Hi All,

i have a client with the following setup. They keep experiencing issues when its loadshedding , as soon as the power goes out, they get a F26 Bus unbalanced fault on the master modbus 01 inverter. Then they loose power over all 3 phases because of the on inverter that died. We have checked the PV for earth leakage, we checked the lightning arrestors. Changed them aswell, with no luck. They only experience this when the PV side of things is low and there is no grid. Mabey once in 2 months. We are stuck on why this would happen, any help we will appreciate.

Phase A - Inverter 1 - Modbus 01

Phase B - Inverter 2 - Modbus 02

Phase C - Inverter 3 - Modbus 03

They all go to a common DC busbar.

Inverter 1 - with the fault codes load on the inverter.

Inverter 2

Inverter 3

Maybe check all the mc4 connections at the panels on the strings of the inverter in question

Does this happen when you switch off the Eskom MCB, or only with loadshedding?

How close are the inverters together, and are you using the supplied comms cables?

All inverters on the same firmware version.

What batteries are on site, cable size and length?

3 hours ago, Divan Du Toit SST said:

They only experience this when the PV side of things is low and...

Most strange, because on change-over from grid to battery and PV, battery takes the instantaneous load, and then the MPPT's catch up if solar is available.

Does this also happen at night with no PV?

Has this fault occurred from installation, or is this something new?

Have you tried setting another inverter as master?

Just a few questions, then I'm sure everyone will jump in. 👍

Measure DC voltage and current at each inverter under load and compare. A significant drop at Inverter 1 suggests a bad connection or higher resistance on the DC cabling. This happens with low pv generation and no utility backup pointing to battery issue on inverter 1.