Akif

So wanted to say a huge thank you to @BritishRacingGreen for coming to my rescue and reviving 3 of the 4 Axpert inverters that I had sent to him. 

Boy oh boy am I glad I got in touch with him as I was given some serious doom and gloom stories from a solar dealer in Malawi that the boards on all the inverters were fried and they could only be repaired by changing these at a great cost! I did my own research and contacted @BritishRacingGreenwho was an absolute scholar and gentleman and has been amazing in this journey and gave me some sound advice whilst he repaired them. 

Happy to say the 3 are back home now and been up and running for the last couple of weeks and are working perfectly. So glad to have them back. Am sure @BritishRacingGreenwill come up with a plan for the 4th one in due course. 

Thanks again Sir and so glad we met. 

So wanted to say a huge thank you to @BritishRacingGreen for coming to my rescue and reviving 3 of the 4 Axpert inverters that I had sent to him. 

Boy oh boy am I glad I got in touch with him as I was given some serious doom and gloom stories from a solar dealer in Malawi that the boards on all the inverters were fried and they could only be repaired by changing these at a great cost! I did my own research and contacted @BritishRacingGreenwho was an absolute scholar and gentleman and has been amazing in this journey and gave me some sound advice whilst he repaired them. 

Happy to say the 3 are back home now and been up and running for the last couple of weeks and are working perfectly. So glad to have them back. Am sure @BritishRacingGreenwill come up with a plan for the 4th one in due course. 

Thanks again Sir and so glad we met. 

Thank you so much @Akif, I am just glad you had the patience for waiting  the number of weeks I had the machines in my possesion. It was a valuable exersize for me, so thanks once again.
And the 4th has had a terrible surge which destroyed all 9 IGBT including some drivers, but is remains my endeavour to bring it up some time in hopefully not too distant future. 

So wanted to say a huge thank you to @BritishRacingGreen for coming to my rescue and reviving 3 of the 4 Axpert inverters that I had sent to him. 

Boy oh boy am I glad I got in touch with him as I was given some serious doom and gloom stories from a solar dealer in Malawi that the boards on all the inverters were fried and they could only be repaired by changing these at a great cost! I did my own research and contacted @BritishRacingGreenwho was an absolute scholar and gentleman and has been amazing in this journey and gave me some sound advice whilst he repaired them. 

Happy to say the 3 are back home now and been up and running for the last couple of weeks and are working perfectly. So glad to have them back. Am sure @BritishRacingGreenwill come up with a plan for the 4th one in due course. 

Thanks again Sir and so glad we met. 

So wanted to say a huge thank you to @BritishRacingGreen for coming to my rescue and reviving 3 of the 4 Axpert inverters that I had sent to him. 

Boy oh boy am I glad I got in touch with him as I was given some serious doom and gloom stories from a solar dealer in Malawi that the boards on all the inverters were fried and they could only be repaired by changing these at a great cost! I did my own research and contacted @BritishRacingGreenwho was an absolute scholar and gentleman and has been amazing in this journey and gave me some sound advice whilst he repaired them. 

Happy to say the 3 are back home now and been up and running for the last couple of weeks and are working perfectly. So glad to have them back. Am sure @BritishRacingGreenwill come up with a plan for the 4th one in due course. 

Thanks again Sir and so glad we met. 

So wanted to say a huge thank you to @BritishRacingGreen for coming to my rescue and reviving 3 of the 4 Axpert inverters that I had sent to him. 

Boy oh boy am I glad I got in touch with him as I was given some serious doom and gloom stories from a solar dealer in Malawi that the boards on all the inverters were fried and they could only be repaired by changing these at a great cost! I did my own research and contacted @BritishRacingGreenwho was an absolute scholar and gentleman and has been amazing in this journey and gave me some sound advice whilst he repaired them. 

Happy to say the 3 are back home now and been up and running for the last couple of weeks and are working perfectly. So glad to have them back. Am sure @BritishRacingGreenwill come up with a plan for the 4th one in due course. 

Thanks again Sir and so glad we met. 

These are RCT branded, and we know that RCT is a genuine reseller. But the MKS II is a fairly old model, though now favoured by clone makers. Is it possible that RCT, desperate to get stock in difficult times, resorted to importing clones? Does the sticker look genuine?
Or perhaps these are just old. What is the manufacturing date?
It may be just the battery-side capacitors, in conjunction with 75 V MOSFETs in those days, causing the whole power train to blow. Can you see any obvious MOSFET destruction?
This is a great repair story in the making; thanks for sharing it.

