3.25kWP Risen panels ;  Battery Pylontech US2000C x 2 ; Inverter Axpert MKS II 5kW

Hi, haven't been on the forum for a year or two but I did a few threads mainly in 2020-2022 with various problems and questions.

My current issue is that the inverter sometimes fails (or at least that's where the error is displayed) causing a power cut. The problem can be solved by turning everything off and back and on again. The power cuts only happen with a low battery (except once), and the transition from battery to grid seems to be a problem. The power cuts seem to happen in the middle of the night or early morning requiring a reset when waking up. Every time it happens I have to go to the back of the garden and reset the time on the watering system.

I actually separated from my wife and kids so I don't live there any more (I am 5 minute walk away though) meaning our tolerance for power cuts and resets is lower than before, and I can't manage the system any more during the day to keep the battery level high.

My inverter does not communicate with my batteries. This may be causing the problem. In this case Coulomb said in the first comment on the 2022 thread 'Are Pylontech UP5000 and US3000C compatible with Axpert MKS II 5kW?' that "if one cell gets over- or under-voltage, the BMS can't tell the inverter to back off with charging or with loads, so it might have to disconnect itself. But hopefully those cases should be quite rare." I wonder if this is the main issue here, since some of the errors are fault code 08 'Bus voltage is too high'. Would that be the expected error when the system disconnects itself for the error Coulomb described above. At least once the error was "BP" battery not connected.

A few ideas I have are:

1 Get a solar specialist to come by and recommend action.

2 Buy new inverter.

3 Get a new circuit bypass . connection or whatever you call it so that in the event of an inverter or battery fail all of that can be automatically bypassed and automatically connect the house to the grid without going through the inverter. At the moment, if the inverter is off or the battery is off there is a power cut even if there is grid connection available.

I suspect buying a new inverter will have a moderate to high chance of fixing the problem, but it will be quite expensive, especially considering we are renting the house, and might leave next year.

Any easy inexpensive solution would be welcomed obviously!

I think there's some software/monitoring solution that's been mentioned before but I never really understood it. If you think that's the solution, you'll have to imagine you're talking to a 5-year old child or an idiot and explain in as much detail as possible, as otherwise it's just gibberish to me. Thanks if you can help.

Edited December 20, 20241 yr by Green Power

6 hours ago, Green Power said:

3.25kWP Risen panels ;  Battery Pylontech US2000C x 2 ; Inverter Axpert MKS II 5kW

Hi, haven't been on the forum for a year or two but I did a few threads mainly in 2020-2022 with various problems and questions.

My current issue is that the inverter sometimes fails (or at least that's where the error is displayed) causing a power cut. The problem can be solved by turning everything off and back and on again. The power cuts only happen with a low battery (except once), and the transition from battery to grid seems to be a problem. The power cuts seem to happen in the middle of the night or early morning requiring a reset when waking up. Every time it happens I have to go to the back of the garden and reset the time on the watering system.

I actually separated from my wife and kids so I don't live there any more (I am 5 minute walk away though) meaning our tolerance for power cuts and resets is lower than before, and I can't manage the system any more during the day to keep the battery level high.

My inverter does not communicate with my batteries. This may be causing the problem. In this case Coulomb said in the first comment on the 2022 thread 'Are Pylontech UP5000 and US3000C compatible with Axpert MKS II 5kW?' that "if one cell gets over- or under-voltage, the BMS can't tell the inverter to back off with charging or with loads, so it might have to disconnect itself. But hopefully those cases should be quite rare." I wonder if this is the main issue here, since some of the errors are fault code 08 'Bus voltage is too high'. Would that be the expected error when the system disconnects itself for the error Coulomb described above. At least once the error was "BP" battery not connected.

A few ideas I have are:

1 Get a solar specialist to come by and recommend action.

2 Buy new inverter.

3 Get a new circuit bypass . connection or whatever you call it so that in the event of an inverter or battery fail all of that can be automatically bypassed and automatically connect the house to the grid without going through the inverter. At the moment, if the inverter is off or the battery is off there is a power cut even if there is grid connection available.

I suspect buying a new inverter will have a moderate to high chance of fixing the problem, but it will be quite expensive, especially considering we are renting the house, and might leave next year.

Any easy inexpensive solution would be welcomed obviously!

I think there's some software/monitoring solution that's been mentioned before but I never really understood it. If you think that's the solution, you'll have to imagine you're talking to a 5-year old child or an idiot and explain in as much detail as possible, as otherwise it's just gibberish to me. Thanks if you can help.

Based on the info available my guess is the load is too high for the inverter and batteries you have to run the whole house. 

