I have set the MultiPlus-II to switch a contactor to heat hot water when the soc reaches 98%. The last couple of days the water remained cold, as the soc never reached 98% due to dull weather so I thought.
Today was a nice sunny day and I kept an eye on the VRM all day and noticed that for some reason the battery bank only now charges to 97% and then becomes idle, while the mppts supply the loads, and at many occasions my mppt 450/100 states 0w on both strings, even though the sun is shining directly onto them. What would the system suddenly behave this way, ot has been charging to 100% all through the summer and heating the water at 98%soc, but now its not charging over 97%.
You do not state what type of battery you have or where the SOC comes from as this may have some bearing on the answer.
What I think is happening is that most battery monitors are not 100% accurate for SOC and can slowly drift a few % over a period of weeks. The batteries need to be charged fully to 100% for the SOC to resynchronise to 100%, there are often criteria for this such as exceeding a certain voltage whilst simultaneously charging at a low current. My guess is your SOC has drifted and you have not met the criteria to resynchronise to 100% despite the batteries getting fully charged as far as the chargers are concerned.
You need to check what settings you have in your battery monitor for synchronisation and see if these need changing. The settings for synchronisation to 100% MUST be less onerous (easier to achieve) than end of absorption so that tje SOC gets reset to 100% before the charger goes to float.
In addition, the linked FAQ discusses the case where SOC syncs to 100% too easily, it has some useful info for how Victron battery monitors do the synchronisation so may be useful.
Remember, SOC is a calculated value, not a measurement.
Today, it’s stopping charging at 96%, not sure what’s going on as the system always used to charge upto 99% and on occasions I even saw 100%.
I do have a lynx smart shunt, but im not using it, it’s merely just an expensive fuse holder as the batteries bms’s are controlling the soc percentage.
I have 8x 7kwh Rahvolt batteries in parallel with a 3 wire data cable daisy chained between them and connected to the cerbo gx.
Today both mppt’s were charging, pushing 3kw into the batteries until it reached 96%soc , which has now caused the battery bank to go in idle state and the mppt 450/100 to stop outputting.
I have not altered any settings, the system has worked for months going up to 100%soc, but as of a few days ago it never reached above 97% and today 96%
If the batteries themselves are causing this, how can I restore normal charging operation?
I have a few questions then. There is not one correct thwory without more information.
I have assumed since you say the bank is in parallel that each battery has the same length connection onto the bus bar. So this is not a set up/current share (and therefor balance) issue.
It is not taking on amps (idle). Ignoring the soc figure, is the battery reaching and holding the absorption voltage for the correct time?
If it is then the soc has possibly drifted. And its time to hold them at full charge for a bit.
Check each individual battery if it has an interface, maybe one or two of them is not balanced and stopping charge because of higher cells.
My lynx shunt 1000 has a drift that my smartshunt 500 doesn’t have. I just manually set it to 100% every few days if I know they’ve had enough absorption (600Ah of 48V).
What i have since found out is that earlier today I turn off the breaker and the bms of battery number 8 , the system (remaining7 batteries) jumped up to 100% and the system started discharging and charging as normal, though we didn’t get much solar today, but it did charge over 97% after dropping to 96%.
The reason i chose battery 8 to disconnect is because it showed a much lower soc compared to the other 7 once the overall soc dropped down to 70% for the first time since 5 or 6 months of being close to 100%, so now that solar is becoming less and my battery bank is dropping below 70%soc, it seems that this problem has started and now won’t charge to 100% anymore due to battery 8 being much lower soc.
One other thing I’ve noticed is that I had set the dvcc to on and set the maximum charge voltage to 55v at the time of initial setup, all those months ago.
Looking at the battery data leaflet that came with the batteries, it states maximum charge voltage as 57.6v, so I have now adjusted dvcc max charge voltage to 57.6v
Did I do the right thing? Im guessing battery 8 is not balanced because it never managed to fully charge due to the 55v charge voltage settings in dvcc?
I will run yhe system tomorrow, hope we get enough sun to fully charge the bank.
Wenn es keine Rückmeldung der Batterien an den GX durch SmartShunt o.ä gibt, dann driftet die Anzeige immer weiter nach unten. Habe ich auch bei meiner Anlage gesehen, geholfen hat: die Einstellung des Shunts etwas unter die MPPTs zu setzen.
Hatte vorher einen Drift von 0,3% je Tag der sich auf summiert hat. Jetzt läd er bis 96-97% und danach hält er die Spannung bis nichts mehr abgenommen wird.
(sinkt sukzessive bis ca. 90W, dann Springt er auf 100%) Das ein Akku aber dermaßen abhaut ist seltsam. Da den Fehler suchen, eventuell auch am BMS des Akkus. Ich lade das System 2x im Jahr auf Max voll und halte bis Labornetzteil abschaltet. Ist vom Hersteller auch so vorgesehen. Die großen MPPT´s von Victron sind da nicht geeignet. Springen zu schnell.
PS - 15S System
