From everything I've read so far it sounds to me that my main problem is the voltage regulator inside the alternator. To address this I am learning now how to either remove the one thats built in or buy one without one built in.

you seem to be, and I appologise if I'm wrong, that a high current alternator in a car iputs out that level of current ALL of the time. But that's not how it works. If they, say in your case, put out 140A at all times they would ruin a battery in no time flat, and that just doesn't happen in real life. The regulator only allows the alternator to put out what is needed by the load. A vehcle, sail boat or car, olny recharges the battery after the starting and then all of the output goes to the running of the vehicle, lights, radio, ignition what ever.

You have a BMS on your Lipo you said. If you were using a BMS connected to the mains for charging, would you be concerned by the available mains current? I should hope not. The BMS is there to monitor and regulate the battery charge, that is it's job, just let it do it.

 

OK, it is clearer now that the "vehicle" is a sailboat. That does explain how you will be able to fit a bigger alternator, probably not possible in a typical car. So really, limiting the current will actually only duplicate the capability of the previous alternator. So it seems that the present battery will still be getting charged rather indirectly. That immediately solves the problem of needing a higher voltage from the alternator to charge the starter battery.
Unless I missed something, the starter battery is NOT charged by the engine driven alternator, while the "House" battery is. That does seem unusual, the systems in motor homes seem to be the opposite, with the house battery being mostly charged by secondary schemes, such as the extra standby power generator system that can also handle the multiple rooftop AC units.
So the field switching control system would seem to be entirely suitable for the application, once the threshold values are set in the control program.
Now with the alternator needing to be oversized to be adequate the case is unique. It seems that possibly the ventilation for the present alternator is not adequate, and that is the cause for overheating. If that might be the case I suggest a careful reading of the cooling requirements for any new alternator, followed by an examination of the cooling system arrangement that is presently in place. There is at least a chance that the overheating is caused by inadequate cooling, not an alternator shortcoming. Of course, it may be that increasing the alternator/engine ventilation is not possible.

 

Unless I missed something, the starter battery is NOT charged by the engine driven alternator, while the "House" battery is.

Yes, this is correct. Big difference between sailboats and motorhomes is that in a sailboat the engine is on for relatively short times in relation to the entire voyage. In a motorhome the engine is on all the time until the destination is reached. The starter battery never gets any use outside of starting the engine. In contrast, when the engine is on, the alternator has to "give" to the house battery all its got. Output does not need to be regulated since lifepo battery will be happy to accept pretty much any amperage as long as it is 14v. My desire to limit the current is mainly to reduce heat in the alternator. Of course, I also dont underestimate what 140A could do to an even slightly corroded lug connector if there is any resistance

40A constant output is fine with me. Say I used 80Amps on my electronics over 24 hours (which is really a lot for my needs). Running the engine for 2 hours would be absolutely fine.

 

If that might be the case I suggest a careful reading of the cooling requirements for any new alternator, followed by an examination of the cooling system arrangement that is presently in place. There is at least a chance that the overheating is caused by inadequate cooling, not an alternator shortcoming.

I am starting to think along the same lines. It is an enclosed compartment with only a small blower style 3" fan that pulls the air out. There is no grill, radiator and 70mph air to cool it down. Perhaps I've not been looking at solving the root of the problem, which is the overall heat in the engine compartment. There is a way I can add a fan to blow fresh air inside. But I would imagine using external rectifier and regulator would also take the heat outside of the engine compartment.

 

I did mis interpret that post.

 

There is a way I can add a fan to blow fresh air inside.

You perhaps could also add a duct to blow that air directly on the alternator.

 

Usually the engine fan is used to remove gasoline fumes before starting the engine. That does not take that much. So improving the ventilation will probably make the engine happy as well.