Hi

  First of all, I apologize for the length, but I wanted to share all the details I have.

  - I have a system of 6 inverters (InfiniSolar 15K) in parallel, with a total of 50 kW of solar panels (the first unit is 2 String, and 1 String for each of the remaining units, 15 pv per strin, with about 634 volts), and 20 Lithium-ion battery (48V 96Ah)

  Note 1:

  With these details, we see that the inverters are not equal in capacity of the solar panels (the first unit is more than the rest of the units), yet the system works perfectly without any errors.

  Yesterday, I upgraded the system by adding about 20 kilowatts pv (distributed among 5 inverters, 1 String for each unit, about 416 volts).

  Note 2:

  With this upgrade, fault 72 started appearing frequently.

  What I noticed in several posts is that there is a common thing, which is that this error appears at the end of the day or at 100% SOC (this is what happens to me as well), and this is what prompted me to the following:

  (I know what I'm saying here doesn't make sense, but maybe this is the solution 😅)

  Tomorrow I will reconnect the new solar panels so that all the strings have the same voltage as the old strings (as much as possible), and I will let you know the results after making the adjustments

 

  my regards

I think that fault code 72 is a current sharing fault (I'm away from the keyboard at present). So my wild guess is that the new wiring has disturbed the paralleling boards, or more likely their wiring or connectors. Particularly the black and red twisted cables, as these directly pertain to current sharing. So these should be checked carefully.

It's possible that the extra charge current is causing extra voltage drops across the battery cables, and that might be upsetting the firmware. So you may care to check for differences in battery voltage, perhaps measuring positive to other inverter positive, etc. It may be necessary to beef up some or all of the battery cables. Either replace existing with thicker, ir add cables in parallel if you can fit all the lugs. I'm sure you will want to leave that as a last resort. 

 

I think that fault code 72 is a current sharing fault (I'm away from the keyboard at present). So my wild guess is that the new wiring has disturbed the paralleling boards, or more likely their wiring or connectors. Particularly the black and red twisted cables, as these directly pertain to current sharing. So these should be checked carefully.

@Coulomb Thank you for your topic.

 Actually what you are saying is actually true, error code 72 is the current sharing error.

 I checked the current sharing cables as you mentioned, and I also checked all the connections, and they are all in good condition.

I have done the upgrade that I talked about in my previous topic (make all solar panel strings for all inverters as equal voltage as possible).

Until this moment, error 72 has not appeared again.

I know this solution method doesn't make sense (at least to me 😅), but I hope to find help from those who have experience with inverter interior design in order to understand why this method works (for now).

 

I know this solution method doesn't make sense (at least to me) 

As I mentioned, it could be changing how much current flows through various battery cables. Though I'll admit that PV voltage should have little effect compared to the total number of panels on each inverter. 

Hopefully I'll get a chance soon to see exactly what can provoke fault code 72. Though I haven't explored the Infinisolar firmwares nearly as much as the Axperts'. 

 

Hopefully I'll get a chance soon to see exactly what can provoke fault code 72...

Well, I don't have a 15 kW firmware, the 10 kW firmware that I have is very old and doesn't seem to mention fault code 72. The old Super 4 firmware does mention it, and it seems to be associated only with the parallel current sharing, nothing to do with battery voltage or the like.

Sorry, that's all I have.

Hi, I have been following this discussion for a long time. Now, I am also a "victim"...

 

I have 3 Axpert 5NB PF1 (Mecer brand) inverters, which have been running fine for at least two years. They are connected to three strings of 397V, 397V and 270V panel configs. Last week, I added three more panels to the low string, which now runs at 390V. Since this upgrade (did not touch anything inside), I get error 72 whenever my batteries (12 X US3000 Pylon) gets to 100%SoC. I run ICC monitoring software, and you can see when the green solar line dips from around 10kW to load wattage, the one inverter (always #2) errors. At this time, my LED lights in the house also go crazy and you can see serious jitter on the output voltage of the inverter.

I spoke to Mustek, who sent me new firmware (71.92) - which I will flash later. I am running 71.86 at the moment.

I had a quick look at 71.86 (for MKS II, there are several overlaps), and it seems that fault code 72 can only occur when the output from a particular inverter is quite far from the expected.

Perhaps you can confirm, by watching the AC output current for the three inverters, either from their front panels, or via monitoring software?

Is it possible that the AC output wiring for this particular inverter was disturbed with recent changes, like adding the new panels?

The only other thing I can think of  is that with the higher PV voltage, you will end up with higher bus voltage, so the control system for output current will be extra twitchy. Though obviously no higher than the other two inverters. Maybe that inverter's bus capacitors are marginal, or some other aspect of the control system.

