My Victron shunt and Multiplus are showing 2 different SOC readings. The shunt is showing 100% but the 24/3000/70 is showing anywhere from 70-80% SOC. I have programmed the shunt to know that the battery bank has 412aH @ 24v nominal.
How do I know which reading is accurate, or if either of them even are correct at all?
is there any specific reason why you have the MultiPlus battery monitor activated when you also have a BMV/SmartShunt? There should only be one battery monitor in the system.
The shunt is the the one to trust while the MultiPlus internal battery monitor relies on calculated data.
That being said, how do I make the SOC reading accurate with the shunt? I'll be charging from solar at 20 amps while the SoC reads 100%
Please post screenshots of your shunt settings and also battery settings from your MPPT.
Batteries:
4x SOK 206Ah 12v
2 Series, 2 Parallel, for 412Ah @ 24v configuration
Victron MPPT (100/50):
Battery Voltage: 24v
Max Charge Current: 50a
Charger: Enabled
Battery Preset: User Defined
Expert Mode: ON
Absorption Voltage: 29.2v
Float Voltage: 27.6v
Equalization Voltage: 29.2v
Rebulk Voltage Offset: 0.80v
Absorption Duration: Fixed
Absorption Time: 15 Minutes
Tail Current: Disabled
Equalize Current: 0%
Automatic Equalization: Disabled
Equalize Stop Mode: Automatic (On voltage)
Maximum Equalize duration: 0 Minutes
Manual equalization: DO NOT CLICK START
Temperature Compensation: Disabled
Low Temperature Cutoff: Disabled
Victron Multiplus 24/3000/70 Inverter:
Charge Current: 50a
Absorption Voltage: 29.2v
Float Voltage: 27.6v
Equalization: DISABLED
Victron SmartShunt:
Battery Capacity: 412Ah
Charged Voltage: 27.6v
Discharge Floor: 10%
Tail Current: 2.00%
Charged Detection Time: 3m
Peukert Exponent: 1.05
Charge Efficiency Factor: 98%
Current Threshold: 0.10a
Time-to-go averaging Period: 3m
Battery Starts Synchronized: Disabled
Doesn't look too bad.
I'm guessing that the battery voltages for absorption and float come from the battery manufacturer?
About the settings for the shunt:
Charged Voltage could maybe be a bit higher, so that the synchronization to 100% doesn't happen too early. I think 27.8V or even 28.0V might fit better, because in this range it can be assumed that the lithiums absorb only little current, which can indicate a nearly fully charged battery.
Tail current is something you just have to play with. This value is also used for synchronization. The optimal value is when the synchronization takes place at roughly about 99.5 - 99.8% and when the Tail Current becomes lower than the set value (2% - variable) for a duration of 3 minutes (Charged Detection Time). In all lithium systems I have installed, 4% has proven to be optimal. Sync occurs at about 99.7%, which then tells me that I am very close to a fully charged battery.
One of the things that could be beneficial of having the battery monitor enabled on the inverter would be to see the battery stats on the Victron Connect while logged into the inverter without having to log out and back into the shunt.
The SmartShunt Charged Voltage should be the absorptiion voltage minus about 200mV or the Smartshunt will declare the battery full too early. The terminal voltage of the battery rises during the absorption phase as the current reduces. When the current reduces to 4% (that is the factory default) tail current. That is 4% of the C1 current (412 amp) or 16.5 amps, and the voltage rises to the "Charged Voltage" for the "Chareg Detection Time" (3 minues) the Smartshunt will deem the batteries to be 100% full. You can check these charge profiles easily using teh VRM. You may choose to reduce the tail current of you think it is too high.
I would set the "Charged Voltage" setting to 29.0 volts.
