we are in the process of connecting a PV system from 2003, which has been running feed in-only for nearly 20 years now, to a Victron system for self-consumption. As of the current string configuration and VOC, we will use an MPPT RS 450/200. It will be connected to a Pylontech US2000C battery bank.
According to the data sheet of the MPPT RS, the max VOC per tracker must not exceed the eightfold of the battery float voltage, which brings us for Pylontech to:
51 V x 8 = 408 maxVOC
Now I calculated the VOC per string using the individual flash values of the manufacturer and one string is fine, two others exceed the 408 VOC limit as they have 19 instead of 18 modules:
- String 1: 406,80 VOC
- String 2: 429,35 VOC
- String 3: 429,22 VOC
As I expect some degradation of these 20 year old modules, which may also affect VOC, I'm not extremely concerned and would test the system for occurring over-charge protection errors. And in case of doubt, one module per string would have to be removed.
But what I'm really interested in: Is this eightfold battery float voltage rule even relevant for GX device managed systems, as the battery charge cycle in this case is managed by the Pylontech BMS values?