My MS 2812 went kaput, passed away, flew the coop, died on arrival, crapped its bed... So I ordered a new MSH3012RV that can combine input powers to help prevent overloading. What I would like to do is install a crapload of Lithium house batteries. Not sure if I can charge both lithium house batteries and start batteries together since the start batteries are lead acid. Has anyone done this? What do I need to do. As it is now, I will install a dedicated inverter sub panel since I have 5 circuits tied together with no breaker that go to the inverter through a 10/3 SO cord. (Coach was built this way) The sub panel will allow me to separate the circuits, properly protect them and finally run a larger cable to the inverter since it can take 50amp input. The charging of the two chemistries is what I am befuddled, confogulated, mixed up, dazed and finally unedumacated with.
If you want the simple version.
Do NOT even think of charging the lithiums directly with the alternator. Unless you are fond of buying new alternators.
Install a B2B charger to trickle charge the chassis battery from the lithiums. Victron makes good stuff.
There are devices available to charge the lithiums from the alternator; they basically limit the time the alternator is on.
You will need to custom program the Magnum to fit the lithium needs and your intended use.
There are hundreds of threads on the RV forums about lithiums. The above fundamentals will give you a starting point as you dig in.
It is best to separate the 2 different batteries, the charge profiles are not compatible. Keep in mind that the Lithium (assuming you mean Lithium iron phosphate such as Battleborns) will accept a much larger charge rate than the lead acids. Current thinking is to use a DC to DC charger. Victron and Sterling make really nice ones. This effectively isolates the two different battery types and limits the amps going to your LIthiums effectively protecting your alternator and wiring. If you'll be doing any boondocking you'll love the Lithiums!
Richard beat me to the punch. B2B is the same as DC to DC charger.
What Richard and Forest said is probably most sensible. That being said, my current class B with a 10.3kwh lithium battery has a separate alternator on the engine. When the battery is depleted it takes 60-90 minutes of driving to fully recharge. This makes sense for us since we drive almost every day which we didn’t do with the Newell. Still, it’s another option if you desire rapid recharging.