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Axpert MKS II Parallel Error 72


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Hi there, I am struggling with Fault code 72 when Utility power goes off (Load Shedding) and after a while the inverters go into Fault Code 72 (Current sharing fault). This only happens when the utility goes away. I have managed to do a fault log on both inverters and they are attached:

Any help would be greatly appreciated.

20200711103227.xls 20200711103240.xls 20200711104204.xls 20200711104221.xls

Edited by Louis0852
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20 hours ago, Louis0852 said:

 Fault code 72... This only happens when the utility goes away.

I believe that's to be expected. Only in battery mode (which you are forced to when the utility goes away) does the inverter need to adjust its output voltage to share the current evenly.

20 hours ago, Louis0852 said:

Any help would be greatly appreciated.

Your output voltage seems to vary a lot in battery mode. I have two paralleled inverters, and my output voltage only fluctuates about half a volt at the most; often it's spot on or ±0.1 VAC. I wonder if your AC wiring is strange: different length or gauge of wires, loose connection (e.g. wire(s) not tightly screwed into the terminals), etc.

Of course the other possibility is loose or bad connection of the current sharing wires. I've heard of them coming loose as well.

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1 hour ago, Coulomb said:

I believe that's to be expected. Only in battery mode (which you are forced to when the utility goes away) does the inverter need to adjust its output voltage to share the current evenly.

Your output voltage seems to vary a lot in battery mode. I have two paralleled inverters, and my output voltage only fluctuates about half a volt at the most; often it's spot on or ±0.1 VAC. I wonder if your AC wiring is strange: different length or gauge of wires, loose connection (e.g. wire(s) not tightly screwed into the terminals), etc.

Of course the other possibility is loose or bad connection of the current sharing wires. I've heard of them coming loose as well.

Hi Coulomb, thank you for the response.

I have checked every possible cable issue including cable lengths and gauges and it is as close to identical as I could possibly get it. With regards to the current sharing wires, which ones are you referring to?

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3 hours ago, Louis0852 said:

With regards to the current sharing wires, which ones are you referring to?

There are two sets of cables for paralleling. The current sharing ones are the ones that have two wires, usually black and red. The bottom ones in the photo below. I don't know what they do exactly, but they are intimately connected with the current sharing process (or at least, with checking that current sharing is successful).

I1146792589_800x.jpg?v=1562607081

Photo courtesy of this page: https://www.communica.co.za/products/vp-mks-5kva-parallel-kit .

Edited by Coulomb
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4 hours ago, Coulomb said:

There are two sets of cables for paralleling. The current sharing ones are the ones that have two wires, usually black and red. The bottom ones in the photo below. I don't know what they do exactly, but they are intimately connected with the current sharing process (or at least, with checking that current sharing is successful).

I1146792589_800x.jpg?v=1562607081

Photo courtesy of this page: https://www.communica.co.za/products/vp-mks-5kva-parallel-kit .

Thank you. I have replaced both the red cables of my system but would like to replace the VGA type cables too just to make sure. I would also consider changing the Parallel board if the problem still persists. Thank you for the advice thus far and will keep the thread up to date with what happens

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Hi @Louis0852, I'm currently facing the same issue with 2x Axpert MKS II. I get the error when it's running in battery mode and the PV is almost the same as the load which causes power to flow in and out of the battery.  At that point the inverter output voltage starts getting less stable (jumps between 238 and 220) until it goes into error 72.  The time this usually happens for me is at the end of the day 16:45 when my PV generation starts to match my load (+-400W) for about 10 - 15mins. During that time I have risk of getting error 72.  Earlier in the day my load will have to match higher PV generation which has produced error 72 but is of course much less likely.

In terms of solving this problem: it seems that if I turn of PV generation my inverter output voltage is very stable and won't ever produce error 72.  I'm currently investigating whether the charging volts will make a difference.  I'm running 3x PylonTech US3000.  Are you also running lithium batteries?

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Another important fact is that it only happens at 100% SOC.  The inverter uses a bit of energy of the battery then charges is back to 100% over and over.  I expected a fluctuating battery voltage but it looks stable.

I don't have a chart for it below, but the PV volts did have a sudden drop at the time of error 72. Unsure how it's involved in everything.

image.thumb.png.ed75978defcfe787f9fbbaa95b90d986.png

image.png.58f8b987c29c71237b65e03c69a6f197.png

 

image.thumb.png.09f74f0ba37ad513105134dfae20d1ee.png

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@Coulomb: Thanks to your advice I'm getting closer to the root of the problem. I've discovered if I run in grid mode then the load on the two inverters isn't exactly the same, there is always a 10% - 15% difference as shown below.  Note (1) means inverter one and (2) is inverter two:

image.png.42bd5521c29b89eb5574e74026b964e5.png

 

My AC in/out cables aren't the same length.  The MKS II manual only specifies that the battery cable should be the same length, however the MKS I manual does say AC cables have to be the same length:

image.png.472f785548d0051744e276b76f41eb4a.png 

Another difference in the MKS II manual is that both live and neutral of the inverters go are connected to each other without a breaker:

image.png.d9fbfac717631bdeb23623dac53dcb84.png

While the MKS I manual mentions live is allowed to have a breaker, but not neutral.

image.png.83a67ec3209ccf650d162b50c12ea298.png

 

What is your opinion on:

1) Should AC cables be the same length?  I'm going to make my AC cables the same length to see what it does.

