I’ve finally installed my solar off-grid-ish setup and I’ve found some miss match on the bms current measurements and therefore, the SoC of my battery.
My system details:
Mppt 250/100 with 3 strings of 4 panels powering about 5.5kw
2x multiplus II 5000 in parallel
About 27kw lifepo4 in batteries with a 123smartBMS gen 3.
Cerbo S GX controlling/monitoring, no assistants yet.
The battery BMS has a hall effect DC current transformer sensor but I’m seeing a miss match in measurements from something like 600w power out the inverters and the BMS claims 170w or even sometimes idle.
I’m about to dump more money into my system in a victron smart shunt but I’m not sure on how to manage the battery charge with 2 current measurements (the BMS and smart shunt)
A couple nights ago at 1AM the power gone out with no warning, “76%” to 0 since the system did not charge to full (I’m not sure why… we had consistent sun those days)
I wonder if the BMS tells to stop pulling charge when he thinks the battery is nearly charged… it should use the maximum and balance voltage to determine the end of charge right?
It’s really hard to have 2 turns of wire on the current sensor but I might need to find a way to do it before running into a victron shunt…
I’m leaving a couple screenshots for reference. O don’t really know where to go from here. I’m still working away some details here and there
Can anyone tell me of I add a victron smart shunt, will I be able to use the voltage control from the BMS (balance voltage and all those details) and use the current measurement from the smart shunt?
I can also add the vsense wires on the master multiplus Inverter.
Last night I was at 99% SoC but I know there was about 7kW missing from the battery charge.
no issues have come up since I’m checking the power charged and discharged.
You can install a SmartShunt as a Battery monitor but this can not control charging by DVCC. You could remove the 123 BMS as the controlling BMS and then let your chargers work on their own charging settings. You would use share voltage sense and share current sense from the SmartShunt to the chargers so you can use tail current to end absorption. You would need to check cell balance and do a longer absorption if required. However, this is only safe if you have a contactor (or 2 contactors) that disconnects the battery from loads and chargers controlled directly by the 123 BMS for safety shutdown on cell or pack over voltage / under voltage / over temperature and under temperature. If the 123 BMS is not the controlling BMS then it can not shut down chargers by DVCC.
I have contactors for loads and chargers. So I can control that way…
I’m going to try and hook up the current sensor from my BMS with 2 loops with thinner wire. I’m sure it will be a little bit warmer but my loads normally are under 6.5/7kW so I should be safe.
I just need a little bit more precision on lower loads measurements since I’m having some discrepancies on the SoC percentage daily
