Yeah I am using USER in the Growatt too, not the Lith setting.
I have both a Growatt 12k Inverter/SCC All in One, AND the external Growatt SC48120 SCC. 11,000 watt 32 panel array broken into 4 arrays, 2 going to the AIO and 2 Going to the SCC
The issue I run into is 2 fold:
1. If the Growatt external SC48120 is NOT connected to the Inverter via rj45 and cat5 cable so that the inverter is the master and doing all the charge control settings for the external SCC, the external charge will reach my set Absorb / Constant Voltage Setting, the current will stop, BUT the voltage will just keep going up and up and up, until the BMS finally turns off charging because a cell in the battery has hit Hi voltage cut off. (not the best protection)
2. If the external SCC IS connected via rj45 and cat 5 to the inverter, it works correctly, following the settings in the Inverters SCC and stops charge and voltage at set point ... BUT ... in the case where the BMS has shut down charging for the batteries (due to low temp cut off protection below freezing or hi voltage cut off, etc) ... When the sun comes out, and there is voltage coming in from the solar array, the external Growatt sc48120 SCC does not know what to do with the power (since it cannot charge the batteries). So the DC in voltage at the inverter starts jumping all around from the Absorb / Constant Voltage user setting up to and over the inverters DC Hi voltage warning cut off (in the case of a 48v system this is about 62v dc) ... this throws the inverter in to a High DC voltage overload fault and shuts the inverter down.
So I wondering if the Sigineer software in their 48120 fixed these issues. Because Growatt is Junk.