question

What is the max. output A of your alternator? If greater or equal to 18, on of the Orion Smart series DC/DC converters could replace your argo fett

@badrock provided the MPPTs and charger are configured correctly for lithium you should not have a situation with overcharging. For the alternator I would suggest leaving the Argofet in place and installing an additional Orion DC charger. The Argofet is a nice way to prevent unintended discharginging of the house battery (while there are multiple ways of doing this the Argofet has zero additional cost as it is already installed and requires no additional configuration) the Orion can be configured with a Lithium profile to allow for improved ‘regulation’ of the charging voltage while also limiting the load on the alternator. This last point depends a lot on the brand of your alternator and presence of any internal regulation - most of the time an Orion with half the rated output of the alternator is recommended to prevent any overloading.

Thanks for the answers.. not really relevant since it's been almost 2 years :-).

For everyone one else following, my main question was around the behaviour of the BMS in case of overcharge. To be honest, there is no way around it, since the charge and load are on the same circuit, is the overcharge scenario triggers, you loose all the loads.

Adding a dc-dc charger with a lithium profile is one way of solving it, but to me it this solution looses the main advantage of lithium, like the fast charging rates, and degrades the battery life, since it will tend to keep the batteries at full charge.

My solution, which I implemented a couple of months after writing this, was to build my own battery out of 12 individual cells. I have my own BMS that controls two different circuits, one for all the loads and one for all the charging sources. It also sends a "fake" voltage to the alternator, in effect regulating it's output.

The result really works for me, but it's not a drop in replacement. There is no drop in without big compromises, and going for the 'proper' solution (regulated alternator/external BMS etc) easily doubles the price. With my current solution I got 90A from my 115 stock alternator, can control how much to charge the batteries (e.g. leave them at 70% charge when not using the boat) can control all the charging sources independently (e.g. motoring back there is no risk I loose the loads). Also, I'm currently working in being able to control everything via n2k and the plotter.

I'm a computer/electrical engineer, so to me it's doable, but it's absurd the solutions of the market at ~10x the price of a DYI.

Hope this helps someone :-)

Cheers