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Are the batteries in a single bank? If so, one Orion or two for faster charging. Don't go over that to avoid alternator burn out.

Remaining 95A goes nowhere, unless other loads connected. Alternators, like solar and generators, supply according to load/demand.

The Orion manuals give fuse sizes for the different models. Wiring must be capable of handling the full output continuously, fuses are to protect the wiring. Speed of fuse blowing depends on fuse type and quality. There's capacity in the fuse sizes for surge/start up currents, which can be quite high for short periods.

Do not oversize the DC:DC converter. It can lead to alternator failure, especially with Lithium batteries which can take a very high charge current. Best to keep the DC:DC converters well below alternator rating and take into account other loads on the alternator as well as the converter(s). One rule of thumb is max 50%, but there are no clear answers that I'm aware of.

Solar power falls out of the sky, and is free.

Perhaps there is scope to extend your solar array's?

Running your propulsion engine to charge your batteries seems like a last ditch effort to keep the lights on....?

Hello @Anonymous37389 .....I am not sure how your alternator is configured but I have just done similar to my boat.....But I configured it differently.

I am assuming the 125 amp alternator has an external regulator. I assume the lithiums have an internal BMS. If that is not the case ignore what comes next.

I suggest you connect the alternator directly to the lithium bank. The alternator in this MUST have an alternator temperature sensor so the external regulator knows the temperature of the alternator. In the case of a Balmar system with an MC614 external regulator this will drop the alternator excitation current when the temperature sensor reaches 100 degrees C. If you dont control the output of the alternator by sensing the temperature, you will destroy it.

I suggest you charge your start battery with the Orion. The start battery doesn't need much current to replenish the start discharge so 30 amps from the Orion is perfect. The orion can aslo be set for an AGM battery which I assume the start battery will be.

You haven't said how big the solar panels are but let's say they can be set to take the house bank to 100%. You could keep the alternator charge profile set to AGM. That will allow a lot of charge current but not quite get to the absorption voltage level of the Lithium house bank. That absorption phase could be handled by the solar regulator to keep the batteries at 100%.

To have a 125 amp alternator and not use it to punch current into the new house bank would be a total waste of a good alternator. The advantage of lithium is fast charge so you should take advantage of that. Please remember, you MUST sense the temperature of the alternator and reduce the alternator output accordingly or you will destroy your alternator. That is because the lithiums will draw maximum current until they are somewhere near 99% full whereas AGM or FLA will taper off very quickly to nowhere near the capacity of the alternator. If your house bank is 50% state of charge it will take 4 hours at 100 amps to get them back to full. That is a LOT of load on a conventional alternator. The AGMs would taper to 40 amps within the first 20 minutes as they surface charge. Thats why it takes so long to charge an AGM or FLA house bank. The lithiums will change your life.

A 40 amp fuse into the Orion will be fine as it will not draw more current than that.

I hope this helps,

Trevor

What I did on my boat was to get my previous (dumb) alternator modified to take an external regulator. Cost about $100 for a local alternator shop to rebuild the alternator (new bearings, new brushes, new diode pack, and the modification) and then hooked it up to a Wakespeed WS500 regulator. It now happily charges my LiFePO4 directly. I then use an 18A orion DC/DC to keep my lead acid battery topped up.

Just on a side note: The fact is you won't be getting 125 amps out of your alternator. After startup the alternator temperature will heat up and you might be lucky to see high 90's. It is a high probability that the alternator will see temps above 200 degrees. Having a temp sensor as Trevor noted is a MUST as stated. Just keep in mind when the alternator temp reaches the set amount on the external regulator it will cut your output of alternator in half. Until the temperature of the alternator cools to temp settings on external regulator your output will be restricted to 50%. If using a Balmar MC614 there is a Belt Manager system you can set which basically derates your alternator output as well so can find a happy medium where you can get a constant output.