Software sync for AC Out 2 battery backup during Grid Off (6x MultiPlus-II, v560)

Q&A and troubleshooting
, , , , , ,
1

Hello everyone. I have a 3-phase system with 6x MultiPlus-II 5000VA (2 units in parallel per phase) running on firmware v560, with a Cerbo GX, Batrium BMS, and a 20kW Fronius on AC Out 1.

I am looking for a configuration that allows me to replace a hardware solution I am currently testing. I have frequent grid drops caused by grid overvoltage during very sunny days. These outages are usually short, and I want all my loads on AC Out 2 to be covered by the battery during these brief moments. If the outage lasts longer than 30 minutes, I manually or automatically disconnect them to switch to a generator via an ATS, but that’s a separate logic I handle in Node-RED.

Right now, to make this work, I am testing a single 6-pole relay with isolated contacts triggered by the Cerbo’s Relay 1. I went with this hardware setup specifically to avoid putting the AUX inputs in direct contact with each other. I felt it was a necessary precaution to keep the Cerbo isolated from the AUX ports and to ensure the AUX inputs of all 6 units stay electrically separated from one another to avoid any interference or potential issues. This relay closes the AUX 1 input on all 6 MultiPlus units at the exact same time to ensure they all toggle their AC Out 2 relays simultaneously and avoid any sync errors.

I would really like to get rid of this physical relay and all the extra wiring by using a software-only solution. I tried wiring the Cerbo relay only to the Master L1 AUX input, hoping to use the General Flag to sync the other 5 units. While I can select “Use General Flag” as a relay in the Programmable Relay (012C) assistant, the “General Flag” option is completely missing from the “Switch Conditions” list in that same assistant. I do see another assistant called “General flag user (013F)” in my list, but I am not familiar with it and I’m not sure if it’s what I need.

Is there anyone out there who knows this approach and could help me set up the assistants on this v560 firmware? I want to make sure the digital flag is stable enough for these 6 units to prevent any “Relay Test” errors (Error 8/11) without needing the physical 6-pole contactor.

image
image463Ă—975 88.1 KB

2

Hi, I understand that there is no Assistant sequence that can take control of Realy AC-OUT 2 in the software area? Wiring AUX 2 to the Cerbo GX Relay would be the only solution!

3

Use an aux to signal a contactor to break the load and have ac2 out always on but have the contactor driven by your SOC conditions.

Break is after the combination disconnect.

4

Thank you, LX. This is a simpler solution. It is frustrating that it didn’t cross my mind, given that I already had all the necessary knowledge. I already have an AF96 3-pole power contactor available, so I will integrate it to break the load after the combination disconnect, using an AUX signal driven via Node-RED based on SOC and countdown.

5

No worries. sometimes we can’t see the forest for trees.

This is why the forum exists. We bounce ideas off each other so we can build awesome solutions.