2) Should the live AC out of inverters go through a breaker before it connects to a joined bus? 

 

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1 hour ago, pierre. said:

1) Should AC cables be the same length?  I'm going to make my AC cables the same length to see what it does.

It certainly can't hurt. But a few hundred millimetres difference would not be significant. Mine differ by perhaps 100 mm, and my Axpert MKS share the loads quite well; within a few tens of watts.

1 hour ago, pierre. said:

2) Should the live AC out of inverters go through a breaker before it connects to a joined bus? 

Yes, I would always have a breaker in the AC-out actives. It's just too frightening connecting the outputs without being able to separate them. Plus, you need to protect the cable.

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On 2020/07/21 at 11:35 AM, pierre. said:

@Coulomb: Thanks to your advice I'm getting closer to the root of the problem. I've discovered if I run in grid mode then the load on the two inverters isn't exactly the same, there is always a 10% - 15% difference as shown below.  Note (1) means inverter one and (2) is inverter two:

image.png.42bd5521c29b89eb5574e74026b964e5.png

 

My AC in/out cables aren't the same length.  The MKS II manual only specifies that the battery cable should be the same length, however the MKS I manual does say AC cables have to be the same length:

image.png.472f785548d0051744e276b76f41eb4a.png 

Another difference in the MKS II manual is that both live and neutral of the inverters go are connected to each other without a breaker:

image.png.d9fbfac717631bdeb23623dac53dcb84.png

While the MKS I manual mentions live is allowed to have a breaker, but not neutral.

image.png.83a67ec3209ccf650d162b50c12ea298.png

 

What is your opinion on:

1) Should AC cables be the same length?  I'm going to make my AC cables the same length to see what it does.

2) Should the live AC out of inverters go through a breaker before it connects to a joined bus? 

 

Hi Pierre. Sorry for only getting back to this topic now. What I have decided to do is take out both the inverters and hand them in for Diagnostic or repair if it requires. I assumed it would be a fault on the current sharing side with the cable lengths, but these were rectified prior to me removing the inverters and it still gave me the same error and eventually jumped to an error 9.

My current setup is with 2 Axpert MKS II and 8 Pylontech US2000B batteries. This system worked seamlessly for over a year with little to no faults.

My design will be changed as soon as I receive the inverters back and the following will be the setup that will be installed with a few additions and changes:

3 x Apert MKS II

Reduce the number of PV modules per inverter so that they don't run on their limits most of the time

All load cable gauges and lengths will be exactly the same length up until the point where the join

12 x Pylontech US2000b of 4 batteries per bank

 

I would like to switch off the Grid supply as long and often as I can as the power that is fed through from the Utility is also presumed to be the culprit of previous minor faults.

Is there anything else that anyone can suggest I change to prevent the nasty error 72 from coming up again and any changes that would make my system 100% off grid?

 

Thanks

Louis

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On 2020/07/23 at 8:01 PM, Louis0852 said:

12 x Pylontech US2000b of 4 batteries per bank

? Paralleled Axperts have to use the same battery. So you parallel all 12 battery modules to a bus bar, and run the three inverters from those bus bars. You can't have separate batteries for each inverter.

But perhaps I misread your statement.

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I've made all my wires the same length, problem is still there.  Just confirmed again that the problem only happens when the PV is generating the same amound of power the load needs, meaning battery watts approaches 0 (not positive or negative). At that point the chargers turn off and on repeatedly and output voltage becomes unstable.  Today I turned on a few appliances until the load matches the PV generation and then recorded a video.  Left inverter is showing voltage while right inverter shows charging current.

 

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Question, as I am suffering similar problems.... Does your come out of 72 on its own or do you have to reset the inverters?

I have 2x Axpert Kings that do the same but trip the earth at the same time... I think I have solved the earth problem but need to look into the 72 error now too

Thanks in advance

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On 2020/07/24 at 2:59 PM, Coulomb said:

? Paralleled Axperts have to use the same battery. So you parallel all 12 battery modules to a bus bar, and run the three inverters from those bus bars. You can't have separate batteries for each inverter.

But perhaps I misread your statement.

Hi Coulomb. You are correct as I am referring to 3 banks (4 batteries per cabinet) but acting as one battery.

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3 hours ago, Jay-Dee said:

Question, as I am suffering similar problems.... Does your come out of 72 on its own or do you have to reset the inverters?

@Jay-DeeOne inverter stays active, the slave goes into fault mode.  I have to shut both down to recover from it.

