Axpert (Isolar) VMIII 5K low battery with Pylontech

[Acuario]

My setup is as follows:

4 X US3000C batteries

ISolar SMV III 5Kw (same as Axpert VMIII)

AC input is connected and recognized.

Batteries and inverter are communicating via BMS, inverter is set to SBU

I have an 04 alarm (low battery) on the inverter.

The battery voltage is 48.5V, SOC is 21%, on the battery 2 led's of the SOC are lit

Inverter is set to PYL for batteries which sets the following parameters automatically:

12 46V
13 54V
26 53.2V
27 53.2V
29 46V

The 'dry contact' is set to NC (i.e. it is not activated).

The inverter hasn't switched to use the utility (ac) input.

QPIWS gives 2 warnings, a12 (Battery low alarm) a14 (battery under shutdown)

 

Any ideas why the inverter isn't switching to utility and charging the batteries?

Is there a way to force a changeover (I guess setting to USB?)

Edited May 31, 2021 by Acuario

[Coulomb]

7 hours ago, Acuario said:

Any ideas why the inverter isn't switching to utility and charging the batteries?

I'd say it's because setting 12 (back to utility voltage) is the same as setting 29 (low battery cutoff). My guess (not owning this model) is that settings 12 and 13 (back to utility and back to battery voltage) are not controlled by the BMS. So making setting 12 higher may fix the problem.

One hassle with unpatched firmware (the only kind available for your model) is that once the battery low warning comes on (at 2.0 V above setting 29), it doesn't go off again until 4.0 V (!) above setting 29.  In your case, it has to reach 50.0 V (3.33 VPC) before the warning goes away. With the flat voltage versus SOC curve of LFP cells, that means that it takes a long time for that warning to go away.

Quote

Is there a way to force a changeover (I guess setting to USB?)

Yes. If you have monitoring software like ICC, it will make that easier to do, e.g. click a button. But all it will be doing is sending a command to change the output source priority to USB.