Lithium Battery Design for Catamaran

[SailBelladonna]

We have decided to install lithium batteries. We have also decided which Lithium batteries we are going to buy. We have consulted an electrical engineer who has installed lithium batteries on their boat. I have prepared a circuit diagram below. We would really appreciate design input in relation to any flaws or improvements.

[CalmSeasQuest]

Have you thought through what happens if your BMS shuts down your house bank. My primary concern in designing our system was that a problem with a single cell (hi voltage/low voltage or even an incorrect reporting issue) can result in the entire bank shutting down and the boat doing dark.

[witzgall]

Chris from Balmar here. One of the biggest benefits of LFP is fast charging. Have you considered upgrading the alternator on and using an external regulator, instead of the B to B charger? Done correctly, you should see a big boost in charging output.

Chris

[SailBelladonna]

Originally Posted by CalmSeasQuest

Have you thought through what happens if your BMS shuts down your house bank. My primary concern in designing our system was that a problem with a single cell (hi voltage/low voltage or even an incorrect reporting issue) can result in the entire bank shutting down and the boat doing dark.

Thanks for the input. That is a really good point. We were thinking of keeping a single battery offline that we could replace the main bank if that happened - but there is a temptation to add it to the circuit The alternative is to take the bad battery out of the house circuit. How have you overcome this problem?

[CalmSeasQuest]

Originally Posted by SailBelladonna

Thanks for the input. That is a really good point. We were thinking of keeping a single battery offline that we could replace the main bank if that happened - but there is a temptation to add it to the circuit The alternative is to take the bad battery out of the house circuit. How have you overcome this problem?

I took an atypical approach and split our A/C and D/C systems. We were able to isolate our critical systems and provide multiple fail-over options.

31.2Kw Victron LiFePO4 Split System Install

[SailBelladonna]

Originally Posted by witzgall

Chris from Balmar here. One of the biggest benefits of LFP is fast charging. Have you considered upgrading the alternator on and using an external regulator, instead of the B to B charger? Done correctly, you should see a big boost in charging output.

Chris

I think upgrading the alternators would be a very good idea for boats with higher power needs or smaller solar systems. Seeing as we have plenty of solar (1.3kW), we don't charge our house batteries using the engine. Your solution is a better design, but we are keeping the entire upgrade including all parts and delivery to around $2,752. Batteries 3 x100Ah $1,260 (Bluetooth or on-battery display)+ 2 x Sterling Power Alternator Protection Device $104 + Battery switches, terminals, fuses, cables $400 + Battery delivery $500 + Victron BMV-702 $168 + Sterling BB1230 12V 30A $320. Also considering 4th spare battery for $420. We could reduce the cost by removing the Alternator Protection Devices and Victron BMV-702.