Is your inverter output voltage stable when running in SBU mode? Specifically when the load watts is about the same as the solar PV watts meaning battery watts approaches 0.  If yours is stable in this scenario, then we have different problems.  Mine will sometimes drop to 200V.

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7 hours ago, pierre. said:

@Jay-DeeOne inverter stays active, the slave goes into fault mode.  I have to shut both down to recover from it.

Is your inverter output voltage stable when running in SBU mode? Specifically when the load watts is about the same as the solar PV watts meaning battery watts approaches 0.  If yours is stable in this scenario, then we have different problems.  Mine will sometimes drop to 200V.

Thanks for the feedback. Both of mine go were going into fault mode and needed to be shut down. 

I have since disconnected the parallel setup and was going to abandon it until re-reading your thread. I am going to give it another try today with matching length and gauge cabling as I know this was an issue on my side but is easily rectifiable for me. 

A quick question and sorry in advanced if it is obvious... Where are you puling the logs from? Watch Power? If so, is there anything that needs to be enabled to store logs...?  I have ICC monitoring my setup at the moment, so have not been using WatchPower... may need to arrange a PC / Laptop in the garage to monitor if needed.

Thanks in advanced

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  • 5 months later...
On 2020/07/15 at 5:48 PM, Denarius said:

Hi @Louis0852, I'm currently facing the same issue with 2x Axpert MKS II. I get the error when it's running in battery mode and the PV is almost the same as the load which causes power to flow in and out of the battery.  At that point the inverter output voltage starts getting less stable (jumps between 238 and 220) until it goes into error 72.  The time this usually happens for me is at the end of the day 16:45 when my PV generation starts to match my load (+-400W) for about 10 - 15mins. During that time I have risk of getting error 72.  Earlier in the day my load will have to match higher PV generation which has produced error 72 but is of course much less likely.

In terms of solving this problem: it seems that if I turn of PV generation my inverter output voltage is very stable and won't ever produce error 72.  I'm currently investigating whether the charging volts will make a difference.  I'm running 3x PylonTech US3000.  Are you also running lithium batteries?

Hi Denarius I have been experiencing Error 72's at a site where we have 8 Axpert MKS II's running in parallel charging 31 x PylonTech US3000's. 

The environment is a totally off-grid data center and the installation is almost clinical. My finding are that as the PylonTech's almost reach 100% SOC bang we get the Error 72.

We tested this with both charging via PV as well as with a Generator. Same results same time - as we were almost at 100% SOC. Strangest thing is that this may occur 9 x on the same day on the same inverter or anyone of the 8 inverters. It also may every day or weeks apart. 

After checking electrical cables, connections, everything x 10 we approached Voltronic whom eventually released a firmware update which we applied. Results were it got worse, then stabilized for 10 days then reoccurred 9 times a day then disappeared for a week then reoccurred again. Ongoing and unresolved. Voltronic are aware of the problems and have been busy with various test to try and overcome the issues but the problems still persists. 

Keen to know brand of inverter (you can email me at [email protected])

We have changed inverters, communications cables, swopped inverters around, changed charge setting to Victron and other settings. There are other sites similar to mine experiencing same issues with MKS II's running in Parallel.  

 

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On 2021/01/05 at 5:22 AM, Geoff Earnshaw said:

Hi Denarius I have been experiencing Error 72's at a site where we have 8 Axpert MKS II's running in parallel charging 31 x PylonTech US3000's. 

The environment is a totally off-grid data center and the installation is almost clinical. My finding are that as the PylonTech's almost reach 100% SOC bang we get the Error 72.

We tested this with both charging via PV as well as with a Generator. Same results same time - as we were almost at 100% SOC. Strangest thing is that this may occur 9 x on the same day on the same inverter or anyone of the 8 inverters. It also may every day or weeks apart. 

After checking electrical cables, connections, everything x 10 we approached Voltronic whom eventually released a firmware update which we applied. Results were it got worse, then stabilized for 10 days then reoccurred 9 times a day then disappeared for a week then reoccurred again. Ongoing and unresolved. Voltronic are aware of the problems and have been busy with various test to try and overcome the issues but the problems still persists. 

Keen to know brand of inverter (you can email me at [email protected])

We have changed inverters, communications cables, swopped inverters around, changed charge setting to Victron and other settings. There are other sites similar to mine experiencing same issues with MKS II's running in Parallel.  

 

Hi Geoff

Before I upgraded my firmware, I noticed the power balance setting slightly improves the situation:

image.png.a059a2d8e9d2315c100cdb66b73a4dca.png

 

Then after upgrading the firmware as described in the topic below the error hasn't happened again.  It seems the inverters try to squeeze less watts out of the MPPT but achieves more stability.  My inverter brand is Full Circle Solar which is Voltronic.

Are you also on firmware 71 82 or later?

 

I also switched from ICC to solar assistant for monitoring, but I doubt that monitoring has an effect on inverter performance.

image.thumb.png.1d5bec01c4ca666044b08d46fd09b07e.png

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