It’d be more of those cell case designs, those epoxy cases are nothing like the current thin aluminum cases of EVE CATL cells.
There has been.
diysolarforum.com
That's what I thought until I bought some (admittedly very old) cells like these. Sadly I didn't know at a time these(blue CATL ones) have not been made in years, but for the time being I'm stuck with them so I tested a lot about them.
Several of us are already on board with that.
I think You mean CALB cells and there are a lot of reasons why nylon cases cell is better than the aluminum cases ones…. Reason number 1 no concerns with shorting between cases, #2 no concerns with galvanic corrosion. #3 the case sizes are more varied, so the makers are not trying to jam In 304 amp hours in a case that originally was used for 240 amp hour cells. You got scammed sorry to hear that but it’s not the cell design that robbed you.
Good points, I guess it goes back to how those cells are designed and managed.
Yes, my experience is with CALB (do you know who else has been making these relatively recently? I'm told CALB has stopped years ago). Of course you're raising important points regarding shorting and galvanic corrosion. Also as I mentioned they do have better hardware.
I was told nylon years ago no clue just repeating what I was told. The Winston rep called them plastic cased cells so who knows? Winston still makes them not sure about sinopoly I think Calb still makes the smaller plastic cased one but not sure. Winston does suggest compression and they sell a kit that uses banding straps and end plates. The compression cannot be that high with those metal straps. I just built my fixture based off of the common calculations for eve cells. A set of springs that keeps the pressure at roughly 12psi at 80% charge ramping up to about 14- 15 at full charge
Nice! I can't wait to see updates.I will respond to all posts before bed (currently at work) but I did want to drop this in here first just for some additional details and insight into the meticulousness and slow-paced/long-term-planning, engineering/data focused nature of this project. I have done thorough testing of every single one of my cells. My testing protocol first takes the cell I received and discharges it at a slow rate of 45W constant power measuring to see how much energy is in each cell at delivery making sure they have roughly the same (Not just a simple voltage reading that most people do). Then a 40A charge to full, 60W constant power discharge rate test, 40A charge to full again, 40A constant current discharge rate test, and finally charging back to roughly 40% SoC for storage. Each cell takes two whole days to test on one of the common EBC-A40L units that most people use. I have the screenshots of the curves and a second-by-second data log of every single cell for the entire duration of all of the tests. Here are some screenshots of the spreadsheet I use to keep track of this data:
View attachment 216575 View attachment 216576
Note the buy dates starting in 2021 and me getting burned by trash quality cells from Varicore lol. I have been slowly increasing my buy quantities after verifying that cells are quality or not in preparation for this project over years. "Initial SoC" column is the amount of energy in each cell after having received it. Interestingly, ignoring the 8 crap cells I bought, the 32 cells (FE001-032) were not tested until a year after I received them since I didn't have a battery tester yet. It is impressive that their energy contained was ~310Wh after sitting for 1 whole year never being used after receiving whereas compared to cells ordered a year later (FE033+) and tested immediately after receipt from the same manufacturer measured at ~340Wh. Meaning an entire year idle and only 30Wh (~3.3%) of self discharge on a cell that stores about 900Wh to me speaks to very high quality and very low self-discharge. Super happy to have been able to glimpse such a neat piece of data that I can't think of any other person having tested
The idea behind this meticulousness is to develop methods to judge the quality of a cell and also be able to forecast cell failure based on pervious data vs new data. I plan on pulling random cells from time to time from this system, throwing them on the battery tester and see how their curves and data compares between each 2-3 year time period of being used. Possibly will be able to develop some software and some modelling around expected performance parameters.
The ability to track individual cells (where, almost all battery packs fail due to individual cells failing) is the primary reason I do not really entertain the idea of server rack batteries. Realistically it would be too much of a hassle to constantly be disassembling those to get at the individual cell level. This project is part research, part experiment, part practical, part desire for self-sufficiency, part money-saving (long term vs just paying for electricity), etc. and ultimately a culmination of my interests and passions.
Robby a lot of that depends upon how your BMS measures/counts cycles. honestly I have no clue how it works with my BMS's as after a couple of years I am still under 100 cycles on all of my packs. I have rewired my calb packs several times between 16s4p, 4p16s, 16s3p, 3p16s now one pack of 3p16s, (CALBS) and two packs of 16s (Winstons) so after trying different strategies its even more hard to discern as I have not figured out a way to reset any of them to zero cycle count.
Yes that is very true. Many of the BMS on the market seem to be terrible at keeping count because some of them reset the counter whenever you update the Firmware. I can see the issue you guys have who rebuild packs might have as my BMS counter also cannot be reset by me or by Firmware updates. They might have a special software tool that does it but I am sure that it is never going to be released to the Public.
The old question, what is a cycle? How much movement up and down the state of charge to actually count as a cycle? Rarely do my batteries get below 60% and may get to absorb voltage once or twice a week. After about two years my oldest battery only reports 155 cycles. The JK bms’s have been extremely accurate and jives with the shunt pretty closely to SOC.
I define a cycle as a contiguous sequence of charge + discharge(loads). The natural add capacity, use capacity cycle of an off-grid system.
In my case, it's the charge + discharge that make a cycle from which I track the hi/low SoC% as a key metric.
My system forces operations in the middle range of 75%-25% SoC for longer life. In winter, the 36% average SoC change is at the lower end of this 50% SoC operational range and in spring/summer at the upper end.
After 6+ years, the oldest battery has 1,982 cycles at an average of 35.9% SoC change within the 50% middle operational range of the powerwall.
you are calculating this yourself correct?I agree a cycle is not well defined, but here's what I do....
Note: I have 18650 INR type chemistry, large Powerwall so voltage change makes this easier than it would for LifePo4 = but the principles apply.
I define a cycle as a contiguous sequence of charge + discharge(loads). The natural add capacity, use capacity cycle of an off-grid system.
In my case, the low is morning. PV adds charge and loads cause discharge till the low is hit sometime after the PV is gone.
In winter it can take a few days before the charge is significant enough to turn on the inverter for discharge. Thus I have <365cycle per year. It's around 330 cycles per year.
I subtract the low SoC% from the hi SoC% in a cycle to get the SoC% change or DOD%. Over the last 6+ years, my overall average is 35.9% SoC change per cycle. Spring and summer can reach as high as 47% SoC change and in winter as low as 24% SoC change.
In my case, it's the charge + discharge that make a cycle from which I track the hi/low SoC% as a key metric.
My system forces operations in the middle range of 75%-25% SoC for longer life. In winter, the 36% average SoC change is at the lower end of this 50% SoC operational range and in spring/summer at the upper end.
After 6+ years, the oldest battery has 1,982 cycles at an average of 35.9% SoC change within the 50% middle operational range of the powerwall.
Since I don't ever shutdown the Powerwall, I'm attempting to track degradation by recording the average ah/v during discharge with no PV (night time is pure discharge) for each month to be able to do year over year comparisons - e.g. am I getting the same capacity per volt. So far, the ah/v are close enough year over year that there's no 'obvious' degradation.
Plus I track kwh of load each cycle and year to year these have remained constant enough that I can't cleary see loss of capacity. BUT - I've added new batteries here and there to expand the Powerwall, so it's a bit of a fuzzy picture.
If I get another 7 years (14 total) and reach 4000+ cycles on the original battery I'll be very satisfied. But honestly, no one knows what happens with 18650 INR chemistry at low DOD / low stress after 14years so I hope to live long enough to find out.
