Overview of the entire system is here
The BMS has a few tasks to perform and there are two main design variants.
Distributed BMS and centralised ones. Distributed BMS have small balance boards
on each cell whereas centralised ones have a central unit. In theory
deistributed ones are easier to extend as simply adding cells with balance
boards extends the BMS. The drawback is that the heat from balancing is
generated at the cell so the battery heats up as it charges and balances.
Decentralised BMS wise the Battrium BMS looks very promising with many
extension options like switching on a fan when over temp is registered. They
have cell level monitoring for temperature and seem to have pretty flexible
software that can be adapted to many different pack sizes, chemistries and pack
conditions. It looks like the best choice in the decentralised camp to me,
highly flexible software, good quality hardware, very responsive support.
In the centralised camp I have found the REC BMS and Orion BMS to look very
promising. They both have CAN bus interfaces that can interface with Victron GX
gear and that brings us to a interesting point. Designing an electric drive for
a sailboat needs to fit into a sailboats electris systems and more often that
means Victron gear. The Victron GX gear has CAN bus interfaces and both, REC
and Orion have profiles that can interface directly with Victron. The other
interesting point with centralised BMSs is the balancing power they can deal
with. Orion comes out of the EV market and is very much tailored towards
electric vehicles. The upside to that is that boat battery packs are at the
lower end of their performance curve so we can easily drive large boat banks
with that BMS without hitting power limits. The centralised Batrium version has
a recommended 200-300Ah rating (has been used with larger packs though) which
is rather small for our needs whereas the Orion and REC BMSs are used in EV
applications with much bigger Ah ratings.
The Orion BMS can be programmed via CAN bus and has enough ports to add the
various safety switches to make the opration of the battery pack save and the
batteries last a long time. When integrating to a Victron GX device it can then
tell chargers and inverters how much power they can feed into the bank or take
out which makes the operation of a Victron Quattro a save option.
The next piece of the puzzle is the electric engine and the engine controller
needs a way to communicate with the bank as well to know how much power it can
pull from the bank. Here the Orion has an interesting mode where it tells the
engine to gradually back off as he bank drains power to not suddenly stop the
engine when the bank is empty but to slow down before shut off.
My takeaway from where my research led me to date is that were I to design a
house bank I would go with Batrium but for an engine bank I think going with an
EV BMS is the better choice so for our combined house and engine bank the Orion
BMS will be the BMS of choice.