I noticed this when I just tried doing a test charge of 2s1p string through the existing contacts on the EMC board to see if it would active balance individual cells back to nominal (it doesn’t).
cells both starting at 3.3V taking it from 6.60 to 6.85 at .5A, one cell basically stayed flat at 3.33V, and the other went up to 3.52V.
Since IR shouldn’t vary with SOC or cycle (unless there’s something different about LiFePo4?), I’m not sure what’s going on.
As for capacity testing, plan is to
separate them all
make and full charge a 1s80p
separate
let sit for a week
measure voltage
bulk discharge strings of 1P at ~1A for 1 hr and see where voltages sit
continue discharge for a total of 2 hrs (for the 80% BCH is promising)
measure final voltage
Main problem is how flat the discharge curve is. Go figure that one of the major draws makes testing tough.
I would just like to revive this thread as there is one question I haven’t found.
I’m starting to get curious in these cells for a high A pack but doesn’t have a ton of Ah I don’t need.
So @Battery_Mooch , what is max continuous current in real life? I saw @hummieee say they could do 30a based on your tests but they date way back from 2016.
I haven’t retested them but I have no reason to think that their performance has gotten worse over time. If anything, it would probably get better.
What is their max continuous current rating in real life? Everyone hates to hear this, but…it depends. I rated them at 30A to give them good cycle life. If a shorter cycle life isn’t a problem then you could easily rate them 40A, 50A, or even higher.
Lithium Werks bought the rights to A123’s tech and makes them now. They rate the 26650 at 50A continuous but they don’t have a cycle life spec at that rate. It will most certainly be shorter than the 4,000 cycle life spec for 1C discharges.
So, the real life rate? You have to choose it.
If you want that 4,000 cycle life you need to rate them at a couple of amps. If you want to run them at 50A continuous then you will have to accept a much shorter life span. I don’t know by how much though.
It will probably still be a lot longer than any non-LiFePO4 li-ion cell when run that hard.
It’s the heat that degrades the battery?
If the battery was enclosed and in contact with a metal enclosure to help dissipate the heat and add fans to keep it below 60°C, there should be no reason you can’t run it at 50a continuous correct?
Oh and one more question now it comes to mind!
How does LiFePO4 behave in cold/subzero temperatures compared to Lithium cells as the ones we use ( 40t, p42a, 30q…I forgot their chemistry name )
Heat is the biggest enemy of a battery but high discharge rates can cause accelerated aging due to other issues. Keeping the cells from getting more than a bit warm will help though. Especially for cells in a pack where they heat each other up.
My impression is that, in general, LiFePO4 has better low temperature performance. You’d have to research that though as I am not sure.
Cold weather reduces range for me based mostly on problems with the meatbag on top of the battery.
Seriously though, if your skate was indoors, and you bring it outside to ride it, and start riding it, then go inside when you’re done — the battery never lowers to outdoor temperatures. If for some reason you stop for a long time somewhere, that’s when the battery would start to get cold.
You can only use 2000mah per cell for excecive drain…the rest you schould go slower…they heat up fast in the last miles…also the sag in the end comes fast…
I think we should have a general Tesla Batteries discussion thread, so we don’t make a ton of new ones for whatever thing they may do over the next years.
I was meaning to update the 4680 thread about how production has been starting up.
Just to add a bit on the Lifepo4 cold temp question: Most Lifepo4 chems are purportedly damaged by charging at sub freezing (30ish F ballpark) temps, but can be safely discharged lower. There are some chems that add Mn to the mix which raises the voltage a tiny amount (half a volt approx) but lowers the charge and discharge temps significantly, many of the ones I’ve seen rated down to 0 deg F if I recall correctly for cycling.
A123 m1b series cells however state -30C (-22F) operating temp, and -40C(-40F) for storage! So I can only imagine they’ve got some special sauce in their chemistries.
They also list max cont discharge 50A, but pulse (10 seconds) at 120A. However as you mentioned Mooch, cycle life greatly affected. Data sheet I’ve got lists >1000 cycles at 20A cont 100% DoD, though most reports I’ve heard (these cells have been extensively used for server backups for a long time) consider this as conservative.
These are one of the few cells that any real long term cycle life testing has been done past the 80% of original cap EOL, and they appear to exhibit really incredibly slow decline (aka great longevity) past this point if treated kindly, where some chemistries can seemingly hit a wall after a certain point and drop most or all capacity.
I’m really glad to see all the renewed interest in Lifepo4, especially some from western industries, because there’s clearly still room to innovate in this segment IMO. LTO still feels like the grail chem for powerwalls but its so expensive and seemingly very little R&D really being pursued, that it still feels like lifepo4 is the near future for long term, personal energy storage, until something new comes along or something changes.
It also seems to me like it would make tons of sense for large vehicles, like trucks and heavy equipment, where weight isnt as much of a concern or in the cases of heavy equipment an actual boon, and space isnt as much a premium either, but huge power(amperage) potential is necessary…
LifepoXX has a very special spot forever in my tiny black heart…
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