In short
- The BMS has two switches: one lets current in, the other lets it out. Each can open on its own.
- A cell too low, a cell too high, too much current or the wrong temperature: each opens a specific switch.
- Reading the switch state and the cells at the moment of the cut usually explains it at once.
Between your cells and the inverter, a Daly smart BMS has two banks of MOSFETs. One controls charging, the other discharging. When the BMS sees something it does not like, it opens the relevant one. The pack itself is fine; it has simply been disconnected in one direction.
The discharge switch opened
The house goes dark, the inverter complains, the charge may still read 30 or 40 %. Common reasons: one cell reached its low-voltage limit before the others, the current went above the discharge limit during a heavy start, or the pack is too hot. A single weak cell is the classic case: the pack average looks comfortable while that one cell is at the bottom.
The charge switch opened
The panels produce but the battery stops taking current. Usually one cell reached its high-voltage limit, or the cells are too cold to charge. The pack may show 90 %, with one cell already full.
Reading what happened
Daly Monitor shows both switch states, for example binary_sensor.daly_monitor_charge_mos, with every cell and the fault sensor binary_sensor.daly_monitor_fault. At the moment of a cut, look at three things: which switch is open, the lowest and highest cell, and the temperature. One of them almost always gives the answer.
Getting power back
Most protections release by themselves once the cause is gone: a low cell recovers a little when the load stops, a hot pack cools down, charging current brings a low cell back up. If the same cell causes the cut again and again, the pack needs attention: balancing time, a connection to check, or a cell to test.
An alert that helps
A notification when the fault sensor turns on, or when a switch opens, tells you about a cut before you notice it in the dark. With the cell history next to it, you will know which cell to look at.
Common questions
Can Daly Monitor close the MOS switches?
No. It only reads the BMS and never sends commands. The switches are controlled by the BMS itself.
Why does the cut happen at 40 %?
Usually one cell reached its low limit before the others. The pack average hides it; the cell table shows it.
Is it dangerous to restart quickly?
Let the cause clear first. If one cell keeps triggering it, check that cell and its connections before relying on the pack again.