Get someone to keep high power items on the grid at all times. Thus only essentials on the inverter. Even with a new inverter you might have comms etc on a APP but if the storage capacity is the problem any inverter would not be connected all the time. 

A 2nd point is for an reputable installer to see why the current inverter does not just switch to grid when battery gets low on discharge. 

Many other ideas can follow. These are just my thoughts. 

23 hours ago, Green Power said:

some of the errors are fault code 08 'Bus voltage is too high'.

That is often caused on these high PV voltage models (99.5% of them now) by leakage to earth from the panels. So you might try disconnecting the panels one night and see if that helps. If you know what you're doing you could inspect the PV wiring and connectors; there may be one cracked, dipping into a puddle of water, etc. It can also be the panels themselves.

Some people actually use a gizmo that disconnects the panels at night automatically.

I have no experience with this problem; all my panels are low voltage (2S, two panels in series).

Thanks @Colulomb you said a couple of years ago, as I mentioned above, I think in relation to no communication between inverter and battery that "if one cell gets over- or under-voltage, the BMS can't tell the inverter to back off with charging or with loads, so it might have to disconnect itself". We are getting 08 bus voltage errors so do you think the issue would be solved with a new inverter that has communication?

20 hours ago, Green Power said:

We are getting 08 bus voltage errors so do you think the issue would be solved with a new inverter that has communication?

I doubt that these bus voltage errors would be fixed this way. You get no control if the BMS calls the shots. 

I would first experiment with battery voltage settings, especially the bulk/absorb/CV and float voltage settings. Often these are too high, as the battery manufacturers tend to recommend. They are more interested in making their products appear to last longer than whether it causes problems with real-world inverters. 

On 2024/12/20 at 4:46 AM, Scorp007 said:

Based on the info available my guess is the load is too high for the inverter and batteries you have to run the whole house. 

Get someone to keep high power items on the grid at all times. Thus only essentials on the inverter. Even with a new inverter you might have comms etc on a APP but if the storage capacity is the problem any inverter would not be connected all the time. 

A 2nd point is for an reputable installer to see why the current inverter does not just switch to grid when battery gets low on discharge. 

Many other ideas can follow. These are just my thoughts. 

Thanks for that. I'm a little reluctant to take high power items onto the grid because it does have some disadvantages, it would cause more pollution and climate change, and cost more money. It would also require some hassle to setup. I am not even sure how I would go about that, but as a minimum it feels like some electrical wiring is needed to achieve it.

The load tends to vary between 60W and 2200W mostly but there can be 2200-3000W for half an hour here and there when people are doing kitchen things and maybe 4000-5000W but that's usually just a few minutes when someone adds kettle or microwave onto existing loads. I assume total power draw to the house, and consequently to the inverter, is what you mean by loads. However the power cuts are happening during the night when the load is around 60W or 100W.

11 hours ago, Coulomb said:

I doubt that these bus voltage errors would be fixed this way. You get no control if the BMS calls the shots. 

I would first experiment with battery voltage settings, especially the bulk/absorb/CV and float voltage settings. Often these are too high, as the battery manufacturers tend to recommend. They are more interested in making their products appear to last longer than whether it causes problems with real-world inverters. 

Here are the inverter settings:

Note that although the thread is from 2022 I still have the same settings now.

26. Bulk charging voltage is 52.5V and 27 Floating charging voltage is 52.5V Any suggestion here? The most common error I get is "Bus Voltage is too high".

I don't really understand the relationship between "bulk" voltage and "floating" voltage and "bus" voltage. if I reduce the "bulk" or "floating" will it stop bus voltage getting too high?

Pylontech said in the past that lower than 52.5V float is OK, but not higher.

ME: If float charging voltage of 52.5V is OK, then I guess a lower float voltage 51.0V or 52.0V might be OK for charging to less than 100%. But never >52.5V. Do you agree?

Pylontech: (That's correct! Because sometimes the voltage sensors on the inverter terminals are not very accurate, the full battery voltage is around 53.2V(smaller than 54V). So 52.5V is a charge voltage value that has been limited in a safe range! You do not need to worry about this. )

 

However, isn't higher voltage associated with higher charge? Most of my power cuts are happening at low % charge, but the error says high bus voltage.

You might try process of elimination to actually determine what is causing bus voltage high error. Disconnect the utility input from the inverter by means of utility input breaker switched off. It seems this error comes up during the evening according to your comment above. Will it be possible to run on battery for the duration of the night? If the error F08 persist after utility input disconnection then disconnect pv input by isolating the pv array via the combiner panel fuses or breaker. If the F08 error still comes up when running only on battery then you might have a faulty inverter.

