I am installing 2 Victron Energy 12.8V/300Ah NG LiFePO4 Batteries using a Lynx Smart BMS and Lynx Distributor.
Due to the high demand of the bow thruster, I was thinking of connecting it directly to the batteries (500A ANL fuse).
Will connecting the bow thruster directly to the batteries cause any issues with the BMS?
You should not do this. The BMS will not measure the discharge current hence the SOC will not be correct, assuming you also take the bow thruster negative directly back to the battery. The BMS not provide any measure of over discharge protection to the batteries, the NG batteries have no internal protection. It may be possible to wire ATD to the bow thruster control somehow, but the final contactor protection would be missing.
Additionally, ANL fuses do not have a high enough AIC (amperage interrupt capacity), for that model of Battery, consider Clas T. At 14V with an internal resistance of 1milliOhm, fault current is potentially 14kA, ANL are rated at 10kA.
Thanks, that was my suspicion. I do have the battery to BMS wires protected by a 300A class T fuse.
Accommodating the bow thruster is a big headache.
I originally calculated 2/0 wires to connect the batteries to the BMS (8’ total wire run, using a 2000W multiplus as the load).
The bow thruster is 5kw and uses 3/0 wire with a 400 ANL fuse and was connected directly to the lead acid batteries that I’m replacing.
Any suggestions as to how best to accommodate the bow thruster?
Can I run the 3/0 thruster wires to the end terminals on the Lynx Distributor?
If so, do you think I should upgrade the battery to BMS wires to 3/0? (just to restate, the thruster is 5kw and the original installers used 3/0 wire for the roughly 35’ total wire run).
You could connect the bow thruster cables to the ends of the Lynx distributor, you would have to cut the plastic case to let them in.
Re the battery wires is that a 2/0 cable per battery connected to the BMS as a pair of 2/0 cables could be OK from an amperage point of view, not sure about voltage drop. If it is one 2/0 cable for both batteries then it is light.
Another thought, re the bowthruster, is it OK with the higher voltage it will see from the lithium batteries as these will not drop as much voltage under load as lead acid.
Ok, I’ll connect to the end of the Lynx Distributor and I will upgrade to 3/0 cables from the battery to the BMS.
Regarding the higher voltage, the manual does not provide any voltage tolerance information. I’ll check directly with Lewmar - but a quick chatgpt query says that “There is no indication that the slightly higher voltage from a well-maintained lithium (LiFePO₄) system—due to lower voltage drop—poses any risk.” Again, I’ll check with Lewmar.
Thanks for your help.