That’s what concerns me. A gut feeling does not include a mechanism. I would like to know what mechanism is at work here.
Two possibilities I think. The one is that there is something wrong with the balancer, or some fault develops in the balancer, allowing the cells to drift out of balance.
The other is very rapid loss of capacity in a cell. To use a crude example, this morning the cell had 20Ah in it, I discharged it by 5Ah and then only got 4Ah back into it before it registered full. 1Ah was lost very quickly… faster than the balancer could keep up.
Those are the two I see. First case, warranty. Second case… which is what I think you and Andy are gut-feeling… that I would still like to see. Sure, it can happen, but that means the battery is toast already. No amount of balancing is going to make it recover once it starts slipping that fast.
Tell me, gut feel, does it count when that is deduced from the BMS App open 24/7/365, the screen sitting between your kbd and the PC screens?
Not concerned. Adding to what you said, and I agree 100% with that:
I realized these things:
The BMS’es installed are:
1.1) New tech. Watch the BMSes in the future … like the NEEY one Andy likes so much, they are upgrading a lot as one example.
1.2) New software … again, NEEY listened and altered/adapted as an example.
1.3) That the BMS is the cheapest part of the systems today.
The balancers are not suited for the purpose over time, them being mA.
The mass production of cells.
Now all of these are 100% fine. I have no problem with any of it.
I just don’t believe Lifepo4 banks are as stable as we think they are. It is inevitable that the cells will go out of balance. I mean, you have 15/16 cells that must all behave in sync all the time for 6000 cycles.
Don’t think that is possible.
When BMSes are upgraded/improved, based on experiences/new tech/new ideas, that will mitigate some of it.
This is what I disagree with. Unless there is a pretty big failure either in electronics or the cells, it is not inevitable.
I can think of only one more way it could happen. If you used the battery for long periods at a voltage that is too low for balancing to work. Then a lot of degradation can take place over time, and when the battery is again fully charged, whichever cell now is the most degraded will have a high voltage event. Re-balancing will help in this case.
I simply don’t buy it that a battery that is fully charged at least a few times a month, with a working balancer, will sommer or even inevitably go out of balance. Once a battery is top-balanced, it will stay in balance.
Like 4 years is 1460 cycles. Long way still to get to 6000, or 3000.
The other thing is, we are talking mV … not volt, mV … it is a very fine balancing act (pun intended), totally reliant on the manufacturing of the 15/16 cells being near perfect, for 6000/3000 cycles … with temp having a rather big impact, the bank not constantly kpet at 25 deg C.
Sounds like what every second anti-vaxer told me in 2020
Jokes aside. The cells do degrade. Balancing over time is necessary. But this happens all the time, gradually. It is a process, not an event. The degradation is gradual, but so is the balancing. It is a race between the cells and the balancer. When the balancer can no longer keep up… well then you have a problem, right? You can fit a larger balancer, of course, but… you see where I am going with this? Race to the bottom, right?
Well, I was supposed to be DEAD by now. Me and 3 billion others. I mean… some of us probably did die, but not nearly as predicted. But yeah, if you give someone a weakened form of the real thing, you should expect a weakened response in the larger population: Some people will have adverse effects. The interesting thing is… these are all things the virus itself also has as side effect. So… not really controversial to me
It’s common, when the SOC gets out of sync. The logic inside the BMS wants to see a certain cell voltage before it will allow the SOC to be estimated higher than a certain amount. It all has to do with the flat voltage curve of LFP. Below 3.4V, it does coulomb counting, and if the SOC is really far off and the BMS didn’t have the advantage of also knowing cell voltages (eg, when using a BMV), it would count to 100% and then continue to charge past 100%. But with the knowledge of the cell voltages, the BMS now caps it at 88% and waits until the cell voltages match.
I know OrionBMS calls it “drift points”. Specific voltages known to correspond to a certain SOC. I’m sure other BMSes do the same.
Finally got BatteryView working (@#%*&@# premade store-bought cable). Had a look at the 3 US3000A’s while around 70% SOC and sitting idle - nothing abnormal observed. Temperature and voltages across all the cells looked fine:
Battery 1: 70% SOC min cell: 3.289v max cell: 3.292v
Battery 2: 72% SOC min cell: 3.289v max cell: 3.292v
Battery 3: 69% SOC min cell: 3.289v max cell: 3.292v
Started charging again at 5A, 52v, will see what happens when the BMS balancer kicks in. After a couple of mins:
Battery 1: 70% SOC min cell: 3.297v, max cell: 3.302v
Battery 2: 73% SOC min cell: 3.297v, max cell: 3.299v
Battery 3: 69% SOC min cell: 3.297v, max cell: 3.300v
No abnormal voltages that I can see - yet. That being said, my high-voltage warnings were fairly intermittent and not “permanent”, so may not see anything for a while.
Apologies all, feels like I’m spamming this thread.
I followed @Louisvdw’s advice and recharged the batteries at a higher speed (50A) with the intention to drop to 5A around 75% SOC again. Of course I got busy (meetings) and ended up charging them 100%.
Any thoughts? Is the error reported by the Pylontech as a warning, which is then logged and displayed by the VenusGX, or is it the Venus’ interpretation of the battery voltages?
If it is on-battery, is there a way to get a log and more detail, or do I have to be there (logging away) to catch it?
EDIT: Nevermind, I figured out how to download a log.
