Turns out that the new ABYC E13 standard for lithium battery installations on boats in effect bans separate busses for loads and charging sources. (Thanks to member Rick for pointing this out.)
220.127.116.11A BMS shall respond to any conditions outside the SOE by activating the output disconnect device.
My guess, and hope, is that this is probably the result of poor drafting, rather than intended. The problem, of course, is the word output.
In my view, compelling the BMS to dump the loads just because of an overcharge does not increase safety, it decreases it, since load dumps are dangerous in and of themselves and overcharge is the most likely scenario to cause a disconnect.
Hopefully ABYC will fix what I believe to be a mistake soon. Banning something that most industry experts I have talked to consider much better design (separate charge and load busses) does their credibility no good at all.
That is very strange wording.
Laptop computers, power tool chargers, electric cars, and pretty much all other engineered lithium-ion devices disconnect the *input only* for a high-voltage / high-state-of-charge condition, leaving the output active
The BMS should disconnect the output for low-voltage, high-current, and high-temperature alerts, but disconnecting the output for *all* limit violations seems like a significant reduction in safety.
I can only assume that this is an error in wording. Hopefully ABYC will clarify it soon.
That’s a good point on the way most every BMS works. That just increases my suspicion that this was the result of sloppy drafting, not intent.
That is unless we want to go with conspiracy theory: this was insisted on by the members of the committee who have a personal interest in selling “drop in” batteries that don’t communicate and therefore can’t use duel busses properly.