Yet another charging Lithium/Lead hybrid setup thread

[WE9V]

Okay, lots of threads on this already, I know. A lot of good ideas, but as one person said, it's all dependent on your system. So instead of a generic question about "what's best", let me pose a specific question: Based on my current configuration, and my goals, what would you suggest that I do? This is a long and detailed post, but I hope that it shows that I did some homework myself instead of asking you to do it for me.

Current system, as purchased new-to-me a ~year ago:

• All 12V system, no desire to change
• 400AH AGM House about to be changed to 2x 230AH LiFePO4 drop-ins, each with 200A BMS
• No warning signal prior to drop-in LFP BMSs shutting down
• Balmar 170A alternator, serpentine belt, Balmar MC-614 external regulator, regulator has alternator and battery temperature sensors present
• 650W Solar, 150/60 MPPT charging House bank
• Separate AGM Start and AGM windlass batteries
• Old Balmar DigitalDuo Chargers, one from House to Start, one from House to Windlass. These DDCs are like 30A ACRs, but when load exceeds 30A, it completely shuts down, not limits to 30A. Occasionally fires back up to see if load <30A. Not a multi-stage charge, but like an ACR.
• Old Victron Centaur Shore Charger, up to 100A, 3 outputs
• 5kW diesel genset that can also power shore charger
• Victron BMV-712 Smart Battery Monitor
• Windlass is 1200W model, but with ~30' run (1/0 or 2/0, don't remember), as battery is under companionway steps. Will not relocate battery, but that's good as it's close to the house and starter batteries.
• For the sake of this discussion, let's say that the boat is equal parts dock queen, ICW-motoring, and at anchorage. In other words, no priority given to any.

Goals/requirements:

1. Lowest additional cost
2. Reasonably low added complexity
3. Charge LiFePO4 at highest possible rate (priority to LFP). 30A DC-to-DC charger to LFP not acceptable / highly undesirable.
4. Protect alternator from voltage spikes due to LFP disconnect
5. Ability to charge all 3 batteries from all charging sources (alternator, solar, shore, genset). Optimal charging for AGMs not a requirement / using LFP profile acceptable.
6. Bonus: Alternator helping windlass
7. Bonus: LFP helping windlass

A recent call to Balmar suggests that the DigitalDuo Charge may not be optimal for charging the windlass battery because it would shut down if current exceeds 30A. So it likely shuts down if the windlass is used (>30A) and/or if the windlass battery has been deeply discharged. I believe this means that the high-amperage alternator is doing nothing for windlass use and/or charging, but due to the relatively low output of solar (I've seen a max of 580W output, to charge the discharged house AGM), it's unlikely to see >30A into the windlass AGM. (Would need the house bank completely charged, the windlass battery discharged, and full sun. But the windlass battery would get SOME current, likely less than 30A, before the house bank is fully charged or as the sun first comes up.) So what I'm saying is that the DDC potentially does nothing during alternator charging, but is likely adequate for solar charging.

Potential solutions:

1. While there's a Renogy 60A DC-DC charger (about $200 on Amazon), I'm not terribly keen on Renogy. 60A charging to Lithium seems minimal, considering 170A alternator. Really dislike the thought of a Victron 30A model ($250), and really don't like the idea of two of them ($500). Violates goal #1 and/or #3.
2. DC-to-DC charger from Lithium to windlass AGM. This does not meet goal #4, protecting alternator from load dump. Ruled out.
3. Add AroFET 200 from alternator to LFP and windlass. At ~$150, it seems to meet goals 1-6.
4. Add contactor or BlueSea ACR between windlass and LFP. These 120A ACRs are about $90-95 on Amazon.
   • Due to LFP's resting voltage of ~13.3v, per BlueSea's suggestion, would need to add tiny relay in ground signal that would close when ignition is on.
   • Bonus: could also use BMV-712 relay in series to stop LFP charging when SoC >90% or voltage >14.2V (setpoints for example).
   • I believe this may satisfy goals 1-7, with #2 slightly more complex due to the additional relay logic but has added functionality/features. (Goal #7 is met only if LFP isn't >90% charged and/or needs ignition on.)
   • Would need to change wiring such that windlass battery has the direct connection to the alternator, and would need to limit the MC-614 belt manager to the 120A limit of the ACR. An alternative would be to get a more expensive ignition-protected contactor (Blue Sea 150A $133, 250A $175). I think I'm okay with the 120A limit. Far better than 30A DC-DC.

So, what do you think? Solution #3, #4, modifications to #3 or 4, or something completely different?

Bonus question: My AGM windlass battery has died after 7 years. Currently a 4D size. What would you replace it with, especially based on your suggested solution? Going with the lowest additional cost, an AGM Group 27 or 31 would be great instead of 4D. Apparently the alternator nor the 30A DDC has helped the windlass while in use...it was all battery.