Tinbum

Your cell SOC's are all over the place you must top balance them. Your bms will never balance them as they are too far out.

The voltages of the cells only vary at high and low voltage. Ie high or low SOC. Look up the charge curve online.

Your cell SOC's are all over the place you must top balance them. Your bms will never balance them as they are too far out.

Agree, that's why I'd like to see the bms logs.

@Coulomb You are right - I should have qualified my statement better.  It was meant in the context of the conversation, not as a generalisation.
 
All true, but not pertinent: we are talking about almost fully charged LFP with negligible current. (The voltage increased by 0.8V in 5 minutes.)
 
 

Also, it is important to understand that physically, there is nothing like 100% SOC for the cell.
A LFP cell is just like an air-filled birthday party balloon:
When is the balloon 100% full? Is it the state when you blow another air molecule into it and it pops? If so, how does it depend on the balloon's temperature? If that 100% full mark is somewhere lower, where more additional molecules would safely fit inside, can I blow some more air into the balloon? How much? The "curse" of LFP is that they are so energy efficient that you can damage them even with just 1mA of charging current, if applied for a long time. With Lead-Acid batteries that would be absolutely no problem, but LFP stores lithium ions in the hard 3D lattice. If there's no more space for incoming ions, the lattice will crush and gas-mix of O2+CO2+phosphate will be produced.
And that is the reason, why some cells are swollen. Either they had manufacturing defect (most of the time it's the the separator failure), or something was hitting them with just a few miliamps of current for a long time, so the lattice started to break.
 
Yes, it would be great to have a BMS that can perform sophisticated monitoring of the cells, but in reality all the BMS-es are just measuring temperature, voltage, current and doing time-based integration of Coulombs in order to "guess" SOC. But keep in mind that more complicated electronic device is, more likely will it fail. Not to mention that it will cost more, consume more energy and produce more heat.
While the Pylontech BMS is far from being perfect, the solution is not to improve and over-engineer the BMS itself, but to configure whole solar system in a way that the margin between "balloon full" and "balloon popped" states will be reasonably wide and safe.
 

The BMS in the Pylontech does not limit the charging current UNLESS the pack has gone overvoltage, cell over temp, cell over volt etc.. The BMS has no current limiting facility other than on or off and requests to the inverter. The different pack currents are due to the slight differences in eg manufacture of the cells, age, usage and temperature etc.

Technically the inverter is not sending voltage, but it's sending current. It's so called "CC mode". The current is being split between all the batteries based on their internal resistance, interconnection resistance and willingness to accept charge that changes with SOC of the individual cells. For the same voltage, different batteries will have different charging current. The 53,5V is the voltage value that the inverter is looking for to stop sending current (stop charging).
Some of the events that signalize end of charging (CC mode) and transfer to the CV mode:
If the battery reports 53,5V the inverter stops charging, even if the cells would still accept current. If the cells stops accepting current, the charging is finished. This might occur even before the cells reach 53,5V. If the BMS reports 100% SOC, inverter will stop charging. If the BMS reports "Advise Charge = 0A", inverter will stop charging. If the BMS reports one of the many possible Errors and Alarms, inverter will stop charging. Most of the time CMOS will be activated by the BMS, so even if the inverter would still continue with the charging, the actual current will be zero amps. Pylontech BMS is really doing nothing to the current that is flowing from the inverter. It has two protective MOSFETs (DMOS and CMOS), that are being operated in the ON/OFF state based on alarms. No analog current modulation feature is in the BMS.

This is normal. As the cells in a module are reaching full charge, their ability to receive charge drops gradually. Therefore the charging current drops too.
For example, here's the charging current of 8xUS3000 in one of my stacks:

The gradual drop of the current is caused by the cells, it's not something that BMS or Inverter does. For each battery in the stack this curve will be slightly shifted in time. That's because each battery has a slightly different charge, therefore slightly different ablility to receive current. Exactly as shown on your BV screenshots. You can observe this even by just looking at the LED bars of the individual batteries - some of them will be fully charged already (LED bar goes off) while the others will still being charged (LED bar with one blinking LED).
Once again, it's pretty normal that you see a different amps for each battery in the stack and the BMS/Inverter has nothing to do with that.
 
