The system runs all week, then faults on the one clear afternoon when the bank finishes charging early. The cause is almost always a charge profile written for a different battery.
Two limits are in play. The inverter has an absorption voltage it charges toward and holds. The BMS has a protection voltage at which it disconnects. If absorption sits at or above protection, a normal full charge trips the protection.
Where the numbers usually sit
Most 48V LiFePO4 packs protect somewhere near 58.4 volts and want absorption near 56 to 57. The default profile on many inverters ships closer to lead acid values, and equalisation, which lead acid needs and lithium must never receive, sits higher still. Any of that will trip a lithium BMS at the top of a charge.
Cell balancing makes it worse in a way that looks random. Balancing happens near the top of the charge, so a pack that has been cycling shallow for weeks reaches that region for the first time on a sunny day, meets a small imbalance, and one cell hits protection while the pack average looks fine.
What to change
Set absorption below the BMS protection voltage with real margin, one volt is a reasonable starting point, and disable equalisation entirely. Then let the pack sit at absorption long enough to balance, which can take several hours on a bank that has never been fully charged.
If faults continue with correct settings, the problem has moved from configuration to a single weak cell, and the pack needs opening or the vendor needs calling.
The cold morning version of this fault
The same disconnect can appear at sunrise for a different reason. Panel open circuit voltage rises as temperature falls, and a string sized on a mild day can exceed the charge controller input ceiling on a cold morning. That fault clears once the sun warms the array, which is what makes it look intermittent rather than structural.
Diagnosing a top of charge fault
Instruments that turn an intermittent fault into a number you can read.
Battery monitors with cell dataClamp meter, DC capableAffiliate links. As an Amazon Associate this site earns from qualifying purchases, at no extra cost to you. Prices and stock change often, and a listing appearing here is not a statement that the pairing above is approved.
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