I doubt that new firmware will fix the issue, but I'm ready to be proved wrong.

What I noticed in several posts is that there is a common thing that this error appears at sunset or at 100% SOC or in cloudy weather.

In other words, in these three cases we have a rise in voltage with a decrease in current.

I think this causes a difference in current at the output of each inverter (taking into account that the efficiency of the internal components of the inverters is not 100% identical).

Any body found the solution? I have the same problem that happend twice, different conditions. Once was when i first connected the inverters in parallel, and then happend one day, with grid, with solar and a 100% soc. Only one inverter get into fault mode 72. I have to completly shut off both inverters to get the error gone and one thing i notice is that: my starting procedure was. 
turn on batteries, turn on grid, turn on PV, and the flip the load switch. As soon as i hit the second load switch that one goes into error 72, so i start again the turn on procedure, but this time i turn both load when the inverter was on the countdown to start, and magic i have power i both inverters. 
my sytem is 2 axpert max ii 10kw, 2 grid , 2 loads, same battery pack. If anyone has any idea for this, would be great

Edited October 3, 20241 yr by Tsmithf

On 2024/10/03 at 11:04 AM, Tsmithf said:

my system is 2 axpert max ii 10kw, 2 grid , 2 loads, same battery pack.

When you say two loads, do  you mean that you have separate loads, i.e.  you are not actually connecting the two inverter outputs in parallel?

Same with 2 grids: do you mean both  inverters have a  connection to the same grid, or you have two independent  sources of AC power?

I'll assume for now that you are actually  paralleling them,  with the paralleling boards installed, and the grey and red/black  wires are connected properly. Fault code 72 seems to be about the sharing of current between the paralleled inverters. Do you have very similar cable lengths from the inverters to where  the outputs are paralleled? If you have a daisy chain situation, then one inverter will have to provide much more of the load than the other.

Are you confident that the current sharing cables (the red and black twisted wires) are correct and tight?

BTW, an Axpert Max II (10 kW) is a rather different model than an Axpert MKS II (usually 5 kW).

1 hour ago, Coulomb said:

When you say two loads, do  you mean that you have separate loads, i.e.  you are not actually connecting the two inverter outputs in parallel?

Same with 2 grids: do you mean both  inverters have a  connection to the same grid, or you have two independent  sources of AC power?

I'll assume for now that you are actually  paralleling them,  with the paralleling boards installed, and the grey and red/black  wires are connected properly. Fault code 72 seems to be about the sharing of current between the paralleled inverters. Do you have very similar cable lengths from the inverters to where  the outputs are paralleled? If you have a daisy chain situation, then one inverter will have to provide much more of the load than the other.

Are you confident that the current sharing cables (the red and black twisted wires) are correct and tight?

BTW, an Axpert Max II (10 kW) is a rather different model than an Axpert MKS II (usually 5 kW).

Hi Coulomb, i have both invertes in paralell so i can share the battery bank. But the have different load and different AC input. The system works great, but i seem to found the problem. When you are in SBU and you are consuming more than the solar and battery can give you, the system doesnt get a third input involve ( grid ). I connect the system to solar assistant and home assistan a looking into the graphs i realize this. I have only 4.400 kw per inverter now so when the load exceed this it will drain battery right? But i had the inverters at 130amp max discharge current and then go to grid, but when solar is high and batteries are full, the system doesnt go the grid. Next month i will be installing more panels to get to 10k each inverters then im sure that the problem will go away. 

On 2024/10/06 at 12:09 AM, Tsmithf said:

Hi Coulomb, i have both invertes in paralell so i can share the battery bank. But the have different load and different AC input. The system works great, but i seem to found the problem. When you are in SBU and you are consuming more than the solar and battery can give you, the system doesnt get a third input involve ( grid ). I connect the system to solar assistant and home assistan a looking into the graphs i realize this. I have only 4.400 kw per inverter now so when the load exceed this it will drain battery right? But i had the inverters at 130amp max discharge current and then go to grid, but when solar is high and batteries are full, the system doesnt go the grid. Next month i will be installing more panels to get to 10k each inverters then im sure that the problem will go away. 

Hi, i found the problem in my setup, do cause i have different load, the sharing load cable should not be connected. i allways said to everybody else always read the manual full, well i didnt read it all of it.

 

i need to do it like this in order nothave the error. 3 days and no error still

Ah! Three phase. I was thinking actual paralleled. I should have realised when you talked about separate loads and AC sourcrs. Sigh.