Hi!
In case of a backup system with a Multi-II and Pylontech batteries, what is the reason for the Venus device requirement? The BMS in the battery should be able to operate stand alone, right?
thanks
eliott
asked
Pylontech batteries with Multiplus-II without Venus device
main reason is : communication
without any GX device, MP must work based on voltage, without knowing the status of the BMS (can distribute / can charge). If BMS decides to shutdown any of those tasks, MP will only react in shutdown because of under/over-voltage
You can operate it that way, though it isn't ideal. You just need to be careful with voltages, especially when new and/or unbalanced. The trade off is the bms may just shut itself off and take the system down with it.
CAN attached, the battery manages the system. It sends its charging limits which the system will track, this keeps it running optimally and reliably.
Given the cost of batteries and the inverter, you don't really save a lot by not buying a cerbo.
The cerbo/GX also coordinates the charging between devices (mppt's etc) and, with internet access, gives you a wealth of performance data and remote management/monitoring.
Something else to consider, iirc the battery warranty is dependent on it being CAN attached.
And charge current and charged voltages and discharge current. So all in all can be done with a properly sized battery bank. They dont need the stay alive signal like BYD, however warranty from some suppliers needs to be considered as well. DVCC is forced on by the battery bms, Pylontec want it to run with that.
As mentioned by Nickdb the GX is so much more than that though and totally worth getting considering the rest of the equipment value. Protect that investment.
The official line from Victron is that Lithium batteries require a GX device.
That being said, you can do this BUT one of the things the GX devices do when they detect a Pylontech is implement a "quirk" to override the BMS supplied Charge Voltage Limit values:
24V - 27.8V
48V - 52.4V
So, please configure with the above voltages and avoid the temptation to go higher.
