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VE.Bus Error 18: AC Overvoltage on the output of a slave has occurred while already switched off

I have an off-grid system with 3 Quattros (48/10000 230volt) in parallel (used to be in 3 phase) and a Fronius Primo 5KW AC coupled inverter connected to a 48v NiFe battery bank. The Batteries are charged by two Schneider MPPT 80/600 charge controllers and the Quattros are set to charge from excess power from the Fronius.

We use the grid as a UPS with an ATS to switch to the grid when the inverters shut down (usually due to low battery voltage).

This setup (minus the Fronius) worked great when it was in a 3Phase configuration.

Recently we added the AC coupled Fronius and reconfigured the whole system be be single phase parallel. The reason was mainly that we did not use any 3-phase equipment and need a larger load on one outlet so balancing between phases became a bit of an issue. By switching to a single phase the Inverters are more balanced.

However, since switching we have this issue occurring occasionally when the battery voltage is low and the inverters switch off;

VE.Bus Error: VE.Bus Error 18: AC Overvoltage on the output of a slave has occurred while already switched off    

I am confused about what could be causing this. I did update the inverters to the latest firmware before making the config change. They are all on 2653496. The Fronius is also upgraded to the latest firmware before installation.

Any help is appreciated!


Some additional information.

(read 'grid' as the local off-grid power network, not the real grid)

It happens in about 50% of the cases when the system shuts down due to load battery voltage. It seems to be at times when the Fronius is actually pushing some power on the local grid.

Could it be the Victron is measuring the (over)voltage coming from the Fronius just before the Fronius switches off because it lost it's 'grid'?

Is there a way to tell the Victron to allow a short period of time where it might measure a voltage on the AC-Out even if it's switched off?

iwan asked
Alexandra commented ·

0 Answers

fronius inverter communication suddenly unstable

I'm running an ESS system with multiplus 2, cerbo, a few mppt's and an grid tied fronius wich is connected on a switch.

This ran flawless for over a year, but since 2 weeks the fronius keeps popin up and disappearing at the dashboard. It can lead for unwanted situations as the limited feed in doesn't work when the fronius isn't recognised.

Any suggestions? Will be network related, but any hints?

Another question, when the system works, is there a way to give the fronius priority for charging against the mppt's, when limited feed in enabled? This would be handy, as the fronius still makes money through energy certificates, and the mppt's don't. Braking the fronius instead of mppt's is not desirable

jejochen asked

0 Answers

Fronius / Multiplus II ESS - Network Issues?

I am about to install a grid tied Fronius AC PV inverter to a Victron Multiplus 2 ESS system with Pylontech batteries.

The original plan was to use one Energy meter ET112 and a network connection to the Fronius. My supplier has said there can be issues with a system set up this way. See explaination below:

For the Fronius to appear on the Cerbo, they need to be on the same LAN subnet and that requires the local LAN router to be operating even if there is a power failure. SOmetimes the networking causes them to stop talking and it needs reinitialising. And all manner of networking issues. An energy meter with a direct cable is always more reliable.

Would I therefore be better using 2 energy meters ET112’s and forgetting about the network connection. This would also mean I could order the non WLAN Fronius, which is a bit cheaper?

Any thoughts or experiences appreciated.

superchargedpolo asked
superchargedpolo commented ·

1 Answer

Fronius Inverter does not appear on VRM portal, why ?


The Fronius inverter is shown on the Venus but not on the VRM portal or it does in advanded but now in the overview


Above shows the Fronius and VRM portal below doesnt show it :


but in theVRM portal i see following in Advanced :


and here it's not shown :


What could be the reason ?

peternielsen asked
adahmen answered ·

14 Answers

Multiplus 2 new instalation some help.


I need some advice about the system that I am doing. I have:

1 Multiplus 2 48/5000 - ESS

1 cerbo gx at ac in with 12v transformer before bypass point

1 fronius primo 5.0 at mp ac out

1 aftermarket 7” display

1 hager sft440 for bypass

1 10kw battery (waiting for delivery for about 90 days)

Despite not having batteries I started to assemble what I could because I want to do all the firmware updates and cable management ready while I am waiting for batteries.

The doubts are:

As you could see in the picture I could install and update all the firmware, and the system is working with no problems after those upgrades, can I still have this running without batteries while I am waiting or it is better to bypass the mp for now.

