State of Charge - Shunt vs BMS

[No1Hunter]

Having been boondocking this last week, I noticed my shunt reports a different state of charge compared to my batteries' BMS. Several times my shunt reported my state of charge was 100% while my BMS stated it was anywhere from 85% to 90%. Shunt is a Victron while my batteries are Renogy. The shunt is set to 400 amps of battery power and the BMS indicates the same.
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Has anyone else noticed this different between what your batteries say compared to the shunt? I assume the BMS is correct. Thoughts?

[creativepart]

I have Renogy batteries and a Victron SmartShunt. It's important to get the correct parameters entered into the Victron setup for the batteries. And, then to get the two synced.

The batteries are different than the SmartShunt in the way they work. Since they shut down totally when not in use (in Storage) I look at it as they are doing their own thing.

When mine deviate much I just charge everything up and hit "100%" in my Victron settings.

In other words... I don't stress about it too much. I feel the batteries are probably more correct than the shunt.

PS. I can't provide my settings for you as the RV is in storage now.

[powercat_ras]

The Victron may be resetting to 100% State of Charge too early, as the defaults are not optimal for LiFe batteries.

(XX) is the Victron parameter #, at least on the BMV series monitors.

1. Setting a higher "charged" voltage (02) than the default of 13.2 volts. I'm using 14.3

2. Increase the "charged" detection time (04) from the default of 3 minutes. I'm using 10. With my LiFe batteries sometimes their internal BMS will cut off charging current, and then 2-5 minutes later the internal cell voltages drops slightly and the BMS will reconnect and the battery will take charge again for another minute or two. This happens in the 97% on up range of LiFe state of charge.

3. If you have several LiFe batteries in series, generally their internal BMS will cut off charge current at different times. So, you want to set the tail current (03) lower than the default of 4%. I have 4 LiFe in parallel (400 AH), so the 4% default would be 4 x 4 or 16 amps. I'm using 4 amps (1% with a 400 AH setup).

With the settings I use the current flowing thru the shunt going to the batteries has to drop to less than 4 amps with a voltage of at least 14.3 volts, for 10 minutes for the Victron BMS to decide the batteries are fully charged and jump to 100%.

Some of this will depend on how agressive your charging setup is. On my LiFe system I let the batteries internal BMS decide when the batteries are charged and the charging equipment is set to output constant 14.4 volts when batteries are at full charge or near full charge and drawing minimal current. Some LiFe setups are more conservative and the charging equipment will not put out 14.4 volts constantly, in which case a lower "charged" voltage setting may be needed.

[No1Hunter]

I have a Victron SmartShunt 500 amp Battery Monitor and 4 - 100amp Renogy LiFePO4 batteries wire in parallel. The Renogy app reports state of charge for the total 400amps, and for each individual battery.

I changed the parameters to match your suggestions, powercat_ras.

"Setting a higher "charged" voltage (02) than the default of 13.2 volts. I'm using 14.3" - should this match the "Present Voltage" of the Renogy BMS - mine is set for 14.4v.

My inverter/charger is set for 14.4v, and I believe my solar controllers are also. I have 380w of solar and as of now, my shunt indicate 100% and my BMS is 99.84%.

We are headed out in a couple of weeks for a 5 day "off grid" adventure and will see if anything changes.

Thanks creativepart and powercat_ras for your words of wisdom!!!

[No1Hunter]

Well, after making the changes and giving my system a stress test over the last 5 day, I can say the changes made all the difference in the world. Both the BMS and shunt were within 1% of each other.