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I have a Solis S5-EH1P6K-L Hybrid Inverter One Pylontech US3000C battery was fitted 14/03/2023 and a second added Friday 14/04/2023

I've now woken up to find I'd had four Under Voltage Battery alarms, they'd all cleared before I could investigate further.

From the Solis Logs:
Times are: start then recovery
Under Voltage Battary 186C6 No Action Required 4h 15/04/2023 03:01 (UTC+00:00) 15/04/2023 06:57 (UTC+00:00) Restored
Under Voltage Battary 186C6 No Action Required <1h 15/04/2023 02:06 (UTC+00:00) 15/04/2023 02:48 (UTC+00:00) Restored

Under Voltage Battary 186C6 No Action Required 11h 10/04/2023 01:36 (UTC+00:00) 10/04/2023 12:15 (UTC+00:00) Restored

Under Voltage Battary 186C6 No Action Required 4h 05/04/2023 01:24 (UTC+00:00) 05/04/2023 05:30 (UTC+00:00) Restored

The attachment screen grab shows the Battery voltage (in blue) for the last two Alarms yesterday with 45V & 60V being the lines below and above.

Are the alarms spurious or Should I be worried about them?
Am I correct in presuming it is Pylontech I should be contacting or could the Solis Inverter be the cause?

Have you CAN communication between the battery and inverter?

What power are you drawing from the battery overnight? What is the actual undervoltage reading?

First I assume the installer actually set the battery to "Pylon LV"? You can check under the "Advanced Mneu" -> "Storage Energy Set" -> "Battery", It should say "Pylon LV"

Assuming that is OK

Can you get a plot of the S.O.C of the battery?, just tick the box further down the column.

As I understand it you can get an under voltage alarm generated by just one of the 15 cells in just one of the Pylontech batteries. Until they have done a few charge discharge cycles they may not be fully balanced.

It is also possible that if the SOC is low, I note the alarms occurred in the "early hours" so quite likely, then if a large load suddenly switches on your Solis will have a go at pulling upto 100A from the batteries which may cause a transient drop in battery voltage below the lower threshold set in the inverter. As there was no "BMSerr" in the message I do wonder if it is the Solis inverter itself that is "tripping" off.

If you look under the "Advanced Menu" -> " Storage Energy Set" -> "Control Parameter" what is "Battery Undervoltage" set to?

Pylontech and Solis don't work 100% together when it comes to voltage limits, though the problem is usually overvoltage alarms in the summer when you have lots of PV generation - largely because Pylontech has only 15 cells so is approx 3.2V less than other batteries - though Solis may have sorted their firmware on later versions.

To put your mind at rest the Pylontech BMS will protect the batteries and if it is a "real" alarm the Solis will disconnect and require powering down to reset. In my opinion most of the Solis "Alarms" should really be warnings, or just recorded as events. If you "catch" the Alarm happening the inverter does go offline for several minutes and then restarts, hence why when you looked it was operating normally.

I installed the system myself (A Electrician made the AC connection)
It is set as battery 'Pylon LV' (I double checked yesterday) though the App and web interface says "Battery Model: No battery" despite showing all other battery info, SOC etc.
CAN communication seems to be working correctly.
Overnight we normally use 200-350w
At least one of the Alarms went off as the dishwasher started its second water heat, as shown in the screen grab.
I'm not sure what the under-voltage actually was as it isn't given in the alarm and the only place I can see historically is in the graphs which show no drop.
SOC was 34%
49.1V

Next time I'm in the loft I'll look at:
"Advanced Menu" -> " Storage Energy Set" -> "Control Parameter" what is "Battery Under-voltage" set to?

Now that I have two batteries should I be able to see anything specific to each battery?
I know the second battery is working as the charge and discharge rates now often exceed the about 1.8KW I was getting with one.

Thanks for all the advice. It does sound like bedding in glitches and not anything to worry about.