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Fronius Galvo 2.5-1 and Multi 5.0 problems with zero feed in and frequency shift

Hello I have a multiplus 5.0/Venus/Fronius Galvo Grid-connected solar backup system. It Is connected to the local grid and must not feed power back to the grid.

I have set up both systems as described in literature (modbus, ip settings, etc) and added the self consumption hub assistant. The fronius appears in the venus menu and everything seems fine at first.

however, sometimes the fronius is temporarily pushing power onto the grid (up to 1000W for up to 10 seconds) and then resetting itself. This happens when the daytime loads are small and the battery backup is 100%. The fronius will turn on, push power to grid and reset again and again. This also seems to be overcharging the batteries. The whole control system seems very sluggish.

I dont understand why the fronius seems slow to respond to frequency shifting. I feel like I am not using the right assistant for this application. I have read everything about fronius and victron on this website a bunch but just cant get the system to respond right in all situations.

I want to understand better the control mechanism. It seems that while the grid is available the victron multi and venus should be controlling the fronius via modbus, and when the local grid goes down it should switch to frequency control. Am I right? Why cant the venus just control via modbus the whole time? Which assistant would this use?

Alternatively, can I just use a fronius smart meter and separate the two systems? Anyone have experience with this?

Thanks for the any help.


MultiPlus Quattro Inverter ChargerFroniusModbus TCPAssistantscommunication protocol
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5 Answers
etarkleson avatar image
etarkleson answered ·

Hello Everyone,

So I sorted the problem and learned a bit while at it. Im still waiting for the ET112 for further learning and training.
I installed a fronius meter I had around and changed the fronius control priority settings to meter control before modbus and removed frequency shifting.
This setup works great. Its like I decoupled the two systems while on the power grid. Fronius works, Victron works, and when the grid goes out the victron effectively controls the output of the fronius without overcharging the battery.
This seems obvious now that I have done it, my confusion was in my experience with multiplus's ability to act as a (limited) islanding device. It makes a ton of sense to just use a meter to ensure everything works even when networks and comms go down. I think here in East Africa our grid and power issues are so much more severe that we end up using different designs than Europe or America, and consequently run into some unique issues.

Thanks for the help from the people here I look forward to learning more complicated topologies for these systems.


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Paul B avatar image
Paul B answered ·

You can separate the two by putting the fronius on the AC-1 in of the multiplus, and this will them make the Fronius export to the grid all the time

You currently have it on the AC1 out I think

However the down side is if the mains goes down then the Fronius will also shut down as well.

Leaving it on AC1 out will allow the Multi to act as a Micro grid and the Fronius will still operate and supply power during a grid out, but the setting have to be correct or you can overcharge your batteries or maybe damage other 230 volt equipment,

However I would suggest that you have the system setup correctly by a Victron Agent and that would be the agent you purchased the system off, as there are quite a different ways to set the systems up,

I myself have not setup a Fronius unit so I do not have the experience to offer advice on the modbus, ip settings .

in my case I only use Frequency shit for my grid Tie inverter NOT Fronius

I have used assistants and generator autostart in the CCGX to get this working HOW I want it.

As I two cant export to the GRID

Mostly I stay disconnected unless I get to 50% reserve and then I connect to the grid and draw power when required , I leave 50% as a backup in case of a Grid failure.

however at over 50% I stay disconneted so that Frequency shift will work as you cant be connected to the grid to use frequency shift

MAKE SURE the Fequancy shift works so test it

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Woops, I didnt see the comment section.

Thanks Paul, I appreciate the response. I have added a new response above.

sean avatar image
sean answered ·

I have a similar system, Fronius Primo, smart meter, Multiplus II & smart meter, GX, ESS - grid parallel, so on AC1, along with some DC PV and wind.

I do now enable export, however even when (for an experimental 7 days) the Primo and ESS were configured for zero export, an amount of export occurs, usually when larger house loads are switched off - the export duration is a function of the inverters ability to alter its output in response to a varying input and load.