 

On 2024/12/24 at 7:24 AM, Green Power said:

I don't really understand the relationship between "bulk" voltage and "floating" voltage and "bus" voltage.

There is a DC-DC converter inside the inverter, between the ~50 VDC battery, and the ~400 VDC bus. The bus voltage gets chopped into a sine wave for the AC output. It can vary somewhat, between a minimum of about 350 V and a maximum of about 500 V. As the bus voltage goes up and down, the DC->AC converter adjusts to keep the AC output voltage fairly steady.

Your problem is mostly when in battery mode, it seems; so the battery is supplying the load. In this state, the DC-DC converter has a fixed voltage ratio; lets call it 8x for ease of maths (is likely actually around 7.0-7.5). So as long as the battery voltage is less than 54.0 V, the bus voltage will be less than 432 V, and all is well. The problem is if the battery BMS decides to disconnect the battery from  the inverter; it has MOSFETs to do that. It does this to save the cells from damage. Suppose that the battery is badly unbalanced, and one cell is lower voltage than all the others. When this cell reaches say 2.8 V, the battery BMS would usually be sending an urgent command to the inverter to shut down. But if you don't have the BMS to inverter cable, either direct or via a monitoring Raspberry Pi etc, then the only thing that the battery BMS can do is to disconnect the battery from the inverter. That saves the cell, but what happens at the inverter? It had a nice stiff battery to keep the battery voltage at a steady level, now suddenly it does not. The battery terminal voltage will likely plummet. At this point, it's not clear what happens. Usually it should stop with fault code 04, battery low, or BP warning (battery not present). But it might attempt to blend in power from AC-in. If it does, it could overshoot, and put way too much voltage at the battery terminals. If the battery terminal voltage goes over about 62.5 V, then the bus voltage could go over 500 V. That's my guess. Though if the battery is getting charged, then the buck converter comes into play, and things get more complicated.

As for the bulk and floating voltages, these are merely settings. The bulk voltage setting is the value that the inverter aims to keep at or below when bulk charging (which is most of the time at the start of a charge). When the battery voltage reaches this level for a certain amount of time, the so-called absorb stage, then the battery is considered full, and the inverter just wants to keep the battery nearly full despite varying loads and varying solar. That's the so-called float stage, when the inverter attempts to keep the battery voltage at or below the float voltage setting. Usually this value is lower than the bulk voltage setting, but you have them at the same value. Earlier in this thread I suggested that you reduce the float voltage setting to about 51.8 V; the battery lives at this voltage for many hours a day, and this lower voltage will allow the battery to last longer (lower degradation), at the expense of a half percent or so of run time each day. At this lower voltage setting, it's also less likely that the inverter will overcharge the battery. for example after a large load comes off. It's possible that these situations could trigger bus voltage errors, though it doesn't seem to match your case.

On 2024/12/24 at 1:34 PM, TaliaB said:

You might try process of elimination to actually determine what is causing bus voltage high error. Disconnect the utility input from the inverter...

Yes, good idea. It could disprove or strengthen my guess above.

Or as I suggested earlier, disconnect the solar input at night for a night or few. Especially if the solar panels are wet. Electrical leakage to earth on these models somehow leads to high bus voltage. But do this separately to the utility disconnection, otherwise you won't know which change led to the change (if any). This solar panel electrical leakage is my other guess.

Edited December 25, 20241 yr by Coulomb

Hi, I changed the float voltage setting to about 51.8 V. We can try disconnecting the utility/panels at night although it could take weeks to get a useful answer from that if the power is cutting out once a week or so.

One of the panels was slightly burnt (scorched) some months back. I had someone come by to look at it and they said that there was a small fire in the wiring and that had reached the panel rather than the panel itself set on fire. And that the fire was caused by heavy rains that affected the wiring somehow. They replaced some wiring, and determined that it wasn't necessary to replace the panel.

I suspect this is not related since the errors are happening more recently rather than at that time.

11 hours ago, Green Power said:

I suspect this is not related since the errors are happening more recently rather than at that time.

Fair point. But has it been rainy recently in your area? We had a rainy start to summer here, dry and hot for the last week, but Chile is a looong way away.

It hasn't rained at all for maybe a couple of months.

Ok. The MKS II 5 kW is quite an old model by now. So  I'm now guessing that the capacitors have dried up inside.

If you are handy with electronics, it can be a fairly economic job to replace the usual suspects, and that might keep it going for several more years. The relevant information is in this post (scroll past the first photo), for you or for someone that you call in.

Otherwise, yes, it might be time to replace that inverter.

I’d suggest getting in touch with after-sales support—they might be able to help fix the issue. Or, you could look into getting another Axpert inverter, which works with your current batteries, or a Solis inverter, which is compatible with most batteries out there. This could be a cost-effective way to sort things out.

