Could it be that there is a typo or a miscalculation in the statement shown below?
I have 800Ah and use 400 in 24 hours. With no load 50A would take 4 hours of engine run time, but you will have some load, so maybe 5-6 hours. Will you be traveling that much each day.
dhays, you may want to reconsider your alternator output circuit.
Consider the typical PNW cruiser who spent the night on the hook and in the morning has his LFP house bank depleted by Steve's 400 Ah's or more. 500-600 Ahs is common overnight on my power hungry ride.
With your described circuits in place, you start the engine and your new 28SI pours it's guts into the thruster bank only, as that's all it's directly connected to.
This helps in bringing the anchor aboard and then while underway at some point (usually not too long) the DC2DC connects the now charged thruster bank to the depleted house bank.
Your new 160A 28SI is loafing along with only an output of 50 A, (thruster bank is full) all of which goes to to the LFP house bank via the 50 A DC2DC. At 50 A, let's just say it will take 8 hours (your house loads are zero) to charge the battery bank that is depleted by 400 Ahs.
Other than possibly a short burst of current into the thruster bank now and again, 50 A of load is all that this 160 A rated alternator will ever see.
Your new 28SI should last a long time as it will likely never overheat with these loads.
The DC2DC on the other hand, is running flat out most of the time.
At some point along this 8 hour charge duration the LFP house bank will get to 13.0 V and then and only then will the Xantrex Echo Charger start to charge the engine start bank.
Up until this point in time the engine start bank has started the engine, ran the intake air heater (if still enabled or equipped) and supplied the engine run loads, which DDW upthread says on his QSB are about 20 Amps, without any charge what so ever.
Even when the Echo Charger engages, it can only supply 15 A, so the engine start bank is still going backwards by 5 A.
So, the question is, do you think your engine start bank can supply all the loads it is asked to supply without seeing a 15 A charge for however long it takes, at a 50 A charge rate, to get your depleted house bank to 13.0 V? For one night, maybe, what about 2 or 3 nights in a row?
If you think it will, then you need to ask yourself, will your instrumentation warn you of a short term low battery condition causing multiple annoying resets, like DDW experienced?
Engine start banks in my world take priority, perhaps that is one reason alternators come connected to them directly, 99% of the time.