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love2learn asked

Syncing Multiplus and Shunt SOC

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?

MultiPlus Quattro Inverter Chargerbattery chargingsmartshuntbattery capacity
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Stefanie avatar image
Stefanie answered ·

@Love2Learn,

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.

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I thought I had the battery monitor turned off. I'll go in and double check.


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%

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Please post screenshots of your shunt settings and also battery settings from your MPPT.

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love2learn avatar image love2learn Stefanie ♦♦ ·

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

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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.

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love2learn avatar image love2learn Stefanie ♦♦ ·
Im asking the vendor about the settings now.


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.

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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.

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