decipher

True, This may cause the inverter to go in low voltage shutdown which is really undesirable and inconvenient.

I noticed it was used for back to grid and back to discharge , low voltage disconnect but i didn’t check it for grid charging as it was not my concern since my main issue was with scc. And grid charging was working properly and was following the defined voltages for bulk and float so i thought even if there was a problem with grid charging i could fix it with those values.

True, my scc never goes above 28.2 so i decided to drop the displayed voltage by 1v and fool the charger to go 1v more i.e 29.2. My bat voltage was displayed 27.2 but it was actually 28.2 but the scc never went even .1v above 28.2

By the way as per my experience the displayed voltage had no effect on SCC, as the voltage of scc (output) is sensed from somewhere else on the board. So if by setting your bulk and float voltage you Get those voltages on the scc you will get right charging parameters regardless of displayed voltage. Regardless of battery displayed voltage. However it did effect on sbu back to charge and back to discharge switching and low battery alarm

Fixed resistor are predictable for their output and can vary a little bit over the range of 21 to 29v. With the variable resistor you wont be able to know what resistance value it is at that given time thus wont be able to calculate its deviation over the voltage range. You might get it right if you keep one side of the rail with fixed and the other as variable. For example fixed with 4mOhm and pot as 5mOhm so you have minor difference to adjust

@Adri76 whats the firmware version of your module? Both main and 2nd cpu. So i should ask my reseller for that firmware since the scc is working fine in that firmware.

Bypassing both rails of resistors of 1004s

If you cut the lines from +ve and -ve at the start of resistors and connect one resistor from +ve to the start of 1212, and other resistor in the -ve side from -ve to 1212 start both same value resistors you might get the voltage right

There is a chance with variable resistor that you may get the voltage right at one point and variation on other voltages

@Coulomb i am not sure about lines coming on that 1212 resistors but the output was for sure used for voltage sensor as i was able to achieve the goal of dropping 1v. Since Scc undercharging my batteries , i am working on designing my own mppt using arduino N-channel mosfets on high side and using a high side driver ir2110. So far i am un able to drive the mosfets on high side @Coulomb can you help in this regards?

there are 4.012mOhm on both top and bottom dropping the voltage about 50% "as per voltage divider rule" which is still to high for any Microprocessor to read, i think it is further reduced somewhere around the control board.

what if you turn off the charging by grid and make it solar only, and monitor the voltage difference. it may trickle charging and at the UPS connector voltage is 27 with very less Amps and at the batt terminals it is 26.

@Adri76 at what voltage was your reading same, and at what voltage was it off by 1V?

Either 2 or 3 not 2 and 3 but both sides same

Below the red wire you can see i had disconnected the pcb line and connected my connection on the first resistor . You may disconnect both of them on pcb and by pass the resistor and connect you resistors on the end of the last 1004 and start Of 1212 resistor on both sides so in case you can later on reconnect that small patch. Also after disconnecting from the battery side you will get accurate reading on resistors

Testing the resistors on board might give incorrect value due to many factor involving other components.. maybe you can take them out and test or replace them with a few mOhm non surface mount ones. Or a single may be 2,3mega ohm resistor one on each +ve,-ve sides. But make sure they both must be as close in resistance as possible. Better if you can get accurate resistors. Only replace ones with 1004 not the 1212

what the picture shows is the voltage sensor , its strange that there are mega ohm resistors, however i could modify the input voltage by adding another voltage divider before them and dropping 1V successfully , the thick wires are the battery connectors.

@Adri76 true. i also noticed that

i am attaching here the setting and the output that i took few days back to test the given setting and SCC behavior and it can be observed that there is no effect on SCC. The SCC is integrated to the same board , has no separate board or it would have been easy to make any modification there.

thanks @Coulomb, first i suspected the same that it might be premature floating bug , but later on i discovered that no matter what i set in floating and bulk charge voltages Scc never look to that,SCC seems to have a default value and only work on those values, there is no absorb time setting however there is equalization setting which is also completely ignored by SCC. for example i set my bulk charge to 29.2 and float on 28.2 , SCC always goes for 28.2 as bulk and 27.2 as float nothing less nothing more. i wasn't able to find any such array of resistors on the PV input side, neither on input side nor on output at the mosfet output side. it is really complex there and seems to be achieving output voltage by sensing the input and regulating the duty cycle. i am sure the firmware it locked as @Coulomb mentioned , but really appreciate that. before this i had firmware main:9.05 and 2nd Cpu : 3.17 so i had to send my unit to the vendor for firmware update and thought i might resolve the issue they updated the 2nd cpu to 3.18 but still the issue presist.

The voltage sensor is on the back side of the board , connected to the series of voltage divider resistors . its located on the bottom right side of the board. and the line goes on the 3rd pin of control board, as shown in the pics. i have a problem with my Inverter it is an axpert VM2.2KW, the problem is that the floating and bulk charge voltages defined in the user setting while the battery type is USER the values are not updated on SCC it reaches those voltages while charging by grid but not while it is charging from solar where as there is enough power in solar. firmware version:9.05 CPU 2 ver:3.18. i tired to fool the inverter and pulled down the voltage by 1V but the SCC still follows its own voltage sensor not the voltage coming from the battery voltage sensor. please respond if anyone has info about this.