Quote:
Originally Posted by Cya3124
On the subject of "to compress or not to compress", may I present the following. I have decided to go non-compressed with my home-built 100 Ah bank (four cells). The lifespan of the normal user is incredible even without compression.
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This reply is extremely detailed.
First, you're looking at a fairly old video (cell anodes have been changed in design, chemistry, and manufacture after that time.) The guy does a lot of unqualified yammering (with no tests), and refers to older-model battery cells with inferior anodes. (Although cells also cost a lot less money, back in the days of this video.) He has nothing to say about specific issues of aging due to high discharge rates, such as electron starvation.
His 'conclusions' seemed to be that you should limit your use of an LFP battery to only 50% or 60% depth of discharge, leaving at least the bottom 40% of battery capacity unused. The chemistry and construction of modern cells of modern cells allows for higher depth of discharge, down to roughly 20%, with virtually no effect on lifespan.
EVE
does know more about their battery cells than this 'garage guy', and they designed their test well. They took the cells all the way down to accelerate the aging process on purpose, shortening the total amount of testing time required.
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My own opinion (which is way more qualified and expert than that of "garage guy"), that "it might not matter so much anymore" is based on the fact that very recent improvements by EVE, CATL, and CALB have been leading to very generous lifespans without adding compression.
If 3000-4000 cycles (old cell designs) is "good enough" for you, and it might be, compression might not be worth the trouble and expense and added cost. In his opinion, 3000 cycles is "incredible", while I think that such a lifespan basically sucks. But, In the most modern cell designs, you can approach or even exceed 6000 cycles WITHOUT compressing them. Even I consider that to be a more than adequate lifespan.
The video showed several supposedly "compressed" battery pack photos which did not use springs. These springs are a very costly item, but any attempt to construct a "compressed" battery pack WITHOUT springs is virtually useless, and may actually be harmful, because the amount of compression varies far too greatly as the cells expand and shrink with changing SOC and temperature.
Only springs can do a half-decent job of emulating the test press, which provided totally fixed PSI on the cell faces (even as their width changed with SOC). With "6000 cycle" cell designs now available in the marketplace, even I think that the cost and hassle of adding springs is hard to justify. In your own case, with a mere 100Ah battery pack, the high cost of the springs (around $40) is also hard to justify. Two end plates, and a set of "L" channels needed in order to spring pressure across the entire surface of the cells, also adds more construction time and money.