That's a very valid concern and one that needs to be addressed in system design.
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And it has been addressed:
(1) Dean does it through having a secondary, always connected small AGM bank.
(2) For my Victron based system, if the BMS decided to disconnect, it ONLY disconnects the load side. The battery bank is still connected to the alternator and the energy continues to flow. If the BMS decides that the batteries can't take any more charge, it doesn't disconnect, it turns off the charging systems.
I don't know enough about Mastervolt, but I'm guessing it's addressed. I cannot speak to other systems.
With lithium, I strongly believe that people need to understand how their systems work. Same with their Genoa furler that has circuit breakers/thermal switches. Same with every system on our boats.
On Tue, May 3, 2022 at 02:44 PM, Mark Erdos wrote:
If a high output alternator is suddenly disconnected from the battery bank with the engine running, that electric energy has to go somewhere. Watch how quickly a fire ensues. I would imagine, if one is using the bow thruster the engine is most certainly running.
With best regards,
Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - French Polynesia
On 5/2/2022 10:05 PM, Alan Leslie wrote:
Thanks Scott...great post....
Everyone has different requirements (and ability to pay!) ... so everything relevant needs to be considered....those Victron batteries are VERY expensive !
n=1 studies are often not useful ...on my previous boat I had AGMs that lasted 10 years, I have an Amel friend who has his set of AGMs now for 9 years, Ours are 6 years and still performing.....because they have been well managed.
But I don't think that's the point.
My concerns, still, are around this sudden disconnect business, and now, about how you deal with periods away from the boat.
I can see now that it is possible to have very high short duration discharges from LiFePO4 batteries, as needed for the bowthruster, but we had better be sure we have enough peak A availability so that the battery BMS doesn't suddenly decide its had enough and disconnect at the worst possible moment.
When Covid struck, we had left the boat in a marina connected to shore power with a battery charger on and the frig and freezer running, fully expecting to be back in a few weeks.
A year later I came back and everything was OK.
How would that work with Lithium?
I understand they don't like to be kept charged and actually prefer to be disconnected - so would it make sense then to have say one or two AGM batteries (with their own charger) just to keep the boat going and disconnect the Lithium when parked for an indeterminate time?
Another option might be, for us, we have a 100A Victron Skylla battery charger which has a Power Supply mode - maybe disconnect the battery bank and put the Skylla in Power Supply mode when leaving the boat??
I really like the potential that LiFePO4 batteries offer but my concerns, as everyone now knows, are wide ranging....and developing daily....but not necessarily in the negative!
2007 A54 #69