1. Are your 450A fuses wired into each of the 2x12V battery pairs before you gang them together in parallel - i.e., if one fuse blows, it takes down two of your Lithium 12V batteries leaving two more 2x12V pairs to continue to provide the load at 24V?
   
2. Not to be pedantic but I suspect that you mean that the pig tails connected to your VE.BUS BMS and your batteries are daisy chained rather than serial connections?  I gather that the Victron batteries send digital information to the VE.BUS BMS so the information isn’t aggregated by putting them in serial configuration as would happen if they were using an analog signal - such as voltage?  So in your system, battery 1 connects to battery 2… connects to battery 6 which connects to the BMS?  I was never sure how these BMS systems connected to the batteries and control them when the batteries  are serially and then parallel connected as in your configuration.  If the system senses an issue with say battery 3 in your system, I would expect that the BMS should somehow signal battery 3 to shut down - but then what happens to battery 4 (the other battery in the series configuration to make 24V) - does it sense getting back fed by the other two banks of batteries and shut down itself? (Late addition - Now I see that you are using the BP-220 to shut down the battery - but it seems to me it would take down the entire system if one battery failed.. no?). This leads me to the next point….
   
3. With respect to your question about the solenoid… Can the VE.BUS BMS be configured to talk to three BP-220’s, each protecting one 2x12V pair of batteries?  I.e. you would have your battery fuses inline with the BP-220’s and then bring them together in parallel. This might also address my question on how the BMS system commands the shut down… I gather the batteries themselves do not shut down but rather you need a system like the BP-220 to shut them down when commanded to by the VE.BUS BMS?  If I’m right, this would simply drop a 24V battery pair in the event of a bad cell and not the entire bank - presumably, you’d also want it to trigger some sort of alarm to let you know you’d just lost 33% of your capacity.
4. Did you consider the LFP-Smart 25.6V/200A batteries and if so, why did you discard them: 
1. Cost; 
2. Size (they seem to be 33% higher, 37% deeper and only 2% more narrow so I guess you may have had an issue fitting them into the existing battery compartment?);
3. Didn’t need the extra power 33% power, or;
4. Other
5. I guess it isn’t that much work to wire up two 12V to get 24V - especially as that is the way the boat originally came anyway but I was thinking it might have simplified the situation where you have to shut down a bank of batteries because of a bad cell.
6. With respect to your idea about automagically starting and stopping your 11KW Onan to keep the bank between 30-75% in the absence of solar, you might think of adding a normally open switch triggered by closing the engine room hatch as a safety feature in your autostart circuit so the genset didn’t fire up automagically when you were working on or around it. (The switch would be open when the hatch is open preventing your Onan from starting while you were down there working on/or around it).

Brent Cameron, Future Amel Owner and Amel Owner’s Registry Moderator