I have an offgrid system with two smartsolar mppts, a multiplus ii with 5kW 48V, controlled by a CCGX, and an 48v Lithium ESS with the following specs.
LiFePO4
Total Energy: 5120Wh
Capacity: 100Ah
Rated Voltage: 51.2V
Working Voltage Range: 44-58.4V
Standard Charge Current: 50A
Max Charge Current: 100A
DOD: 100%
Comunicated by CAN with CCGX.
The ESS is detected by te system and working correctly as long as I keep the charging voltage limited by DVCC to 54V. If not the BMS will allow more voltage to charge the battery, all is ok until it reaches 100% SOC, then the BMS Max/Min voltage will increse going over 3.6V, giving an overvoltage error.
At 54V limit I managed to limit the imbalance, but it keeps happening, and I guess this should not happen.
Fairly normal on new batteries, you didn’t say which brand, unfortunately not all batteries, especially BMS’s are equal.
Self builds can have variable quality cells from different batches.
Some take much longer to balance before issues disappear.
If it’s been installed for a while, or this is a new issue, then it can be a bad cell.
That is a small battery for that inverter, that often makes the issue more likely as smaller packs can spend insufficient time balancing, and are put under higher demands under load.
Without history it’s difficult to say.
It is usually a good idea to involve the battery manufacturer for analysis and assistance.
Ultimately it tends to be a battery issue, you can shuffle charger parameters to try mask the issue, or to assist balancing, if that is indeed the issue.
It’s fairly normal to see cell imbalance when reaching 100% SOC, as most BMS’es only start balancing at that point.
3.6V cell voltage is not a hard limit, during balancing that can easily increase to 3.7V.
Seeing cell overvoltage warnings during balancing isn’t a bad thing.
Hard errors mainly indicate that your BMS isn’t configured or functioning properly.
I said error, but should have said Overvoltage alarm [512] in Victron.
I guess this is normal, what should be the best approach in this case, should I leave it voltage restricted for months until it reaches balance by itself?
With minor warnings, it’s best to set the ESS to “keep batteries charged” for 3 days, that tends to help sort it out faster.
Very common on new batteries.
I would keep the batteries at 100% SOC for a while and increase max voltage slowly up to 58.4V so all cells can balance properly.
In a 16S cell configuration, 58.4V equals 3.65V per cell which should be perfectly fine.
Limiting to 54V would only be 3.375V per cell and that seems on the low side.
For an LFP cell, 3.2V is nominal voltage, 3.6V is high-end voltage and charging voltage can be 3.65V - hence the 58.4V rating.
Stick to manufacturer advice, they should provide guidance on the correct settings.
It will be driven by the CVL sent anyway.
58V is on the higher end of what commercial manufacturers tend to use.
There is so little additional capacity achieved by pushing the voltages up at that end of the range, and it does affect the life which is why most are triggering warnings around 3.6V per cell and above.
My BYD Premium LVS sets Max Voltage at 58.4V, like OP’s system.
During balancing at 100% SOC the highest cell voltage goes >3.7V for a while and a warning (not an error) is thrown, but they all settle around 3.6V in the end.
For testing purposes I’ve now limited the max voltage to 58V, will see how the system responds
BYD is different as it varies its CVL, I don’t know the make the OP has, perhaps it is similar, or more likely it uses a fixed CVL as is popular with other manufacturers.
The BYD rapidly drops, the voltage down to 56V-ish when it gets to the business end of charging. While the CVL requested is initially higher earlier during charging, the system generally is actually charging nowhere near this limit.
Cells are typically kept at or below 3.55V per cell, and the spikes above this trigger a correction from the BMS.
Depending on if keeping it charged for an extended period fixes your issue or not, you may want to consider limiting CVL in DVCC, 57.6V is on the higher side.
Pylon has similar issues, and it is now coded into the charger to lower and adjust charge voltages, overriding the BMS. This is something that can also be done in nodered, if you are comfortable doing some dev work. First I would try resolving this with an extended full charge of at least 3 days. Then monitor and decide from there.