I understand that this is expected behaviour.

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Hi Sean,

Yes! This is what is happening and its not really acceptable for us, specifically because the meter only runs forward so this export of power is actually costing my customer. It seems as though everything works expect for the momentary kilowatt output to the grid for maybe 10 seconds at a time a few times a day (when large loads are turned on) I would love to chat with an advanced victron expert about this. I do feel that there are advanced ways to program this operation.

Via VRM you will be able to determine exactly how much is being exported, it's a tiny amount (in comparison to MP throughput).

Zero export doesnt really mean zero export, more accurately it's zero export within xyz seconds, the speed at which the system responds to a change in demand is just a function of how fast the feedback loop works, this is expected behaviour.

I've just noted you dont have a ET112 installed - I assume you are using the external CT on your main grid incoming feed in order to meter your consumption/export, connected to your Venus device via 485 ?

Using the meter will result in a slightly faster, more accurately measured response, you may also find altering the grid set point results in less export.

Hi sean,

I missed this response earlier. I am using the current measurement of the multiplus. It is hooked up to the grid and then everything else is afterwards.

Ive already ordered an ET112. Its not too expensive and it cant hurt.

Thanks again for the advice.


Thanks Sean, Interesting that its accepted behavior. It pushes a lot of power on to the grid (compared to the PV power available) and then shuts off when control realizes whats happening.

So an ET112 will definitely improve this behavior?

So I guess now my question is, with an ET 112, Fronius Symo, Victron Multi, Venus system, what is the best assistant to use to have no power export and to run daytime loads off of the symo but keep the batteries fully charged? (think of this really as a backup system which tries to always keep the batteries completely full and runs daytime loads, which vary from almost none up to the rated solar production (~2.5kw)).

It seems I need an ESS assistant, but will need to ensure no export. Anyone have any comments on this? Am I missing anything?

Thanks again,


Paul B avatar image
Paul B answered ·

Keep in Mind that frequency shift CANNOT work if the multiplus is still connected to the grid as it cant change the frequancy as the grid is two powerful. Thats why I am using the setup above as it works well for me and does not allow export to the grid, unless I want it to occur (sometimes as it suit's me) however I still can suck from the grid if the batteries are below a set level, all works seemlessly and so far I have had NO issues

however I have not used the Fronius setup as its also got some other controls that directly report back to it via another cable. and this then works a different way. and I dont have the experience to comment there.

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Yes, This is where I believe MODBUS comes in. And ive used modbus in other industrial applications and it is a very fast and robust comms protocal. However there is a delay (it seems) between the different operation modes that causes a period of unknown operation, many times this causes excess solar power to be exported to the grid for a short period.

Thanks again.


Yes, Your are correct. When the grid is connected I believe that the modbus (run over ethernet) between the fronius and victron should control the fronius power output. Then when there is no grid it changes to frequency control. Which works, but I may try to slow down its response.

The question is, does anyone out there know how to maybe use Modbus comms all the time? Instead of frequency control I would like the multi to let the fronius know how much power to supply all the time instead of only when there is a grid. I was wondering if I could write a custom assistant for this?



etarkleson avatar image
etarkleson answered ·

Thanks Paul,

I appreciate the helpful and detailed answer.

Yes I am connected to ACout1 as you say, and no moving it to ACout2 is not a great option because I want to power backup and large loads with the fronius when sun is available.

I was under the impression that there was an assistant and architecture for these systems to work like the following...

Fronius on ACout1 on multiplus grid-connected backup system
Large Loads on ACout2 of multiplus
Fronius helps to charge batteries and run daytime loads (both large and small)
Grid available during daytime to help run daytime loads (and charge batteries if needed)
No Grid Feedback allowed for even a short period

I have a fronius energy meter and am happy to purchase an ET112 in order to make this system perform as expected.

The victron distributor I bought this equipment from is unable to help with this technical of a question.

Anyone have any other ideas?


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