question

Unfortunately there is not a direct answer, all three are possible and will work. It comes down to a system design and overall approach and what you are trying to achieve.

The critical design consideration is to ensure that the high acceptance rate of the Lithium battery can be managed so that the alternator does not over heat and burn out. All three will constrain the demand on the alternator and current available for charging, The BMS 12/100 and BMS 12/200 do this based on the size of fuse installed, while the DC-DC approach it through a charger approach that constrains the maximum amount of charge current. The DC-DC will constrains to a maximum of 30A, as that is the largest unit available. The 12/100 is up to 100A and 12/200 up to 200A.

In my view it would come down to what is the size of the existing alternator, and what you are using as a BMS. If you are using a VE.Bus BMS then you could use either of the following

• External regulator that takes alternator temperature into consideration.
• DC-DC
• BMS 12/200 with the VE.Bus to BMS 12-200 alternator control cable (https://www.victronenergy.com/upload/documents/VE.Bus-BMS-to-BMS-12-1200-alternator-control-cable-EN.pdf).

If you are not using the VE.Bus BMS then the BMS 12/200 or BMS 12/100 are options.

The BMS12/200 works on the negative side; while the BMS12/100 works on the positive side.

So it comes down to what you need and want, they all work but in different ways.

The manuals for the BMS 12/100, BMS 12/200 and DC-DC are very informative about how they work and how they can be configured.