Just know that dust of organic nature can burn...grain dust, wood dust, even shaving from plastic. If enough dry dust of those types is suspended in the air it can go boom...if a ignition source is present.They are large format prismatic (pouch).
They look like very early black Sinopoly cells - but they are Australian (made in Taiwan) LiFeTech cells. I believe the earliest of these cells was 2008.
This is after about 5 years of neglect - fitted with Batrium. I blew the dust off and fitted a REC after that once REC started making 16cell BMS’s.
I’m not saying there won’t be better cells available in a decade, fact is these are a decade old and the same thing was said back then.
Better sometimes is just lower cost.
Precisely.I agree, if my system costs twice as much it better throughput more than twice the kwh, or its a fail.
I suspect the OP is looking to maximise pack life without going overboard.
Meaning less likely to make as much difference compared to the other factors you’ve listed below, correct?The difference between mainly living in the bottom 25% of the SOC or mainly living in the top 25% of the SOC is likely one of the lower factors in the life of his pack.
So just to make sure I understand correctly, allowing your cells to reach temps of over 30C / 86F is the single most damaging thing you can do followed by ‘floating’ or allowing low-current charging such as what you get in Constant Voltage Charging mode above the upper knee (in the handle of the hockey stick), am I getting that right?Based on my experience, i would rate it like this:
1- high temperature (above 30°C)
2- low current charging in the upper knee
3- high current charging in the upper knee
4- time spent in the upper knee
5- high current (>1C) charging
6- high current charging at low SOC
7- time spent in the bottom knee
My cells are OK with it, but many cells are damaged by any charging below 0°C.
The first two combined are by far the greatest killers i have experienced.
Good question. Since EVE’s spec is for charging at 0.1C to 3.65V, I guess I assumed it meant charge levels well below that (such as charging in the low single-digit amp level) as the cells charge up above 3.5V towards 3,65V.What c rate constitutes low current?
Another good question which I assumed means charging to 3.65V at ‘safer’ specified charge levels of 0.1C or higher.What c rate constitutes high current?
What c rate constitutes low current?
What c rate constitutes high current?
Low current is < .5c, high current is > .5c and .5c is the Goldilocks value?Depends on individual cells, generally the lithiaton reaction is different above 0.5C charge rate. (it is also different in the upper voltage knee).
That’s where i separate high and low current charging, my packs never see above 0.5C.
Actually, I’d guess the answer to the question will likely be an important consideration in whether you elect to top-balance or bottom-balance…There is a lot to digest in this thread, There is no way that I can address all the issues but for analytical simplicity it might be useful to break it down into whether the pack has been top balanced or bottom balance, I used to frequent DIY EV forums and I suspect in some circles the top balance versus bottom balance debate rages on, I an not proposing to revive that debate here, but the answer to the question in the title of this thread may turn on whether the pack is top balanced or bottom balanced.
Our application is identical, but we made opposite choices. In my case, my battery is larger than my highest daily production level and letting my SCC charge the battery up to the point that it exited CC mode just translated to lost solar energy I otherwise could have used/captured.Anytime a user anticipates taking a pack to anywhere near the top or the bottom there are risks. My own experience with using a pack for load shifting and occasional backup means that my pack sees various levels of discharge but typically gets fully charged each day.
Yes, that’s the way to do it if you need to maintain a top-balance, but that long CV time translates to wasted solar energy that you otherwise could have captured…For that reason I have top balanced my pack and rely on my BMS/balancer to adjust the balance during the typical charge cycles that take place each day. I have set my inverter to give me a long absorb time (CV phase} to optimize that process.
If your daily production is barely-enough to cover your peak usage, that’s the best way to do it (and the way I originally had my system set-up).My use case is that after the pack finishes charging I have only a few hours until my system moves from using solar production to drawing down the battery to provide power during peak TOU period.
My system was originally configured just like yours. I was ‘holding’ at a high SOC for a short amount of time in order to maintain balance.Therefore my pack does not stay at a high state of charge for very long, My point is the answer to the question in the title depends on each users circumstances, In other words it all depends on where you are standing whether discharging to empty or charging to full is worse.
You’ll need to find a chemist that is experienced in LiFePO4 design to explain it further, as my understanding of chemistry limits my ability to explain.
My understanding is that there are two distinctly different types of lithiation reactions, at high SOC and high current the intercalation is more localised and is a higher chance of seeding a dendrite.
This risk isn’t present at low current or low SOC.
I never even reach 0.1C or 25C, so I’m fine on those last two.The advice i was given is after SEI formation, don’t take the cell into either knee, don’t charge above 0.5C, and keep below 30°C.
Plenty of people have other ideas, i’ve seen a lot of short-lifespan packs that have followed a different path.
Nothing i’ve seen has shown me i should change the way i use this chemistry.
I never even reach 0.1C or 25C, so I’m fine on those last two.
I need to learn more about SEI formation (since I have absolutely no idea if I have any or not), but is there some generally-accepted conventional wisdom about what voltage levels represent the beginning of the upper and lower knee?
Is below 3.15V ‘in’ the lower knee? Below 3.2V?
And is ‘into’ the upper knee above 3.375V? Above 3.363V? Above 3.35V?
Low current is < .5c, high current is > .5c and .5c is the Goldilocks value?
That’s what i use, picture 2 “phases” of lithiation, one resulting in an even spread of intercalation, and one resulting in more localised intercalation. You want to avoid the second phase. Depending on your exact cell chemistry (even within LiFePO4) the parameters will be slightly different.
The point of this thread is that the second phase lithiation reaction also occurs at low current, high SOC. This can be eliminated by staying in the low SOC range, which is what the OP was asking.