Hello,
I have Victron system more than 2 years. Before winter (October) when there is low PV yield I changed min SoC of battery to 45%. When there is some of PV yield in the winter I barely touch 70% of SoC. So because of that I wanted to “calibrate, rebalance or synchronize” battery and have set min SoC 100% or Keep battery charged (tried both) and I have charged battery from grid. Expected to reach 100% SoC but I can get max 95-96% only. Where can be the problem?
My setup:
3x MultiPlus-II 48/3000/35-32, Cerbo GX, 2x MPPT 250/100, 9,2kWp in 2 strings, Pylontech L1 10,65kWh,
Min cell voltage - 3,39V, Max cell voltage - 3,41V
Hi Martin.
You will need to tell us some voltages.
Here are some possibilities;
If your 250/100 is pushing say 3.41 per cell, and your cables are dropping 0.07v, your cells will only see 3.34 which is about 95% - tell us your charging voltage number - your battery is probably providing that number to your GX if those Pylontech’s are communicating. Your BMS doesn’t know the cable voltage drop, but in some situations the GX will tell the MPPT to raise its charging voltage (by up to 2v) to compensate. Check your voltage at the battery terminals while you are at 95% - is there enough voltage there?
If your array is not getting much sun, and its a 65kwh pack over a 9.2kwp (i.e. ratio of 7) its going to take a long time if the power draw is close to matching the incoming. You don’t say what the draw is in kwh, but if its around 20 then maybe you are on the point of balance
Check your battery BMS - any alarms? If your cell diff is getting into silly numbers, the battery will not be full but the BMS will prevent any further charging
20mV of cell difference is fine, but if all the cells were 3.41 it would be full - you might have an SOC vs voltages difference, i.e. the calibration of your shunt is out, so based on voltage your battery is full, but based on an arbitrary counter (mAh) there should be more capacity left in the battery. Most BMS will have a voltage and current where if you get to that voltage (sometimes called “full pack voltage”), and the current is less than X, the battery will reset its mAh counter to whatever the full battery value is - eg 100000 for a 100Ah battery.
Your Pylontechs will struggle to reach 100% with 3.45V per cell as you have it now (51.8V)
Set the charging voltage to at least 3.48V per cell (52.2V) and you’ll see more often and quickly 100% SOC.
Remember, the batteries (BMS) ask for 53.2V for charging, but that’s a tad too much.
Set it to 52.2V and you’ll be OK. I personally have it at 3.5V per cell (52.5V) and all is OK.
Just so that other readers are aware: Martin’s battery is a 15 cell battery, so don’t get confused when the voltages seem low!
This is where references to cell voltage rather than battery voltages are sometimes easier to deal with;
3.40v - 3.45v per cell is typically “charged”
3.65v is typically the alarm point, but this can vary a lot.
3.23v is roughly the 20% SOC point.
3.00v is roughly the low cell alarm point.
So a 15 cell battery will typically cycle 20% to 100% around 48.45v to 51.75v
but
a 16 cell battery will typically cycle 20% to 100% around 51.7v to 55.2v
We generally charge our 16 cell batteries at 3.6v per cell, 15s = 54v
LX is saying 53v (i.e 3.53v per cell)
Alex is saying 3.48v per cell, so 15s = 52.2v
You are currently at 3.45v per cell, lower than all of us, so that looks like the main issue?
Your screenshot shows cells at mostly 3.47v - you’ll never get any higher if the charging voltage is 51.8 (3.45v/cell)
Jokes aside, i did help a user who was about to cook their battery after reading on the interweb that “56.5v is the best setting for your SCC” and he didn’t realize his battery was 15s
Or I just deactivated maximum charge voltage limit in DVCC and let BMS control it itself. I think with this I can reach 100% and rebalance cells easily in a few hours.
