josephm avatar image
josephm asked

ESS and Fronius : Feed-in Limiting active turns to NO when grid is lost.

I noticed that the Feed-in Limited active status turns to NO when grid is lost that almost made my house burn as the fronius could not limit the power and my batteries were already full, the batteries got overcharged !overcharge.jpgno-more-limitation.jpg

Any other requirements needed ? Fronius Primo 3.16, Cerbo 2.70-17, Multiplus v282, modbus tcp OK.

ESSFroniusModbus TCP
overcharge.jpg (212.3 KiB)
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3 Answers
rainerb avatar image
rainerb answered ·


in my opinion and by definition, the GX Feed-in limiting is only designed to limit the grid feed-in. So if there is no grid -> no feed-in -> no limiting.

In an offgrid situation the Fronius should be throttled down by the "Frequency shifting regulation" that is part of the ESS assistant in the Multiplus. From a safety point of view this is the only reliable way to reduce the power. You should check the Hz-settings of the ESS assistant in the Multiplus.

This are the default settings.


You could also look at the "AC Output Frequency" widget in the VRM portal. There you should see the change of the frequency when the grid is lost.

Hope that helps.

Regards, Rainer

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Thanks Rainer ! I use the ModBus TCP to reduce power of the fronius when the grid is connected and as I inject only 100W it works great. I thought it would do the same when I loose the grid, it is very dangerous for the installation. I will try the frequency shifting to cut off the fronius, let s see if there will be a conflict between the 2 solutions. Thanks again !!

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The two solutions will not have a conflict because ESS limitation works when the system is on grid and the frequency shifting kicks in, when the system is off grid.

With an PV inverter at AC out it is obligate to configure the frequency shifting in the ESS assistant properly and you have to select that there is a PV inverter at AC out.

Here a few more information:[]=ess&s[]=manual

As palom170 already mentioned, the fronius must be set to country code MG50 or 60Hz.

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Have you configured the ess selecting that the system has a inverter on AC out?

And, have you set up the fronius in mg50 or 60hz? Have you change this value in fronius? Or does it keep configured in your country?

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Yes, ACOut, I'm in Spain 50Hz. I configured yesterday evening the freq shifting, I will check today if the control is done with MobBUS when I'm with the grid ON and will see if the freq shifting works only when the grid is OFF. For me it does not make sens all this, if the multiplus can control the fronius with modbus when the grid is ON why not when OFF ?

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When everything is working properly, the ModBus regulation would theoretically work off-grid too but it is simply not safe enough. For an off-grid situation it is THE essential function to throttle down the inverter.

Think about what would happen if your pv array is producing 3,7kW and your ethernet/modbus connection fails due to a defective ethernet hub or something else (bye bye modbus). Where should the power go when the batteries are full, no loads available and the grid (for injection) is not available too? This could lead to a very destructive overcurrent/overvoltage event - especially with larger systems than yours.

The 230V connection between multiplus and pv inverter is always there and therefore frequency shifting should always do its job (if configured correctly). This ist the simple reason.


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You are totally right, I made now the test, MP controls with modbus when grid ON, when OFF, the freq shift works perfectly ! Thanks a lot for the help !! Still don't know why the control via modbus does not work when grid is OFF.

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tozz avatar image
tozz answered ·

If your batteries were able to overcharge, you are missing a critical part in your setup: A BMS

Your BMS should have disconnected the batteries from the inverters/chargers once the voltage threshold was exceeded.

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josephm avatar image
josephm answered ·

You are totally right, I have a DIY BMS to balance and still did not connect it to a DC relay breaker :( I have leaf module last generation; float in 56,7V and during the issue, it has reached 66V, I was lucky that did not burn and strangely, it seems working perfectly still.

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