question

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jacob-neitling asked

Smart Shunt SOC issue - with alot of detail to understand why it wont reset to 100% automatically

To start off let me paint the picture of this small setup 3 320W solar panels in a 3s1p to 150V35A victron SmartSolar Mppt with a Victron Smart Shurt and Victron 48V/500W inverter.


The key issue is the Smart Shunt State of Charge. The Smart Shunt I have is the 500A 50mV model. I want to understand why I cant make this reset to 100% when clearly it is going through full cycles, and As I have attempted to tune this setup. I cannot understand why it wont ever go back to 100% SOC even though the system so far ~ 1 week + into use is working as expected and device has not gone offline even though now my SOC states it is at 0%. Clearly it is charging and keeping the battery charged otherwise this would not work given I have pulled ~5x the Ah of the bank of battery I have attached.


Technical details:

I have the following.

8 x lifepo4 12.8V 12Ah Lithium Battery - LiFePO4

Link to battery: https://www.amazon.com/dp/B0CMQB4B48?psc=1&ref=ppx_yo2ov_dt_b_product_details

They are setup to be a string of 48V ( I understand the voltage is actually higher ) but it is a 48V system.

Each battery has the following specs

12V – 12AH

153.6Wh each battery

Nominal Voltage 12.8

Voltage range 10-14.6

Charge voltage 14.6

Max charge current 15A

Recommended Charge Current 7A

Max discharge rate 15A


This setup is configured as a 4S2P ( are 4 in a Series and 2 in parallel ) making this a 48v at 24Ah bank of batteries.


I recently setup a Pi 4 with Venus OS so I can remote monitor vs local Bluetooth. I have this setup and online so I can look at devices. ( data from online and Bluetooth local is same data )


The key issue is the Smart Shunt State of Charge. The Smart Shunt I have is the 500A 50mV model.


The above battery bank has a bus bar on Negative and positive. So I can attach items as needed.

The smart Shut comes off the Bus bar.


I have a set of 3 solar panels in series connected to a SmartSolar Charger which is the MPPT 150/35

Each panel has the following specs which combined output a Nominal Voltage of ~97V to 103V

Each are Trina Solar 320W industrial panels. ( each tests good with all known tests I can preform )

Pmax – 320W

Vmp- 33.4

Imp -9.58

Open Circuity Voltage ( Voc ) – 40.3

Short Circuity Voltage ( Isc ) 10.2

Max Seriese Fuse – 20 A

Per the Smart Solar history tab Daily I am generating on average 360-370Wh of Yield with a Pmax of 130 to 470 give or take.


My only load is the raspberry pi at a constant ( per smart shut ) 17-20 Watts of usage 24 hr a day ( this takes into account the draw of the inverter which is a Victron 48/500 120V inverter set to Non ECO mode.


All items in this whole setup are Victron ( minus the obvious battreys, pannels and fuses )


As of this writing the Smart Solar shows my panel voltage is 99.12V and current is 0.2A


The battery is at 68.8V with a current of 0.30 A in the Absorption state

In the Smart Solar settings the settings are as follows


Battrey Voltage 48V

Max Charge Current 12A

Charger is enabled

Battrey preset is Smart Lithum ( LiFePo4 )

Expert mode is off

Absorption rate is 56.8V

Float is 54.0 V

Low Temp cut off is 41

The remaining settings are disabled as this is a preset.


My load output is operation mode Battrey Life

Streetlight is off

Switching to smart shut here is my current information


Volrage at battery which ( at this time is in absorption mode from MPPT ) is 56.8V

Current is -0.3A

Power is -17W

Total Consumed Ah is -54.7Ah

Time Remaining is 0m

Which shows the Low SOC Alarm in red

Using history I have deepest discharge os -55Ah and Communitive discharge of -111Ah

Discharged energy is 6.0Kwh


Last tiem since full charge is now 6D and 20Hours soon to be 7 Days


The following are the smart shut settings


Battrey capacity is 24 Ah

Charged Voltage is 53.9V

Discharge Floow is 10%

Tail Current is 5%

Pukert Exponent is 1.05

Charge Efficiency factor is 98%

Current threshold is 0.10A

Time to go average is 3M ( min )


Current SOC 0%


Knowing a few things


This setup is fune for my application.

With a 500W inverter at 48V the max amp I can have is 10.416 max A draw which is below the Inverter and battery limit.



I would love to know more about why the SOC cant or seems to not go back to 100% I can provide more details as needed.


Thanks Jacob




MPPT SmartSolarSmartShuntSOC
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Alexandra avatar image Alexandra ♦ commented ·
@Jacob Neitling

Alot of detail, true.

Missing an important one, how are the mppts connected? You mention battery bus bar shunt.... Is there another bus bar then with the inverter and mppts on the other side of the shunt?

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jacob-neitling avatar image jacob-neitling Alexandra ♦ commented ·
I will take a photo but they are all on same bar. as that was what was "instructed" to me in many many videos. So the MPPT is on the same bar as the Smart Shut. Let me get a photo



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jacob-neitling avatar image jacob-neitling jacob-neitling commented ·

Here are the photos of the "Bus" bars. the to Battrey Minus goes to the Bar, which has the two strings attached. The To System Minus goes direct into inverter. The Mppt Bat negitive goes direct to Bus bar.

20240619-110119.jpg

20240619-110128.jpg

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20240619-110128.jpg (3.5 MiB)
4 Answers
jacob-neitling avatar image
jacob-neitling answered ·

here is my touching the Negitive from the to System Minus that goes to inverter.

20240619-110103.jpg


20240619-110103.jpg (3.1 MiB)
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derrick thomas avatar image
derrick thomas answered ·

The only thing connected to the battery negative side must be the shunt, nothing else can be connected to the battery negative side. Everything else (negative ) goes to the shunt. The way you have the system wired, the shunt does not 'see' any charging going into the batteries from the mppt. One connection from battery negative to the shunt, and nothing else.

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jacob-neitling answered ·

SO @derrick thomas if i move the Mppt Negitive from the bus bar to the System Minus that will hopefully resolve this? which means I can add a Negitive Bus Bar off the To sysetm Minus and Put the Mppt Negitive and the Negitive from the Inverter?

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derrick thomas avatar image derrick thomas commented ·
Yes. All negatives go to the shunt 'system' and the shunt 'negative' connects to the battery. You will need to complete a full charge cycle before the shunt will calibrate and report properly.
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jacob-neitling avatar image
jacob-neitling answered ·

Swinging that wire from the bus to Negative terminal ( safely , disconnecting the links so there was no load and shutting off the inverter ) looks to have made it jump to 100% charge. I will monitor for the next few days. That was a much easier fix than I though. Thank you for the details. I am not sure why I didn't try that but I thought I was wired up correctly.

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derrick thomas avatar image derrick thomas commented ·

Raise the charged voltage setting of the shunt to 56.6 or you will have continuous false syncs to 100% SOC. Especially important with solar charging. I would also set the soc to zero and let it do an actual calibration.

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kevgermany avatar image kevgermany ♦♦ commented ·
Agree with everything so far.

I assume both negs are joined before the shunt as it's a 2p setup.

Might be worth posting your battery settings from the smart shunt.


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