remi avatar image

Victron Pylontech BMS Dropping SOC Daily Trend

Hello, I have a Victron systemsl in a remote location with poor utility grid supply.
BBIC: Quattro 48/8000/100, SCC: Smart solar 2x 150/70, S olar PV: 5.94 kWp, B attery: Lithtech (brand) LFP 3x 100ah 16s (300ah 51.2v) which shows up on VenusGX as with a "Pylontech BMS". Software unknown.
Monitor Pylontech BMS on CAN-Bus. There's no BMV installed.

Location is mainly used as a UPS during the week with low weekday loads of about 270w. Weekends are busier with regular family loads. It connects to the grid via a transformer

The system is currently on Virtual Switch settings which limit grid input to events of heavy loads or low SOC.
I have tried successfully ESS when the system is totally off-grid. However DVCC doesn't work well with the bad-grid mains power.

28 August: system shutdown when the Grid-In breaker tripped off apparently due fault on the grid supply transformer. Location changed from ESS back to Virtual Switch. Grid-In breaker was left off so the system became totally off-grid.
20 September: (chart attached) a trend of dropping %SOC was noticed. Despite the batteries reaching full absorption and float voltages (54.8v and 54.2) and current reducing to 0.00A by midday, the SCCs would enter float and merely supply the AC loads. Battery would idle at 0w. But max SOC trend was down daily: 100, 98, 97, 95, 93, 91, 89, 87, 85... About 2% per day.


21 September: I used remote veConfigure to increase the BBIC absorption to 55.2v and float to 54v. SOC jumped from about 63% the previous night to 100%. But the following day, SOC declines returned. By 5 October, at 3-4% daily decline!
Daily overnight discharge is about 7.0A (chart attached). The batteries report full charge voltage and 0.00A current around midday.

I have tried without further success to revive the daily dropping SOC trend by
(1) tweaking BBIC or SCC settings back to absorption 54v and float 54v; (2) changing the moniter from Pylontech BMS to Quattro device; or (3) connection of Grid-In supply; or
(4) increasing solar charge current limit up to 70A. (This results in faster charging but doesn't shift the dropping % SOC.

All Victron kit have the latest firmware.
Lithtech cannot provide updates for the "Pylontech" BMS in its batteries. Lithtech also seems incapable to diagnose the problems or perform other quality technical support.
2 of the battery 3 units 5.12kWh packs are unresponsive to onsite scanning by Pmodbustools software. Perhaps these 2 packs have weak cells that are dragging down the average daily %SOC?

Suggestions of alternative Pylontech-compatible software will be very welcome, especially if capable of remote monitoring.

At wit's end! Apologies for the long post. I have searched the Victron community, Diysolarforum, powerforumcoza and online, but cannot discern a solution. What else could be wrong? How to resolve the falling %SOC?
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

6 Answers
remi avatar image
remi answered ·

VenusGX view of fully charged voltagebut at 63% SOC


2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

I guess it is a problem with the batteries. You should contact the seller of the batteries and/or the manufacturer.
The GX device is only showing the SOC provided by the batteries and the MPPTs are voltage regulated.
The datasheet of the batteries should show what charging voltages you have to set.

One or more faulty batteries/cells can cause such problems but if the batteries are new this should be covered by a warranty.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

raymiller avatar image
raymiller answered ·

You should contact Pylontech support directly, I found them helpful, but may not reply until next week due to holidays in China.

Pylontech support should also be able to provide you with Windows software "BatteryView" to connect by RS232 on each battery to check the individual state and each cell voltage to check your cell voltage is reaching 3.55V per cell. You also may try activating the VRM advanced widget to give max and min cell voltages. As you can see my UP2500 (24V) batteries SOC graph are going from 90% to 100% when the cell voltages reach >3.50V. (please note the VRM on my display reverses all max and min values i.e. data etc) So it would seem the Pylontech battery SOC is more of a guide, its accuracy seems questionable.


But I would still suggest the Victron Battery Monitor would be a good investment to give a more accurate SOC.

1633559117598.png (73.4 KiB)
1633559187348.png (54.5 KiB)
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

remi avatar image
remi answered ·

Mattias, thank you. I also suspect weak or unbalanced cells. But 2 packs respond with "Abnormal" to the Pymodbustool software.

Raymillar, thank you.

Have thought to contact Pylontech.

Lithtech China "nudged" me to purchase 3 extra BMS units after 2 packs initially failed to boot up. Curiously the BMS do not have Pylontech brand.

Will a BMV as monitor override the battery BMS? The Quattro reaches 100% SOC daily if set as monitor, but falls to the level reported by the BMS when the latter is selected as monitor. So the BMS seems dominant.

Batteries reach full charge voltage daily. But the BMS %SOC trend continues to fall. Prediction is 60% today. The system is set to shutdown at 15% SOC, so maybe 20 days left before the system collapses with batteries at full charge.

20211011-132401.jpg (617.4 KiB)
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

remi avatar image
remi answered ·

The horror continues. The SOC has trended downward to 50% at full charge voltages as if today despite all changes to settings made to Charger settings for absorption and float voltages through remote veConfigure, and to choice of battery monitor in remote console. How has anyone been able to resolve SOC behaviours of this sort with their installs? Does anyone recognise the BMS above as Pylontech or other OEM?

Side Notes:

Lithtech (battery maker) acknowledges that "weak cells may have been used in the packs". They have been unable to resolve any technical or programming issues beyond

1) asking that the BMS be removed and reinstalled

2) sending Pmodbustools software which did not unarchive and so cannot be used by the

3) Their latest solution is to offer me to buy 5 packs to replace these malfunctioning 5 packs. Never mind that I bought 3 replacement BMS which didnt work. How can I best get a refund?

edits to post larger pics


socfalltrend1.png (79.2 KiB)
socfalltrend2.png (48.1 KiB)
socfalltrend3.png (56.8 KiB)
1 comment
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Sorry, but what do you expect us to say about it?

It is not a Victron product/failure and this is a Victron support community.

PS: the pictures are in the size of postage stamp.


remi avatar image
remi answered ·

I have just seen this Q&A:

The issues seem similar to mine. They were resolved in one case by by disconnecting everything on the load side of the shunt and then syncing the BMS (BMV) back to 100%, and in another case the above was insufficient, so both the BMV and the Shunt were replaced.. Mysystem does not have a BMV because the Pylontech BMS acts as battery monitor. Any ideas on how to sync a Pylontech BMS back to 100% (even if the shunt is replaced by a Smart Shunt or reinforced with a BMV712?

1 comment
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

I think "jjack811088" accidentally wrote BMS instead of BMV.
He did the "Zero current calibration" of the BMV
I don't think there is a way to get access to the BMS to change settings in there.

If you battery works fine then just add a SmartShunt to the System and select it as battery monitor.