UPDATES : REPAIR : 4 x RCT MKS2  Inverters Received from Malawi
Machine MR3 : 
When I unboxed machine MR3 , it appeared to have no defect . However I decided to let it burn-in for a while , and eventually it started to click inadvertently the same as MR1 and MR 2. This is good news for me under the circumstances. So it turned out that I have received 3 machines with identical problem as the one I repaired for Cape Town . I believe the 5V supply filter capacitor had still some last breathe left , because initially the clicking cycle was slow , and gradually increased in frequency , so the last drop of electrolyte  had literally evaporated. While the fix is straight forward by now , it raises a new issue in general : How do we asses Electrolytic  and measure the capacitor's degradation , in order to asses whether we can still  revive the machine to lets say operate for 3-5 years. I will cover this in  a next post. 
So out of 5 MKS2 machines I have received so far , no less than 4  has this failure mode. How many more is out there in the wild that is failed like this , or in waiting . Interesting.
 
Machine MR4 :
Axpert Error Code  F09 is the one that's gets me going. It mostly throws everything but the kitchen sink at you . IGBT failure , IGBT driver failure , IGBT driver transformer failure , MOSFET failure etc. So I opened the lid hastily , and after going thru the standard procedure of disassembly of the inner , the main board indeed exposed destructed/exploded  IGBT's . In fact , all 9 IGBTS have blown and damaged, including the 4 on the HF DC-DC full bridge  , the 4 on the DC-AC Full bridge , as well as the Buck IGBT . I have never seen this level of destruction , typically the DC-AC full bridge but not the others . So that makes one wonder , what was the initial cause of this big-bang.?     In order to assess whether this machine is still serviceable , I will have to remove the devices , and check the quality  of IGBT driver signals. However , this machine will stay on the back burner until such time I have successfully repaired and refurbished the other three.


 
 

The New and the Old
Below on the left is the mainboard for an Axpert MKS4 5.6kw and to its right is the mainboard of Axpert MKS2 5KW , two generations earlier. Not much difference really . The MKS4 is dated 2021 and the MKS2 2015 . After cleaning the MKS2 with compressed air , it looks as new if not even better than the MKS4 .  But the MKS2 has been in operation for probable >5 years , while the MKS4 only a number months. So this is one of the qualitative issues i am reffering to : how can we ensure that the MKS2  be serviced to ensure another couple of years of performance.  Example , what can we measure to verify that the two large bus capacitors will hold , or should we proactively replace them . This is where I will be consulting Coulomb and others .
 

 
One thing I have noticed on the MR1-MR4 machines from Malawi is a massive heat sink mounted on the top of the machine. Remember I am only a 18 month rookie in solar , so I have not seen to many of the older machines. 
Turns out this is the heat sink of the MPPT module, totally different to that of other MKS2,MKS3 and MKS4 machines.
 

When I opened the first machine I went like - WOW! - this is some engineered MPPT module. Its got a presence and the quality and PCB layout is something !  Wonder if this is tooo expensive , why discontinue it ?

REPAIR : 4 x RCT MKS2  Inverters Received from Malawi
Went to receive the boxes from Alrode destination  as fast as my feet could fly.  I will refer to the inverters as MR1,MR2,MR3 and MR4 . MR1 and MR2 had been paired as parallel units  in a single location , MR2 and MR3 also paired but different location.
 

The initial bringing up of the inverters done by current limited dc source on battery.
MR4 :  error code 09 . That's nasty , indicates IGBT and/or MOSFETS blown , but great opportunity for me  to show my experienced gained in this regard
 
Below is short video showing the symptoms of MR1, MR2. 

WhatsApp Video 2023-01-28 at 9.11.19 AM.mp4  
MR1,MR2 :  You cannot believe this . Exact same problem as the previous Cape Town machine. Frequent clicking sound . Couldn't resist the temptation . Immediately disassembled , and powered the main board and control board standalone. Exact same  problem . The input electrolytic capacitor on  U5 (5V regulator) has given up on life. Temporary soldered on a 470uF and problem solved.  Two exact machines in same location , same symptons , same remedy , crazy is it not !  Main boards marked 2015 .
MR3 :  This one has a major problem as far as I am concerned : it has no problem at all. So here comes the start of an issue regarding quantative  vs qualitative  measures.  So if we cannot quantify an error , we will have to use qualitative measures to ensure this inverter is good for a number of years ahead, and that we can dispatch back to Malawi with a calculated measure of confidence . This also holds true really for MR1,MR2 and MR4. 
So all in all all four inverters appears to be serviceable and I am looking forward to start with MR4 and document the findings and repair.
  
