Output Over-current Fault and changes of Inverter State

[Kosymodo]

As per my recent posts, my system is driving me crazy right now, with lots of unexpected behaviour. I'm therefore trying to narrow down what the issue is. One of the 'benefits' of looking so closely at the system these days, is that I have my finger on the pulse of all the different sensors being displayed in HA via the Modbus connection.

I am noticing a lot of intermittent errors, which clear themselves without intervention. Output Over-current Fault is the culprit 99% of the time, so I'd like to understand what this is, and what it might be a symptom of. I've had 22 such faults today (all of which occurred between 13:03 and 15:07).

The other thing I'm noticing is a lot of Inverter State changes. So far today, the state has changed (from On Grid -> Waiting -> Checking -> On Grid) 26 times. On 22 of these occasions, it was linked to the Output Over-current Fault, which was shown as Recoverable Fault (On Grid -> Recoverable Fault -> Waiting -> Checking -> On Grid).

Any ideas guys what I should look to do? I'm planning on raising a support ticket with Fox in the coming days, once New Year is out of the way. Maybe they'll be able to suggest something...

[maccoylton]

Is it cold outside? Do you have heating enabled?

I see similar, my theory is this is related to the heater function switching to heating from grid once the battery SOC reaches the 40% cross over level ( below 40% I believe it will only charge form solar or grid)

For me last couple of times it has happened the battery has required heat, the SOC has been at or below 40% and there was no solar. Posted a chart in the Ep11 forum.

Another user who has reported similar say there is a new 1.11 battery firmware they have just installed and will repot back if that helps

[Kosymodo]

Just coming back to this thread by way of an update...

Fox Support took a look and stated "In winter, the open-circuit voltage of the PV panels increases, and a high DC bus voltage can potentially trigger an overcurrent on the PV side. With this inverter, sometimes it may remain in “waiting” or “checking” status even without reporting an error. In your case, the voltage on PV3 is too high, which is triggering the fault. You will need to ask the installer to move some of the PV panels from this string to another string/input."

PV3 has 12x 450W panels on it, so have reached out to my installer to see what they can do. However, it's not easy, as splitting the strings (currently 6/6/12, Fox suggest 6/9/9) would mean panels from different aspects (E and W) being on the same string. I've cheekily asked the installer to swap the inverter out for a KH9 (4 MPPTs). We'll see lol!

[WyndStryke]

... would mean panels from different aspects (E and W) being on the same string ...

There are two main alternatives, getting 4 MPPTs would be preferable, but you can also use optimisers to combine the two aspects.

Getting the correct number of panels onto a string is fairly basic - the design tools will flag issues like overvoltage in winter.

Was the panel design changed on the installation date or something?

[maccoylton]

Do you have a modbus/ha can you see how high the voltage has gone on that string?

If so can you see a correlation between a high voltage and the error?

Would be interested to the high voltage that versus the inverter rating, which I believe is 80-500v normal operating range with a max of 600v.

Do you know the spec of your panels?

[Kosymodo]

Was the panel design changed on the installation date or something?

Yeah, it all got a bit crazy at install time. The original plan was for 20 panels (12 East + 8 West). However, when they came to install, they installed the 12 East on day 1, then installed 6 West on day 2, as they couldn't fit a row of 8 onto the roof (!) I complained, and they came and fitted an additional 6 West on day 3. Hence why I've ended up with 12 East and 12 West. They said that having 12 panels on PV3 wouldn't be an issue...

[Kosymodo]

Do you have a modbus/ha can you see how high the voltage has gone on that string?

If so can you see a correlation between a high voltage and the error?

Would be interested to the high voltage that versus the inverter rating, which I believe is 80-500v normal operating range with a max of 600v.

Do you know the spec of your panels?

Yeah, I'm running HA and Modbus. I can view all voltages etc

I've actually completely disconnected PV3 now, which has (temporarily) resolved all issues. However, this has left me with only 50% of my array.

