question

I'm just finishing months of researching before making the leap in a few days myself, so no real-world Victron experience yet. From my studies and vendor discussions, it seems that one of the key components of getting the VE.Bus BMS to work is to have another VE.Bus device, such as your Multiplus. VE.Bus BMS seems to be the one that enables the most functionality from other Victron components.

A lot depends on the output of your alternator, which is only 70A, vs the size of the bank. The Li-Ct will close the charging relay and attempt to charge your 300Ah bank as quickly as it can which can burn out the diodes in your alternator without limiting it. I'm sure you alredy know this, but if you're using the Li-Ct there needs to be a load-dump (such as an AGM start battery) wired in on the alternator/starter side of the Li-Ct in case the current to the lithiums is cut by the BMS. There is a built-in current limiting function in the BMS 12/200 via 80% of fuse's (max 100A) rating. You'll need to check your alternator manual for maximum continuous current and select your fuse appropriately on the BMS 12/200. I don't believe that the VE.Bus BMS will attempt to current-limit your alternator (someone please correct me if I'm wrong here). It's my understanding that you will also need other gear like Battery Protects x2 etc. if you go the VE.Bus BMS route.

There is a great webinar from Victron available, "Victron Q&A Webinar 1 - Using your Alternator to charge Lithium" which will likely answer most of your questions on this topic:

https://www.youtube.com/watch?v=dzU_pQFa19s

There are several ways to limit the current your alternator puts out. The video goes into a few of the pure Victron options in detail. If your alternator is externally regulated, you might be able to limit the current or de-rate it right from it's own regulator such as the Balmar MC-614-H.

Hope this helps, and keep us posted. Best of luck!

If it helps, I plan on having a Smart Battery Protect on the 12v load side of batteries, and a Cyrix Li-Ct on the charge side, both controlled by the Ve.Bus BMS. I'm not inputting directly from the alternator though, I'm using an Orion DC-DC 30A from the vehicle battery to charge (via the Cyrix)

I presume your are asking what BMS to put on your batteries, if this is the case we use

123 smart BMS this has bluetooth and is very good and quite easy to install as well

and Chargery BMS, this is well priced but harder to setup.

The alternator problem is on the other side. If the BMS opens up while under charge, the resulting surge can damage the diodes.

Also, the bms 12/200 is limited to 200 amps. On a mulitplus 12/3000 that is only 80% of the capacity. Also because there is no communication on ve.bus the inverter won't have any information for limiting charge or discharge. The ve.bus bms with an LI-CT and a Battery protect is a better system combination.

Just an FYI, if you use VE.Bus BMS and a Multiplus together, you will not be able to turn the inverter on/off from the app or through the Cerbo. Only with a Digital Multi Controller panel, or the switch on the inverter. It's a really annoying bug and you can see there are multiple threads about it:

https://community.victronenergy.com/questions/64501/vebus-bms-and-multiplus-cerbo-combination.html

https://community.victronenergy.com/questions/59581/vebus-bms-and-multiplus-remote-switch-off-off-mult.html

https://community.victronenergy.com/questions/96609/vebus-bms-alternative.html?childToView=96725#comment-96725