Haha… Sorry. I‘ll hit the key points. Lithionics 12V external BMS installation by Ocean Planet Energy. BMS was turned off for installation of ancillary equipment. BMS was then turned back on, resulting in alarms and then BMS shutdown. They were unable to restore BMS operations, possibly due to a contactor failure.
Something is missing here. I know OPE prefers external BMS's over internal BMS's because all BMS are not alike. The old adage "you get what you pay for" seems particularly true with many of the off brand LFP batteries with an internal BMS. The criticism of these cheap LFPs has been the inability of the BMS on one battery being able to communicate with other batteries in the bank. This can lead to one BMS failure shutting down the whole system. With a single BMS for the whole system, this won't happen.
In my opinion, the main benefit of the external BMS is that the input/output is routed through contactors rather than FETs. The contactors (controlled by the BMS) are rated at higher currents than the typical FET based internal BMS. But you have a single point failure in the single BMS. However, if you use multiple FET based BMS batteries in parallel, the current handling capability increases, and you can potentially reach, or exceed the capability of a single contactor. Multiple batteries with individual BMS also has some redundancy. It is true, however, that if you are operating on the edge of the combined BMS ability, that a single BMS going offline could have a cascading effect… resulting in complete power loss. But if you have a reasonable margin (ie your max expected current could be handled with one battery offline) this shouldn’t be an issue.
The AGM would only be used to start the engine, unless the LFP house bank was off line. If the AGM is connected to the load bank and the LFPs are offline, it can't be charged and that is exactly the time it needs to be charging because it is being used.
Exactly. It seems a potential loss of the BMS (at least temporarily) was anticipated since there was a combine switch installed to allow the AGM to connect to the load bus. I find it odd that being able to charge the AGM in this configuration was overlooked. Perhaps the B2B should have been powered via the charge bus, relying on the Orions internal input voltage lockout to protect the LFP from over discharge.
Jordan was installing the switch after the failure. Which is puzzling, why didn't OPE provide for this at the beginning? Or did Jordan skip that part of the installation.
The switch being installed in the video was a switch to combine the load and charge busses (in order to allow charging of the AGM). There was already an existing switch to connect the AGM to the load buss.
To be fair to lithium, there isn’t one known-best reference design for lead acid banks either. Some boat builders use ACR’s, some use 1-2-B switches, some use individual on/off switches, and some use a combination of these. Lithium brings new considerations whose solutions are less mature, but either way the design of a robust electrical system takes some forethought into how the boat will be used and what set of compromises is best.
It will be interesting to see where we end up. I think Battleborn may be heading in the right direction with self contained BMS batteries capable of communicating with each other and the rest of the system.
Excellent points. I guess I thought everyone had settled on one way with FLA, but now that I think of it, it's not the case. I wonder what the mega-yacht guys are doing?
The batteries are likely very small relative to the size of the boat and just large enough to start the diesel and run emergency lighting. The vast majority of the 12 volt stuff would be on the bridge, easy to put a battery there with a charger.
Interesting topic. I just read something from Victron where some designs use batteries for night, and are sized for 24 hours of such use. But I'm sure most just run one or more generators all the time.