The panels are Eurener MPEV-450. Therein lies some confusion...

I asked a similar question to this on one of my Facebook groups, and a very helpful chap replied with lots of useful info. He stated that these panels have a Voc of 49.98V. 49.98*12=599V which is outside MPPT voltage range (500V?) However, the installer states that the Voc is actually 39.33V, bringing total max voltage to 471.96V not 599V. I then double-checked the datasheet I could find on the web, which shows Voc as 48.03V STC or 45.96V NOCT.

If anyone can clarify for sure what the Voc actually is, I'd be grateful!

[maccoylton]

The spec’s are interesting but what is HA actually recording for that string, particularly at the time the error happens ?

[Kosymodo]

The spec’s are interesting but what is HA actually recording for that string, particularly at the time the error happens ?

Here's a couple of examples...

5 Jan @ 15:13:49 - fault triggered, PV3 473V
5 Jan @ 09:04:55 - fault triggered, PV3 446V

I then noticed that there have in fact been 2 faults this morning (none yesterday at all), with PV3 disconnected...

7 Jan @ 09:21:33 - fault triggered, PV1 238V, PV2 238V
7 Jan @ 09:25:23 - fault triggered, PV1 237V, PV2 238V

I then had a scroll through the history for PV3 and noticed this...

5 Jan @ 08:55:15 - PV3 119V
5 Jan @ 08:55:25 - PV3 444V

That's quite a jump in 10 seconds, right? Also, not sure why a West-facing roof would be showing any activity at all at 08:55?

[maccoylton]

Most sites quote the normal operating range as 80-500V per MPPT with a. max of 600V, FOX data sheet sates normal operating voltage as 360V, and max at 600V.

I'm no expert but Is it really the size of your string given the real world numbers you are seeing?

[Kosymodo]

I'm no expert but Is it really the size of your string given the real world numbers you are seeing?

That's exactly what Fox Support have said - "the voltage on PV3 is too high, which is triggering the fault. You will need to ask the installer to move some of the PV panels from this string to another string/input."

I'm no expert either, but hope they are!

[Dave Foster]

I had a quick look at the panel specs, the 49.98V is the VoC (open circuit voltage), your installer is correct the Vmp is 41.36V at 25C so your operating voltage would be ~496V which in theory is in range at Vmp.

But when it is very cold on a bright day and the MPPT’s are starting up (when panel voltage is nearer V0C) it’s going to be awfully close to the 600V max, Fox support are usually on the ball with this stuff so i’ll keep my fingers crossed.

[maccoylton]

I had a quick look at the panel specs, the 49.98V is the VoC (open circuit voltage), your installer is correct the Vmp is 41.36V at 25C so your operating voltage would be ~496V which in theory is in range at Vmp.

But when it is very cold on a bright day and the MPPT’s are starting up (when panel voltage is nearer V0C) it’s going to be awfully close to the 600V max, Fox support are usually on the ball with this stuff so i’ll keep my fingers crossed.

How do this match up with the issue today with PV3 disabled, or what the inverter is reporting for the voltages?

[Kosymodo]

I had a quick look at the panel specs, the 49.98V is the VoC (open circuit voltage), your installer is correct the Vmp is 41.36V at 25C so your operating voltage would be ~496V which in theory is in range at Vmp.

But when it is very cold on a bright day and the MPPT’s are starting up (when panel voltage is nearer V0C) it’s going to be awfully close to the 600V max, Fox support are usually on the ball with this stuff so i’ll keep my fingers crossed.

Thanks Dave - the installer is actually stating the Voc is 39.33V with Vmpp of 32.71V??? I think they're wrong, but who am I to tell them? This is what they emailed me

Screenshot 2026-01-07 155528.png (5.12 KiB) Viewed 297 times

[Kosymodo]

I had a quick look at the panel specs, the 49.98V is the VoC (open circuit voltage), your installer is correct the Vmp is 41.36V at 25C so your operating voltage would be ~496V which in theory is in range at Vmp.