 

REPAIR : MKS2  AXPERT CLONE
The owner  was woken up by a repetitive clicking sound very early on Christmas day. he discovered that his Axpert's display backlight and LED's   was cycling a number of times per second  , on then off. Also the relays was clicking at the same rate.
So he sent the machine to me all the way from CapeTown , I was surprised as the cost of courier was only R165 and it was delivered within 4 days (2 working days) . 
So it landed , and again I connected the now standard 50V current limited bench supply on its battery terminals . Awful , it clicks and clicks and clicks and clicks , and flashes and flashes , etc., etc. Neatly at a deterministic rate. I put my money on two failures, either the control board or the SMPS supply rails , 12V and or 5V.
So its time to open the unit . No physical damage . I  disconnected the MPPT and other peripheral as to only power the control and main board . same story.
So i removed everything and powered the main board on its own , without control board . Steady 12V , -12V and 5V . Plugged in the control board without display . Measured the voltages gain , 5V was cycling between 4.0 and 5.0V  , as much as the multimeter could keep up with it. 
First thought is overload on the 5V , but there was no component or section  getting hot , and neither the 5V linear regulator. So this meant two things , either the unregulated DC not enough or , the capacitor input filtering not enough . unregulated DC on scope was ok peak to peak , but there was severe ripple . 
So I soldered on a temporary electrolytic cap , and problem solved.
On the left is the faulty cap , the one on the right is a new one. It could be the green one is inferior, The new one is Rubycon , good capacitor .

The reason for the solid 5V when control board is out , is because there is also a 100nF film cap on the input , so this actually provided smoothing under no load.
The cap electrolytic has run dry , its has lost its ability to store . The machine is about 7 years old .
So I upgraded all the PSU caps as standard procedure.
I am waiting for 4 RCT Axperts arriving from Malawi next week . Now guess what !!!, all of them  4 has the same problem . They cycle the clicking at slower level , but I assume the smoothing cap is slightly better  , but obviously still at fault . I will report my findings.
 
 

Ha Ha seems like a case of lost in translation and not sure who went wrong  
The tail current I had already set at 1% when you first recommended it, was always after what to set the current threshold as that was one setting you hadn't elaborated on! Anyways no worries will keep it as it is. (had fun yesterday trying to figure out why it wouldn't go above 2A till i read the parameters in the manual that you have posted above). Thanks for the explanation on what this setting does! Oh and it's a 500A shunt with the BMV-712 not a 1000A.
Thanks again chaps and have a good weekend! 

1% of the Ah capacity of the battery.
I'm told that the bluetooth protocol could have been simpler, but it isn't... and because of that it sometimes doesn't (and never will) work on some devices, usually where such devices might not fully implement some part of the bluetooth spec (which in the other 99% of cases doesn't even show up because most programmers are lazy and do things the simplest possible way :-) ).
There was a joke that did the rounds around the time Eskom did their load shedding this side.
What did they use for light in Africa before they used candles? Electricity.

^^^

Most chargers use three stage charging. Bulk, followed by Absorption, followed by float. For example, let's say you set absorption to 57.6V and float to 54V.
Bulk: the charger will charge with the maximum configured current until the voltage rises to 57.6V.
Absorption: The charger holds the voltage at 57.6V, while the charge current tapers off on its own as the battery charges.
Float: The battery is about 90% full at this point. The charger drops its charge voltage to 54V in order to reduce off-gassing. Because the battery isn't full yet, it needs to spend quite a bit of time at float level.
Now, the battery will always accept more charge current at the absorption voltage than at the lower float voltage. So a tail current of 1% at the higher voltage is a better indication of a full battery than the same tail current at the lower voltage.
So, the recommendation from Victron, for solar systems that are cycled daily, is to set the BMV "charged voltage" to just a little bit below the higher absorption voltage. If you do this, the BMV can never reset once the charger goes to float. It can only do a reset if the tail current drops really low while it is still in absorption charge.
This is not a problem when using other Victron kit: They don't go to float too easily. Their absorption phase is calibrated according to how long bulk took.
But the Axpert goes to float really easily. If you use the Victron advice, it might never reset because it doesn't spend enough time at the higher voltage. So I'm saying you then need to use a little bit less than the lower float voltage and hope for the best.
Of course, it is not a problem on systems that are not cycled too often.