Yes, the BMS IS able to tell the inverter what to do, but the charging information is sent for the whole stack, not for individual batteries. For example, this is the info, that BMS sends via CAN BUS during charging of the above mentioned stack of 8 batteries:
charge with 300A max charge with 120A max charge with 100A max charge with 90A max charge with 0A max
 
 
Yes, some of the batteries might experience manufacturing defects, resulting in premature damage. That's what warranty is for. But the examples shown in this thread, where 10+ batteries "blown" at once are not that case.
 
 

Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell). 
Add the facts that:
1) The voltage is not distributed perfectly among the cells. Some will be At 3,4V while the others will be at 3,6V already. It is a job for the balancer to level the cells.
2) Pylontech balancer is quite weak, unable to burn amps of current.
3) Inverters like to overshoot voltage when AC load fluctuates.
The result is constant stress and hidden overcharging, as discussed in the Victron threads many times. On the Victron side this was fixed by firmware tweaks, luckily. But when comes to Axperts, the problem is even more dangerous as it is not solved in the official firmwares, AFAIK.
IMHO, the first step on the road to hell is that one of the cells gets damaged by that hidden overcharge. Then a chain reaction starts as all other cells become stressed even more. From that point there's no way back. It does not make sense to replace the cells if all other parts of the system will stay configured the same, as the damage will appear again.
From my experience, for the longevity, the best is to ignore charging voltage value that BMS is announcing and set 52,6V instead. Based on the setup it might be +-0,2V but definitelly not 53,5V. Shame is, the batteries that already experienced the stress for weeks or months cannot be saved as some of the cells started to swell already.

Many people have no problems at all with them and pylontech seem good at warranty replacement. It's often an inverter problem that causes the problem.

Also be carefull as we suspect some firmware may require inverter communication and their may also  be a new 'new chip' hardware version.

Yes no problem at all. Have the newest as the master.
Check what setting you have for showing decimals, numbers etc. Think it should be US but search batteryview on here and you will find similar errors.

It's a pleasure to help you. I can't imagine what you have to go through.

I would leave well alone unless you have a problem.

Yes no problem at all. Have the newest as the master.
Check what setting you have for showing decimals, numbers etc. Think it should be US but search batteryview on here and you will find similar errors.

Seems like the old chip is now the new new chip.

Yes I totally agree. Your post seemed to sugest pylontech would try to get out of it. Often the supplier does, but if you go direct to pylontech they often instruct the supplier to replace them.

I would imagine it means until the battery gets to 70% SOH.
Go on recommendation in choosing a supplier, their are a lot of bad batteries out there.
JK BMS's seem ok.

Forget about lead acid and go for LiPo.

Good to hear that it worked okay for you.
 
Since Pylontech is not publishing release notes for the FW, it's hard to say what are the improvements and if they are significant or not.
Version 1.7 for US3000C is the first one that is able to report cells with the lowest/highest voltage/temperature in the stack, while not exhibiting "cell overvoltage" bug. Should work perfectly with the Victron Cerbo and CAN comm, if you have it.
Personally, I am running version 1.7 on 8 batteries in a stack for years, connected to non-Victron inverters. And I'm not planning to upgrade the FW, since the setup works fine for me.
Some of the newer FW versions are relevant for UP5000, since they allow higher discharging current that was not possible on UP5000 hardware in the past. (BIN file for US2000C, US3000C and UP5000 is unified.)
Also, beware that version 2.2 might introduce some unwanted features, like the mandatory heartbeat - see the discussion led by @Tinbum on the previous pages.
 
Anyway - if your battery has a fluctuating voltage issue, I would suggest you to contact Pylontech support via email first, since the solution might be a bit more complicated than just a FW upgrade.

Seems like the old chip is now the new new chip.

Seems like the old chip is now the new new chip.

Seems like the old chip is now the new new chip.

They are shipping with FW 3.0 preloaded for the old chip? And even using the old chip for the new SerialNumbers, after C2? Hmm, what a mess 😮