Short version:
Can an off-grid system recover using solar power only when BMS has entered ‘off’ mode?
Long version:
I am looking at a 48V off-grid system based on Lynx Smart BMS, Lithium Battery Smart, GX, Multi RS Solar and possibly also a SmartSolar.
I need the system to be self-maintained so if the BMS hits the discharge floor and enters ‘off’ mode, it needs to recover using solar power only whenever PVs start producing again.
The BMS manual states:
“The BMS will resume normal operation and close the contactor, when it detects a charge voltage on the system side of the BMS.”
and a bit below under ‘Force the BMS out of OFF mode’:
“Please also note that the above procedure is not required when DVCC controlled chargers are present in the system. They will charge for a few minutes or MPPT chargers will stay on regardless of whether the GX device and/or ATC status is off.”
Great, sounds like my problem is solved. Except, I find no information in Multi RS solar or SmartSolar manuals that mention this behavior. I would appreciate it if someone could point me in the right direction.
Solar can black-start an inverter, but if your battery has been driven so low to shut off, then you would need to consult the manufacturers recovery procedure, as many will need manual intervention.
I plan to use the ‘off’ mode during winter to keep the batteries safe if PVs are covered in snow for a prolonged period. Assume I raise the BMS discharge floor to a somewhat safe level, say 75%. So when recovering from ‘off’ mode, the batteries should be far from depleted. Would that work?
Once the Lynx BMS has opened its contactor there is very little current draw in the batteries themselves, they quote 12 months storage time from full. The Lynx BMS has a 0.6W draw when on standby so 12mA at 50V, 9Ah per month (even less when off). Therefore, the batteries will survive many months without power if you have a high enough discharge floor. The Lynx BMS powers down the Cerbo assuming you have one fitted and supply this from the aux power supply on the Lynx BMS.
Good that the batteries should survive! But then we return to the question of whether the BMS will wake up once the snow has melted. The BMS is ‘off’ so the system bus is disconnected and Cerbo is off. Will the Multi RS Solar and/or SmartSolar output enough voltage on the system bus to wake up the BMS?