On 2024/12/24 at 12:34 AM, TaliaB said:

You might try process of elimination to actually determine what is causing bus voltage high error. Disconnect the utility input from the inverter by means of utility input breaker switched off. It seems this error comes up during the evening according to your comment above. Will it be possible to run on battery for the duration of the night? If the error F08 persist after utility input disconnection then disconnect pv input by isolating the pv array via the combiner panel fuses or breaker. If the F08 error still comes up when running only on battery then you might have a faulty inverter.

 

@TaliaB @Coulomb (+please feel free to jump in anyone else of course).

I have a panel switch. It is a big thing you flip up and down, possibly called an isolator/interrupter. When you flip it for some reason solar panel power can't be provided directly to the house/inverter.

Since my last post this switch was disconnected every night for 10 days in a row (off/down 9pm-10pm, back on/up in the morning). When this was done, there were no power cuts overnight, or at any time, for the whole 10 days.

After that, that panel switch was left continually up night and day for 4 days and there were 2-3 power cuts, all overnight.

So it seems likely that something at the panels, or in the connection from the panels to elsewhere is causing power cuts at night, even with zero power being generated from the panels at that time. Could that make sense?

What should I do now do you think, to avoid having to manually flip that switch all the time. I don't have any equipment - even an amp/volt meter. Could a regular electrician make some measurements to diagnose and solve the issue if one of you provides directions, or should I call a solar expert. I could also call the person that installed the system and they could come up send someone else, however the system has had many errors and issues during its years of operation, and I'm past the point of getting free fixes, so not sure if that is the best course of action. A new solar expert would be harder to find than a regular electrician for me at this time, so keep that in mind. I can do it if necessary though.

Edited January 21, 20251 yr by Green Power

On 2025/01/01 at 10:28 AM, Coulomb said:

Ok. The MKS II 5 kW is quite an old model by now. So  I'm now guessing that the capacitors have dried up inside.

If you are handy with electronics, it can be a fairly economic job to replace the usual suspects, and that might keep it going for several more years. The relevant information is in this post (scroll past the first photo), for you or for someone that you call in.

Otherwise, yes, it might be time to replace that inverter.

Not handy with electronics. A little reluctant to replace the inverter as it will be annoying if I spend say US$800 (I'm guessing the price) and it doesn't solve the problem. Also, there is probably a 50% chance we'll move out of the rented house this year and a 80% chance within 4 years. So we could end having to sell off the inverter for a fraction of the spend not long after.

Also, looking at my above post, I'd interpret that for the time being as the inverter being most likely not the source of the problem?

On 2025/01/13 at 7:17 AM, Green Power said:

So it seems likely that something at the panels, or in the connection from the panels to elsewhere is causing power cuts at night, even with zero power being generated from the panels at that time. Could that make sense?

Yes, that makes perfect sense. There will be leakage to earth somewhere in the panel wirings or one or more panels. This somehow pushes up the bus voltage, and the inverters stop with a fault code (often F08) to protect themselves.

On 2025/01/13 at 7:17 AM, Green Power said:

What should I do now do you think, to avoid having to manually flip that switch all the time.

The fact that the fault doesn't show during the day suggests to me that it's a condensation issue. You might be able to find the problem yourself merely by inspection, but there are lethal voltages up there. The problem is that these are not straight forward faults; it might take a clever solar expert to find it.

On 2025/01/13 at 7:20 AM, Green Power said:

A little reluctant to replace the inverter as it will be annoying if I spend say US$800 (I'm guessing the price) and it doesn't solve the problem.

Definitely sort out what's on the roof first, because the next inverter will likely have the same problem.

On 2025/01/12 at 11:17 PM, Green Power said:

Could a regular electrician make some measurements to diagnose and solve the issue if one of you provides directions, or should I call a solar expert.

Yes a electrician could do an insulation resistance test on the solar system using a normal Megger tester and provide you with an solution. This method will take time as individual solar panels needs to be tested isolated from the solar wires and mc4 connectors. Should all the panels pass the IR(>2MΩ, test, then all the wiring needs to be tested. 

A solar expert with a string maintenance tester could pin point your problem within a short period of time with 1 test and all components intact. My company have invested in this tester very very expensive but worth while in the long run. Maybe you can enquire of such a solar expert with a string maintenance tester. Below picture of the tester and connection diagram as how it pin points the fault.

 

Edited January 14, 20251 yr by TaliaB

Thank you both. I've reached out to a local electrician and the person that installed the system. If that doesn't work I'll hunt for another solar expert.

And feel free anyone else to comment, thanks.

Edited January 15, 20251 yr by Green Power