question

you maybe finding that the 100A/H batteries internal BMS CANNOT supply the power required to run the inverter at 12000VA or at overload levels - A 100A/H Lifep04 batterys BMS may only have a 50amp or less max amps draw (check its BMS specs) or the power to Pre charge its capacitors. - Pre charge can take large amps and thus the BMS shuts the battery down.

you must measure the battery voltage when the inverter is being connected and or as it is turned on, as if you try testing with a volt meter after the inverter has shut down than you will find that the batteries internal BMS has already turned back on. Try a a battery that does not have a inbuilt BMS with FET shutoff included for testing

Thanks for the responses. The problem doesn't seem to be battery related, I hooked the inverter up to another battery without bms and the problem continues in exactly the same manner. No drops in voltage were read on the battery when turning on and off the inverter or initiating load on the inverter. I have since added a smart shunt to the system to see if this would help but unfortunately the Pheonix 12/1200 cannot sync with the smart system and therefor cannot share the actual voltage. I had the battery fully charged and the inverter was running smoothly for a day, however once the battery reaches 70%soc the inverter will shut down, showing low voltage alarms, even though the voltage the Pheonix is reading is still well above the low voltage alarm threshold, while again the actual voltage is well above that still. Currently the smart shunt is reading the battery as 13.52 while the inverter, after charging the battery again and applying a small load, is showing battery voltage of 6.18v. If I disconnect the inverter from the battery and reconnect, SOMETIMES the voltage reading will go back up closer to the actual voltage (but still off the actual voltage), but once a small load is applied the voltage will drop hugely, the inverter will shut down.

I dont understand it. It was running smoothly all day and all night after I installed the shunt but ince it shut down I cannot get it to run again

I have exactly the same case with the same inverter.

Did you find a solution?

I’m also interested in the solution, as I have the same issue with the same inverter, but have 2 x 100ah SLA batteries in parallel and a Victron BSC IP22 12/20 charger connected, but obviously powered off. Not sure if there is perhaps a diode on the charger’s output, that could affect the inverter’s voltage measurment…

Yes I have the same problem on a brand new Pheonix 12/250. It's just a secondary inverter I use to power my starlink. It's hooked up to 400AH of lithium batteries. My big Multiplus inverter is fine, never skips a beat, but for some reason this little Pheonix craps out like you are saying. At this point I'm returning it. I ordered another just to see if it's a defect. Someone said they solved this problem with a firmware update, but that update didn't fix mine.

I have the same problem on my 1200 inverter. It’s actually the second one, first replaced under warranty for the exact same thing. Running 3 -100ah battleborn batteries in parallel. I had an 800 watt version that never did this (and we overloaded it often) same wires, fuses, etc. maybe the BMS causes the inverter voltage to read incorrectly. Have 7 other Victron products on Bluetooth that read the proper voltage.