Good day everyone,
I hope all is well.
To begin with, OGM staff please note this is a rough duplicate of a contact form I submitted. I realized after submitting the form that posting here in the forum would make the discussion available to the world, available to future readers, and would allow the community to offer any thoughts or ideas as well. Please feel free to respond wherever is most appropriate.
I am investigating REC BMS solutions for a sizeable house in a remote region. The energy storage system is being designed such that the reserve battery capacity allows for a substantial number of so called Days of Autonomy. To accomplish this, the number of REC units involved would be substantial... hypothetically in excess of 30 2Q Slave units once the system is complete. Given the size of the investment, I would like to discuss some particular capabilities of REC equipment prior to commiting to purchase.
In case my fundamental understanding is flawed I would like to start with the relevant limits as I understand them:
With that foundation laid, a possibly complicating factor has arisen.
Paralleling cells at the sub-pack level prior to series connection is not sought at this time for reasons that are worth a thread of their own.
That is to say, each Battery Pack will be composed of 16 cells in series, for a 16S(48v) configuration. Per the above, that implies a maximum possible system size of Fifteen (x15) such 16S packs.
There is concern this may not be sufficient reserve capacity. Solutions are being sought.
One such possible solution is the use of a Secondary bank of x15 16S batteries each with its own 2Q BMS. Consider a scenario where x15 2Q + Battery Packs are in active use and connected to a single x1 Master BMS.
Ideally, from the Master BMS' perspective, all that occured is 2Q BMS #10 was briefly disconnected and then re-connected. The sole difference being that it is now reporting a higher SOC.
If we assume this switching is done electronically over the course of some number of milliseconds, and for each of the x15 Banks in rapid succession what will the response of the Master BMS be to such transient interruptions?
There are some non-BMS electrical concerns that also arise from this type of switching- but for now I would like to focus specifically on how the REC Master BMS will handle a temporary interruption of the communication bus in this manner.
Namely, I am concerned:
If the 2Q BMS, when they cannot properly establish a connection with the Master BMS, revert to their local/individual settings then I expect power interruption to the system bus to be minimal.
It is also possible to switch the Comms cable going to the Inverter from the Master. So a Primary Master BMS at the head of a battery array would have its Comms cable switched with another Master BMS that is at the head of a second battery array.
The final point I should mention is that I intend to use Victron's DVCC utility. I believe I could, in a manner of speaking, run the Master/2Q array independent of the Quattro Inverters and use the programmable outputs to signal end of charging and the like but doing so introduces another set of problems which DVCC very conveniently solve.
It is specifically for the use of DVCC why I am endeavoring to maintain a physical communication channel between a Master BMS and the Inverter at all.
In summation then, the question is how might an excess of 15 battery packs be used with the REC ecosystem without fully cutting off power to the system bus and with the clarifier that there need not be more than 15 connected at any given time. There just needs be a way to rotate out depleted packs and introduce fresh ones while having features like DVCC function as expected afterwards.
Thank you for your time.
All the best.
