MLT Powerstar G2 lifepo4 charging problem

[DrewZA]

Joined the MLT club recently, picked up an absolute beast of a machine, a Powerstar G2 12kVA 48V of 2010 vintage. 

I have it hooked up to a 16s 304ah prismatic lifepo4 bank completely off-grid. Solar charge is coming from victron mppts and "utility" on Src A from a 6kw ryobi generator.

The firmware seems to be a bit older than what can be seen in the manual as there are a few items missing from the menus. I have set bulk charge to 2.35VPC (56.4V) and float at 2.33VPC which I won't actually be using, planned to shut down genny when stage 2 completes...

The problem I'm having is that I can't get through stage 2, the constant voltage part of the charge. Stage 1 runs smoothly at 60A constant current for about 4 hours, then charge moves to Stage 2 and the current starts tapering off, when it's around 50A the contactors disengage and it throws 'Src Stop Low AC V'. If left to continue it goes into a loop of reconnecting to the source, charging for a minute or two and error, disconnect, repeat.

The error implies that the voltage is from the generator is dropping out, but watching the display on the unit I see no big fluctuation in the AC voltage and confirmed with a multimeter on the terminals while it was complaining about low voltage it looks rock solid to me. I've cleaned the contactors and tried charge rates all the way down to 10A, sinewave fault tolerance up to 50% and low voltage cut off is 80% so there is plenty of headroom for the generator. Being off-grid I unfortunately don't have another AC source to rule the generator out completely as the culprit, but current tapering off it should be less demanding if anything, so something weird is going on here.

Thinking now maybe there is something in this old firmware charge profile that isn't lifepo4 tolerant. Anyone have experience with these older units that could shed some light?

[DrewZA]

I would really also like to get RS232 access to the unit, hoping I might find a clue to troubleshooting in more granular data. I first tried MLT Coms but it didn't want to connect to either of the 2 db9 serial ports. The modbus manual shows connection to the lower port, a serial sniff shows the lower db9 is spitting out AT commands. Seems like it was connected to a modem for remote monitoring in a previous life.

A peek inside confirms that it is connected to what looks to be a port labeled MODEM. There is a header labeled DSP_SERIAL that I imagine could be the local RS232 I'm looking for but it's a different connector so I would need to probe. Anyone have a pic of this control board with the DSP_SERIAL connected?