About the cerbo gx, I live in a stable grid power area, can I connect the cerbo gx with from ac with a simple 20000mah powerbank with a step up converter that outputs 0,8a at 12v. By the multimeter value yes but anyone tried it?






lopcarlo asked
Kevin Windrem answered ·

1 Answer

Can you use an AC-Coupled Fronius Primo Light in an Off-grid installation?


If I would not use SolarWebApp monitoring, couId I use an AC-Coupled Fronius Primo Light version (without Datamanager) in an Off-grid installation? Only Victron inverter/charger would be monitored via VRM. The communication between Fronius and Victron would be possible via LAN?

Gracias por adelantado :)

David Gómez asked

0 Answers

Fronius on ESS without MG50?

Hi there,

since Fronius Support is taking some time to answer the question, I might as well post it here.

The local utilities require a specific cosPhi setting in the inverter, which - for my knowledge - requires a countrysetup other than MG50.

How does changing from MG50 to i.e. DE2U affect the behaviour of the inverter in an ESS?

Feed-in only needs to be limited to 70%, so no zero feed-in required.

As always, thanks for the help!


chriss83 asked
baxter answered ·

4 Answers

Unstable Microgrid Multiplus II - Fronius


Multiplus II 48 5000, Cerbo, Fronius 501 @ ACOut, no feed in,


Fronius: - set to MG50,

Multiplus II:

* programmable relay and general flag assistants are used to ignore AC In1 if SOC >50% not ignore if SOC <30%;

* PV inverter support at last position in assistant list.

Fronius is connected via WIFI to Cerbo and it looks as it should.


Cerbo is showing: Fronius 350W, AC Load 105W.

The issue is that the battery state changes from charging with 900W to discharging with 700W couple of times per second. BMS shows similar values.

In this stage ESS assistant is not an option.

Somebody has this issue before, is there a fix for it ?

popnic asked
fnaf commented ·

4 Answers

Ground Relay Error 8 with Fronius IG Plus when switching back to grid

Hy All,

we deliverd a new Installation (Number 8) to an "existing" Farm House with a 3 - Phase ESS 15 kVA - Multiplus II System.

There is a Fronius IG-Plus 120-3 running for more than 12 years. So good for now.

Everything is working fine except we start the system in "Island" Mode with an Active IG-Plus. When AC Mains is connected, the System performs its Relais Test and after about 5 Minutes it is going to switch back to grid. Immediately, when switching back we get an Ground Relais Test Error 8.

When starting in Island Mode with a disconnected IG Plus everything is working fine.. after switching back to grid and connecting the IG Plus everything is working like a charm.

When coming from Grid with a GridLost, we also encounter the same problem when switching back to grid.
To make a conclusion.. When the Fronius IG-Plus is "Connected" (we switched off the system, because it starts working after 30 seconds.. so we could not test, if its a problem when standing by connected and producing), we get an Ground Relais Test Error when switching back to grid. (Always)

Whats wrong...

There is no mixed Ground and Netral (We have controlled that several times)

The Multis are showing those ERRORS:

Phase L1, device 1 (0) #44 0x820002
Phase L2, device 1 (0) #15 0x800024
Phase L3, device 1 (0) #19 0x800024

From the wiring...

AcMainSwitch - SwitchOverToGenerator - 100 mA 3 Phase FI - MulitplusII - FI-s to different Loads

the IG Plus is connected:
IG-Plus - LS 16A - FI- 003 A -To The MulitplusII Ac Out

As talking to Fronius Service Personal the have no Idea what s going on, because they say they do not connect Neutral to Ground ... so do we have issues with the 100 mA 3 Phase FI, or the FI 003A connected to the IG Plus?

The System is running the latest Firmware 487.

Unfortunately there is no Support from our Dealer, because they do not have the knowledge.

Have a nice day, always Sun and I hope to get some good feedback...

thank s in advance


Bernhard Matschinger asked
Bernhard Matschinger commented ·

0 Answers

Quattro/BYD/GX/Fronius - High Voltage Alarm when reaching 100% SoC


I got an AC coupled system installed about 3 weeks ago. Quatrro 8k, Fronius 8k, GX and BYD LVS Premium 24kwh. Grid is available between 0 and 6 hours a day, very random, and we could go 10 days with total grid outage. Configuration made by the installer is ESS with "keep batteries charged".

Things are running as expected, except that I am worried about two things that I think are related. High voltage alarm from BYD whenever it gets to 100% and the delta between cell min/max once the SoC is at 100%. Here's an example from today.

