We have a sailing catamaran with two house banks of FLA batteries, one bank in each hull. The banks combine via a make-before-break manual battery switch (select bank 1, 2, both, or off). We plan to upgrade to LFP batteries but seek to maintain the two-bank arrangement such that, should one bank have a BTV fault, we can switch off that bank (maintaining system functionality with power from the working bank), while we work to isolate that fault or remove a faulty battery, etc. This could be done relatively quickly and without tearing apart beds to gain battery compartment access while sailing in rough seas at night (Because that is when things go wrong). Battery cable runs to the switch would be balanced in length. Both banks will be identical (2x 330aH smart LFP each). We would have a documented protocol for disengaging and engaging the banks to assure no charging and minimal loads during switching and to make sure the battery voltages are balanced between the two banks before recombining. The combining switch would be labeled with a warning to not change connections without first walking through the protocol. Normal operating procedure would be to run with both banks connected which we expect to be virtually a constant situation. Isolating a bank would only be done if absolutely necessary and after all attempts to correct the BTV fault without bank isolation are exhausted.
We currently have a Victron Energy (VE) Multiplus II, VE MPPTS, BMV-712 and a CerboGx. We plan to stay with VE components throughout, including the LFPs. We would use a Lynx Smart BMS as the BMS management device as well as battery monitor (retiring the BMV-712). The Lynx would be connected directly to the common contact on the battery combiner switch and all loads and charging devices connected downstream of the Lynx via 1-2 Lynx distributors. For the system to operate on a single bank we need to bypass the disconnected bank from the BMS monitoring. Unless someone has a better suggestion, I would simply disconnect the BMS extension cables connecting the two banks in the BMS daisy chain and connect the working bank cable direct to the Lynx.
We would use DVCC charge control to provide ATC control of the Multiplus and the MPPTs and supply power to the loads via BatteryProtects controlled by the ATD signal. We will implement Wakespeed WS500 regulators, following the Lynx integration protocol to assure protection of the alternators from LFP charging loads and protection of the batteries with the Lynx ATC connection to the WS500s.
We would of course follow all other safety protocols for LFP including class T fuses at each battery and appropriately sized conductors and fuses/breakers for each load and charging source.
We would appreciate constructive input on this concept, especially that which is useful to safe implementation. Thank you.