If Utility priority leave the setup as 57.6 bulk and 54.4 float (or there about, try and find your battery spec for standby voltage), if you keep your batteries at a high voltage for a long time they will dry out and fail prematurely.
I can do it because on SBU setting my batteries don't spend a long time at [57.6/56.8] - some days not reaching there at all. On average my BMV will sync every second day.

That is exactly my current setup - bulk at 57.4 and float at 56.8 to avoid excessive gassing.

That's probably better than dropping to float too soon. I'm just talking from my own observation after moving from a Microcare MPPT to a Victron charger. They stay in absorb much longer. Then I did a full charge with a Multiplus, goodness, it remains in absorb even longer! In the beginning I thought it was overcharging the batteries... then I noted how the tail current continues to drop... right down to below 1%. And then the inverter went to float. That's when I realised what it really takes to get a full charge on lead acids...

Hi Pilotfish - when I  use to have AGMs I would do exactly as you describe. Before I changed to Coulomb's firmware due to the charging bug we would go to float early and I noticed that the batteries would still accept 15-20A at the lower float voltage and then tail off. Only after I changed the firmware did it behave correctly with <3 A going into the batteries at float. I mention this since it seems that batteries not near fully charged it still can accept a fair charge rate even at the lower float voltage. At 25°C the gassing voltage is 57.4V but this drops to 56.8V if batter temps reach 30°C. I have found my AGMs were about 3-4 degrees above ambient temperature while charging so it is something to consider with VRLAs.

I agree with this statement, but I have recently come to believe that it is as a result of incorrect advice on the forum and not necessarily an Axpert fault.
If you look at any number of AGM/GEL battery spec sheets for example the advice is fairly similar (but please use your own spec sheet);
From Vision 6FM100P-X spec sheet Cycle Use = 2.4 to 2.45 VPC = 14.4 to 14.7 per 12v battery = 57.6 to 58.8 per 48V bank Standby use = 2.2 to 2.3 VPC = 13.2 to 13.6 = 52.8 to 54.4 per 48V bank The thing is that we are (mostly) using our batteries in Cycle Use and not Standby, but for some reason we all charge out batteries to Cycle Use voltage and then drop off to Standby Use voltage, not allowing the time to fully charge and equalize. Nowhere on the spec sheet does it mention dropping to standby voltage when in cycle use!
So why not set bulk and float BOTH to 57.6V (the lower end of the scale to minimize gassing and stay away from 60V capacitor limit), then your batteries will get charged properly - problem over!
 

BMV settings for lead acid, pretty much:
Charged Voltage: At least 54V (recommended 0.3V below your float voltage). It is not too sensitive, it must just be a voltage that is higher than the resting voltage of the batteries, but lower than float.
Tail current: 1% (default is 4%, which is a bit high for large lead acids).
Charged detection time: 15 minutes
Peukert factor: 1.25
Charging efficiency: 95% is the default. I find that one has to play with this one a bit. If the BMV reaches 100% while still accepting lots of current, this figure needs to be turned down a bit.
Also see Marianka's video here.
Edit: Just need to add something about the recommendations in the video regarding the charged voltage. For A Victron system I would absolutely recommend that you set the charge voltage about 0.4V below the absorption voltage. If you do that, the BMV will only ever reset if the charge current drops low enough while its still in absorption charge. When the tail current drops below 1% under absorption... you know that battery is full.
Unfortunately I cannot advise this setting on the Axpert because even with the modified firmware it simply doesn't stay in absorption long enough.

The low DC cutoff (setting 29), I thought, was the point at which the inverter will switch off (in the absence of grid power). The point at which it would return to grid (i.e.  start recharging the batteries) is setting 12.
 
Off course I might be misunderstanding the question.

26 - 12v Gel batteries in CYCLE use would typically have charge voltage of 14.4 to 14.7v, I would go in at 14,4V x 4 = 57.6V 27 - Use the typical standby voltage as your float voltage, so 13.8 x 4 = 55.2V (if too low then you will struggle to fully charge), 29 - 48V cut-off sounds about right, you may need to drop slightly if you have heavy loads which cause short term voltage drops. Note the above is my opinion, others may differ.
 

I believe that the bulk charge voltage that I gave you is correct for most AGM/GEL batteries, so I doubt it is too high. The batteries will warm depending on the amount of current passing through them, but should not be hot to the touch which indicates problems. The battery room should be well ventilated to try and keep a temp as close as possible to 25C - above which battery life drops off fast.
@plonkster is the right guy to ask regarding the BMV - he is PAID to supply quality support