SoC reaching 100% at 9:11


Increase in min/max cell voltage, and the delta stays large as long as the batteries are not discharging:


And I also get the alarm (visible on the GX as well in the notifications):


Here's an example from yesterday showing the delta while SoC is 100% for a longer period. I reached 100% yesterday, through Grid in the early morning hours, then discharged a bit, then 100% again once the sun rose.


I don't mind sharing my exported config from vrm or any data that might help to understand what's happening. There are some days that I don't get the alarm, but the delta is always there. I read in different posts that this is normal for new installations, but I would assume after 3 weeks, I should be seeing some improvement?

I also read somewhere to keep the batteries at 100% for a week or so. Grid wise this is impossible. I could run a generator for that long but the cost would be very high.

micmak asked
micmak answered ·

3 Answers

ESS setup for fronius on AC IN side

Hi all. Is it necessary to add in the setup of the Assistant ESS. That I have a pv on ac out if the pv is on ac in ? I ask the question because I have a small problem.

System design 3 phase multi 48/5000/70 with fronius symo 8.3-2 ( 7.0 kw pv panels) on ac in side.

In the ESS Assistant I answered no acpv on out side.

During mid day the fronius is showing production on 8.2 kw even if the pv panels are 7.0 kw... can someone tell me where to look at ?


Can I set somehow to be 7.0?

mihaimicu asked
marekp answered ·

2 Answers

ESS, Fronius, Zero Feed-In, 1:1 Rule

Whilst understanding that the 1:1 Rule applies when Fronius is connected on AC-Out so that a Multi/Quattro will control output of Fronius with frequency shifting, there appears to be a different approach when ESS is used.

In the document AC-coupled PV with Fronius PV Inverters ( it states:

2.5 Zero Feed-in
It is possible to make a Zero feed-in system with Victron & Fronius. The Venus device will the control
the Fronius output power. See the ESS manual, chapter 4.3.11 Fronius Zero feed-in for details.

This suggests the Multi/Quattro does NOT do frequency shift to control output of Fronius.

ESS manual 4.3.11 talks about setting the GX device & changing some parameters on the Fronius. The communication method between GX & Fronius must be TCP & both devices must be on the LAN.

So, this raises a question.

Given 2.5 Zero Feed-in suggests GX controls Fronius output (not Multi/Quattro), does the 1:1 Rule still apply?

Let us assume that a 3kva Victron with full batteries and a 5kva Fronius (on Victron AC-out) on a STC day and generating 5kva.

Suddenly, the only load of 4kva stops.

The Fronius must reduce its output by 2kva to 3kva.

The rationale of the 1:1 rule is that frequency shifting to reduce output is too slow to respond.

The intent of the question is does the GX device respond fast enough to communicate to the Fronius to reduce output by 2kva (and possibly does the Multi/Quattro have enough surge capacity and duration on AC-out) before 'bad things happen'.

If it can, the 1:1 rule is probably not necessary.

bipedalprimate asked
baxter commented ·

3 Answers

Victron Comms with a Fronius Tauro?

Can Victron communicate and control with the Fronius Tauro as it can with Primos, Symos and Ecos?

Kym asked
da9el84 edited ·

1 Answer

Fronius Primo an MP2 ESS Grid resynchronisation

Hi There,

a question is bugging me:

assume the following setup:

MP2 5000 in ESS setting with Fronius Primo 4.6 (with 4.4kwp) on AC1

Fronius is set to MG50

pylontech battery

What happens when the Grid fails ? --> Multi is taking over and is regualting the Primo via Frequency.

So Far so good.

But when the battery is nearly full or full, and the grid is comming back online ?

I think the multi needs to synchronise back to the grid. It goes back to 50 Hz. But what will the primo do ? When the primo output power goes up and the battery is full and the grid is not yet connected via the ess relays ?

Will there be a DC Ripple problem an system shutdown ?

Best Regards


rl78 asked
Rob Duthie answered ·

1 Answer

Is grid feed in from battery possible?

Hello, I am Alain.

My system is:

Quattro 10kva, 2 x fronius primo, 48v lifepo4 battery bank 50kwh connected to the grid.

Everything works perfect, as in, the solar that is not used feeds to the grid.

I want the excess solar power stored in the battery to feed to the grid later in the evening.

The reason for this is the compensation I get is highest in the evening.

Somebody out there with a solution?


stella asked
paragon edited ·

3 Answers


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