I have added an additional US5000 to my Multiplus II GX configuration making 1 x US5000, 1 x US3000C and 3 x US 3000s. THe system has recognised I have six betteries but when the overall SOC gets to 84% more than 2kw is going to the grid and the battey charging appears to have stalled.
Do I need to change any of the settings for the addition of an new battery, if so which setting.
Your 5th battery, as seen in the picture, is heavily unbalanced. Almost 150mV between min and max cell voltages.
Let the system for a period of time in “Keep batteries charged” mode to allow them to balance and hopefully charge to 100%.
Also the order of batteries should be from the newest firmware to the oldest one (first being the newest) and from US5000 to US3000, US5000 being the first one. See item 15) on the Features chapter, in the Pylontech manual.
More of that, there is something odd with your picture of the system… No solar, battery charging and, in the same time, feeding to grid… 
The full configuration is as follows:
1/ 1 x Solax SU3700E Hybid Inverter (AC coupled to the Multiplus II GX)
2/ 16 x 250W Solar Panels
3/ 1 x VM-3P75CT Grid Meter
4/ 1 x Multiplus II GX 48/5000/70-50
5/ 6 x Pylontech Batteries
a) 1 X US 500C Master - added this morning
b) 1 x US3000C
c) 4 x US3000
I was told by Voltacon Solar that my shipment, of the US5000C, was delayed due to a new firmware revision.
The batteries have been charging correctly until today when I added the new battery. I had previously looked at the cell balancing and had to have 2 of the batteries rebalanced about 6 weeks ago.
I have changed the charging setting to “Keep batteries charged” and the whole stack is now at 100% albeit the charging was only about 800W.
Dashboard from the 14th (last sunny day)
Dashboard from today
I have a diagnostic cable and software if necessary.
Steve W
If the new battery is not charged as the other ones, then yes, this could be the situation. You’ll have an average percent.
It charged, as you’ve already saw, up until 100% during time.
Which are the lowest and highest cell voltages now?
Pylontechs are quite OK at balancing themselves, no need to have them rebalanced periodically as you said…
This, if you allow the system to sit for a while at above 52V (manufacturer is saying at least 52.5V)…
Hi Alex,
I’ll keep an eye on them for the next few days. It’s a least two years since I bought the US3000C and I now remember that I had to let the batteries find a common charge level…
Pylontech batteries can be balanced by switching everything off and then disconnecting the canbus connector t, disconnect the inter battery rs485 leads and the positive and negative connectors to the inverter. this should leave you with the pylontech’s completely disconnected but with the positive and negative leads between the batteries still connected, switch batteries on via the switch and the green lights should light up, if one battery has a green led flashing then it is discharging to the other batteries, leave until all flashing of leds stops then your batteries should be balanced.
That’s kinda “equalizing” the SOC… 
The problem is that when in a total floating mode, like you described above, the voltage of a fully charged (100% SOC) Pylontech 48V LiFePo4 (15S) is at about 51.45V (3.43V per cell)
Then, it will quickly drop below 3.36V per cell (50.4V) at 98% SOC.
Why I mentioned this 3.36V?
Because the BMS inside is programmed to balance the cells only above 3.36V and only if cell delta voltage is above 30mV.
So, in that floating mode, if you have the batteries below 98%, then the cell balance will not take place and you’ll only equalize the SOC among batteries.
Thanks Alex, appears to be yet another “myths and legends” dispelled. The batteries got up to a full 100% which was maintained for several hours. I’ve now had a look at the batteries and the difference between the highest and lowest cell is now 25mv which looks to be a lot better. I have also changed the ESS schedule to fully charge the batteries on a Sunday night and 80% the rest of the days. Over the summer I would expect the batteries to be fully charged on a regular basis, however I live in the land of rain in Manchester UK.
My next one before the winter is cabinet heating as batteries are in the garage which although doesn’t actually freeze it’s not too warm in the winter.
Those voltages are when the SOC is about 80%, right?
At that SOC the batteries are on the flat zone of the voltage curve and are not so relevant, not mentioning the fact that are way below 3.36V, the balancing trigger value.
Like I’ve said, the useful values are the ones when the batteries are at 100% SOC, fully charged, when the voltage curve is much steeper and the differences are more significant.
LE.
Not want to worry you, but in that flat zone of SOC, where you’ve posted above the cell voltages, the difference should be much smaller.
See below on a good maintained pack of Pylontech batteries. Only 2mV difference on this moment, at 86% SOC.
Barring cloudy days, they are daily charging to 100%, at 52.5V final/float voltage. Totally off-grid.
To explain a bit of this (let me know if im wrong), there were 2 things wrong with Steve’s pack - the new battery was probably introduced at ~50% (the typical shipping SOC) while the rest of the pack was at a much higher SOC.
The 2nd issue is that at least one battery (likely the third one, given the “0103” in the “details” screen) had a large difference between min and max cells.
The bolded text that Steve posted from the Pylontech manual will resolve the difference in SOC between batteries, while the min to max cell delta will only be resolved (for a “top balancing” BMS) by charging to full and leaving it charging to give the BMS time to balance the cells.
Most BMS software will have a “parameters” page which might allow you to change the rules about when the bms balances (pack voltage above X, when delta is above Y).
It would have also taken a long time to equalise because of the daisy chain set up.
@wrightste consider adding at least another set of cables to your bus bar from the bank.
There is a neat visualization here of what is happening.
Many for the great replies I have received. I now have a better understanding of how and when the BMS works. I will monitor the batteries and hopefully the cell voltage differences will gt less over time.
Overall the system as a whole is doing a great job.
I don’t know whether this link has been posted elsewhere on the Foum but is an article “Active Magaement: Expect more from your BMS” which describes how the Pylontech BMS balances the batteries.
Active Management: Expect More From Your BMS — Intelligent Controls
In today’s age of lithium batteries, battery management is a familiar concept. Every battery has some form of internal or external battery management system (BMS), which plays a crucial role in ensuring the safety and performance of lithium batteries. At its core, the BMS acts as a protective mechanism, safeguarding the battery cells from external influences such as excess voltage, current, and temperature. However, the functions of a BMS can go well beyond simple protection.
Well worth 5 minutes to read
Hello everyone, I’m very interested in this discussion.
Alex Pescaru, when you say: “Because the BMS inside is programmed to balance the cells only above 3.36V and only if the cell delta voltage is above 30mV.”
I wasn’t aware of this feature of the Pylontech BMS.
What are your sources for this information?
Thank you.
I wrote in the other thread.
Very interesting, thanks for the feedback.
