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ddrueckh avatar image
ddrueckh asked

SmartShunt Settings

I have a question regarding the SmartShunt. It says to set the charged voltage to .2-.3 below the float voltage set on my SmartSolar MPPT 100/30 controller. I am using two 6 volt GC2 batteries and have my controller float set to 13.5. Therefore the SmartShunt charged voltage is set to 13.2. With this setting, it seems that my shunt resets to 100% full when the controller is still in bulk charging and above 13.2 volts. Shouldn't the shunt show a 100% charge only after the controller finishes charging and switches to Float? Thanks.

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2 Answers
Paul Green avatar image
Paul Green answered ·

I am not sure of this answer, but let me try and see if anyone corrects me if I'm thinking wrong.

The SOC is not dependent on what the charger is doing. It's based on actual voltage not charging voltage or surface charge in the battery bank.

A fully charged battery is between 12.6v to 12.8v. So, that's 100% SOC. Battery chargers routinely apply voltages higher than this to fully charge the battery. But the Shunt should not read that voltage but only your battery bank's actual voltage.

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snoobler avatar image snoobler commented ·
@Paul Green


SoC is dependent on battery capacity and net current flow in/out of the battery relative to its capacity, e.g., 100Ah battery with a net 10Ah discharged = 90% SoC


When determining 100% SoC, it is VERY dependent on what the charger is doing - the absorption voltage and tail current.


Using voltage alone to determine the SoC requires that the battery be left in a completely dormant state with absolutely no charging or discharging for at least 10 hours. Not practical let alone reliable.

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jeffb avatar image
jeffb answered ·

@ddrueckh I have exactly the same setup and found the default SmartShunt settings did the same thing - reset to 100% too soon. First, I lowered the Tail Current setting - somewhere around 1%. Still fine tuning that setting, but the last charge cycle I monitored had the State of Charge flip to 100% just as the MPPT charger switched to Float. Then, if I was only ever charging from the solar panels, I would raise the Charged Voltage to around 14.2V - 0.2V less that the Absorption voltage from the solar charger. However, I can also charge my batteries using shore power or a generator, and that voltage will not get above 13.6V - so I have to keep the voltage setting lower to accommodate multiple possible charging sources. Ignore the advice based on resting battery voltages - that's not relevant to these SmartShunt settings.

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