Solar inverter has issues detecting battery at night while on grid

[PVguard]

Hello,

I have a 5 kVA/5 kW hybrid inverter (model name: MKS II 5KW-B) and a 16s 48v 230aH LiFePO4 battery bank with a Daly BMS 150A for about half a year now.

Everything worked like clockwork up until a week ago when at night time the inverter couldn't detect the battery anymore (the monitor was blinking "bp"). I checked the battery voltage: the inverter displayed around 25v but when I tested the battery with a multimeter, it said 47v. I restarted the BMS and everything was fine for a few minutes, and then the voltage on the inverter dropped again. I repeated the process a couple of times to no avail. The issue was resolved when I set the inverter settings to charge the battery from the grid (I usually have it set to charge only from the panels).

The next day, it happened again. This time, I pressed the button on the Bluetooth module, and voila - problem solved.

A day after this, again. Battery not detected by inverter. This time the pressing Bluetooth module didn't do anything. I had to reset the BMS manually and set the inverter to charge from grid.

I checked the nuts on the inverter and battery. All of them are tight.

What is going on? I have no slightest clue anymore. The button on the Bluetooth module is for the Bluetooth itself, not to reset the BMS. Is something wrong with the BMS? Or is the Inverter to blame?

Any and all help is greatly appreciated.

If you need any more info, please ask.

 

[DIYrich]

47v is basically discharged. Are you reading before or after the BMS?
Voltage at Battery?
Voltage at BMS?
Voltage at Inverter?

What are the above voltages when normal discharge?
What are the above voltages when charging?

If inverter is not providing charging voltage, then problem is the inverter.
If inverter is providing charging voltage, but voltage is not reaching the BMS, then problem is between the Inverter and the BMS.
If charge voltage is reaching BMS (line loss allowed), but voltage not reaching battery, then BMS is the problem (or fuse/switch if you have one between BMS and Battery).
If charge voltage is reaching battery, but battery is not charging, then it is a battery problem.

If battery charges, then check where in the line you are not getting battery voltage when discharging.

 

[PVguard]

47v is basically discharged. Are you reading before or after the BMS?
Voltage at Battery?
Voltage at BMS?
Voltage at Inverter?

What are the above voltages when normal discharge?
What are the above voltages when charging?

If inverter is not providing charging voltage, then problem is the inverter.
If inverter is providing charging voltage, but voltage is not reaching the BMS, then problem is between the Inverter and the BMS.
If charge voltage is reaching BMS (line loss allowed), but voltage not reaching battery, then BMS is the problem (or fuse/switch if you have one between BMS and Battery).
If charge voltage is reaching battery, but battery is not charging, then it is a battery problem.

If battery charges, then check where in the line you are not getting battery voltage when discharging.

I completely forgot about this thread. So sorry,

Turned out to be a bad cell. Replaced it and now the battery is fine.