ESS throttling MPPT without valid reason (AC + DC system, battery not full, reproducible

DIY
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21

Thank you for your explanation.

In my case, the behaviour seems much more extreme than a normal rescan. As you can see in the attached video, the MPPT power drops very close to 0W even though solar conditions are stable.

This does not look like a typical short rescan that lasts only a few seconds.

Also, this behaviour happens more often, not just at long intervals like every 30 minutes.

Could this indicate a possible issue in the MPPT firmware or some specific interaction in my setup (ESS + Fronius + battery)?

I am happy to provide more data or run additional tests if needed.

22

Hi @Oldrich77 , I added some additional monitoring on my side to see if we can catch enough data to diagnose this. Now we wait for data.

23

Thank you, I appreciate it.

I will continue monitoring the system and provide timestamps and additional data if I observe another drop.

24

I think we already have something to work with. You are right. You can see the rescan squigles on this chart, plus that one time where it completely drops out.

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The Multi is lowering the charge voltage. Let me look into this some more. This is not the first time I’ve seen something like this, but it is the first time I’ve seen it where there is no PV-inverters involved.

25

Thank you for your analysis, I really appreciate you looking into this and working on it.

I will keep the system running as is and continue monitoring.

I fully trust that your team will get this resolved, and I am glad I could help identify a problem that is not easy to detect.

26

Just to let you know, I have updated the system to the latest beta version (3.80.14).

I will continue monitoring and will report any changes in behaviour.

27

This might be simpler than we thought.

Your site did this again today around 10:33AM. Data logging says the reason for the outage is no input power. Check your PV wiring, it might be as simple as a loose connection.

28

Thank you for the suggestion.

I will check all PV wiring and connections to make sure everything is secure.

However, the behaviour seems very fast and the power returns immediately, which made me think it might not be a physical connection issue.

I will verify and report back.

29

Just a quick update – I checked and retightened all PV connections at the MPPT, as well as all DC and AC protections.

I will keep monitoring.

30

The issue occurred again today at 10:31.

All PV connections have been checked and tightened, so it seems unlikely to be a wiring issue.

31

Hi,

I would like to share a final update regarding the issue.

After a detailed inspection, I decided to redo the entire DC side to eliminate any potential weak points.

The following changes were made:

  • all MC4 connectors were replaced with original Stäubli EVO2 and properly crimped
  • MC4 Y connectors were replaced with original EVO2 splitters
  • fuse holders were upgraded to a higher quality Eaton unit
  • fuses were replaced with correct gPV 32A (Mersen)

After these changes, the system is now stable with no more drops or fluctuations under load.

I believe the root cause was related to connection quality on the DC side rather than the system itself.

Also, many thanks to Izak Burger (iburger) for the analysis and guidance, which helped me focus on the DC side and identify the issue. I really appreciate it.

Currently, the system occasionally performs an MPPT rescan after a few minutes. During this, the power briefly drops, but it no longer falls to zero. Within a few seconds (around 10 seconds), it always returns to maximum power without any instability.

I would appreciate it if you could continue monitoring or reviewing setups like this, as I believe this configuration could be useful for further improvements or optimizations in the future.

Thanks again for your support.

32

Thank you @Oldrich77 for confirming. On my end the issue wasn’t dead, I had discussed it with one of the solar charger firmware guys, who was just as puzzled as I was. I’m glad that you managed to resolve it in the mean time. Always good when it turns out to be something simple.

33

Hi Izak,

thank you very much for your help and the time you spent on this.

I really appreciate your analysis, it helped me focus on the DC side and find the root cause.

In the end it turned out to be a simple issue, but not easy to identify at first.

The system is now stable and working as expected. I will continue to monitor it over time.

If I need any further assistance in the future, I hope it would be okay to reach out to you again.

Thanks again and have a great day.

34

Something similar experienced few days ago with a Bluesolar 150/35 and 3S-2P panels.

Personal prefference is to install fuses for all strings, in a box and parallel after. Much easy to diagnose.

After few hours of monitoring in a cloudy day, delivered power from calculations was off.

To my surprise, one of the brand new fuse, Eti 10x38/1000v 16A was open.

35

Hi,

thanks for sharing your experience.

That’s interesting, especially that a brand new fuse was already open – I wouldn’t expect that either.

In my case, the issue turned out to be a bad MC4 crimp connection, which caused unstable behavior under higher current.

But I agree with your point – having each string fused and properly separated definitely makes troubleshooting much easier.

Thanks again for the input.

38

Hi Izak,

as you already have access to my system and we have worked on it together before, I’ll describe the current behavior I’m observing.

Issue

After fixing all DC-side issues (connectors, fuse holders, etc.), the hardware side should now be OK.

However, when the battery approaches high SOC (~95–100 %), the system behaves as follows:

  • The Fronius inverter continues producing normally.
  • The Victron MPPT suddenly drops to 0 W (no PV input).
  • Feed-in is allowed and there is still load/export path available.

At this point:

  • The MPPT does not recover on its own.
  • Only a Cerbo GX restart brings it back to normal operation.

Additional observations

  • This happens repeatedly near full battery.
  • DC wiring and connections have been checked and corrected.
  • Another user with the same system configuration is experiencing the same issue.
  • If I switch on a high-power load, the MPPT starts contributing again when the Fronius inverter is no longer sufficient.
  • After restarting Cerbo GX, the system behaves correctly and MPPT operates normally.

Notes

  • It looks more like ESS/control behavior rather than a hardware issue.

Could you please check if this is related to ESS regulation (possibly interaction between AC-coupled inverter and MPPT near full SOC)?

Thanks.