But when it is very cold on a bright day and the MPPT’s are starting up (when panel voltage is nearer V0C) it’s going to be awfully close to the 600V max, Fox support are usually on the ball with this stuff so i’ll keep my fingers crossed.

How do this match up with the issue today with PV3 disabled, or what the inverter is reporting for the voltages?

I can't answer that. I'm way out of my depth with this

[Dave Foster]

How do this match up with the issue today with PV3 disabled, or what the inverter is reporting for the voltages?

It would only affect PV3, with that disconnected it doesn’t make a lot of sense at the reported voltages - @Kosymodo I would leave PV3 disconnected and make sure Fox investigate the PV1/2 faults.

Thanks Dave - the installer is actually stating the Voc is 39.33V with Vmpp of 32.71V??? I think they're wrong, but who am I to tell them? This is what they emailed me

Screenshot 2026-01-07 155528.png

It could be a different panel you have, but this is what I see for Eurener 450 panels.

[Kosymodo]

I had a quick look at the panel specs, the 49.98V is the VoC (open circuit voltage), your installer is correct the Vmp is 41.36V at 25C so your operating voltage would be ~496V which in theory is in range at Vmp.

But when it is very cold on a bright day and the MPPT’s are starting up (when panel voltage is nearer V0C) it’s going to be awfully close to the 600V max, Fox support are usually on the ball with this stuff so i’ll keep my fingers crossed.

Dave, this is the datasheet I found - https://eurener.com/wp-content/uploads/ ... enafcf.pdf

Specs as below:

[WyndStryke]

I think there are several different 450W Eurener panels, since they tend to supply them in a variety of sizes.

Here's an example of a newer one (54-cell size):

https://midsummerwholesale.co.uk/pdfs/e ... enbace.pdf

And one in the 60-cell size:

https://eurener.com/wp-content/uploads/ ... enafce.pdf

[Kosymodo]

I think there are several different 450W Eurener panels, since they tend to supply them in a variety of sizes.

Here's an example of a newer one (54-cell size):

https://midsummerwholesale.co.uk/pdfs/e ... enbace.pdf

And one in the 60-cell size:

https://eurener.com/wp-content/uploads/ ... enafce.pdf

Oh gosh, how am I to work out what was installed? My MCS certificate shows this, for what it's worth

[Kosymodo]

@Kosymodo I would leave PV3 disconnected and make sure Fox investigate the PV1/2 faults.

I've added this to my open ticket with them

[WyndStryke]

If you google for the 'BABT' code, you'll find this:

https://midsummerenergy.co.uk/pdfs/eure ... -annex.pdf

So there are at least 4 different 450W panels, the one matching the code is the model name ending in 'S'.

[Kosymodo]

If you google for the 'BABT' code, you'll find this:

https://midsummerenergy.co.uk/pdfs/eure ... -annex.pdf

So there are at least 4 different 450W panels, the one matching the code is the model name ending in 'S'.

OK, so I'm looking for a datasheet for MEPV450 S - wish me luck!

[Kosymodo]

@Kosymodo I would leave PV3 disconnected and make sure Fox investigate the PV1/2 faults.

Fox have taken a look, and can't see any errors. They asked me to check in FoxCloud. I confirm I can't see any erorrs there either. However, the errors show within Home Assistant. I therefore asked why I can see errors in HA, but not in FoxCloud, and was told "Home Assistant is a third-party platform. Please rely on the Fox platform as the authoritative source."

On this basis, I guess I just need to ignore the errors shown in HA. If anyone has any ideas why these might show in HA, but not in FoxCloud, please shout!

[Kosymodo]

I've cheekily asked the installer to swap the inverter out for a KH9 (4 MPPTs). We'll see lol!

Result! The installer will be swapping the KH8 for a KH9, and will be restringing the 12 West panels into 2 6-panel strings

[WyndStryke]

Probably best to raise a query or issue on the github?