

Don't know about a curve or test data, but I do know that a few other members (I beleive @cinergi, @Gazoo, and others) have mentioned that swelling (or 'breathing') was a factor even at low C-rates.

While I haven't seen a specific recommendation that you should use compression at low C-rates, I also haven't seen any statements or data that suggest you shouldn't worry about compression at low C-rates.

Swelling is normal and even with low C rates it's going to happen. My biggest concern is terminal stress due to lack of any compression. I think the best way around this is to use braided bus bars. Personally I am not concerned with compressing to extend cycle life.

My cells are stationary and lightly compressed and are doing fine. In a mobile environment one has to be very careful.