Pylontech questions. BMS - SOC% - Firmware

[bpabpa]

HI

I have 10 off Pylontech batteries. 6 off US2000 purchased in 2017 and 4 off US2000C purchased in late 2024.

Battery Inverter is Lux AC coupled LXP 3600 ACS.

Prior to adding the US2000Cthe original batteries just worked exactly as expected and as far as I am aware never alarmed.

After adding the US2000C I noticed the master battery occasionally alarmed . So I fitted a console cable and set up a monitoring PC using MultiSIBControl. It quickly became clear the alarm was caused by one of the old US2000 going below 10% SOC.
I had been charging to nearly 100% and discharging to 10%. I set discharge level to 15% and the system no longer went into alarm.

However I noticed another US2000 was not charging to the same SOC level as the others. Observation over a number of days made me realise that if I charged to 100% and left it charging for an hour or so eventually all the batteries reached 100%.
I also noticed that the discharge rate on the US2000s varied considerably and lower than the US200Cs which were all virtually had the same discharge rate. The pack capacity off the US2000 batteries is about 4.0 Ah lower than the US2000C but that seems reasonable as they are nearly 8 years older

My questions relate to the BMS balancing. Is this active at all charge levels or only when at 100% SOC?

The firmware on the older US2000 is original as purchased. Should this be updated as I assume there have been improvements which may help with the issues I am seeing?

Regards

Ian

[greentangerine]

AFAIK any US2000 (B) should only be discharged to 20%

[SimonSays]

OK, some speculation here, but I've been building batteries since NiCad days and will be building an LFP stack soon.

Balancing in most commercial packs only operates at high state of charge. I see this in my Growatt batteries where SOC hangs around at 96% and then suddenly jumps to 100%. You can most certainly balance at all states of charge but that isn't the norm.

You can mix batteries of different capacity - as long as the chemistry is the same - and the lower capacity packs will (in an ideal world) simply provide a lower amount of power and the higher capacity packs will provide a larger share of power. Voltage across the batteries should remain the same, subject to the cables not being an impediment.

How are the batteries cabled to the inverter? Could you re-arrange the cables such that your battery cables are short and connect to a chunky bus bar, then from somewhere central in the bus bar to the inverter?

[Tinbum]

You can most certainly balance at all states of charge but that isn't the norm.

It's not the norm because it's not advisable. The charge voltage curve is so flat balancing at anything less than nearly full is pointless.

[nowty]

You can most certainly balance at all states of charge but that isn't the norm.

It's not the norm because it's not advisable. The charge voltage curve is so flat balancing at anything less than nearly full is pointless.

Its actually quite good at the bottom end as well to reduce the risk of voltage collapse on weak cells.

[nowty]

AFAIK any US2000 (B) should only be discharged to 20%

If its a US2000 (B) "Plus" version they can go down to 10% SOC.

[bpabpa]

AFAIK any US2000 (B) should only be discharged to 20%

If its a US2000 (B) "Plus" version they can go down to 10% SOC.

Front panel shows US2000.

Part no US2000NB02V00101.

Also realised its a 2018 battery. PV went grid tied in 2017 and batteries followed 6 months later.

Google suggests 2000B started production in 2015 but I cannot find a date for the Plus

Any thoughts on the benefit of Firmware update?

[nowty]

AFAIK any US2000 (B) should only be discharged to 20%

If its a US2000 (B) "Plus" version they can go down to 10% SOC.

Front panel shows US2000.

Part no US2000NB02V00101.

Also realised its a 2018 battery. PV went grid tied in 2017 and batteries followed 6 months later.

Google suggests 2000B started production in 2015 but I cannot find a date for the Plus

Any thoughts on the benefit of Firmware update?

If it does not say "Plus" on the front after "US2000" its not a Plus version.
The ones I had were manufactured in late 2017.

[SimonSays]

After adding the US2000C I noticed the master battery occasionally alarmed . So I fitted a console cable and set up a monitoring PC using MultiSIBControl. It quickly became clear the alarm was caused by one of the old US2000 going below 10% SOC.

As the old US2000 tolerates being discharged to 10%, I'd say the issue is that the lower capacity batteries have a lower cable resistance than the newer batteries. Can you put together a wiring diagram or take a picture and illustrate it to show us how they're wired?

EDIT: Is one of the "C" variants now master? I think the newer models should always be the master in a Pylontech stack, no?

[bpabpa]

After adding the US2000C I noticed the master battery occasionally alarmed . So I fitted a console cable and set up a monitoring PC using MultiSIBControl. It quickly became clear the alarm was caused by one of the old US2000 going below 10% SOC.

As the old US2000 tolerates being discharged to 10%, I'd say the issue is that the lower capacity batteries have a lower cable resistance than the newer batteries. Can you put together a wiring diagram or take a picture and illustrate it to show us how they're wired?

EDIT: Is one of the "C" variants now master? I think the newer models should always be the master in a Pylontech stack, no

?

The issue of the older battery going below 10% was resolved by discharging to only 15% SOC.
This is not an issue as in a weeks time I am adding 2 more batteries to bring total capacity to 28.8 nominal kWh. Having only 3.6 kW inverter I will be limited by IOG tariff charging until I add more charging capacity.

The wiring is exactly as per Pylontech manual using supplied interconnect cables.

The master battery is a US2000C. Pylontech stack just wont recognise all batteries if not in the correct order. I know this as a fact from actual experience!